Special Permafrost Alerts: Permafrost-Related Abstracts,
American Geophysical Union - Fall Meeting 2018

2019038082 Aalto, Juha Antero (University of Helsinki, Helsinki, Finland); Hjort, Jan; Karjalainen, Olli; Westermann, Sebastian; Romanovsky, Vladimir E.; Nelson, Frederick E.; Etzelmuller, Bernd and Luoto, Miska. Statistical permafrost modeling suggests high risk for Arctic infrastructure by 2050 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Accurate modeling of pan-Arctic ground thermal regime is critical to understand the impacts of climate change on high-latitude ecosystems and societies. The degradation of near-surface permafrost can limit the use of natural resources and jeopardize the sustainable development of Arctic communities. We produced geospatial layers of ground temperature and active layer thickness (i.e. seasonally thawed surface layer on top of permafrost) over the northern hemisphere at unprecedented fine spatial resolution (~1 km²), that is unreachable with existing ground thermal models. Using the modeled ground thermal data, a consensus of multiple geohazard indices and open-source infrastructure data, we identified infrastructure hazard areas over the permafrost domain under several greenhouse gas emission scenarios, and quantified key engineering structures (residential, transportation and industrial) at risk by 2050. Our results show that favorable conditions for permafrost prevail over an area of 15.1±2.8´10⁶ km². This extent will substantially contract in the future due to climate change, with region-specific changes in the ground thermal regime. Consequently, nearly four million people and 70% of infrastructure in the permafrost domain are in areas of high potential for permafrost degradation. Moreover, one-third of pan-Arctic infrastructure and 45% of the natural gas production fields in the Russian Arctic are in regions where thaw-related ground instability may damage built environment. Our approach provides new opportunities to assess future changes in Arctic ground thermal state with implications on global climate and land surface systems through alterations in e.g. carbon cycling, hydrology and vegetation. From an applied perspective, the spatially-detailed infrastructure hazard assessments can help planners and policy-makers to pin-point areas that are likely to be affected by the degrading permafrost, thus supporting sustainable development of pan-Arctic region.

2019040656 Abolt, Charles (University of Texas at Austin, Austin, TX); Young, M.; Atchley, A. L.; Harp, D. R. and Coon, E. T. Geomorphic feedbacks enhance the stability of high-centered polygons [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Pan-Arctic ice wedge degradation has accelerated abruptly in the past 30 years, driving widespread formation of high-centered polygons (HCPs) across tundra landscapes. This rapid geomorphic transformation alters near-surface hydrologic processes and influences the mobilization of soil organic carbon. However, the pathways by which ice wedges degrade are incompletely understood, causing high levels of uncertainty in projections of future landscape function. Here we use the Advanced Terrestrial Simulator, a physics-based modeling framework for surface and subsurface hydrologic and thermal processes in porous media, to explore the influence of geomorphic feedbacks during ice wedge degradation and re-stabilization. Our model simulates the thermal regime of the active layer in radially-symmetric polygons, using soil physical parameters inferred from field samples and validated using historic meteorological data and observed ground temperature. By varying microtopography and trough inundation among simulations, we isolate the influence of these variables on active layer development in conditions representing various stages of thermokarst. Our results indicate that ice wedge degradation is influenced by a mix of positive and negative feedbacks associated with trough subsidence and inundation, but that negative feedbacks predominate at almost all stages. Impoundment of water in deepening troughs modestly enhances thawing processes, but this effect is counteracted by the concurrent destruction of rims, which diminishes a conductive heat flux toward the ice wedge in summer. In most cases, rates of soil accumulation in the trough during thermokarst are sufficient not only to re-stabilize the ice wedge, but to increase the thickness of a protective layer of frozen soil atop it several fold compared to pre-thermokarst conditions. Overall, these results imply that currently observed development of surface water bodies in degrading ice wedge troughs is intrinsically limited. Because partially-degraded ice wedges become more stable than those unaffected by thermokarst, we forecast that HCPs are durable landscape features, which will exert a long-term influence on soil moisture, runoff generation, and rates of carbon export as CO₂, CH₄, and dissolved organic carbon in a warmer future.

2019040613 Ackley, Caren J. (Wilfrid Laurier University, Geography and Environmental Studies, Waterloo, ON, Canada); Quinton, W. L.; Tank, Suzanne; Rezanezhad, F. and McCarter, Colin Patrick Ross. Low-severity wildfire on a tree covered peat plateau; interactive effects of runoff flowpath and ground thaw dynamics on porewater chemistry [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33M-2850, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The increasing frequency, size and severity of naturally ignited wildfires in northern boreal regions justifies investigations into potential short- and long-term post-fire ecohydrological impacts. Many studies focus on large scale, expansive, and high-severity burns due to the large amounts of CO₂ released from burned organic matter and the significant and immediate threats posed to the health of ecosystems and local communities. Furthermore, significant organic matter (OM) loss leads to changes in runoff chemistry and soil moisture regimes, and enhanced permafrost degradation. This can lead to ground surface subsidence and convert peat landscapes from long-term C sinks to sources. Using space-for-time analysis of post-fire changes and recovery can pose challenges due to changing climatic conditions and natural landscape heterogeneity across regions. Yet, little is known about the implications of small-scale, low severity burns. In 2014, a low-severity wildfire burned half of a 0.05 km² treed permafrost plateau in the wetland dominated landscape of the Scotty Creek drainage basin, NT, providing a unique opportunity to examine post-fire changes within a single landform unit. Seasonal peat porewater chemistry showed elevated nutrient concentrations in the burn, likely due to the translocation of dense ash and char particulates from the surface, and leachate from OM. Physical properties measured in the lab showed significant changes between burned and unburned samples. Particulates that clogged burned peat pore spaces created smaller interparticle pores characterized by lower saturated hydraulic conductivity, reduced non-equilibrium flow, and greater soil moisture retention. Longer porewater residence time promoted diffusive solute exchange between relatively dilute mobile porewater and more concentrated porewater tightly held within smaller diameter and immobile pores. The higher thermal conductivity of wetter soils, enhanced by more consistent and uniform incident shortwave radiation resulting from canopy removal, promoted deeper more homogeneous ground thaw and reactivated previously frozen permafrost porewater. This study suggests that post-fire changes in porewater chemistry are controlled by abiotic forces and runoff flowpath.

2019038053 Alexeev, Vladimir A. (University of Alaska, International Arctic Research Center, Fairbanks, Fairbanks); Walsh, John E.; Brix, Kaja; Hock, Regine and Kaden, Ute. Research experience for undergraduates; understanding the Arctic as a system [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract ED51A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Today, more than ever, an integrated cross-disciplinary approach is necessary to understand and explain changes in the Arctic and the implications of those changes. Responding to needs in innovative research and education for understanding high-latitude rapid climate change, scientists at the International Arctic research Center (IARC) of the University of Alaska Fairbanks (UAF) established a new NSF-funded Research Experience for Undergraduates site, aiming to attract more undergraduates to the arctic sciences. The science focus of this program, building upon the research strengths of UAF, is on understanding the Arctic as a system with emphasis on its physical component. The goals, which were to disseminate new knowledge at the frontiers of polar science and to ignite the enthusiasm of the undergraduates about the Arctic, were pursued by involving undergraduate students in research and educational projects with their mentors using the available diverse on-campus capabilities. IARC hosted a group of nine students this past summer, focusing on a variety of different disciplines of the Arctic System Science. Students visited research sites around Fairbanks and in remote parts of Alaska (Toolik Lake Field Station, Canwell glacier, Bonanza Creek ecological research site, the CRREL Permafrost Tunnel and others) to see and experience first-hand how arctic science is done. Each student worked on a research project guided by an experienced instructor. The summer program culminated with a workshop that consisted of reports from the students about their experiences and the results of their projects.

2019037866 Atchley, Adam Lee (Los Alamos National Laboratory, Los Alamos, NM); Jafarov, Elchin E.; Harp, Dylan R.; Coon, Ethan T.; Dafflon, Baptiste; Anh Phuong Tran; Hubbard, Susan and Wilson, Cathy Jean. Estimation of polygonal tundra soil properties by coupled inversion of ERT and hydrothermal data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1059, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Observations of the spatial and temporal evolution of thaw and soil moisture changes are needed to understand thermo-hydrologic dynamics in periglacial regions and to inform models that forecast changes in permafrost hydrology under future climatic conditions. However, obtaining spatially and temporally distributed observations of thaw depth and moisture content is difficult. An indirect approach to achieve this information is Electrical Resistivity Tomography (ERT). ERT is sensitive to many parameters such as grain size, porosity, water phase, and chemical concentrations and therefore requires site data and expert interpretation to extract the ERT response of interest. Complimentary site data can constrain ERT sensitivity that then allows for higher ERT interpretation confidence. Here, we investigate the use of sparsely collected borehole measurements of temperature and moisture content to augment ERT surveys. To accomplish this, we combine the Arctic Terrestrial Simulator (ATS) with the Boundless ERT (BERT) simulator to model ERT response to parameter combinations. Petrophysical relationships are used to convert the ATS simulated temperatures and saturations into spatially distributed electrical resistivities. The BERT simulator then uses the petrophysically-derived, distributed electrical resistivities to simulate the ERT survey response (i.e., the ERT survey that would be collected given the petrophysically-derived, distributed resistivities), which can be compared for consistency with the measured ERT survey. We implement a gradient based parameter estimation approach to infer permafrost soil properties based on the consistency of simulated temperature, moisture contents, and resistivities to observations. We tested our inverse approach with data from a continuously recording ERT transect and co-located temperature and soil moisture measurements at a polygonal tundra site near Utqiagvik, Alaska. The results indicate that the inverse approach applied to data from this type of environment can identify porosities and thermal conductivities. The use of this approach with co-located ERT surveys and point measurements has the potential to significantly increase the spatial coverage of hydrothermal property estimates in permafrost environments.

2019040646 Aygun, Okan (University of Quebec at Trois-Rivieres UQTR, Environmental Sciences, Trois-Rivieres, QC, Canada); Kinnard, C. and Campeau, Stéphane. Modelling cold region hydrology in an agricultural catchment in southern Quebec, Canada [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1793, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Cold regions hydrology is largely governed by a number of unique processes related to snow and frozen ground, and the multiple interactions among these processes can result in complex and variable hydrological responses. There is thus a need to better understand and represent cold region hydrological processes within hydrological models in order to improve model assessments of potential climate change impacts on catchment hydrology. In this study, a physically-based hydrological model has been developed using the Cold Regions Hydrological Model (CRHM) for the l'Acadie River catchment in southern Quebec, Canada. Almost 75% of the catchment is occupied by agricultural fields, being representative of the intensive farming landscape of the southern St-Lawrence lowlands, while the remaining fraction is mostly forested. CRHM was parameterized to model the major hydrological processes thought to be important in the catchment, such as the redistribution of snow by wind, sublimation, frozen soil infiltration, snowmelt and runoff generation over a 20-year period. Simulated snow water equivalent (SWE) at the mixed forest hydrological response unit (HRU) was evaluated against the 20-year snow survey record from the Hemmingford Station located within a mixed forest landscape in the same region, while simulated streamflow was compared against streamflow records at the basin outlet. Preliminary results indicate that there is an adequate match between the simulated and observed SWE at the point scale. The simulated SWE varied among the different landscape units in the catchment, which is mostly due to snow redistribution by wind in response to changes in vegetation and topography. Snow is predominantly transported from agricultural fields and deposited in drainage canals and forest patches. Graphical comparison of modelled and measured streamflow indicated that the model tends to overestimate flood peaks while underestimating low flows. This is mostly attributed to the existence of the tile drainage system in the catchment, which is not explicitly represented in CRHM. Our next step is to improve the drainage representation in the model to account for the impacts of the tiles on the river hydrograph.

2019040644 Azarderakhsh, M. (Fairleigh Dickinson University, Teaneck, NJ); Prakash, S. and Arunyavikul, Patty. Detection of freeze and thaw states using sentinel SAR measurements and ground observations; a case study in Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1788, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The objective of this study is to evaluate the potential of Sentinel-1 Synthetic Aperture Radar "SAR" data (C-band) for monitoring the states of the earth surface in terms of freeze and thaw (FT) cycles. FT cycles especially in high-latitude regions have a crucial role in many applications such as agriculture, biogeochemical transitions, hydrology and ecosystem studies. Satellite-based passive microwave observations successfully have been utilized for the freeze and thaw detections in the past. However, their coarse resolution (about 25 km) makes them less helpful for many regional and local-scale applications. However, alternatively active microwave backscatter measurements from radar sensors can provide much higher spatial resolution (about 10 m). Here, we examine C-band backscatter data from Sentinel-1A Synthetic Aperture Radar (SAR) from April 2014 to June 2018 to detect high-resolution freeze/thaw states in Alaska where has shown signs of thawing permafrost. Under cold winter conditions, much of soil water freezes, which leads to a significant decrease of the soil dielectric constant. A decrease in the radar signal of several dB, therefore, could serve as a proxy for high resolution FT states detection. The contrasts between frozen and thawed states are used to define FT states after performing several required corrections such as radiometric corrections, calibrations, and earth flattening terrain corrections. Similar studies using other sensors have tried to use average backscattering values between the winter and summer time as a threshold for defining the soil state which may not be accurate for all surfaces and soil conditions. As a more novel approach, we define the threshold values using in situ observations of soil temperature, air temperature, snow depth, and soil moisture which consider the soil conditions and land cover type. The results of this method were compared against independent ground measurements from SNOw TELemetry (SNOTEL) observations. Varying values of backscattering, when the soil temperature was around 0 °C, were observed in the processed data which further analysis suggested that they might be due to the effect of snow cover and melting snow in transition season.

2019037814 Bakermans, Corien (Pennsylvania State University, Division of Mathematics and Natural Sciences, Altoona, PA) and Emili, Lisa. Biogeochemistry and microbiology of Arctic soils; a synthesis [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2581, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We review what is known about effects of abiotic factors of Arctic soils on the microbial communities that influence carbon cycling in these habitats. Arctic soils vary in mineral composition, snow cover, water content, connectivity, type of vegetation, organic content, and extent of permafrost. While united by low temperatures, the heterogeneity of abiotic factors results in a mosaic of site-specific conditions across the Arctic. This mosaic is unique to the Arctic and contributes to the site-specific biogeochemical regimes and microbial communities that develop. Site-specific microbial communities likely form in response to variations in local conditions often due to variations in micro-topography. Other biogeochemical trends in Arctic soils include increasing carbon content along a north-south gradient and distinct vertical layers. Microbial community composition also varies by depth and often correlates with pH. It is anticipated that as the Arctic warms, the activity of these microbial communities will increase both directly and indirectly leading to the conversion of previously stored organic carbon to metabolic waste products like CO₂ and CH₄. For example, increased soil temperature may increase weathering, cryoturbation, and permafrost thaw resulting in higher nutrient availability. Alternatively, thaw may increase soil saturation, increasing nutrient sequestering. The extent of organic matter decomposition in Arctic soils will depend on many factors in this complex terrestrial system. While trends are evident in biogeochemistry and microbial communities, the heterogeneity of soils in the Arctic and the limited number of soil types examined to date leads to variation in results and makes extrapolation across the entire Arctic difficult. In particular, the paucity of studies examining the effect of abiotic factors on microbial community composition in permafrost limits interpretation and limits modeling of carbon cycling in the Arctic and of global climate regulation.

2019037812 Barczok, Maximilian (Kent State University, Kent, OH); Smith, Chelsea; Kinsman-Costello, Lauren E. and Herndon, Elizabeth. Influence of iron (oxyhydr)oxide crystallinity on phosphorus bioavailability in fluctuating redox conditions [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31G-2577, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic soils will experience redox shifts as changing climate and permafrost thaw alter hydrologic regimes. Redox shifts can form poorly crystalline iron (Fe) (oxyhydr)oxides that have the potential to adsorb the limiting nutrient phosphate. As Fe (oxyhydr)oxides crystallinity decreases, its ability to sorb phosphate increases; however, the crystallinity and mineralogy of the Fe (oxyhydr)oxides that form as a function of redox fluctuations remain unknown. Phosphorus (P) bioavailability may therefore decrease as climate-driven hydrological changes drive the precipitation of Fe (oxyhydr)oxides, potentially limiting plant growth in the arctic. To investigate these complex interactions, an in situ incubation experiment was conducted to explore how hydrologic changes affect crystallinity and phosphate sorption of Fe (oxyhydr)oxides. Mesh bags filled with peat moss and synthetic Fe (oxyhydr)oxides of different crystallinity (ferrihydrite, goethite and hematite) were buried in a vernal pond in northeast Ohio. Vernal ponds are flooded during spring months but progressively dry out over the summer, similar to dynamic redox patterns we would expect in arctic wetlands as permafrost thaws. Fe (oxyhydr)oxides were either phosphate-free or had high concentrations of sorbed phosphate and were buried either in the pond during flooded conditions or in the surrounding unsaturated upland to capture contrasting redox conditions. Background conditions were monitored by recording redox, water depth, and soil moisture. Bags were removed after either four or twelve weeks to capture flooded and dried conditions, respectively, in the pond. Changes in Fe abundance, crystallinity, and mineralogy are being analyzed using x-ray fluorescence (XRF), x-ray diffraction (XRD) and x-ray absorption fine structure (XAFS). P extractions will be performed to investigate changes in phosphate adsorption. Redox conditions in the pond shifted from anoxic to oxic in the top soil layer as the pond dried out. Wet weight of removed bags were higher if phosphate was sorbed to iron oxides compared to phosphate-free treatments, suggesting preferential microbial growth on P-bearing substrates. Results from this study will provide insight into the effect of Fe (oxyhydr)oxide crystallinity on P bioavailability.

2019040659 Benmesbah, Fatima Doria (French Research Institute for Exploitation of the Sea, France); Ruffine, Livio; Clain, Pascal; Osswald, Véronique; Fourniason, Laurence and Delahaye, Anthony. Experimental study of methane-hydrate formation and dissociation in sand; kinetics and gas storage capacity [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS14A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Investigating hydrate formation and dissociation in porous media is key to better understand the formation, growth and fate of gas hydrate deposits, in both permafrost regions and marine sediments (Kvenvolden et al., 1993, Lorenson, 2001). Such a study also finds applications in various promising industrial processes such as cold production and storage (Gawron & Schroder, 1977, Delahaye et al., 2010). Yet, lab experiments of hydrate formation in porous materials like sand remains quite challenging due to the continuous change in the permeability of the porous medium which may hinder the gas flow and considerably slow down the hydrate growth process. Accordingly, parameters such as the gas flowrate and the particle grain size can strongly affect the hydrate formation. In the present work, we used an high-pressure apparatus (Ruffine, 2015) to study the influence of water saturation and volume gas flowrate on the formation and dissociation kinetics of methane hydrates in silica sand. The amount of hydrates formed for each experiment is determined by direct measurement of the amount of gas released during the dissociation step. Experimental results obtained at a volume flowrate of around 50 mln/min showed different pattern of hydrate growth in the porous media. The conversion of water to hydrates is not completed above a water saturation of 40% due to the formation and dissociation of hydrate plugs over the course of the experiments.

2019040617 Bennett, K. A. (University of New Hampshire, Durham, NH); Burke, S. A.; McCalley, C. K.; Palace, M. W.; Crill, P. M. and Varner, R. K. Using stable isotope analysis of methane in the bubbles and sediment porewater of ponds to determine methane production pathways [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B41G-2794, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic and subarctic ecosystems in the northern hemisphere are warming faster than any other region of the globe. Rising temperatures, in this region, are causing changes in the natural cycles of these systems, such as the thawing of permafrost. As permafrost thaws it forms ponds that emit methane (CH₄), a potent greenhouse gas, predominantly through ebullition. Microbes present in these systems produce CH₄ through two primary pathways, acetoclastic methanogenesis forms CH₄ using organic carbon (C) sources while hydrogenotrophic uses inorganic C. Stable isotopes can be used to characterize the relative importance of these two pathways for overall CH₄ production, providing information that can improve modeling of current and future CH₄ emissions. This study uses stable isotopes carbon-13 (¹³C) and deuterium (D) to determine the presence of acetoclastic or hydrogenotrophic methanogenesis in this system.Isotope analysis was performed on porewater and ebullition (bubble) samples taken from seven ponds in a subarctic peatland located in the discontinuous permafrost region of northern Sweden. The seven ponds vary in physical attributes related to their formation, allowing observations to be made on the relationship between these attributes and CH₄ production pathways. Initial data suggest that more recently formed, hydrologically isolated ponds have lighter ¹³C-CH₄ signatures, suggesting that CH₄ production is predominantly hydrogenotrophic, while ponds that are more hydrologically connected have heavier ¹³C-CH₄, indicating acetoclastic methanogenesis. Five years of unmanned aerial vehicle imagery and additional satellite imagery allows for determination of potential pond formation age and vegetation cover around the ponds to be compared with the isotopic characteristics. Minimal literature exists on the types of microbes and metabolic pathways present in subarctic ponds, therefore, conclusions drawn from this study will inform how ponds contribute to the global CH₄ budget.

2019038111 Bibi, Sadia (University of Chinese Academy of Sciences, Beijing, China); Wang Lei; Li Xiuping; Chen, Deliang and Zhang Xiaotao. Response of groundwater storage and recharge to climate variations in the Qaidam Basin (Tibetan Plateau) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H11T-1717, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Groundwater and recharge are the main drivers of the water budget that are challenging to quantify, due to the complexity of hydrological processes and limited observations. Understanding these processes in relation to climate is crucial for evaluating future water availability of Tibetan Plateau (TP). In the Qaidam Basin (northern TP), a spatial and temporal variability of temperature and precipitation were firstly analyzed from 2000 to 2015. Terrestrial Water Storage (TWS) from the Gravity Recovery and Climate Experiment (GRACE) revealed significant increasing trends of 0.15 km³ per year (P<0.05), while the Global Land Data Assimilation System (GLDAS) revealed a TWS of 0.05 km³ per year (P<0.05) from 2003 to 2015. Groundwater (GW) also exhibited a significant increasing trend of 0.1 km³ per year (P<0.05). There was a fair agreement between GW estimates and in situ observations from monitoring wells, indicating that GRACE could reasonably capture the variation in GW in this region. The spatial trend of TWS was further evaluated by lake-height variations. Lake Jingyu and Lake Aukkum had significant increasing trends of 0.59 m per year (P<0.05) and 0.31 m per year (P<0.05), while Lake Dabshan-hu showed a decreasing trend (-0.02 m per year, P<0.05). While recharge had a slightly decreasing trend of -0.04 km³ per year for the analyzed period. Moreover, GW was less affected by precipitation variations than recharge. We concluded that increased GW over the basin was not only recharged by precipitation, but also from glacier recession and permafrost degradation due to climate warming in the TP region.

2019038119 Boggs, Katherine Janet Elizabeth (Mount Royal University, Calgary, AB, Canada); O'Connor, Kevin; Eaton, David W. S.; Gilbert, Hersh J. and Zens, Josef. Community engagement through citizen science projects for Canadian Cordillera array and EON-ROSE [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract IN22B-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

EON-ROSE (Earth-System Observing Network - Reseau d'Observation du Systeme terrestrE) is a new research collaboration to bring an EarthScope-like program to Canada. The Canadian Cordillera Array (CCArray), extending across the Cordillera from the Beaufort Sea to the U.S. border was designated as the pilot phase to benefit from the USArray stations currently in Alaska and northwestern Canada. The first station was installed in July 2018 at Kluane Lake Research Station in the Yukon Territories (funded by seed grants from the University of Calgary). Collaboration with the German Helmholtz Association will facilitate the installation of further stations starting in 2019. In the Canadian context it would be impossible to fund a repeat of the EarthScope program, therefore our intention is to expand the research network to permit holistically examining entire Earth Systems from the ionosphere through the Critical Zone into the core. The foundation for EON-ROSE will be >1400 telemetered and powered observatories with broadband seismometers, GNSS equipment, meteorological packages, riometers, permafrost monitors, and other sensors that will produce openly available, real-time data. We are developing a "Community Science Liaison" (CSL) program that will support Canadian communities to design K-16 curriculum- and place-based citizen science research projects using the data produced by their local observatories. This CSL program will contribute to a very successful place-based education program in northern Canada and expand upon the Calgary based "Geological Bumble Bee Program" which guides grade 2-8 students towards improving our understanding of the impact of climate change through geological "deep time" to the present. The EON-ROSE research community will support these CSLs by developing their training program, providing guidance for project design, assisting with data interpretation, and providing presentations. Representative citizen science project teams will present their results at the annual EON-ROSE conference. Community input will also be included when designing the future Earth System Observatories. The purpose of this design is to ensure that the Canadian general public is well informed about Earth System Sciences and to create community engagement for the EON-ROSE program across Canada.

2019037868 Bolton, Bob (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Helene, Genet; Lara, Mark J.; Romanovsky, Vladimir E. and Riley, William J. Simulation of landscape changes on the Alaskan Arctic Coastal Plain with the Alaska thermokarst model [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1061, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Landscape change in permafrost regions, caused by thermokarst, can result in profound impacts on the water, energy, and carbon fluxes; wildlife habitats; and infrastructure. Changes in the landscape due to thermokarst occurs when ice-rich permafrost thaws and the land surface subsides due to volume loss when ground-ice transitions to water. The important processes affected by thermokarst include changes in surface ponding, topography, vegetation composition, soil moisture and drainage patterns, and related erosion and biogeochemical turnovers. The Alaska Thermokarst Model (ATM) is a large-scale, state-and-transition model designed to simulate transitions between landscape units affected by thermokarst disturbance. The ATM using a frame-based methodology to track cohorts (unique landscape representations) transitions and their respective proportions within each model grid cell. In the arctic tundra environment, the ATM tracks thermokarst related transitions among wetland tundra, graminoid tundra, shrub tundra, and lakes. The transition from one cohort are initiated by pulse disturbance (i.e. extreme heat, large precipitation events, or wildfires) or by gradual active layer deepening that eventually results in penetration of the protective layer. The results of our research will be used to inform resource managers to better inform decision making. Further, the frame-based methodology of tracking transitions between landscape units is conceptually consistent with the watershed delineation approach being developed the Department of Energy's E3SM (Energy Exascale Earth System Model) land model. We will utilize and apply the recent approaches to translate the intermediate-resolution modeling results into functional responses applicable for integration into the E3SM framework. This model integration will improve the representation of landscape changes and its consequences on hydrological, biogeochemical and energy processes in the Arctic region. This study will present our results to date on the Alaskan Arctic Coastal Plain and our plans moving forward into the near future.

2019038065 Borhani, Sanaz (University of South Carolina, Civil and Environmental Engineering, Columbia, SC) and Viparelli, Enrica. Modeling tracer dispersal during channel bed aggradation and degradation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP41B-2657, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The vast majority of the morphodynamic models that accounts for the non-uniformity of the bed material (tracer and not tracer, in this case) is based on a layer-based description of the alluvial deposit. In layer-based models the deposit is divided in two different regions; the active layer and the substrate. The active layer is a thin layer in the topmost part of the deposit whose particles can interact with the sediment transport. The substrate is the part of the deposit below the active layer. Morpohdynamic formulations based on the active layer approximation, however, have well known limitations: 1) they neglect the vertical fluxes within the deposit associated with e.g. bedform migration; 2) they cannot capture the infiltration of fine sediment in a coarse bed; and 3) they cannot effectively model tracer dispersal in equilibrium beds and at time scales that are short compared to the time scales characterizing channel bed aggradation and degradation. In this study we try to model the dispersion of tracer particles with the continuous, i.e. not layer-based, morphodynamic framework introduced by Parker and co-authors in 2000. This framework is based on a probabilistic description of the temporal variation of bed surface elevation associated with sediment transport processes, of particle entrainment and deposition. Entrainment rates are computed as a function of the flow and sediment characteristics, and particle deposition is modeled with a step length formulation. The main goal of this study is to investigate the effects of channel bed aggradation and degradation on tracer dispersal, which is important to study tracer and contaminant dispersal at time scales that are comparable with those characterizing channel bed aggradation and degradation.

2019040672 Burgess, Isobel (Mount Holyoke College, South Hadley, MA); Schmidt, Britney E.; Duarte, Kayla; Romero, Vivian; Sizemore, Hanna G.; Scully, Jennifer E. C.; Schenk, Paul; Hughson, Kynan; Nathues, Andreas; Castillo, Julie C. and Raymond, Carol A. Characterizing potential pingo morphology on Ceres [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P33D-3868, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

NASA's Dawn Mission has explored Ceres since arrival in 2015. Recent low-altitude Dawn orbits during its second extended mission (XM2) have brought the spacecraft as low as 35 km above Ceres, collecting new high resolution imaging data with the Framing Camera including possible evidence of pingos in Occator crater. On Earth, pingos and other frost-heaves are a product of groundwater flow and freezing which create an ice-cored mound (e.g. Burr et al 2008). An open-system pingo has a supply of water, where the groundwater is under artesian pressure, which causes uplift, and creates an ice core underneath the permafrost (Soare et al 2014, Vasil'chuk 2016). In contrast, a closed-system pingo has a limited water supply which freezes and pushes sediments up into a dome, as hydrostatic pressure grows the ice lens. In both cases, ruptures can occur at the top of the pingo due to ice expansion or fluid pressure. Pingo centers may also collapse, due to fluid drainage or sublimation of ice, forming an apex pit or a ring structure. Most terrestrial pingos are ~100 m in diameter, but can grow to 2 km and candidate pingos on Mars range 20-1000 m (Burr et al. 2008), thus comparisons between Ceres and these larger planets are possible. In preliminary analysis of XM2 images of Occator, we identified »200 domical features, some of which are candidate pingos. These formations could be evidence of frost heave, given that Ceres' gravity could facilitate frost heaving (e.g. Sizemore et al 2018), and likely emplacement of large scale flows consisting of silicate materials entrained in melted ice during Occator's formation. We observe »33 features with apex depressions that we consider strong candidate pingos, most with diameters »40-60m. Additionally, there are »15 features that are morphologically similar, but require further investigation to disambiguate any relationship with frost heave. Two large pingo candidates are »500 m in diameter, and Occator's central dome »2 km wide is also a candidate. Several candidates have potential flows associated with or emanating from them. We also observe other evidence of ground ice on Occator's floor. The new imaging results shed light on possible ground ice and periglacial analogs and will provide new ways to test hypotheses regarding both subsurface ice as well as the formation and evolution of large impacts on Ceres.

2019040603 Butman, David E. (University of Washington, School of Environmental and Forestry Sciences, Seattle, WA); Bogard, Matthew; Kuhn, C.; Spencer, R.; Johnston, S. E.; Dornblaser, M.; Wickland, K. and Striegl, R. G. Re-examining the role of lakes in carbon cycling across high latitudes; results from ABoVE [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B13E-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic and boreal lake ecosystems are commonly considered sources of atmospheric carbon dioxide on an annual basis. This results from the mineralization of particulate and dissolved organic carbon (C) produced in situ and exported from terrestrial landscapes and from surface and ground water inputs of dissolved inorganic C. Hydrologic input of terrestrial C to lakes requires C source, surface and/or subsurface hydraulic connectivity, and sufficient water flow to maintain transport. The pan-arctic region is dominated by very flat landscapes and annual precipitation is on average below 38 cm yr^-1. Consequently, there is significant uncertainty quantifying terrestrial inputs of C to lakes in these semi-arid low-slope environments. As part of the Arctic and Boreal Vulnerability Experiment, we present the results of field campaigns designed to quantify the role of lakes in C-cycling within the Yukon Flats National Wildlife Refuge, in the Yukon River Basin, Alaska. This refuge includes over 24,000 lakes (NHD-AK) that make up 2.7% of the total refuge area, and average slopes are less than 1% where lakes dominate. Our results indicate that lakes in in Yukon Flats are not large sources of atmospheric CO₂, but are nearly balanced or slight sinks of carbon over time. This is supported by evidence that despite having C-rich soils in their watersheds, these lakes show little input of terrestrial carbon biomarkers. The lakes in the Yukon Flats are not unique across the pan-arctic, and may represent nearly 30% of all lakes within landscapes susceptible to permafrost thaw. Lakes have been estimated to contribute »4 g C m² Yr^-1 of total carbon emissions across northern latitudes or nearly 175 Tg C yr^-1 (Raymond et al 2013). Our results will be discussed in the context of a refined understanding of lake ecosystems in the cycling of carbon across northern latitudes.

2019032000 Cardenas, M. Bayani (University of Texas at Austin, Department of Geological Sciences, Austin, TX); Neilson, Bethany T.; O'Connor, Michael; Rasmussen, Mitchell T.; King, Tyler and Kling, George W. Groundwater flow and exchange across the land surface explain carbon export patterns in a continuous permafrost watershed [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23C-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Groundwater flow regimes in the thin, seasonally-thawed soils in areas of continuous permafrost are relatively unknown despite their potential role in delivering water, carbon, and nutrients to streams. Using numerical groundwater flow models informed by observations from a headwater catchment in arctic Alaska, USA, we show that different mechanisms result in substantial surface-subsurface water exchanges during downslope transport and create a primary control on solute loading to streams and rivers. The models indicate that surface water flowing downslope has a substantial groundwater component due to rapid surface-subsurface exchanges during unsaturated to flooded hydrologic states. Field-based measurements corroborate the high groundwater contributions, and river dissolved organic carbon (DOC) concentrations are similar to that of groundwater across large discharge ranges. The persistence of these groundwater contributions in arctic watersheds will influence carbon export to rivers as thaw depth increases in a warmer climate.

2019031998 Chadburn, S. E. (University of Exeter, United Kingdom); Fan, Yuanchao; Aalto, Tuula; Aurela, Mika; Bartsch, Annett; Boike, Julia; Burke, Eleanor; Christiansen, Casper; Comyn-Platt, Edward; Dolman, A. Johannes; Friborg, Thomas; Gedney, Nicola; Hayman, Garry; Holl, David; Hugelius, Gustaf; van Huissteden, Ko J.; Jammet, Mathilde; Kutzbach, Lars; Lee, Hanna; Lohila, Annalea; Marushchak, Maija E.; Parmentier, Frans-Jan W.; Richter, Andreas; Sachs, Torsten and Shurpali, Narasinha J. Including microbial dynamics is essential for modelling Arctic methane emissions [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane (CH₄) emissions from the high latitudes represent a potentially important feedback mechanism with the Earth's climate. Latest estimates of CH₄ emissions from high latitude wetlands range between 20-70 TgCH₄/yr, out of a global total 500-600 TgCH₄/yr, and this region is experiencing a rapid warming under climate change, which could lead to major changes in CH₄ emissions, which would impact global warming. Thus it is important to include high latitude CH₄ emissions in climate models. Several recent land surface schemes - which are used in climate models - include process-based CH₄ models, which represent production, oxidation, emission, and the various transport mechanisms of CH₄ through the soil and into the atmosphere. These build upon the original CH₄ schemes in such models, which are simple functions of soil temperature, wetland area and substrate. However, while the recent transport schemes are well-developed, a simple function is still used for CH₄ production. We study two land-surface schemes (CLM and JULES) and find that CH₄ production is a key determinant of wetland emissions. Thus more attention should be focussed on modelling production of CH₄. We then show that it is possible to recreate the observed CH₄ fluxes over a number of sites by including microbial dynamics. Microbial dynamics explain an apparent large temperature sensitivity in CH₄ emissions: the active microbial biomass increases during the summer, which amplifies the summertime emissions. The RMSE between the timeseries of CH₄ emissions in model and observations is reduced for every site by including microbial dynamics. For this work we made use of detailed observations from a range sites, including two cold permafrost sites in Siberia (Samoylov and Kytalyk), two somewhat warmer sites in Scandinavia (Abisko and Lompolojankka), and Seida in Western Russia. CH₄ was measured by eddy covariance and adjusted to include only the wetland flux. High resolution timeseries of soil temperatures over multiple years, along with soil carbon profiles, were used to model the CH₄ fluxes. We include the new microbial CH₄ production model in a global land-surface scheme (JULES) and assess pan-Arctic CH₄ emissions. This work will lead to improved projections of Arctic carbon-cycle feedbacks.

2019037787 Chae, Namyi (Korea University, Seoul, South Korea) and Lee, Bang-Yong. Soil CO₂ efflux in various tundra ecosystems of polar region [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2501, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Response of the Arctic to global warming is seen as a high-sensitivity indicator of climate change. Considering that 25% of Earth's terrestrial surface is underlain by permafrost, warming permafrost may play important roles in carbon cycle of the Arctic. The soil CO₂ efflux from representative tundra ecosystems in polar region should be monitored in order to evaluate the potential future sensitivity of the carbon cycle to climate change. Soil CO₂ efflux were measured in the Council in Alaska, Ny-Alesund in Norway, and Cambridge bay in Canada using chamber system to estimate emission of CO₂. In Council, Alaska, which are moist tundra near tree-line in subarctic, the long-term measurement of soil CO₂ efflux was conducted using automated chamber system during summer from 2012 to 2016 except 2013. In Ny-Alesund and Cambridge, which are semi-arid tundra in high-arctic, soil CO₂ efflux was measured using potable systems at several locations a few times in 2016 and from 2016 to 2018, respectively. The magnitude of soil CO₂ efflux was compared in three types in tundra ecosystem. The variability of soil CO₂ efflux is affected by local environmental and climatic factors, such as soil temperature, soil water contents, micro-topography, spatial heterogeneity of vegetation communities. This study was supported by a National Research Foundation of Korea grant funded by the Korean government (MSIP) (NRF-2016M1A5A1901790 and NRF-2018R1D1A1B07047778).

2019037776 Chang, Kuang-Lu (Lawrence Berkeley National Laboratory, Berkeley, CA); Riley, William J.; Crill, Patrick M. and Grant, Robert. Large carbon cycle climate sensitivities across a permafrost thaw gradient in subarctic Sweden [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2486, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost stores large amounts of carbon potentially vulnerable to decomposition and its return to the atmosphere. However, permafrost responses to a changing climate remain uncertain in models due to complex interactions among hydrological, biogeochemical, microbial, and plant processes. In this study, we estimated effects of climate forcing biases present in global reanalysis products on carbon cycle predictions at a thawing permafrost peatland in subarctic Sweden. The analysis was conducted with a comprehensive biogeochemical model (ecosys) across a permafrost thaw gradient encompassing intact permafrost palsa, partly thawed bog, and fully thawed fen. Reanalysis data from the Global Soil Wetness Project Phase 3 (GSWP3) was bias corrected by site observations taken from 1913 to 2010. The simulations driven by the bias-corrected climate suggest that the three peatland types are currently annual carbon dioxide (CO₂) sinks from the atmosphere, although the bog and fen sites can have annual positive radiative forcing impacts due to their higher methane (CH₄) emissions. Our results indicate that projected precipitation increases could accelerate CH₄ emissions from the palsa area, even without further degradation of palsa permafrost. The differences in simulated CO₂ and CH₄ fluxes driven by uncertainty from climate forcing biases (i.e., with and without proper bias corrections) are as large as those from landscape heterogeneity across the examined permafrost thaw gradient. Future studies should thus not only focus on the transition of net carbon balance proportional to the morphological changes in thawing permafrost, but also incorporate the dynamic effects of climate sensitivity on carbon cycling.

2019038077 Chen, Lin (University of Montreal, Département de Géographie, Montreal, QC, Canada); Fortier, Daniel; McKenzie, Jeffrey M. and Sliger, Michel. Heat transfer triggered by mobile subsurface water degrades permafrost and impacts overlying highways [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In northern regions, transportation infrastructure is experiencing severe structural damage due to the degradation of permafrost. Water infiltration and subsurface water flow under an embankment alter the energy balance of roadways and of the underlying permafrost. However, the quantification of these processes and a detailed investigation of their thermal impacts remain largely unknown due to a lack of available long-term embankment temperature data in permafrost regions. Here, we report observations of heat advection linked to surface water infiltration and subsurface flow based on a decade (from 2008 to 2017) of thermal monitoring at an experimental road test-site built on discontinuous permafrost conditions in southwestern Yukon, Canada. Results show that snowmelt water infiltration caused a step temperature increase of 5.0°C on average over several days, down to a depth 2.9 m. Infiltrated summer rainfall water warmed embankment fill materials at depth of up to 3.6 m, while simultaneously lowering the near-surface temperatures. Heat advection (as opposed to purely conduction) is caused by the flow of subsurface water and produces warming rates at depth in the embankment subgrade up to two orders of magnitude faster than by atmospheric warming. We conclude that the thermal stability of roadways along the Alaska Highway corridor are not maintainable in situations where water is flowing under the infrastructure unless mitigation techniques are used. Severe structural damage to the highway embankment are expected to occur in the near future.

2019038117 Chen, Richard H. (University of Southern California, Los Angeles, CA); Yi, Yonghong; Tabatabaeenejad, Alireza and Moghaddam, Mahta. Profile representation of permafrost active layer properties in support of radar retrievals [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H51V-1621, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The capability of retrieving soil moisture using synthetic aperture radar (SAR) polarimetry has been demonstrated through missions like Soil Moisture Active Passive (SMAP) and Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS). Radar backscatter is sensitive to soil dielectric properties, which are strongly correlated with soil moisture, texture, and freeze/thaw state. To enable accurate radar retrievals, we often rely on detailed soil maps for soil texture parameters in the forward model to convert dielectric constant to soil moisture. For retrieval of permafrost active layer properties, the spatial and vertical distribution of soil organic matter (SOM) is crucial because it can greatly affect subsurface thermal dynamics and hydrologic processes in the seasonally thawed active layer. However, the SOM maps available for arctic regions are still of limited quality and require more detailed SOM profile measurements and better spatial coverage. Instead of treating SOM profile as an ancillary data layer in the retrieval, we propose to retrieve SOM and soil moisture profiles simultaneously using P-band radar backscatter. To this end, we first parametrize soil moisture profile as a function of both soil porosity and saturation fraction. Soil porosity is then further expressed as a function of SOM, because SOM can determine the mass ratio of organic to mineral soils from which volumetric fractions can be calculated with respective specific densities. With the observation that SOM decreases exponentially with depth in the active layer, we can reduce the number of unknowns for the profile parametrization in the radar retrieval. In this presentation, we will describe the profile representation for active layer soils, and show the sensitivity of radar backscatter to active layer properties, including active layer thickness (ALT), water table depth, and soil moisture and SOM profiles. Retrieval results using the AirMOSS data acquired as part of the Arctic-Boreal Vulnerability Experiment (ABoVE) airborne campaign in 2017 will also be presented. Since the retrieved variables are commonly used by most permafrost soil models, this active layer soil profile representation can serve as the first step towards an integrated framework for remote sensing and modeling of permafrost active layer dynamics.

2019037815 Chen, Yaping (University of Illinois at Urbana-Champaign, Plant Biology, Geology, Urbana, IL); Lara, Mark J. and Hu, Fengsheng. Impact of burn severity on thermokarst initiation and expansion in Arctic tundra ecosystems [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2582, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Burn severity influences various biophysical and biogeochemical processes, and it is projected to increase in the coming decades across high-latitude ecosystems. However, the impact of burn severity on thermokarst (e.g., land subsidence after ground ice melting) is not well understood. We used time-series image analysis to assess the effects of burn severity and ground ice content on thermokarst processes in the Noatak National Preserve, northwestern Alaska. To extend the temporal depth for illustrating fire-thermokarst linkages, we evaluated eight existing fire indices derived from visible and near-infrared (380-1100 nm) spectral bands and developed burn severity maps of historical fires using Landsat MSS sensors (operation between 1972-1992). Our results reveal that tundra fire is a significant factor in creating thermokarst landforms (p<0.01), and that the magnitude of thermokarst varies with burn severity levels and ground ice content (p<0.05). An abrupt increase in thermokarst occurred one year after fire but the rate of thermokarst decreased after three years. The area of thermokarst three years after fire was highest in high-severity burns (385±47 m² thermokarst area/ha burned area), followed by moderate- (255±32 m²/ha) and low-severity (201±42 m²/ha) burns. Ground ice content interacted with burn severity to affect thermokarst; the area of thermokarst was twice as large in landscapes with high ground ice (356±67 m²/ha) as in landscapes of low ground ice (167±39 m²/ha) three years after fire. Among the eight fire indices, the Global Environmental Monitoring Index (GEMI) demonstrates the strongest correlation with field-based estimates (R²=0.8). Burn-severity maps reconstructed with GEMI reveal that over a 40-year study period, thermokarst expansion occurred more rapidly in high-severe burns than in low-severity or unburned areas. Our results suggest that the projected increase in burn severity may result in abrupt and long-lasting permafrost degradation in tundra ecosystems with potential consequences on Arctic carbon stocks.

2019040621 Christensen, T. R. (Aarhus University, Department of Bioscience, Roskilde, Denmark); Arora, Vivek; Gauss, Michael; Hoglund-Isaksson, Lena and Parmentier, F. J. W. Arctic methane as an amplifier of global warming [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43D-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Future concentrations of greenhouse gases (GHGs) in the atmosphere will determine the degree of warming the Earth will experience. Atmospheric methane, a powerful GHG, is controlled primarily by its anthropogenic and natural emissions and its destruction in the atmosphere. Natural methane emissions are noticeably influenced by warming of cold arctic ecosystems and permafrost. An evaluation specifically of Arctic natural methane emissions in relation to our ability to mitigate anthropogenic methane emissions is needed. Here we use empirical scenarios of increases in natural emissions together with maximum technically feasible reductions in anthropogenic emissions to evaluate their potential influence on future atmospheric methane concentrations and associated radiative forcing (RF). The largest amplification of natural emissions yields up to 42% higher atmospheric methane concentrations by the year 2100 compared with no change in natural emissions. The most likely scenarios are lower than this, while anthropogenic emission reductions may have a much greater yielding effect, with the potential of halving atmospheric methane concentrations by 2100 compared to when anthropogenic emissions continue to increase as in a business-as-usual case. In a broader perspective, it is shown that man-made emissions can be reduced sufficiently to limit methane-caused climate warming by 2100 even in the case of an uncontrolled natural Arctic methane emission feedback, but this requires a committed effort towards maximum feasible reductions.

2019040653 Christiansen, H. H. (University Centre in Svalbard, Arctic Geology Department, Longyearbyen, Norway); Gilbert, Graham Levis; O'Neill, H. and Neumann, U. Ground ice types and amounts in permafrost on Svalbard; overcoming the challenge of coarse-grained sediment [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Knowledge of ground ice in permafrost are important to assess the potential geomorphic response of different periglacial landform to climate change. To measure ground-ice content typically core drilling is used to retrieve frozen core samples. Quantifications of ground ice have so far focused on fine-grained sediments, with only few results from coarse-grained sediments. This is because a large proportion of the circum-Arctic permafrost area is in low-relief landscapes dominated by fine-grained sediments, and retrieval of undisturbed core samples from coarse-grained sediments is difficult due to thaw during drilling. Since 2012, field campaigns in the high-relief landscape of the Svalbard archipelago have provided ca. 25 drill cores between 3 m and 25 m in length, using a medium sized drill rig and hand drilling, mainly from silty and sandy sediments in the large fjord-valleys, but also from different lower slope landforms. Cryostratigraphical and sedimentological analyses on these cores show that ground ice type and amount are linked to the landform and sediment type, but also that there can be locally large scale variability in the ground ice amount. However, the ground-ice content particularly in hillslope colluvium remains largely unknown due to inadequate drilling techniques and equipment. Recent observations from Svalbard indicate that landslides, increase in frequency and magnitude during prolonged thawing seasons, which might be due to degradation of ground ice. It is impossible to predict the response of these sensitive portions of the landscape without knowledge of the ground-ice conditions. This presentation will summarize recent quantifications of the ground-ice content in different landform on Svalbard and present future steps to improve frozen sample retrieval from coarse-grained sediments. These results will be applicable to mountainous permafrost environments including the widespread coarse-grained periglacial landforms with permafrost such as rock glaciers, talus, blockfields and weathered bedrock. This is necessary to be able to better understand how entire periglacial landscapes will react to changing climates.

2019037819 Coch, Caroline (Royal Meteorological Society, Reading, United Kingdom); Ramage, Justine Lucille; Lamoureux, Scott F.; Meyer, Hanno; Knoblauch, Christian and Lantuit, Hugues. Impacts of permafrost disturbance on DOC, total dissolved solids and suspended sediment in Low Arctic coastal catchments [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2586, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic climate change leads to permafrost degradation and to associated changes in freshwater quality. There is a limited understanding how disturbances impact water biogeochemistry on a catchment scale. In this study, we investigated concentrations and fluxes of dissolved organic carbon (DOC), total dissolved solids (TDS), suspended sediment (SS) and water stable isotopes in paired and adjacent Low Arctic watersheds that have been subject to permafrost slope disturbance. We combined data on permafrost disturbance between 1952 and 2015 with data on geochemistry along longitudinal stream profiles. Our results show a decrease in total disturbed area by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66% for the six studied watersheds. The spatial variability of hydrochemical parameters is connected to catchment properties, which are not necessarily reflected at the outflow. Degrading ice wedge polygons were found to increase DOC concentrations in one headwater stream, whereas hydrologically-connected disturbances were linked to increases in TDS and SS downstream. Although hydrochemical concentrations varied considerably in the paired watersheds, we found a linear relationship between catchment size and daily DOC and TDS fluxes for all six streams. Suspended sediment flux did not show a clear relationship as a hydrologically connected retrogressive thaw slump impacted the overall flux in one of the streams. Overall, water composition in this Low Arctic landscape is influenced by permafrost degradation and understanding the spatial variability will help to model the geochemical fluxes from Arctic catchments.

2019037869 Conroy, Nathan Alec (Los Alamos National Laboratory, Los Alamos, NM); Newman, Brent D.; Wilson, Cathy Jean and Wullschleger, Stan. Temporal variance in Arctic polygonal ground surface water sources [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1062, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Surface water samples were collected at the Barrow Environmental Observatory (BEO, Barrow Alaska) during and after the snowmelt period in the late spring and summer of 2013. Deuterium and oxygen-18 ratios were assayed, in addition to a suite of inorganic ions. Geographic variability during the snowmelt period was evident, as well as temporal variability within a site selected for more intensive study. Distinct deuterium/hydrogen and oxygen-18/oxygen-16 ratios were observed, and were correlated to the snowmelt period, active-layer melt period, and recent precipitation events. Stable hydrogen and oxygen isotopes were used to estimate the timing and duration of the snowmelt and active layer thaws, as well as the relative contributions of snowmelt, active layer water, and recent precipitation to the surface waters. Consequently, measured concentrations of inorganic ions could be correlated to changes in the predominant source of surface water at a given time. These data and correlations will inform the development of improved hydrological and biogeochemical models of Arctic polygonal ground.

2019038138 Cook, Ann (Ohio State University, Earth Science, Columbus, OH); Waite, William F.; Spangenberg, Erik and Heeschen, Katja U. Petrophysics in the lab and the field; how can we understand and quantify gas hydrate pore-morphology and saturation? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS13A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Accurately quantifying the amount of naturally occurring gas hydrate in marine and permafrost environments is important for assessing its resource potential and understanding the role of gas hydrate in the global carbon cycle. In the laboratory and using geophysical well logs in the field, gas hydrate saturation (S_h) is often determined by two petrophysical measurements: compressional-wave velocity (V_p) measurements and electrical resistivity (or its inverse, conductivity). Almost twenty years ago, Dvorkin established four models for linking S_h to V_p. Each model assumed gas hydrate was homogeneously distributed in one of four idealized morphologies, and choosing the proper model required knowing which morphology was present. Research has increasingly pointed gas hydrate existing as a separate, connected phase in the pores when formed from dissolved-phase methane. This formation process is the most common in marine environments, and the resulting trend of V_p with S_h follows the predictions of the 'load-bearing' model. Moreover, we show recent work that indicates ice can be an accurate 'load-bearing' hydrate analog for V_p measurements to determine gas hydrate saturation, significantly lowering the time required for laboratory studies and eliminating the need for high pore pressures. Electrical resistivity measurements of gas hydrate and ice-bearing sediments, however, do not yield the same results in the field as they do in the laboratory, suggesting ice is probably not a reasonable analog for gas hydrate in this case. Here, we discuss possible reasons for differences between resistivity measured using downhole logging tools and resistivity measured in the laboratory. Furthermore, we share a newly-developed field-based technique that uses a combination of V_p and electrical resistivity to solve for a crucial petrophysical parameter, Archie's saturation exponent (commonly referred to as n). Using this technique at the Mallik gas hydrate research well in Canada and several wells with hydrate-bearing sands in the northern Gulf of Mexico, we found n=2.5±0.5.

2019040658 Coon, E. (Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN); Jan, Ahmad; Jastrow, J. D.; Painter, S. L. and Wilson, C. J. Exploring the interactions between thermal hydrology, soil structure, and dynamic topography in warming polygonal tundra [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Observations of warming Arctic polygonal tundra suggest significant changes in hydrology and geomorphology at multiple scales. The magnitude and pattern of these changes are fundamentally affected by ground ice and thermal and hydrologic properties of the landscape, potentially affecting both the water and energy balances. Answering seemingly simple questions like, "will a warmer Arctic be wetter or dryer than current conditions?" and "will carbon stored in polygonal tundra decompose into methane or carbon dioxide?" requires a careful consideration of the interplay of these processes. Such basic understanding is critical to predict the fate of carbon stored in thawing soils, infrastructure stability, and water fowl habitat. In coastal regions like Barrow, Alaska, systematic geomorphic change has been observed, including both subsidence across scales of 100s-1000s of meters and local polygon degradation at scales of 1s-10s of meters. As soils warm, ground ice thaws and soils subside and compact. The active layer gains new soil, but porosity decreases, changing where and how much water is stored in the soil column. As polygons degrade, poorly connected low centers that store significant snowmelt become well-connected high centers, resulting in significant increase in runoff and less potential for infiltration. The tradeoffs between these and other considerations are difficult to understand. We present a mechanistic model coupling permafrost thermal hydrology to a simple soil subsidence representation based upon grain consolidation. This model is parameterized by data derived from entire cross-polygon profiles (3m deep) at Barrow (reconstructed from analyses of soil horizons sampled via trenching and coring). A multi-decade regional subsidence record at Barrow is used to evaluate one-dimensional, regional subsidence simulations, and 100-year projections are explored. Finally, a first-of-a-kind, multiscale model integrates these columns through a dynamic parameterization capturing the impacts of polygon degradation on lateral flow. Predictions are made of how these processes interact to determine the fate of polygonal tundra under a warming climate. This work was supported by the DOE Office of Science, Biological and Environmental Research, through the NGEE-Arctic and Argonne TES-SFA projects.

2019038130 Creighton, Andrea (University of Wyoming, Geology, Laramie, WY); Parsekian, Andrew; Engram, Melanie J.; Jones, Benjamin M. and Arp, Christopher D. Trends in bedfast lake ice extent on the Arctic Coastal Plain of Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic landscapes are susceptible to stronger and earlier impacts from climate change than are the mid-latitudes. Thermokarst lakes are abundant landforms and ecosystems throughout the Arctic Coastal Plain of Alaska that play an important role in hydrology, ecology, and biogeochemical cycling. Whether lake ice freezes to the lake bottom or not is an important environmental parameter that has garnered extensive study. Changes in lake ice extent and depth through time have important implications for regional hydrology as well as potential sub-lake permafrost thaw and associated changes in the permafrost-carbon system. Previous studies have addressed the question of ordinal lake ice classification change through time (bedfast, floating, transitional, intermittent), but due to high levels of interannual variability in the short time window of data availability, have found no significant trends in lake ice regime in some areas. Analysis of space borne synthetic aperture radar lake ice regime classification over a 25-year study period using statistical methods focused on modes of probability density functions for multiple geographic regions across the Arctic Coastal Plain of Alaska, revealed no statistically significant relationship in ordinal regime changes for all lakes; however, trends in areal bedfast ice extent in the 0-60% bedfast ice interval emerged. This encompasses variation for lakes that are classified as transitional, intermittent, and some floating ice lakes that have bedfast shelves but precludes lakes that are greater than 60% bedfast. Lake depth and ice thickness are the determining factors for ice regime. Shallow lakes that are always bedfast do not respond to thinning lake ice; however, lakes and portions of lakes that are between 1-2 meters deep will show a response to ice that is thinning. Simple linear regression analysis revealed statistically significant slopes and good model performance in the vulnerable sub-population of lakes that are mostly floating ice. The results of this study elucidates the smaller scale changes occurring in the areal bedfast ice extents that could be indicative of future larger-scale changes.

2019040679 Cuozzo, Nicolas (University of Washington at Seattle, Department of Earth and Space Sciences, Seattle, WA); Sletten, Ronald S. and Stone, John. Constraining ages of glacial deposits recorded in a Victoria Valley permafrost core [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract PP23E-1536, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The past stability of the East Antarctic Ice Sheet (EAIS) remains an important, yet unsettled question. Efforts to address this question focus on EAIS stability during the Pliocene (5.33-2.58 Mya), a period characterized by CO₂ levels comparable to today's levels and global mean temperature comparable to those predicted for the end of the century. While the marine record from the Antarctic Drilling Project (ANDRILL) and recent ice-sheet models suggest a dynamic EAIS during the Pliocene, there is not yet strong corresponding terrestrial evidence of a dynamic Pliocene EAIS. Stratigraphic and geomorphic evidence of glacial deposits from EAIS outlet glaciers in the Antarctic Dry Valleys may provide the much-needed terrestrial record of EAIS stability. Here, a 15-meter ice-cemented permafrost core collected in Victoria Valley is analyzed using cosmogenic nuclides to provide quantitative constraints on the timing of the EAIS glacial history in the Dry Valleys. Based on the presence of oxidized layers from apparent paleosols, the core appears to have recorded four depositional events that are believed to represent different periods of glaciation. Each depositional unit was deposited and exposed to cosmic rays at the surface until subsequently buried during the next glacial event that then shielded the sediment from further cosmic ray exposure. Sediment was subsampled in the core at the upper, middle, and lower limits of each depositional unit and analyzed for ¹⁰Be and ²⁶Al, as well as texture, soluble salts, and other parameters. Several possible models of the burial history, accounting for exposure time, burial time, and inherited nuclides, are tested using inverse modeling techniques to provide a timeline for EAIS history in Victoria Valley. Preliminary results of the four units show ages of 30 Ka, 1.05 Ma, 2.4 Ma, and 3.9 Ma, suggesting the earliest expansion of the EAIS coincides with the warmer and wetter conditions during the Pliocene and corroborates the ANDRILL findings.

2019037861 Daanen, Ronald P. (Department of Natural Resources, Fairbanks, AK); Liljedahl, Anna K. and Schulla, Jorg. Modeling surface water and soil freezing processes using WaSiM [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1052, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Hydro-thermal soil processes drive surface and permafrost temperatures in northern regions. We are developing WaSiM to be a state of the art permafrost hydrology model that can simulate the thermal regime of permafrost in addition to the hydrological response of the landscape to variably frozen conditions. WaSiM is a capable hydrological model for the simulation of dynamic glaciers, snow and permafrost. We are currently interested in developing better surface hydrology interaction with thermal processes. Especially in ice wedge degradation regions the presence of surface water ponds can significantly change the thermal behavior of the ground. In this study we show strong delay, due to latent heat release from surface ponding, on the freezing of the active layer in the fall. WaSiM has a surface routing module that we use to simulate standing water on the frozen tundra in the summer. We take that amount of standing water that is in equilibrium with other hydrological fluxes and use it to simulate freezing ponds. Rather than simulating the surface processes separately we choose to include the standing water column in the soil column in order to simulate the freezing process of the standing water integrated with the freezing of the underlying active layer. We show that including the process of freezing surface water in the thermal regime of a high resolution simulation of an ice-wedge polygon landscape in Barrow Alaska, improves soil temperatures significantly especially during fall when surface water in these ponds freezes.

2019037867 Dafflon, Baptiste (Lawrence Berkeley National Laboratory, Berkeley, CA); Akins, Hunter; Lamb, Jack; Leger, Emmanuel; Ulrich, Craig; Uhlemann, Sebastian; Shirley, Ian; Peterson, John E.; Biraud, Sebastien and Hubbard, Susan. Development and use of a distributed temperature profiling (DTP) system to estimate arctic soil thermohydrology and depth to permafrost, and their relationships with geomorphological and vegetation properties [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1060, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

A substantial improvement in our ability to quantify and monitor soil and permafrost thermohydrology is important for improving our prediction of Arctic ecosystem feedbacks to climate under warming temperatures. In particular, understanding the relationships between soil thermal and hydrological behaviors, soil physical properties (incl. fraction of soil constituents, bedrock depth, permafrost characteristics), and landscape properties could greatly improve our predictive understanding of the subsurface storage and fluxes of water, carbon and nutrients in permafrost environments. However, obtaining such information is extremely challenging using conventional measurement approaches. We developed a novel approach called Distributed Temperature Profiling (DTP) to address this measurement challenge. This system involves a network of vertically-resolved thermistor probes (>10 thermistors/probe) with an accompanying data acquisition system to autonomously sense the temperature regime at numerous depths and locations. The DTP system has been developed with an extraordinarily low production and assembly cost; uses automated data acquisition, management and transfer; and leverages open source software and hardware to encourage community-based development and deployment. Here, we describe the new DTP system and its joint use with electrical resistivity tomography (ERT) datasets, soil sample analysis, soil moisture data, and UAV-inferred vegetation indexes, digital surface elevation models and snow thickness to investigate the characteristics of and controls on permafrost processes in a watershed on the Alaskan Seward Peninsula. Together, the various datasets allowed us to distinguish shallow permafrost from deep permafrost with an overlying perennially thawed layer (i.e., suprapermafrost talik) implying year-round subsurface fluid flow and transport. In addition, relationships between the subsurface permafrost/soil characteristics, the topography, the snow thickness and vegetation distribution were identified. Finally, spatial and temporal variations in DTP and ERT, both showing strong lateral variations over a few meters, indicate the presence of preferential flow paths to depths of ~20m.

2019037797 Dann, Julian (Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM); Bolton, Bob; Charsley-Groffman, Lauren; Jafarov, Elchin E.; Lathrop, Emma; Musa, Dea; Wullschleger, Stan and Wilson, Cathy Jean. Understanding controls on Arctic soil moisture using in-situ soil moisture and thaw depth observations and airborne SAR data at Barrow and Seward Peninsulas, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2535, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The DOE Office of Science Next-Generation Ecosystem Experiments, NGEE-Arctic project is a multi-lab effort working to improve the representation of arctic terrestrial processes in Earth System Models. By co-analyzing in-situ and remote sensing data at multiple sites, we aim to extend local observations to regional scales. Here we present an analysis of in-situ measurements of soil moisture and thaw depth collected during the summer of 2017 coincident with airborne overflights of L and P-band SAR instruments in collaboration with the NASA Arctic Boreal Vulnerability Experiment (ABoVE) project's Airborne SAR Campaign. In particular, we examine how local geomorphology, topography, climate and vegetation properties interact with thaw depth and soil moisture across a range of field sites and settings near Utqiagvik, AK and Nome, AK. In Utqiagvik, in-situ data were collected at high-center, flat-center, and low-center polygons during the June SAR P-band and September L-band overflights. At all sites on the Seward Peninsula, in-situ data were collected in May and August, coincident with P-band overflights. At each field site the same measurement techniques were used including the establishment of multiple 100 m by 100 m plots designated for SAR ground-truthing. Within each "SAR plot" two 60 meter transects were established along which both soil moisture and thaw depth measurements were taken. This configuration is consistent with the ABoVE protocols which enables proper averaging of multiple pixels for airborne or spaceborne SAR data. Moisture data was collected using a Hydrosense-II soil-water sensor and data logger which relies on the dielectric properties of the soil to estimate volumetric moisture content (VMC). Soil moisture and thaw depth are key factors controlling subsurface biogeochemistry and surface ecosystem type and function. Our observations and analysis provides a unique benchmark dataset with which to test predictions of spatial variation and temporal evolution of soil moisture in local and regional permafrost models. Dataset DOI:10.5440/1423892 LA-UR-18-27341

2019037862 Debolskiy, Matvey Vladimirovich (University of Alaska at Fairbanks, Fairbanks, AK); Alexeev, Vladimir A.; Nicolsky, Dmitry; Hock, Regine; Romanovsky, Vladimir E.; Shiklomanov, Alexander I. and Lammers, Richard B. Modeling the response of permafrost affected mesoscale watersheds to long term warming [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1053, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Recently observed increase in the Arctic river runoff and subannual reshaping of the hydrographs demand an explanation of processes responsible for these changes. Theoretical models of heat and water dynamics in the ground material suggest a non-linear response of permafrost to increase in air temperature. In this work, we employ a distributed water-balance model WaSiM to investigate how a synthetic mesoscale watershed reacts to changes in the air temperature on a millennial timescale. All case studies are completed using the same precipitation forcing for Alaska. The change in temperature we apply is based on the observed trend for the same area. We analyze the sensitivity of the present-day steady state and its potential responses to different levels of warming and to soil parameters within the watershed such as the van Genuchten soil retention parameter, hydraulic conductivity and the anisotropy of soil properties. In addition, we investigate how roughness and steepness of the watershed terrain affect the permafrost and water-balance responses to the warming on the millennial timescale. Furthermore, we analyze changes in the water-balance components: evapotranspiration, river runoff and groundwater recharge as well as changes in the runoff components: surface flow, interflow, and baseflow. Preliminary results suggest that timing and severity of an increase in the baseflow and an associated decrease in the interflow strongly depend on the physical parameters of the ground material and occur on the millennial timescale, whereas the surface flow and evapotranspiration responses are triggered almost immediately.

2019038108 Destouni, Georgia (Stockholm University, Physical Geography & Bolin Centre for Climate Research, Stockholm, Sweden). Modelling permafrost thaw relationships with local landscape conditions and waterborne spreading pathways as basis for assessing pathogen exposure-risk in northern regions [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GH33B-1239, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Climate change is greatly felt in northern regions, which experience greater climate-driven change rates and magnitudes than elsewhere, including permafrost thaw as an essential change component. Permafrost serves as a natural bank for a variety of organic material, dormant propagules (seeds, eggs, cysts, or spores from plants and invertebrates) and other viable vectors (bacteria, viruses). Thawing of permafrost may lead to re-emergence of these, with increased health and wellbeing risks for animals and humans. In Russia in 2016, for example, reappearance of buried anthrax-infected animal carcasses under permafrost thaw led to hospitalization, quarantine and/or relocation of indigenous peoples in the Yamal-Nenets Region, while their reindeer also perished from either infection or extermination. A key question for the change evolution of permafrost under global warming is how the increased surface temperature interacts with local landscape conditions in determining where thawing is likely to occur and as such lead to increased health risks. This paper synthesizes results from systematic simulations of various permafrost systems and surface warming trends, as basis for starting to answer this key question. Simulation results show that, even under moderate surface warming of up to 2°C or less over the coming decades, major permafrost thaw is likely to occur more at depth and lead to possible re-emergence of more pathogens and infectious diseases in peat lands than in other local soil-rock formations. Exposure risks associated with such re-emergence are further amplified by quantified faster waterborne pathogen spreading from the subsurface to the surface biosphere after thawing than under intact permafrost. In general, such systematic simulations of permafrost thaw development under various local conditions and warming trend scenarios is essential for assessing associated pathogen-exposure risks in permafrost regions.

2019037788 Dillon, Megan (Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences, Berkeley, CA); Xue, Yaxin and Tas, Neslihan. Arctic permafrost microbiomes; a meta-analysis [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2502, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic soils will be a net source of greenhouse gas (GHG) emissions (CO₂, CH₄, and N₂O) as temperatures rise according to warming experiments and field observations. Indeed, permafrost is already melting, as evidenced by increasing active layer thickness, and increased rates of permafrost loss in the past decade. Microbes contribute substantially to permafrost GHG emission. Recent studies suggest that permafrost types and features vary greatly across the Arctic, and topography and local hydrological conditions, specifically, appear to be important determinants of microbiomes and GHG emissions. However, knowledge of their geospatial variation or connectivity across the Arctic is limited. Similarly, microbiomes across permafrost soils appear to have some common features, including dominance by Actinobacteria and a shift from DNA repair and survival strategy genes to carbon mineralization genes as permafrost thaws, but landscape-level differences have yet to be analyzed. To predict future GHG emissions, we must quantify the effects of permafrost soil properties on microbiomes across the Arctic. This meta-analysis of permafrost metagenomes across the Arctic quantifies soil characteristics and microbial community composition and metabolic potential. We obtained metagenomes from Alaska, Sweden, Canada, Russia, and Antarctica (MacKelprang et al. 2011 Nat; Hultman et al. 2015 Nat; Chauhan et al. 2014 Gen Announc; Emerson et al. 2018 Nat Microbiol; Rivkina et al. 2016 Biogeosci; Goordial et al. 2017 Environ Microbiol) to compare environmental drivers including but not limited to water content, topography, continuity, active layer depth, and vegetation. The microbial communities inhabiting these soils have some common members and metabolic capacity, including the prominence of Actinobacteria and stress response genes, but differ in the extent to which Eukaryotic and viral populations were represented and in the abundance and biochemistry of methanogens. These results contribute to an understanding of global variation in the microbial ecology of permafrost. Recognizing geospatial patterns in soil properties and microbiome characteristics across Arctic permafrost landscapes will allow us to better predict how permafrost responds to global climate change.

2019037796 Dogaheh, Kazem Bakian (University of Southern California, Ming Hsieh Department of Electrical Engineering, Los Angeles, CA); Chen, Richard H.; Silva, Agnelo; Yi, Yonghong; Tabatabaeenejad, Alireza and Moghaddam, Mahta. Low frequency behavior of organic soil for a multi-phase study of a permafrost soil dielectric model [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2530, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Accurate electromagnetic dielectric characterization of the soil organic horizon (in conjunction with below-ground biomass) is a necessary step for accurate soil moisture retrieval within land with high organic matter content. It is also needed for retrieval of permafrost active layer properties with active or passive microwave remote sensing techniques in boreal and arctic regions. The reason is that microwave remote sensing measurements are sensitive to dielectric properties of soils in these regions. An additional step is needed to convert dielectric properties to soil moisture or soil organic content. This work presents a method to characterize low frequency dielectric behavior of soil samples that we will collect at multiple locations in Alaska's North Slope (along the Dalton Highway) in August 2018. These soil samples are expected to have different amounts of soil organic matter (SOM)-measured with the loss on ignition method-root biomass, and mineral texture. We will measure the vertical distribution of SOM as well as the dielectric constant of each soil sample from saturated to dried states. To this end, we are developing an automatic soil measurement system that is capable of simultaneously measuring physical parameters of multiple soil samples such as soil dielectric constant (using METER TEROS12) and soil water matric potential (using METER Teros21). These measurements will provide a preliminary dataset to develop a model as a primary step for developing a more advanced soil dielectric model, which would translate retrieved dielectric constant from radar backscatter to soil moisture. We will discuss findings of our study, including the required inputs for a universal soil model. We will also present the design and performance of our novel automatic soil measurement system, as well as the measurement sites, their characteristics, our sampling protocols, and measurement methods. The developed dielectric model will be presented at the end.

2019038124 Donaldson, Yonesha Y. (Rutgers University, Newark, NJ); Cambeiro, Joaquin; Pope, Gina; O'Neill, Paul; Mount, Gregory; Keating, Kristina; Brantley, Susan and Nyquist, Jonathan. Characterizing the subsurface of the critical zone in the Garner Run catchment at the Susquehanna hale hills critical zone observatory using electrical resistivity [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS41B-0819, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Electrical resistivity tomography data were collected in the Garner Run subcatchment of the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO) from 19 May to 2 June 2018. Garner Run is a headwater subcatchment with a small stream parallel to a syncline fold axis of an erosionally resistant orthoquartzic sandstone with interbedded shale units. The surficial geology at Garner Run is largely controlled by periglacial processes, such as slumps and solifluction lobes that are associated with thawing permafrost soils. Electrical resistivity tomography data were collected to better understand the subsurface architecture and to identify variations in and delineate the depth of valley fill. The valley fill consists of poorly sorted sand to cobble size sediment that has been transported downslope. Understanding the depth and location of these deposits across the valley can be used to better constrain the geomorphological process that formed this region.

2019037779 Douglas, Peter Monroe (McGill University, Earth and Planetary Sciences, Montreal, QC, Canada); Gonzalez Moguel, Regina; Crill, Patrick M.; Wik, Martin; Walter Anthony, Katey M.; Eiler, John M. and Sessions, Alex L. Methane radiocarbon and clumped isotope measurements in lakes from permafrost landscapes link methanogenesis kinetics with the age of carbon substrates [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2489, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The potential for substantial quantities of old carbon stored in permafrost to be released as methane is of great concern, but is also poorly constrained. A key unresolved question is whether old organic matter released from thawing permafrost is as efficiently converted to methane by microbial communities as recently produced organic matter, since older organic matter is generally more biologically recalcitrant. To address this question we compared measurements of methane radiocarbon (¹⁴C) content with clumped isotope measurements, or the relative abundance of methane containing multiple rare isotopes, in a set of fifteen ebullition gas samples from eight lakes in permafrost landscapes. Specifically, we sampled three glacial lakes in Sweden and five thermokarst lakes in Alaska. Methane ¹⁴C content indicates the average age of methanogen carbon substrates, while clumped isotope measurements of microbial methane are thought to be a sensitive indicator of the kinetics of methane formation, with faster cell-specific rates of methane production leading to lower clumped isotope values. We observe a significant positive correlation between methane ¹⁴C age and clumped isotope values in the samples from both the Swedish glacial lakes and the Alaskan thermokarst lakes. However, the relationships are distinct for these two lake types, with older ¹⁴Cages for a given clumped isotope value in the thermokarst lakes. Clumped isotope values are a stronger predictor of methane ¹⁴C age than conventional methane isotope ratios (dD or d¹³C), methane concentration, or methane flux for both lake types. The observed correlations imply that, in these ecosystems, cell-specific methane production is progressively slower with older carbon substrates. The different clumped isotope-¹⁴C age relationships observed in the glacial and thermokarst lakes could reflect that the relationship between methanogen kinetics and substrate age is controlled by the depth of methane production in lake sediments or underlying permafrost, as opposed to the absolute age of the carbon substrates. Overall, these data suggest that in northern lakes old carbon reservoirs are not as efficiently converted to methane as recently produced carbon, a finding that could have implications for future methane emissions from thawing permafrost.

2019040630 Douglas, T. A. (Cold Regions Research and Engineering Laboratory Alaska, Fort Wainwright, AK) and Blum, J. D. The source and fate of snowpack mercury in a watershed underlain by continuous permafrost near Utqiagvik, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B54B-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We measured mercury (Hg) and major ion concentrations and Hg stable isotope ratios of snowpack and melt water in spring melt runoff for two years at a site near Utqiagvik (formerly Barrow), Alaska. Permafrost peat and sediment cores were collected and analyzed for Hg concentrations and Hg stable isotopes. Our field site, a small (2.5 ha) watershed on the Arctic coastal plain, is exposed to Arctic Mercury Depletion Events (AMDEs) with Hg concentrations in snow and sea ice sometimes approaching 1,000 ng/L. In late winter prior to snowmelt (April) and during snowmelt runoff in May and June 2008 and 2009, we made over 10,000 snow depth measurements and 80 snowpack water equivalent measurements within the watershed. Snowpack, meltwater, and stream channel water were sampled and analyzed for total dissolved Hg, major ions, and stable oxygen and hydrogen isotopes. Airborne LiDAR and and high resolution GPS surveys were used to delineate the watershed area to cm scale accuracy. We identified an "ionic pulse" of mercury and major ions in runoff during both snowmelt seasons with total dissolved Hg in runoff of 14.3 (+/- 0.7) mg/ha in 2008 and 8.1 (+/- 0.4) mg/ha in 2009. This runoff flux is five to seven times higher than what has been reported from other arctic watersheds and from lower latitudes. We calculate 78% of snowpack Hg was exported with snowmelt runoff in 2008 and 41% in 2009. Hg stable isotope measurements indicate the majority of the snowmelt Hg originated as gaseous elemental mercury (GEM; Hg(0)) that was oxidized in the snowpack by reactive halogens. »75% of the Hg exported from the watershed in snow melt came from non-AMDE sources while »25% is attributable to AMDE deposition. Our Hg stable isotope analyses indicate Hg was deposited directly to the snowpack as GEM and converted to Hg(II) in the snowpack by reactive halogens. This Hg comprises the majority of the mercury remaining until snowmelt discharged into meltwater of our Arctic coastal ecosystem. We surmise that the halogen rich snowpack facilitated oxidation and retention of gaseous elemental Hg. Projected future warming in the Arctic will produce an increasingly dynamic sea ice regime with more first year ice and open sea ice leads. This will likely enhance the source of reactive halogens, promote GEM oxidation, and lead to greater Hg deposition to coastal and marine snowpacks.

2019040663 Duggan, Brian (University of South Carolina Columbia, Department of Earth and Ocean Sciences, Columbia, SC); Scher, Howie; Haley, Brian A. and Goldstein, Steven L. Neodymium isotopes in the western Arctic highlight the role of sediment-water interaction in the distribution of Nd isotopes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS23E-1662, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We measured neodymium isotopes (Nd) from eight high-resolution profiles across the Bering Strait into the Canada Basin in an effort to further constrain the sources and sinks that control the distribution of Nd. In seawater, neodymium isotopes retain provenance information from the water mass source area and often are observed to behave conservatively with water mass mixing, however, the isotopic composition can be altered via reversible scavenging, boundary exchange, and groundwater inputs. Recent studies indicate rising temperatures in the Arctic have led to reduced ice cover, permafrost thawing, and increased river discharge, which can alter the distribution of Nd throughout the basin. We observed a large gradient across the Bering Strait, from the radiogenic Pacific endmember of -1.6 to -4.4 upon entering the Canada Basin. This change can be attributed to the relatively unradiogenic sediment inputs entering the strait from the Western Alaskan Yukon river (-8.4; Yoshihiro et al., 2011). Within the Canada Basin we observe near surface water (~100 m) to be less radiogenic than expected based on the composition entering the basin. Similar to the Bering Strait, we suggest pore fluid flux from the sediments would lead to the less radiogenic composition observed for near-surface water in the Canada basin, which is corroborated by radium isotopes (Kipp et al., 2018). Nd in the deep Canada basin shows a fundamental shift with respect to measurements made more than a decade prior. Porcelli et al. (2009) show Atlantic sourced water with an Nd of -10.8 dominate the deep Canada Basin, however, our measurements depict a more radiogenic composition along the deep Chukchi slope of ~-9.5. We point to boundary exchange processes in the eastern Arctic, where dissolved iron has been shown to be released via resuspension of sediment along the margin at a depth such that it would flow into the western Arctic Ocean (Klunder et al., 2012). Moreover, sedimentary iron- manganese coatings from the shelf in the Nansen basin are more radiogenic (~-8.4; Haley and Polyak, 2013) than the Atlantic inflow and could alter the composition of the water as it traverses the margin to the western Arctic Basin.

2019038093 Dvornikov, Yury A. (Russian Academy of Sciences, Siberian Branch, Earth Cryosphere Institute, Tyumen Scientific Centre, Moscow, Russian Federation); Leibman, Marina O.; Khomutov, Artem and Kizyakov, Alexander I. Gas emission from permafrost; new possible mechanism of the lake formation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1401, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Limnicity of Yamal is 10% on average (Trofimov eds. 1975). The origin of these lakes is described in numerous publications (Beletskaya, 1987, Romanenko, 1999). However, no publications describe the possible gas-emission mechanisms for a lake basin formation. After the appearance of gas-emission crater (GEC) in Yamal peninsula (Leibman et al., 2014) we started to monitor this permafrost feature and observed that it can form a new lake in three consecutive summer seasons. Here we suggest that other lakes in the North of Wester Siberia might have similar origin. For proving this hypothesis, we analyze hydrochemical and morphometric features of GEC-lakes (on Yamal and Gydan) and compare them with background lakes in this area. GEC1 lake was characterized by elevated dissolved methane (dCH₄) concentration at the bottom layer throughout 2015 and 2017 (winter and summer). Values of dCH₄ were almost 50 times higher than in Yamal lakes on average (45 ppm). Given this distribution it can be assumed that source of methane existed after the GEC appearance. Most likely the gas is continuously delivered from the gas saturated sediments and further oxidized at the upper part of the lake. Our dataset on methane isotopes suggests that the source of methane is primarily biogenic as the values of d¹³C are less than -60 ppm (Bernard et al., 1976). Values of d¹³C of methane extracted from deep boreholes of Bovanenkovo gas field (depths 28-120) varies from -74.6 to -70.4 ppm also corresponding to biogenic origin (Skorobogatov et al., 1998). Geochemistry of lakes in central Yamal with a domination of Na and Cl ions reflect the marine origin of sediments. The domination of HCO₃ anion in GEC lakes can be a signal of close connection to tabular ground ice (TGI). This implies that thaw of TGI is a considerable source of water in GEC lakes. Isotopic composition of water also supports this hypothesis. In western Siberian lakes crater-like depressions have been observed and named as gas-explosion craters (Kuzin, 1975, 1980, Sizov 2015, Bogoyavlenskiy et al., 2017). Detailed bathymetric survey in 21 lakes revealed several crater-like depressions with relative depth of 10-20 m below the average surface of lake bottom and steep slopes (>36 degrees, 8.4 on average). Such depressions can be a remnant of former gas flows from permafrost.

2019040622 Dyonisius, M. (University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY); Petrenko, V. V.; Smith, A. M.; Beck, J.; Schmitt, J.; Menking, J. A.; Shackleton, S.; Hmiel, Benjamin; Vimont, Isaac; Hua, Q.; Yang, B.; Seth, B.; Bock, M.; Beaudette, R.; Harth, C. M.; Baggenstos, D.; Bauska, T. K.; Rhodes, R.; Brook, E.; Fischer, H.; Severinghaus, J. P. and Weiss, R. F. The contribution of geologic emissions, thawing permafrost and methane hydrates to the global methane budget; perspective from ice core records [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43D-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Studies of methane (CH₄) mole fraction and isotopes from trapped air in ice cores provide a long-term perspective on the natural CH₄ budget. Among the CH₄ isotopes, ¹⁴CH₄ is unique in providing a definitive top-down constraint on the total fossil CH₄ emissions from old carbon reservoirs (marine hydrates, permafrost, natural geologic seeps). We present new measurements of ¹⁴CH₄ throughout most of the Last Deglaciation (»15-8ka). Our ¹⁴CH₄ data show that ¹⁴C-depleted CH₄ sources (marine hydrates, geologic seeps and old permafrost) were not significant contributors to the deglacial CH₄ rise. As the relatively large deglacial global warming (»4°C, with warming further amplified at high latitudes) did not trigger CH₄ emissions from old carbon reservoirs, such emissions in response to future warming also appear unlikely. Our results also strengthen the suggestion from an earlier study (Petrenko et al. 2017) that natural geologic emissions of CH₄ are much lower (less than 15 Tg CH₄ yr^-1, 95% confidence) than recent bottom-up estimates (54-60 Tg CH₄ yr^-1) (Etiope 2015; Cias et al. 2013) and that, by extension, estimates of present-day total anthropogenic fossil CH₄ emissions are likely too low.

2019040586 Eicken, H. (University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK); Starkweather, Sandra; Loescher, H. W.; Pirazzini, R.; Sueyoshi, T.; Bradley, Alice C.; Koyama, T.; Eaton, Claire; Kodama, Y.; Sobin, Jacob; de Halleux, Sebastien; Frank, C.; Shichang, K.; Kang, S. H. and Chierici, M. Towards structured coordination of sustained observations of Arctic change; an update from the Arctic Observing Summit 2018 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A24K-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Understanding, predicting, and responding to a rapidly changing Arctic requires sustained observations that capture variability and transformative change of the Arctic systems with all its major components. A key challenge for researchers, Arctic communities, and others tasked with effective responses to such change is to achieve structured coordination of numerous individual observing activities and networks. These have different regional and thematic foci. Many are driven from the bottom-up by research interests, while others are mission-oriented operational networks. The Arctic Observing Summit (AOS) is an effort that seeks to help coordinate such disparate activities and support efforts such as the Sustaining Arctic Observing Networks (SAON) initiative. We report on progress as part of an AOS 2018 working group focused on implementation and optimization of sustained observations. Drawing on the Framework on Ocean Observations, our group identified effective approaches and barriers to integration of different observation requirements and activities/platforms into a coherent observing framework. Case studies for benthic communities, sea ice prediction, and permafrost highlighted the importance of allowing for independently driven activities to coalesce into a uniform framework. This in turn requires clearly defined requirements that ideally serve multiple societal benefits. Such clear definitions also aid private-public partnerships and the development of new observing system business models. Prerequisite to better coordination is a comprehensive, international assessment that describes the current set of systems, community-based networks, sensors, networks, and surveys that are used to observe the Arctic today. Pieces of such an endeavor are starting to emerge, and SAON may serve as a home for integrating and building upon these pieces. Essential to this goal is the development of a knowledge map that collates and connects observing resources to societal benefits, helps identify and prioritize essential variables, data management needs, and critical products and services. The AOS 2018 calls for the launch of an optimization and implementation team of experts that would conduct such an effort under the auspices of SAON. We explore different elements of such a team's portfolio of tasks.

2019040600 Elder, C. (Jet Propulsion Laboratory, Pasadena, CA); Thompson, D. R.; Thorpe, A. K.; Walter Anthony, K. M. and Miller, C. E. Broad-scale geospatial analysis of CH₄ emissions using high-resolution airborne hyperspectral imagery across Alaska and Western Canada [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B12C-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane (CH₄) emissions from northern-high-latitude permafrost regions, containing roughly half of Earth's soil organic carbon pool, contribute significantly to the global CH₄ budget. As permafrost degrades, under warming rates twice the global average, increased CH₄ emissions have the potential to accelerate a warming climate. Despite these concerns and decades of study, we have poor understanding of the heterogeneous environmental processes that regulate CH₄ emissions across space and time in permafrost regions. Here, we report novel airborne imaging spectroscopy from NASA's Next-Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) which observed CH₄ enhancements at 5-meter resolution across broad regions in Alaska and western Canada. These results provide unprecedented resolution and coverage of CH₄ emissions, enabling a new perspective on the key environmental regulators of emissions from plot-level to landscape scales. Preliminary analysis from the 2017 Arctic Boreal Vulnerability Experiment Airborne Campaign revealed tens of thousands of enhanced CH₄ emission hotspots associated with ponds, lakes, streams, rivers, and other wetland features. Domain-wide statistics relate the likelihood of strong CH₄ emissions to the distance from standing water (Figure). The relationship is consistent with two power law functions that dominate at different scales. Within 40 m of standing water, CH₄ enhancement rate is highly correlated with distance, demonstrating the importance of lake littoral processes and/or active thermokarst. For distances > 40 m from standing water, the CH₄ enhancement rate follows a more gradual power law function, which may track a deepening water table and/or transition to upland soils and vegetation. Initial results from simultaneous ground-based flux observations and AVIRIS-NG overflights in 2018 show general agreement with the domain-wide power laws and provide an empirical parameterization for AVIRIS-NG CH₄ enhancements. This work represents the early steps in revolutionizing remote CH₄ observations at scales relevant for process-level understanding of permafrost CH₄ emissions. This new dataset also shows potential to reshape our understanding of landscape-scale controls on CH₄ emissions relevant for land models and satellite observations.

2019040599 Engram, Melanie J. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Walter Anthony, K. M.; Sachs, T.; Kohnert, K.; Serafimovich, Andrei; Grosse, G. and Meyer, F. J. Quantifying methane ebullition from northern lakes with space-borne synthetic aperture radar (SAR) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B12C-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Lakes in the northern permafrost region are a significant source of atmospheric methane (CH₄), a potent greenhouse gas, yet large uncertainties exist in quantifying lake-source CH₄. In thermokarst (thaw) lakes, the dominant pathway of CH₄, ebullition (bubbling), is sporadic and spatially irregular. These lakes are also generally remote and difficult to access, resulting in challenging and costly field measurements. Scaling up field measurements from a few study lakes to regional and pan-Arctic scales relies on the assumption that the sampled lakes are a fair representation of all lakes across a landscape, which is not always the case. We present an innovative new method of quantifying lake-source CH₄ using space-borne synthetic aperture radar (SAR), an instrument which can image at night, through clouds and dry snow, valuable attributes for Arctic remote sensing. Our recent work using satellite-based SAR data showed a significant correlation between polarimetric L-band SAR backscatter from lake ice and field-measured ebullition bubbles: L-band SAR backscatter intensity increases with the amount of ebullition bubbles trapped by early winter lake ice. We developed a regionally robust empirical model based on this correlation to quantify ebullition across surfaces of over 5,000 individual Alaskan lakes in satellite SAR scenes. We produced SAR-based ebullition fluxes from each lake across the landscape and created CH₄ maps for five sub-regions in Alaska. Our SAR-based lake-source CH₄ fluxes compare favorably with airborne CH₄ measurements on the Barrow Peninsula and Atqasuk regions, and with scaled-up field measurements. We examine how our SAR remote sensing application can 1) improve selection of study lakes for field work, 2) provide regional estimates of CH₄ ebullition from lakes in remote areas where field work is limited, 3) improve lake-size vs. flux relationships for upscaling field measurements and 4) shed light on the discrepancy of top-down vs. bottom-up CH₄ flux estimates in the Arctic. This new approach to estimate lake-source CH₄ from ebullition offers a unique opportunity to improve knowledge about CH₄ fluxes for seasonally ice-covered lakes globally.

2019038059 Escarzaga, Stephen Michael (University of Texas at El Paso, El Paso, TX); Kinsman, Nicole and Tweedie, Craig E. Structure-from-motion production and analysis of digital surface models of NOAA coastal airborne imagery from Alaska's North Slope [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2365, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Alaska's northern coastline from the Canadian border to Kotzebue Sound is notably lacking in elevation data that is needed to estimate volumetric change along the coastal bluff, identify areas of permafrost degradation, and update shoreline positions. In 2016 and 2017, NOAA's Remote Sensing Division collected 50 cm resolution, semi-oblique and nadir georeferenced RGB imagery along Alaska's southeastern, western and northern coastlines as baseline datasets to aid in navigation, determine pre-storm conditions and facilitate in coastal-zone management. The 2017 imagery extends along approximately 800 km of Alaska's remote North Slope coastline, includes an additional near-infrared (NIR) band and was collected with overlap sufficient for the application of Structure-from-Motion (SfM) photogrammetric techniques. SfM techniques have the ability to produce Digital Surface Models (DSMs) of complex topography from overlapping imagery and minimal ground control, with resultant ground sampling distances that are comparable to LiDAR. Although photogrammetric methods such as SfM do not offer the multi-return capabilities of LiDAR that allow for the discrimination between vegetation and bare ground, SfM methods are well suited to the coastlines of the North Slope of Alaska where vegetation is sparse or low-lying. DSM production from this image collection fill a vital gap in elevation data for this region and, when combined with near-infrared (NIR) imagery, present opportunities to better understand vegetation phenology and health in Arctic areas undergoing substantial change. Here we present a protocol for Structure-from-Motion processing into DSM datasets from a subset of the 2017 NOAA airborne imaging data collected in the Arctic National Wildlife Refuge and its comparison to other elevation data sources. We also present coastal volumetric change estimates and assess the potential for these DSMs to be used in extraction of vector coastline features.

2019038062 Etzelmuller, Bernd (University of Oslo, Department of Geosciences, Oslo, Norway); Krautblatter, Michael; Myhra, Kristin Saeterdal; Hermanns, Reginald L.; Jakobs, Benjamin; Magnin, Florence; Westermann, Sebastian and Hilger, Paula. Permafrost as an important factor for valley formation in glaciated regions [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP24B-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Ground temperatures is steep slopes are a well-recognized factor for slope stability. In rock walls cold permafrost tends to be stable due to additional cohesion provided by ice bonds. A warming of such rock faces influences the ice rheology in rock joints, and decreases tensile and compressive stresses in rock masses. During the transitions between glaciation and inter-glaciation many oversteepened valley slopes encounter repeatedly strong cooling and warming, leading to permafrost aggradation and degradation over relatively short time periods depending on regional deglaciation patterns. We hypothesize that this dynamic is a major factor for slope instabilities after deglaciation in addition and in concert to debutressing. To test this hypothesis, we have employed a 2D heat flow model over glacial-interglacial cycles, which subsequently has been input into a thermo-mechanical stability model. In addition, emerging sliding planes and deposits from major rock slide events were dated using cosmogenic nucleides. The results indicate the development of progressive instability modulated by permafrost development that acts to transiently influence the mechanical stability of bedrock. Therefore, permafrost dynamics may be an overlooked factor for understanding valley forming processes during glacial-interglacial transitions, while at the same time influencing present-day rock fall processes in deglaciated areas.

2019031995 Euskirchen, Eugenie Susanne (University of Alaska at Fairbanks, Fairbanks, AK); Kane, Evan S.; Turetsky, Merritt R. and Edgar, Colin. Divergent responses of a rich fen in interior Alaska to inundation; interannual variation in carbon fluxes and water balance [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The areal extent of boreal rich fens in interior Alaska has increased in recent years in conjunction with permafrost degradation, and is expected to continue to increase in the future. The increase in the extent of these fens, which store large amounts of carbon in deep organic deposits, is coupled with changes in their water inputs, including projected increases in precipitation, runoff, and groundwater discharge. Despite these recent and expected changes, we have little understanding of how differing sources of inundation to these fens will influence carbon and water fluxes. Here, we examine interannual variations in carbon and water fluxes at a rich fen in interior Alaska during years in which the fen remained inundated, with a water table depth that remained well above the surface due to differing sources of inundation, as well as years during which the water table depth dropped below the surface. We found large variations in the water balance (precipitation - evapotranspiration; -208 mm to +101 mm) that were driven more by precipitation than evapotranspiration, but the water balance could be either positive or negative under flooded conditions. Over the full course of measurements, from May 2011 - December 2017, the fen was estimated as a source of CO₂ of ~146 ± 60 g C m^-2. Much of this source strength was related to an anomalous year, 2014, when winter emissions were greater than other measurement years and more rainfall was recorded than any other year in a 100-year record, causing inundated conditions and annual release of 266 ± 25 g C m^-2. While the fen was also inundated in 2017, this was more related to runoff and groundwater discharge than precipitation inputs, and the fen net carbon uptake was neutral, 0 ± 19 g C m^-2. However, the CH₄ emissions were more than three times greater in 2017 (21,020 ± 3,982 mg m^-2) than 2014 (6,191 ± 1,167 mg m^-2). Across four growing seasons of CH₄ measurements from 2014 - 2017, inclusion of total CH₄ emissions in the carbon budget resulted in increased emissions of 1,548 g CO₂ equivalents m^-2. Prior work has shown an oxidizing effect of meteoric inputs, and we suggest here that this has significant consequences for methane production and C balance. Overall, our study suggests that is important to consider the source of inundation (flooding by meteoric inputs vs. flooding by runoff and groundwater flow) when estimating carbon budgets for boreal fens and that the CO₂ emissions, but not the CH₄ emissions, are higher in years with extreme precipitation.

2019037860 Evans, Sarah G. (Appalachian State University, Department of Geological and Environmental Sciences, Boone, NC); Godsey, Sarah; Rushlow, Caitlin R. and Voss, Cliff. The role of subsurface freeze and thaw on groundwater storage and connectivity in a variably saturated upland Arctic hillslope [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1051, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Upland permafrost regions occupy approximately one third of the Arctic landscape. In these regions, hydrologic fluxes along zero-order geomorphic features known as water tracks, can be promoted or impeded by seasonal freezing. Flow enhancement or impedance depends on multiple factors: field measurements suggest that soil moisture and subsurface flow differences between water tracks and their adjacent hillslopes may strongly influence ground thermal response to varying air temperatures. As continued warming of air temperatures in the Arctic may amplify the depth of seasonal freeze and thaw of the subsurface, it is imperative to examine the relationship between subsurface freeze and thaw and water tracks' variable flow and soil saturation status. Here, we characterize how the rate and timing of subsurface thaw interacts with subsurface water storage and hillslope connectivity in an upland Arctic hillslope using SutraICE, a coupled subsurface flow and heat transport model with freeze and thaw capabilities for variably saturated media. The model is applied to a representative Arctic hillslope and narrow water track with a drainage area of 0.029 km² in the Upper Kuparuk River watershed, North Slope, Alaska, USA. We calibrate the model with hydrologic and thermal field data including subsurface temperature, air temperature, precipitation, snow depth, water table depth, and discharge collected in the water track and its adjacent non-water-track hillslope from 2013-2014. Initial results suggest that variable saturation strongly influences summer ground thermal patterns and consequently, subsurface flow paths. The results of this work may inform our understanding of how variably saturated active layers in Arctic uplands influence terrestrial and aquatic thermal and hydrologic responses to warming temperatures.

2019038098 Ezhova, Ekaterina (University of Helsinki, Helsinki, Finland); Suhonen, Elli; Lappalainen, Hanna K.; Ponomareva, Olga; Kukkonen, Ilmo T.; Kulmala, Markku Tapio; Gravis, Andrey; Gennadinik, Victor; Drozdov, Dmitry and Melnikov, Vladimir. Transient heat transfer model for characterizing permafrost dynamics in Nadym region [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33E-1411, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost plays an important role in the global environmental change, with its impact on the dynamics of ecosystems and hydrological cycles. As climate in Northern hemisphere is warming faster than anywhere else and permafrost is sensitive to the change in temperature regime, understanding on the processes characterizing permafrost dynamics is urgent. Here we focus on the important factors of the on-going thawing of permafrost using numerical modelling and field observations. Our study reports the results from the transient heat transfer numerical model (Simulator for HEat and MAss Transport, SHEMAT), characterizing the complex relationship between the annual cycle of air temperatures and the permafrost thermal regime. The model is calibrated to several measurement sites. We use data of the permafrost temperatures along with the soil properties information. The data originates from Nadym region, situated in the north of the northern taiga subzone (Russia). The model is used in predicting of important characteristics of changing permafrost: active layer thickness, temperature and depth. The effects of local energy balance conditions are taken into account by calculating the freezing and thawing indices with monthly averages of soil and air temperature data.

2019040591 Fang, X. (Chengdu University of Information Technology, Chengdu, China). Observed soil temperature trends associated with climate change in the Tibetan Plateau, 1960-2014 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A53K-2640, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Soil temperature, an important indicator of climate change, has rarely explored due to scarce observations, especially in the Tibetan Plateau (TP) area. In this study, changes observed in five meteorological variables obtained from the TP between 1960 and 2014 were investigated using two non-parametric methods, the modified Mann-Kendall test and Sen's slope estimator method. Analysis of annual series from 1960 to 2014 has shown that surface (0 cm), shallow (5-20 cm), deep (40-320 cm) soil temperatures (ST), mean air temperature (AT), and precipitation (P) increased with rates of 0.47 °C/decade, 0.36 °C/decade, 0.36 °C/decade, 0.35 °C/decade, and 7.36 mm/decade, respectively, while maximum frozen soil depth (MFD) as well as snow cover depth (MSD) decreased with rates of 5.58 and 0.07 cm/decade. Trends were significant at 99 or 95% confidence level for the variables, with the exception of P and MSD. More impressive rate of the ST at each level than the AT indicates the clear response of soil to climate warming on a regional scale. Monthly changes observed in surface ST in the past decades were consistent with those of AT, indicating a central place of AT in the soil warming. In addition, with the exception of MFD, regional scale increasing trend of P as well as the decreasing MSD also shed light on the mechanisms driving soil trends. Significant negative-dominated correlation coefficients (a = 0.05) between ST and MSD indicate the decreasing MSD trends in TP were attributable to increasing ST, especially in surface layer. Owing to the frozen ground, the relationship between ST and P is complicated in the area. Higher P also induced higher ST, while the inhibition of freeze and thaw process on the ST in summer. With the increasing AT, P accompanied with the decreasing MFD, MSD should be the major factors induced the conspicuous soil warming of the TP in the past decades. Keywords: soil temperature, climate change, Tibetan Plateau

2019037864 Fortier, Daniel (University of Montreal, Département de Géographie, Montreal, QC, Canada); Coulombe, Stéphanie; Lacelle, Denis; Kanevskiy, Mikhail Z.; Fisher, David Andrew and Shur, Yuri. Origin, burial and preservation of late Pleistocene-age glacier ice in Arctic permafrost (Bylot Island, NU, Canada) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1055, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Over the past decades, observations of buried glacier ice exposed in coastal bluffs and headwalls of retrogressive thaw slumps of the Arctic indicate that considerable amounts of Pleistocene glacier ice survived the deglaciation and are still preserved in permafrost. Identifying the origin of ground ice is required to model its spatial distribution and abundance, which is necessary to model the response of circumpolar permafrost regions to climate change. Here, we present a detailed description and report physical and geochemical properties of glacier ice buried in the permafrost of Bylot Island (Nunavut) as well as identify geomorphic processes that led to the burial and preservation of the ice. The buried glacier ice consisted of clear to whitish englacial ice having large crystals (cm) and small gas inclusions (mm) at crystal intersections, similar to observations of englacial ice facies commonly found on contemporary glaciers and ice sheets. However, the isotopic composition of the buried ice differed markedly from contemporary glacier ice and indicated the late Pleistocene age of the ice, interpreted to be a remnant of the Laurentide Ice Sheet (LIS). This ice predates the aggradation of the permafrost and can be used as an archive to infer paleo-environmental conditions at the study site. The d¹⁸O records of LIS remnants found along its northern margin can also be used to establish ice elevation in their source area during the late Wisconsinan, based on the d¹⁸O-elevation relation, and to constrain modeled, physics-based, LIS geometry reconstructions. In the Canadian Arctic, the resiliency of icy permafrost to past warm intervals preserved relics of the LIS; these ice-marginal landscapes, now poised for thaw, should uncover more valuable clues about the conditions of the last major ice sheet on Earth.

2019038054 Frederick, Jennifer Mary (Sandia National Laboratories, Albuquerque, NM); Bull, Diana L.; Mota, Alejandro; Thomas, Matthew A.; Jones, Benjamin M.; Jones, Craig; Kasper, Jeremy; Connolly, Craig T.; McClelland, James W. and Roberts, Jesse. Development of a tightly coupled numerical model for Arctic coastal erosion, infrastructure risk, and evaluation of associated coastal hazards [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2351, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Erosion is accelerating along many stretches of the coastal Arctic, putting critical infrastructure at risk and threatening local communities. These permafrost-laden coastlines are increasing vulnerable to erosion due to declining sea ice and increasing duration of open water, more frequent storms during ice-free periods, and warming permafrost soils. Predicting the shoreline erosion rates is therefore extremely challenging because of the highly non-linear behavior of the coupled and changing environmental system. Here we detail the development and testing of a numerical model (called ACE - Arctic Coastal Erosion), a multi-physics based finite-element model designed to capture the thermo-chemo-mechanical dynamics of erosion. Our approach can facilitate a probabilistic assessment of future Alaskan coastlines, unencumbered by the limitations of traditional, empirically-based methods. It will be validated via a parallel field campaign at Drew Point, Alaska (summers of 2018 & 2019), specifically designed to gather the data needed to accurately calibrate model parameters. Major advances in the 3D ACE model will include: (i) failure mechanisms that are not pre-determined or empirical, but rather can result in any form of deformation allowable (block erosion, slumping, etc.) from the material's constitutive relationships; (ii) material strength parameters that vary with temperature and unfrozen water content; (iii) changes in bluff geometry (such as niche formation) that are determined directly from the thermo-chemical-mechanical governing equations and as a result of the evolving, complex interaction of the atmospheric and oceanographic boundary conditions; and (iv) the ability to track sediment deposition in the nearshore after erosion events. The ACE model will not only inform our scientific understanding of coastal erosion processes and rates, but is designed to provide the simulation engine required to assess risk and develop mitigation strategies to meet national security objectives for critical infrastructure and coastal communities.

2019037778 Fuchs, Matthias (Alfred Wegener Institute, Center for Polar and Marine Research, Potsdam, Germany); Lenz, Josefine; Jock, Suzanne; Jones, Benjamin M.; Strauss, Jens; Nitze, Ingmar; Günther, Frank and Grosse, Guido. Organic carbon and nitrogen storage along a thermokarst lake sequence on the Arctic Coastal Plain of Northern Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2488, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Thermokarst lake landscapes are permafrost regions, which are prone to rapid changes. The thaw of ice-rich permafrost leads not only to surface subsidence and lake formation but also to drainage of existing thermokarst lakes. Such a thermokarst lake sequence from initial pond formation to thermokarst lakes to eventual lake drainage has implications on the carbon (C) and nitrogen (N) stored in these dynamic landscapes. We analyzed three lake sediment cores as well as twelve permafrost cores from drained thermokarst lake basins (DTLB) of a typical thermokarst landscape north of Teshekpuk Lake on the Arctic Coastal Plain of Alaska. In addition, we included one core from a remnant upland not affected by Holocene thermokarst processes. This ensemble of collected cores within 5 km distance allows investigating the effect of thermokarst processes on the C and N stocks in the top two meters of soil while radiocarbon dating was done for reconstructing the thermokarst lake succession history in the study area. We show that organic C and N contents as well as the carbon-nitrogen ratio are considerably lower in lake sediments than in the adjacent DTLB or upland cores. This indicates a degradation of C during the thermokarst lake phases. However, we found similar amounts of total C and N mass, with 45.7 kg C m^-2 and 2.6 kg N m^-2 for terrestrial sediments and 51.1 kg C m^-2 and 3.8 kg N m^-2 (0-100 cm) for lacustrine sediments. The similar amount of C and N, despite the lower concentration of both elements in lake sediments, results from the higher density of lacustrine sediments caused by the lack of ground ice compared to DTLB sediments. This indicates the importance of including lake sediments in C and N estimations to fully assess the C sink-source potential of rapidly changing thermokarst landscapes. In addition, the radiocarbon-based landscape chronology reveals five successive generations of partially, spatially overlapping DTLBs for the past 7000 years in the study region, reflecting the dynamic nature of thermokarst lake sequences during the Holocene in these ice-rich permafrost deposits. Our study shows the effect of the dynamic thermokarst landscape on C and N stocks in the top two meters of soil and reveals the importance to include these ice-rich permafrost areas to fully understand the permafrost carbon climate feedback.

2019040611 Fuson, Tabatha (University of Texas at El Paso, El Paso, TX); Cody, Ryan P.; Vargas Zesati, Sergio A.; Escarzaga, Stephen Michael; Oberbauer, Steven F. and Tweedie, C. E. Documenting microtopographic change of tundra landscapes using terrestrial LiDAR; a case study in a High-Arctic tundra ecosystem [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33K-2813, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Microtopographic variability and change is an important determining factor of ecological structure and function in the Arctic. As permafrost responds to environmental change, microtopography is altered, leading to shifts that result in hydrological and plant phenological change. Subsidence following thawing of ice-rich permafrost leads to drainage of inundated wetlands or the formation of thermokarst and polygonal patterns that result from heaving. Distortions in the landscape displace surface water creating drainage networks, ponds, and lakes, altering nutrient availability, consequently causing previously wet areas to dry and vice versa, altering plant species composition and distribution. The study of these processes and their influences over hydrological dynamics and vegetation changes in the Arctic are becoming increasingly important as rising global temperatures continue to melt frozen Arctic soil, thus, it is important to develop tools and methods to quantify and track microtopographic changes. To date, few studies have tracked these changes at high spatial resolutions over multiple years and across multiple locations in the Arctic. Recently, studies have elevated the urgency of this research, to help discern the causes and consequences of such landscape change. The primary objectives of this study are to quantify the spatial and temporal microtopographic change in four contrasting sites in the North Slope of Alaska using terrestrial light detection and ranging (LiDAR) technologies, and determine how small-scale topographic change is associated with shifts in surface hydrology and seasonal phenology. Ten years of peak season LiDAR datasets have been collected, filtered, and cleaned for each site using RiScan Pro and ArcGIS software packages. A preliminary analysis of point clouds across sites revealed annual subsidence trends. Future directions will focus on quantifying changes in surface hydrology and plant phenology from digital imagery and spectral reflectance acquired concurrently with LiDAR datasets for all sites. The methodology presented here shows great potential in highlighting the impact of local terrestrial change for arctic tundra and in turn might suggest how these transformations affect global biodiversity, surface energy budgets, and atmosphere carbon exchange.

2019040626 Gagne, Kristin (University of Alaska Fairbanks, Fairbanks, AK) and Guerard, Jennifer. Spectroscopic characterization of permafrost natural organic matter composition and reactivity from a sub-arctic discontinuous region [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43K-2984, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Discontinuous permafrost regions are currently the most susceptible to thaw in a changing climate. Upon thaw, sequestered carbon in permafrost natural organic matter (PNOM) leaches into the aquatic sediments and surface waters. This ancient carbon has the potential to incorporate and/or transform modern NOM and thus, may influence the transformation and biogeochemical cycling of carbon within the watershed. Determining the chemical composition and photochemical reactivity of PNOM will allow for an increased understanding of its impact on surface waters. This study observes two discontinuous boreal forest permafrost sites in sub-Arctic interior Alaska. 48" permafrost cores were collected from each site, and had a maximum radiocarbon age of 7,200 years. Sections of these cores were subsequently leached with various media (18MW, pH 10 with NaOH, and 0.5M K₂SO₄) to determine the chemical composition and photochemical reactivity of different fractions of leachable PNOM. After leaching, PNOM was isolated using PPL cartridges. Permafrost soil, leached soil and PNOM chemical composition were analyzed by ¹³C multi-CP nuclear magnetic resonance (NMR) to determine the relative abundance of carbon functional groups. PNOM was further analyzed by SPR-W5-WATERGATE ¹H NMR to obtain the relative abundance of hydrogen functional groups. Preliminary results indicate that the aliphatic content of PNOM was retained on the soil after leaching, indicating preferential leaching of specific functional groups. Additionally, relative carbohydrate content decreased with depth while aromatic content increased with depth past the active layer. Following functional group analysis, PNOM reactivity was studied via photobleaching kinetics experiments. These experiments used chemical probes to observe triplet excited and radical reactivity in the presence of artificial sunlight. Current results show photobleaching occurring at different rates among core sections, indicating variability in photoproduction ability of these reactive species. Overall, through the use of NMR and photochemical experiments this study highlights the complex heterogeneity of PNOM chemical composition and reactivity and the importance of assessing its potential biogeochemical contribution upon thaw.

2019040618 Gagné-Landmann, Anna (Laval University, Quebec City, QC, Canada). Robust, low-cost, energy-efficient sensors; improving the detection limit of off-the-shelf MOS-type methane sensor for high latitude measurements [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B41H-2820, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

As global temperatures rise, methane captured in permafrost threatens to come out. Methane (CH4) has a high green house warming potential (GWP), and its emissions must therefore be monitored, both spatially and temporally, to allow the scientific community to gain better understanding of the processes involved. Investigators would particularly like to know the seasonal and annual variations in CH4 emission rates. Data collected is also needed for forcing data in climate models. Though optical sensors can already measure CH4 levels at the PPB detection level through spectroscopic methods, these are either expensive, and/or not suitable for long-term exposure in harsh environments such as north-western Canada and Alaska where CH4 emissions are most potent. In addition, a 0.1 - 0.5 ppm detection limit is sufficient for measuring variability in methane emissions. Other detection methods are currently under development, but no clear solution yet exists for affordable, energy-efficient, large-scale monitoring of CH4 emissions in harsh environments. Building on Bossche's 2016 work in which a commercial, low-cost, low-energy consuming MOS type sensor was optimized by calibrating for humidity and temperature to achieve a desirable detection limit for measuring methane, this current study seeks to improve the detection limit of similar sensors. By calibrating, in addition, for the difference in partial oxygen pressure of the air, more accurately measuring the sensor's internal resistance, better stabilizing the voltage applied to the sensor's internal heater and providing a more controlled environment for accurately measuring humidity and temperature, it is estimated that a 0.1 - 0.5 ppm detection limit can be obtained (versus Bossche's notable 1.7 ppm). To account for this sensor's lack of strict selectivity to CH4 - it also responds notably to hydrogen - a filtering method or parallel optical detection method are also being explored.

2019037782 Garnello, Anthony (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Celis, Gerardo; Ledman, Justin; Mauritz, Marguerite; Marchenko, Sergey S.; Natali, Susan; Romanovsky, Vladimir E.; Schaedel, Christina; Taylor, Meghan and Schuur, Edward. Numerical modeling of historical and projected permafrost soil temperatures with carbon flux implications [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2493, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Recent and decadal warming trends in permafrost soils have been observed across Alaska and much of the Arctic. Discontinuous permafrost zones are particularly vulnerable to warming because slight changes in soil temperatures can lead to widespread reduction in near-surface permafrost extent. Deep soil temperatures respond to long-term climatic shifts in snowfall regimes and air, while shallow layers are highly sensitive to inter-annual variability. Soil column thermodynamics impact function of the entire ecosystem, such as driving micro-topography patterns and annual carbon balance. Thus, a historical context for contemporary studies of such areas is needed understand long-term ecosystem trajectories. In this study, the numerical Geophysical Institute Permafrost Laboratory (GIPL) model was implemented to describe historical and projected soil temperature dynamics at a site in the discontinuous permafrost zone in interior AK. The model was parameterized with five years of daily air temperature and snow depth, daily shallow soil (0.05-1.25 m), and annual deep soil (2-28 m) temperatures. Historic and projected soil temperatures were constructed using modeled air temperature and snowfall from the Coupled Model Intercomparison Project (CMIP5/AR5) and the University of East Anglia Climatic Research Unit (CRUTS3/3.1). Future projections of permafrost thaw were explored under multiple CMIP5 climate scenarios. For the five-year calibration period, GIPL-modeled soil temperatures were in strong agreement with observed values. Modeled mean annual temperature (MAT °C, ±standard deviation) was 1.31±0.75 for 5 cm (1.38 observed), -0.55±0.87 for 30 cm (-0.66 observed), and -0.52±0.01 for 105 cm (-0.62 observed). For deeper layers, modeled MAT was 0.83±0.12 for 5 , was -0.89±0.002 for 10 , and was -0.87±0.002 for 20 m. Modeled deep soil temperatures experienced 0.04°C increase annually during the validation period, in close agreement with observed values, suggesting potential for significant thawing by 2100. In the next steps, relationships between soil respiration and temperature modeled and used to estimate the impact of warming on ecosystem carbon balance.

2019037855 Gergel, Diana R. (University of Washington at Seattle, Seattle, WA); Hamman, Joseph and Nijssen, Bart. Seasonal precipitation elasticity and temperature sensitivity of runoff, evaporation and active layer depth in the Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51B-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The partitioning of runoff and evaporation and the response of soil temperature profiles in the Arctic are highly sensitive to changes in seasonal and annual mean precipitation and temperature. Active layer thickness (ALT) is the layer of soil that freezes and thaws annually, and shifts in the depth of ALT are projected to occur due to large-scale changes in permafrost extent and snow cover as a result of warming temperatures. In this study, we use the Regional Arctic System Model (RASM), a fully-coupled regional earth system model that uses the Variable Infiltration Capacity (VIC-5) as its land model. We have developed a new, high-resolution set of soil and vegetation parameters for the VIC-5 model using high-resolution global soil datasets (1-km) and a new set of vegetation classes drawing from the plant functional types (PFTs) used in the Community Land Model, the land model in the Community Earth System Model (CESM). We use these parameters to run RASM at a 25-km land/atmosphere resolution over the pan-Arctic domain with prescribed atmospheric forcings (CRU-NCEP v7). To understand how changes in precipitation and temperature affect the partitioning of runoff and evaporation as well as ALT, we apply an artificial perturbation of 1% and 5% and 0.1°C and 1°C increases in precipitation and temperature, respectively, to the CRU-NCEP forcing data. We then evaluate the sensitivity of runoff, evaporation and ALT at multiple spatial scales in the Arctic: grid cell, hydroclimate classification, and major subbasin. For evaluating results over each major subbasin, we use the RVIC routing model to route runoff for each basin. We will use our results to better understand how projected changes in temperature and precipitation in the Arctic will affect the hydrologic cycle and ALT and to inform fully-coupled, high-resolution RASM simulations.

2019040597 Goeckede, M. (Max Planck Institute for Biogeochemistry, Jena, Germany); Castro-Morales, Karel; Heimann, M.; Zimov, N. and Zimov, S. A. Higher snow pack leads to rapid increases in soil temperatures and associated higher wintertime carbon emissions in East Siberia [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B12C-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The stability of Arctic permafrost is largely dependent on the degree of freezing during the Arctic winter. Higher wintertime minima would diminish the buffer against summertime soil warming, and therefore could lead to increased active layer depths and associated degradation of permafrost layers beneath. At the same time, a delayed or slowed-down refreezing process in fall and early winter can substantially change carbon and energy cycle processes, i.e. the prolonged persistence of unfrozen layers may trigger enhanced cold season carbon emissions to the atmosphere. Here, we report on rapid changes in wintertime soil thermal regimes and associated carbon emissions observed since 2013 in the Kolyma lowlands region in Northeast Siberia. Wintertime minima in soil temperatures at our study site have risen >5 degrees centigrade over the past 5 winters, with the most substantial shifts observed 2016/17 and 2017/18. Over the same period, the zero-curtain period in fall has been extended by more than 3 months. While mean wintertime air temperatures showed a minor warming trend since 2013, the largest impact on soil warming can be attributed to substantial increases in snow pack, with maximum snow height about doubled over 5 years. Also antecedent moisture conditions in early fall increased in recent years, linked to higher precipitation in late summer, contributing to extending the zero-curtain period. Continuous measurement of CO2 and CH4 fluxes with eddy covariance systems show that the increases in soil temperatures over the recent years were accompanied by higher wintertime carbon emissions to the atmosphere. While net fluxes remained quite stable in 2013-15, over the two winters since 2016 CO2 emissions have increased by about 40%, and CH4 emissions by about 30%. Preliminary analyses of atmospheric CO2 and CH4 mixing ratios from a tall tower indicate that these locally enhanced wintertime carbon emissions are representative for the larger East Siberian region. Summarizing, our results demonstrate that recently observed increases in snow pack hold the potential to substantially contribute to permafrost warming, and in turn trigger a positive feedback with Arctic warming through enhanced carbon emissions in affected regions.

2019040587 Goeckede, M. (Max Planck Institute for Biogeochemistry, Jena, Germany); Pallandt, Martijn; Kumar, J. and Jung, M. Past and current state of the Arctic eddy covariance network [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A24K-16, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Arctic stores enormous pools of sequestered carbon currently locked away in permafrost soils. Due to projected climate change and specifically Arctic amplification, the future sustainability of these stocks is unclear. There are strong indicators that the Arctic could turn from a sink into a source of carbon to the atmosphere. Depending on local environmental conditions, the largest portion of this carbon could either be released as CO₂ or CH₄. One of the most reliable methods to measure long-term surface-atmosphere exchange of carbon is through the use of eddy covariance (EC) towers. However, due to logistical difficulties, in the Arctic the existing EC network is still comparatively sparse, with apparent gaps regarding certain regions and ecosystem types. To facilitate an objective evaluation of this network, in this study we first assessed the availability of Arctic EC datasets for past and current timeframes, and made this information available to the research community through an online mapping tool. Subsequently, we applied two different methods to quantify the representativeness of the EC network regarding the quantification of pan-Arctic carbon budgets, and identified locations where new flux towers would ideally complement the existing infrastructure. Based on our first method, we indicate the networks representativeness with regards to its coverage of the ecoregions of the Arctic. Here ecoregions are computed based on combinations of key ecosystem variables, such as e.g. land cover type or prevailing temperature regimes. The representativeness of different subsets of eddy covariance sites from our database was subsequently evaluated based on how well the conditions found at the chosen EC sites correspond to the means of ecosystem variables within each ecoregion. Through our second network evaluation we focus more on the carbon fluxes. Here, key variables used for the upscaling of CO₂ fluxes identified by the Fluxcom project were utilized with a K nearest neighbors method to compare EC site coverage to the drivers of these flues. Both methods show clear gaps in data acquisition: Even though the network has clearly expanded over the last two decades, coverage is sparse in mountainous regions and large parts of Russia. More specifically, wintertime fluxes and CH₄ fluxes are clearly lagging behind.

2019038096 Grebenets, Valery I. (Lomonosov Moscow State University, Moscow, Russian Federation); Tolmanov, Vasiliy Andreevich and Streletskiy, Dmitry A. Influence of dangerous cryogenic processes on linear technogenic systems of the Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33E-1405, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Arctic is the territory of perspective development. Strengthening of technogenesis and noticeable climatic changes affecting the state of permafrost are most negatively manifested for linear technogenic systems (LTS). The main feature is its continuity and declining of variability in the choice of the routes. We conducted complex field studies, numerical modelling, forecasting of the LTS state under changing conditions in the Arctic regions and defined five main types of LTS: pipelines (aboveground, onground and underground), city waterlines, electric lines, autoroads and railways. Pipelines, paved on the permafrost are traditionally arranged on supports that are raised above the surface and frozen into the ground; the main problem in this case is uneven frost heaving in the active layer. Deformations associated with dangerous cryogenic processes - thermokarst and thermoerosion develop in the zone of discontinuous and sporadic permafrost, which intensity is increasing due to climatic changes of recent decades; revealed that 30-40% of such LTSs are substantially deformed or even destroyed after 5-10 years of operation. Water pipelines of various purposes located in industrial centers of the north are laid in underground reservoirs (utilidors): uneven thawing of soils of different composition and ice content leads to intensive destruction of these systems. About 70% of underground communications in the largest Arctic cities of Russia are in poor condition. The electric lines are pulled out due to the frost heaving in the active layer and wind loads that have intensified in the Arctic due to climate change. We have analyzed the potential hazards for the first time for all regions of Eastern Siberia and the Far East (about 300 administrative areas) for roads and railways associated with thermokarst, thermoerosion, thermoabrasion, icing, frost heaving, frost cracking, moving of the rock glaciers. Negative effects from dangerous cryogenic processes are manifested in the form of frost cracks, formation of ice, dips, sliding slopes, wavy deformations, strengthening thixotropy of soils, lowering the bearing capacity of frozen bases. Linear technogenic systems of the Arctic are most vulnerable to the impact of dangerous cryogenic processes.

2019037817 Guerard, Jennifer (University of Alaska Fairbanks, Fairbanks, AK) and Gagne, Kristin. Characterization of natural organic matter in surficial waters of a watershed underlain by discontinuous permafrost in interior Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2584, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Northern latitudes, especially areas of discontinuous permafrost, are experiencing dramatic changes. These include permafrost thaw, which has the potential to impact surficial water composition and quality. Natural organic matter (NOM) reactivity is dependent upon its source inputs, and is expected to thus vary with respect to compositional differences. Organic matter in permafrost has been observed to differ from modern boreal NOM, potentially altering carbon cycling upon thaw by NOM release and transformation. However, the impact of permafrost thaw on the character of NOM in overlying watersheds is not well understood. This study sampled waters from multiple lakes and streams seasonally over the course of three years within a watershed underlain by differing degrees of talik formation in interior Alaska. Aqueous geochemistry and natural organic matter composition were characterized in surficial samples, pore waters, and PPL isolates. NOM in sampled waters and isolates was characterized through optical spectroscopy (absorbance, fluorescence) as well as nuclear magnetic resonance (NMR; ¹H-SPR5-WATERGATE on aqueous samples and ¹³C multi-CP-MAS on solid-state samples). Preliminary results suggest seasonal differences in groundwater contributions and metal concentrations, especially during winter and just prior to thaw. Variation in NOM character was also observed both seasonally and among water bodies, including differences in functional group composition as observed by NMR. NOM characterization was coupled with aqueous geochemical analyses to identify trends in talik development and in order to integrate hydrological characterization with the extent of influence of thaw on NOM composition. Understanding the mechanisms governing carbon and elemental cycling are critical for predicting the potential influence of permafrost thaw in sub-Arctic systems.

2019038060 Gulick, Virginia C. (NASA Ames Research Center/SETI Institute, Moffett Field, CA) and Glines, Natalie H. Gullies and thermokarst landforms in the central peak region of Lyot Crater; implications for a late Mars microclimate [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23F-2384, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Detailed morphologic analysis and mapping of gully, channel, and valley systems and the surrounding landscape can reveal much about their formational environments. In our recent mapping of Lyot Crater's gullied central peak region, we have identified intriguing flat-floored depressions connected by channels trending south towards the lowest elevation (~-7100 m) in the N. Hemisphere. These features are similar to beaded streams in terrestrial permafrost terrains experiencing seasonal freeze-thaw processes over several 10² years. Because these systems terminate near ~-6800 m, we suggest they delineate a paleolake existing during a period of higher obliquity. Gully formation restricted to the western central peak region suggests a local orographic effect. Here we propose a local hydrological cycle where westerly winds blowing over an ice-covered lake evaporate/sublimate sufficient water vapor to deposit snow at a cold trap ~2 km higher on the central peak. Assuming current THEMIS surface T_max(~265 K) on Lyot's floor, snow could accumulate on the central peak over similar areas at a rate of several m/yr of equivalent water with estimated snowfield sublimation rates of 10s of cm/yr (Gulick et. al 1997). Further modeling will be explored. Could liquid water have flowed in Lyot crater? Haberle et al. (2001) addressed water stability on Mars and found that liquid water need not be stable with respect to evaporation, but only with respect to boiling and freezing. They pointed out, that liquid water is generally not stable on Mars or Earth with respect to evaporation, as the lower limit of liquid water stability is defined by the freezing curve and is independent of ambient pressures. Furthermore, the boiling point is the temperature at which the saturation vapor pressure equals the total external pressure, regardless of the external pressure source. They estimated that the T and P range in which liquid water could exist on Mars is between the triple point of water and 283 K and ~12 mbar. Within this range, the total pressure can be supplied by CO₂, and water vapor need not be present to stabilize liquid water against boiling. We are continuing to explore this potential water source. This mechanism if correct would have important astrobiological implications for Mars' late paleoclimatic history.

2019040645 Guo, H. (University of Arkansas, Fayetteville, AR); Feng, S.; Zhang, T. and Peng, X. The spatiotemporal variations of active layer thickness in the Northern Hemisphere during 1901-2016 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1792, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The active layer thickness (ALT) in permafrost regions had significantly increased in recent years. Understanding the spatiotemporal changes of ALT is crucial to understand the impacts of climate change in cold regions. Due to sparse ALT observations and limited understanding of soil thermal mechanisms, it is difficult to accurately evaluate and predict the ALT changes at the hemispheric scale. Here we present a simulated gridded ALT dataset in the Northern Hemisphere during 1901-2016 based on observational climate datasets. The simulations agreed well with the site observations (RMSE = 52 cm, R² = 0.77), indicating that the model did a reasonable job in simulating the ALT variations. The ALT demonstrated a consistent increasing but region-specific trend during the analyzed period. The trend is significant at the 95% confidence level in most regions. Additionally, the Empirical Orthogonal Function (EOF) analysis was used to examine the spatial and temporal characteristics of ALT. The first EOF mode (EOF1) of ALT shows homogeneous positive values over the permafrost regions, especially over the northeast Eurasia and central Canada. The principal component associated with this mode (PC1) shows an obvious increasing trend after 1980s, consistent with the temperature variations in the Northern Hemisphere. The second EOF mode (EOF2) is characterized by of strong positive over northwest Eurasia and negative over northeast Eurasia. The PC2 shows strong quasi-sinusoidal oscillations and linked to sea surface temperature in the North Atlantic. The third EOF mode (EOF3) shows an out-of-phase relationship between the central Siberia and the Alaska. The PC3 shows strong interannual variations and might be linked to the short-term variations of the Arctic sea ice. This study could provide a more realistic assessment of ALT changes and its physical mechanisms in the Northern Hemisphere in the context of global warming.

2019040648 Haghnegahdar, Amin (University of Saskatchewan, Global Institute for Water Security, Saskatoon, SK, Canada) and Razavi, S. Towards improved subsurface representation in land surface-hydrology models [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1799, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Land surface models (LSMs) have become a key component of many hydrologic, atmospheric, and ecologic models. Proper configuration and parametrization of these complex models are critical for improved model application and performance. While hydrologic modellers have been extensively investigating the impact of (horizontal) spatial discretization on model responses, vertical subsurface discretization and representation have been often neglected. In this work, we aim to highlight the importance of proper representation of the shallow subsurface in LSMs and hydrologic models. In particular, we illustrate how three important factors, namely soil permeable (active) depth (sometimes known as depth to "bedrock"), vegetation rooting depth, and soil vertical discretization, individually and through their interactions, influence model responses in ways that are often unexpected or neglected. For this purpose, we conducted both local and global sensitivity analysis (GSA) experiments of a coupled land surface-hydrology model, Modélisation Environmentale-Surface et Hydrologie (MESH). GSA experiments were carried out using a new variogram-based sensitivity analysis technique, called Variogram Analysis of Response Surfaces (VARS). Results reveal that soil permeable depth has a dominating influence on water balance calculations by MESH. Furthermore, not only the actual permeable and root depths, but also their positions with respect to each other, and with respect to the soil layers will impact model simulations. It is observed that the common 3-layer soil profile used in MESH (with a very thick layer of nearly 4m at the bottom) is very susceptible to ET overestimation. There are studies (mostly when dealing with permafrost) that adapt a finer and deeper vertical soil discretization, which is less prone to this issue. However, they impose a large computational burden, particularly at large scales. As a trade-off and simpler solution to this issue for large scale applications, we show and recommend adding at least one extra soil layer right below the rooting depth. Using these observations, it is emphasized again here that a proper understanding and representation of the internal model functioning at the subsurface level is a key to improve the performance of hydrology and land surface models.

2019038099 Hayman, Garry (Centre for Ecology and Hydrology, Wallingford, United Kingdom); Comyn-Platt, Edward; Huntingford, Chris; Collins, William; Webber, Christopher P.; Sitch, Stephen A.; Burke, Eleanor; Chadburn, Sarah E.; Gedney, Nicola; Lowe, Jason A.; Harper, Anna B.; Powell, Tom; Cox, Peter Michael and House, Joanna. Contrasting impacts of methane from anthropogenic and natural sources in meeting the Paris Climate Agreement [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC43E-1571, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The stated aims of the Paris Agreement of the United Nations Framework Convention on Climate Change are "to hold the increase in global average temperature to well below 2°C and to pursue efforts to limit the increase to 1.5°C". Using the JULES UK community land surface model, coupled to the IMOGEN intermediate complexity climate model, we investigate the carbon-cycle feedbacks of transitions to different stable warming levels. In this work, we develop an inverted version of the IMOGEN-JULES framework, in which prescribed temperature pathways are followed, specifically to achieve the 1.5°C or 2°C warming targets of the Paris Agreement. For three plausible mitigation levels of anthropogenic methane emissions, we find that the extra allowable carbon emissions from the CH₄ mitigation can make a substantial difference to the feasibility or otherwise of achieving the Paris climate targets [Collins et al., 2018]. This benefit is further enhanced by the indirect effects of CH₄ on ozone (O₃), whereby reduced atmospheric methane concentrations lead to lower tropospheric ozone concentrations and thus a reduction in the harmful effects of ozone on productivity and carbon uptake. We also consider natural methane-climate feedback processes, which could act in the opposite direction to the mitigation of anthropogenic methane sources. Wetlands are the largest natural source of CH₄ to the atmosphere and these emissions respond strongly to climate change. A second natural feedback is from permafrost thaw. In a warming climate, the resulting microbial decomposition of previously frozen organic carbon is potentially one of the largest feedbacks from terrestrial ecosystems. In our recent study [Comyn-Platt et al., 2018], we find the carbon and CH₄ feedbacks from natural wetlands and permafrost thaw to be substantial, causing anthropogenic CO₂ emission budgets to be reduced.

2019037863 He Ruixia (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Jin Huijun; Chen Xuemei and Lv Lanzhi. Sand wedges and cryoturbations on the Ordos Plateau since 50 ka BP and their paleo-environmental implications [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1054, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The periglacial phenomena, such as frost-cracking sand wedges and cryoturbations, are important evidence for rebuilding the paleo-climate and permafrost environment in the Late Quaternary. The Ordos Plateau is one of the regions in China where periglacial phenomena have been extensively identified since 1980s. However, the existing research is mainly focused on the division of the southern limit of permafrost in different periods, and the evolution of permafrost environment on the Ordos Plateau since 30 ka BP. In order to rebuild permafrost evolution and environmental changes since the Late Pleistocene, several field investigations were performed on the Ordos Plateau in 2008, 2015 and 2018, and many sand wedges and cryoturbations were identified or verified. Based on field surveys and dating of these periglacial phenomena, the formation of sand wedges and cryoturbations during the last 50 ka are divided into six major periods: Period VI (>50 kaBP), Period V (50-45 kaBP), Period IV (Last Glaciation Maximum, or LGM 2: 30-23 kaBP), Period III (LGM 3: 25-10 kaBP), Period II (early Holocene, 10-7 kaBP, and Period I (mid-Holocene Neoglaciation, 5 to 4 kaBP. Analyses show that, the cold periods with well-developed permafrost were conducive for forming ice and sand wedges and large polygons, and warming climate and degrading permafrost favor that of cryoturbations and ice-wedge pseudomorphs. At ca. 30 kaBP, based on the cryotubations along the Salawusu River, it was 6-7°C colder than present. During the LGM, ice-wedge pseudomorphs, sand wedges, and large polygons were well developed and most widely distributed. Based on the temperatures required for the formation of ice-wedges, the lowest ground temperature, 12°C colder than today, occurred at 25-13 ka BP. Continuous permafrost occurred extensively on the Ordos Plateau, and its southern limit extended southwards to 37°-38°N, and tundra landscape prevailed. Under a generally warming climate since, permafrost gradually degraded and vanished, making the Ordos Plateau now an area of seasonally frozen ground. Furthermore, these results suggest that other proxies, such as paleo-flora and -fauna fossils, paleo-anthropological artifacts, river and lake facies, and aeolian deposits, should be cross-examined to supplement with the studies on the paleo-permafrost and -environment, and these results should also be integrated with those from the adjacent Northeast China, Qinghai-Tibet Plateau and bordering areas in Mongolia and Russia. Key Words: Sand wedges, cryoturbations, Last Glaciation Maximum (LGM), Holocene, Ordos Plateau

2019040598 Heffernan, Liam (University of Alberta, Edmonton, AB, Canada); Estop Aragones, Cristian; Knorr, K. H. and Olefeldt, D. Long-term net effect of permafrost thaw on the carbon balance of Boreal peatlands; evidence from several complementary approaches [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B12C-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Boreal peatlands are historically important ecosystems in global carbon (C) cycling as they are one of the largest stores of soil C as well as a significant source of methane. Increasing temperatures at northern latitudes are accelerating permafrost thaw, threatening the stability of C stores found in peatlands underlain by permafrost. The net effect of thaw on a peatlands C balance occurs on the decadal to century timescale making it difficult to assess. Measured C stocks indicate the net impact of thawing on C balances but do not provide any information on processes; short-term C balances are monitored via surface greenhouse gas (GHG) flux measurements; estimating the age (¹⁴C) of respired C determines the contribution of old C to GHG emissions; and observing enzymatic activity may be indicative of controls on decomposition post-thaw. Here we present evidence from these four approaches performed at a single site in boreal western Canada, providing a comprehensive understanding of the C balance in a thawing peatland complex. We observed net losses of 170 - 2 g C m^-2 yr^-1, the majority of losses occurred in the initial decades post-thaw. Modelled GHG fluxes for a two-year period indicate recently thawed areas have greater net losses via surface GHG exchange. ¹⁴C dating of respired C suggests minimal contribution of old C to surface emissions post-thaw. Measured rates of enzymatic activity suggest the majority of microbial decomposition occurs in the upper layers of recently thawed areas, despite waterlogged conditions. Previous research shows that large C stores found in permafrost peatlands are susceptible to losses post-thaw. However, our results suggest that it may only be C accumulated post permafrost aggradation that is vulnerable to loss and C which accumulated prior to this is unaffected, an important factor when considering the contribution of thawing peatlands to the permafrost C feedback.

2019032034 Heffernan, Liam (University of Alberta, Edmonton, AB, Canada); Olefeldt, David and Estop Aragones, Cristian. Stability of old soil C in boreal peatlands following permafrost thaw; contrasting and complementary findings from anaerobic incubations, radiocarbon analysis of field fluxes, and priming experiments [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23G-2608, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Accelerated rates of warming and wildfires in the circumpolar region are predicted to promote thaw in peatland plateaus and accelerate thermokarst bog formation. Deep organic matter in these bogs is exposed to microbial activity and may result in a potential loss of soil C to the atmosphere in form of greenhouse gases CO₂ and CH₄. Anoxic soil conditions in these waterlogged bogs limit rates of decomposition but the temperature sensitivity may increase with higher humification and thus, deep peat may be more susceptible to decomposition and result in substantial soil C loss. We measured during 2 years anaerobic CO₂ and CH₄ production rates in soil incubations from a peatland plateau, a young and old thermokarst bog in the discontinous permafrost in northern Alberta. Samples were selected from depths where peat was exposed to seasonal thaw (active layer) and from deeper, previously frozen organic matter along 5 m profiles. Most of the production is driven by the top meter of peat, especially in the thermokarst due to peat accumulated post-thaw where also the highest CH₄ production rates are measured. Data suggests that deeper peat, presumably more recalcitrant, has higher temperature sensitivity to decomposition but estimates of soil C loss from deep layers based on incubation data are much larger than those estimated based on field measurements. Thermokarst bogs are associated with high vegetation productivity post-thaw and fresh C inputs in soil derived from plants could increase peat decomposition but this potential mechanism on enhanced peat decompostion is poorly investigated. We added ¹³C labelled glucose to investigate priming effects once the labile C pool was majoritarily depleted and production rates were stable over time (after >2 years of incubation). Preliminary results indicate a short-lived increase of soil respiration after sugar addition followed by a reduction in soil respiration rates. Fourier transform infrared (FTIR) spectroscopy will be used to determine how peat quality is related to anaerobic decomposition rates, its temperature dependence and priming effects.

2019037793 Henderson, Lillian (University of Rochester, Rochester, NY); Magen, Cedric; Dallimore, Scott; Whalen, Dustin; Fraser, Paul; Orcutt, Beth; Wheat, Charles Geoffrey and Lapham, Laura. Methane production rates from laboratory incubations of Arctic Coastal Plain permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2509, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Studies have shown that thawing permafrost has the potential to release significant amounts of greenhouse gases directly to the atmosphere. Yet, some areas of the world with continuous permafrost containing mineral soils have not been characterized and need to be constrained to gain a global picture of the potential impact of thawing permafrost on global warming. In this study we report on recent cores drilled from terrestrial permafrost, as well as permafrost underlying shallow marine waters, in Tuktoyaktuk Island, Northwest Territories, Canada. Material was subsampled from ~1 m increments and measured for concentrations of dissolved methane. Methane concentrations ranged from 0.03 to 0.13 mg CH₄ per kg soil, with a peak in concentration at 2 m, just below the active layer. These concentrations are similar to other mineral soil permafrost cores. Material from the active layer and 2.8 m below the surface was incubated for ~6 weeks under aerobic and anaerobic conditions at -20°C, -5°C, and +15°C to quantify the amount of methane and carbon dioxide being released from microbial activity. These biotic treatments were compared to killed controls to determine if any abiotic processes may be contributing to methane and carbon dioxide release. Under anaerobic conditions, methane concentrations increased over time at all temperatures compared to the killed controls, suggesting microbial production. In addition, methane concentrations increased faster under warmer conditions, but we did measure appreciable amounts of methane in the -20°C treatment. This poster will present both the aerobic and anaerobic incubation results, within the broader context of the in situ characterization work. It will also discuss how the results fit into the larger framework of permafrost incubation experiments.

2019037810 Herndon, Elizabeth (Kent State University, Kent, OH); Barczok, Maximilian; Thompson, Aaron; Kinsman-Costello, Lauren E. and Smith, Chelsea. Iron speciation across redox regimes in Arctic tundra soil [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31G-2575, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic and subarctic regions contain extensive wetlands that generate redox gradients and drive iron (Fe) redox cycling; however, soil Fe speciation and the extent to which Fe biogeochemistry affects carbon storage in these systems remain unclear. Iron redox cycling influences terrestrial carbon storage by facilitating anaerobic decomposition, promoting the formation of free-radicals that degrade organic molecules, physically sequestering organic matter, and/or regulating nutrient availability. In the organic-rich soils that characterize northern high-latitudes, Fe can exist as complex mixtures of (oxyhydr)oxides and organic-bound ions that uniquely affect these ecosystem processes. The objective of this study was to evaluate Fe speciation in organic soils obtained from across pH and redox gradients in tundra and boreal ecosystems. Surface soils from two tundra and two boreal ecosystems were examined using a combination of sequential chemical extractions, x-ray absorption spectroscopy (XAS), and Mossbauer spectroscopy (MBS). Short-ranged ordered (SRO, 27±21%) and crystalline (23±29%) (oxyhydr)oxides comprised the majority of extracted Fe, while organic-bound Fe accounted for most of the remainder (42±29%). Soils contained 83±12% Fe(III), as measured by XAS, that was consistent with organic-bound and oxyhydroxide phases with lesser contributions from Fe(II) species. MBS also revealed a disordered Fe(III)-oxyhydroxide phase that may correspond to amorphous iron (hydr)oxides co-precipitated with organic matter. Differences in Fe concentrations and fractions were largely explained by differences in soil pH. SRO Fe oxyhydroxides increased while organic-bound Fe decreased with increasing pH, and the proportion of crystalline Fe oxides was not pH-dependent. These differences generally followed topography, where acidic soils in uplands contained primarily organic-bound or crystalline Fe, but saturated soils in low-lying areas accumulated high concentrations of Fe (oxyhydr)oxides. From this result, we infer that Fe (oxyhydr)oxides accumulate above the redox interface in saturated soils. Thus, Fe redox cycling in topographic depressions may be particularly relevant to tundra ecosystem processes, although influences on carbon and nutrient processing warrant further study.

2019040605 Hollingsworth, Teresa N. (U. S. Department of Agriculture Forest Service, PNW Research Station, Fairbanks, AK); Bolton, B.; Hollingsworth, J.; Brinkman, Todd Jared; Brown, Caroline and Cold, Helen. Linking changes in access to subsistence resources to ecological mechanisms in the lower-middle Yukon River area, interior Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B13E-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Interior Alaska's climate is changing as fast as any place on earth. The effects of climate-related changes include widespread drought, changes in net primary productivity, and shifts in disturbance regimes. Most of Alaska is inaccessible by roads, leaving rural communities reliant on seasonal travel networks on rivers and trails to access traditional hunting, fishing, and gathering areas. These seasonal travel networks are susceptible to changes in climate and can challenge access to the subsistence resources on which rural communities depend. We present an overview of work in the lower-middle Yukon River area, or "GASH" region. This region is defined by subsistence users in Grayling, Anvik, Shagaluk, and Holy Cross based on travel networks and traditional harvest areas. Communities nominated local hunters/trappers to collect data using GPS units with photo-capturing abilities to document encountered sites of ecosystem disturbances influencing their access to subsistence areas. These knowledge holders provided the ethnographic, historical and experiential descriptions of the effects of these changes. In this regional landscape, access concerns primarily involved direct changes in vegetation and interactions between wildfire and thawing permafrost. To explore this further in an ecological context, we used remote-sensing imagery and GIS analysis to look at how these sites change over time and identify potential key environmental drivers affecting access. Within the GASH region, we spatially defined areas of high susceptibility to ecological change based on wildfire, thermokarst, and erosion characteristics and further measured vegetation changes through the Normalized Difference Vegetation Index (NDVI). This research allowed us to quantify how many GPS points were linked to areas determined to be highly susceptible to ecological change, and thus form a more specific understanding of how climate change is affecting the resources and access to resources that are the foundation of Alaska's rural subsistence economies. Our research provides novel insight on the complex interactions among multiple ecological changes that are impacting availability of ecosystem services. Understanding these associations enhances local planning and adaptation.

2019040596 Hough, M. (University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ); Blazewicz, S.; Tfaily, M.; Dorrepaal, E.; Crill, P. M.; Rich, V. I. and Saleska, S. R. Impacts of fresh litter inputs on microbially mediated C fluxes across an Arctic permafrost thaw gradient [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B11C-2165, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Thawing arctic permafrost contains 30-50% of global soil carbon and is expected to drive substantial alterations to carbon (C) cycling that will accelerate climate change. As permafrost thaws, old C may decompose and be released as carbon dioxide (CO₂) and methane (CH₄, a more potent greenhouse gas), but thawing soil can also increase plant-derived C inputs as perennial shrub communities transition to faster-growing annual wetland plants. Hence, the net effect of plant community changes on the C cycle trajectory is not yet well understood. To quantify patterns of microbial decomposition of fresh plant litter and the associated C gas emissions, we incubated ¹³C-enriched plant material from sedge and moss plants (Eriophorum and Sphagnum) with arctic peats from pre- and post-permafrost thaw areas under near-in situ conditions. CO₂ and CH₄ fluxes were highly ¹³C enriched allowing partitioning between unlabeled soil and labeled litter-induced decomposition. This partitioning showed positive and negative effects of litter addition on decomposition of soil, depending on thaw phase and gas species (CO₂ vs CH₄) and also showed three distinct phases of flux after litter addition which were not seen in incubations with no litter added. To characterize the microbiota responsible for these differing patterns of gas production, microbial DNA from incubations was density fractionated, revealing DNA enriched in ¹³C, due to uptake of C from the labeled plant litter. DNA profiles are currently being analyzed to reveal the individual lineages involved. Surprisingly, concomitant with the second peak in CH₄ flux there was a spike in low GC-content organisms in non-enriched incubations, seeming to indicate rapid growth of methanogens on fresh litter inputs. We conclude that the quantity and quality of litter inputs to thawing permafrost-associated soils will heavily impact the fate of C stored in these soils through influence on microbial activity.

2019040631 Hu, Y. (Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, Hong-Kong); Liu, L. and Zhao, L. Active rock glaciers and protalus lobes in the western Kunlun Shan of China; a first assessment [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C21E-1383, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Active rock glaciers (ARGs) and protalus lobes (PTLs) are characteristic periglacial landforms indicating the presence and creeping process of permafrost underground in an alpine environment. However, little information of such landforms has been provided in mountainous western China. In this work, we compiled an inventory including ARGs and PTLs in part of the western Kunlun Shan based on satellite Synthetic Aperture Radar (SAR) interferometry and optical images from Google Earth. Six interferograms generated from ALOS-1 PALSAR images were used for identifying ground movements. Their geomorphic parameters such as aspect, area, altitude and slope angle, were quantified using the SRTM digital elevation model. Within the 700 km² study area, we identified 30 ARGs and 25 PTLs. The preliminary results reveal that the mean Line-of-Sight (LOS) velocities of the ARGs and PTLs are 36 cm/yr and 16 cm/yr, respectively. The maximum LOS velocity for the ARGs is about 95 cm/yr. The aspects of the landforms vary significantly: 43% of the ARGs are located on northeast-facing slopes while 28% of the PTLs are located on southeast-facing slopes. Our inventory shows the total areas covered by ARGs and PTLs are 4.8 km² and 0.7 km², respectively. The largest ARG has an area of 0.6 km². Both the ARGs and PTLs are located between 4100 m and 5600 m a.s.l. and have a mean slope angle of 18°. Compared with the existing rock glacier inventories in High Mountain Asia such as the northern Tien Shan and the Hindu Kush Himalaya, the distribution density of ARGs and PTLs in the western Kunlun Shan is much lower.

2019038118 Huang Lingcao (Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, China); Liu Lin; Luo Jing and Lin Zhanju. Mapping retrogressive thaw slumps in the Beiluhe region (Tibetan Plateau) using Planet CubeSat [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract IN21E-0751, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In many cold regions underlain by ice-rich permafrost, ground warming and thawing results in distinct thermokarst landforms including retrogressive thaw slumps. Once a thaw slump initializes, it remains active for more than a decade and affects the local environments. The distribution and evolution of thaw slumps are prerequisites for understanding the permafrost degradation under climate changes. The images acquired by the Planet CubeSats, covering global land surface every day, provide an unprecedented opportunity to map and monitor these landforms. The objective of this study is to evaluate the capabilities of using Planet CubeSat images to map the distribution of thaw slumps on the Tibetan Plateau. Focusing on the Beiluhe region, we (1) downloaded daily images via the Planet Education and Research program, (2) mosaicked and extracted red, blue, and green bands using Geospatial Data Abstraction Library, (3) stretched and sharpened the images using OpenCV, and (4) manually identified 192 thaw slumps. We also conducted a field study to validate some of the mapped thaw slumps. The results show that (1) most of the thaw slumps are in the northwest of the basin and north-facing slopes, (2) the area and slope of thaw slumps range from 0.005 to 0.4 km², 2 to 12 degrees, respectively. (3) their shapes are both nearly-round and narrow (60.9% of them have a circularity smaller than 0.5). Our study demonstrates that Planet CubeSat images can be used to map active thaw slumps whose area are greater than 3000 m². Moreover, the shade of slump headwall, NDVI and NDWI derived from the images can help identify thaw slumps. The pixels within an active thaw slump have less vegetation and wetter than the surrounding. However, due to the spatial resolution (3.9 m²) of the Planet CubeSat images, the smaller (<3000 m²) slumps are challenging to be identified. Most of the stabilized thaw slumps, which become drier and covered by new vegetation, are similar to the surrounding and hard to be identified.

2019038057 Irrgang, Anna M. (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany) and Lantuit, Hugues. Coastal changes on a pan-Arctic scale; update of the Arctic Coastal Dynamics Database [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2357, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

One third of all coastlines worldwide consist of permafrost. Many of these permafrost coasts are presently exposed to greater environmental forcing as a consequence of climate change, such as a lengthening of the open water season, intensified storms, and higher water and air temperatures. As a result, increasing erosion rates are currently reported from various sites across the Arctic. It is crucial to synthetize these data on Arctic shoreline dynamics in order to improve our understanding on present coastal dynamics on the pan-Arctic scale. A first synthesis product was released in form of the Arctic Coastal Dynamics databse in 2012, which included data published until 2009 (Lantuit et al., 2012). Since then, numerous publications and data products were published on short and long term changes of Arctic coasts across a wide range of study sites. We made an extensive literature review of publications released within the last 10 years and updated the shoreline change data section in the Arctic Coastal Dynamics database. While in 2009 for one percent of the Arctic shoreline data on coastal dynamics was available, the addition of new data leads to a broader data coverage, which is mainly the effect of the greater availability of remotely sensed products for analyses conducted in these remote regions. Further, the additional data allow us to update the current mean rate of Arctic shoreline change.

2019038109 Irzak, Olga (Frost Methane, San Francisco); Barker, Laughlin; Chaleff, Ethan; Habryn, Miki; Walter Anthony, Katey M. and Hanke, Philip. The economics of mitigating geological methane release through carbon market revenue [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GH41A-1431, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane, a potent greenhouse gas, seeps from concentrated geological sources documented in large quantities across the terrestrial, marine, and permafrost environments. Of particular concern is arctic permafrost thaw and glacier retreat that may expose parts of the arctic methane reserves to the atmosphere. These reserves are estimated to be at least two orders of magnitude larger than current atmospheric levels. We seek to understand the distribution of methane emissions and investigate a cost-effective means of mitigation. Significant geological methane release into the atmosphere has been widely documented from reservoirs that are too small or distributed to be of interest to commercial resource extraction ventures. Therefore, we investigate the viability of mitigation through carbon-market-based revenue. We analyze voluntary and compliance carbon market mechanisms to understand the verification burden and revenue potential. We then prototype and deploy a device in a thermokarst lake exhibiting geological methane release to validate cost, longevity and deployment assumptions. Voluntary carbon markets fund methane mitigation largely through the flaring of landfill methane at approximately $10 Million per year. Compliance markets offer an order of magnitude larger funding avenues, though are limited to specific regions. All carbon markets value methane mitigation at 25 times higher than CO2 due to its potency as a greenhouse gas; therefore, flaring captures 96% of the carbon market value while posing smaller logistical and infrastructure challenges compared to sequestration. For terrestrial and shallow water sources, we performed a sensitivity analysis to determine the site characteristics, mitigation device specifications, and carbon market prices which characterize an envelope of an economically self-sustaining deployment. Our analysis reveals high sensitivity to deployment cost and device longevity/maintenance needs. We propose a design for a deployable methane-flaring system that is self-funding for point sources with flux rate above 10,000 cu ft/day in voluntary carbon markets and above 2,000 cu ft/day for compliance markets such as 2018 California-Quebec.

2019037799 Iwahana, Go (University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK); Muskett, Reginald R.; Saito, Kazuyuki; Ohno, Hiroshi; Yokohata, Tokuta; Uchida, Masao and Busey, Robert. Spatial variation in thermokarst subsidence after the Anaktuvuk River fire on the North Slope, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2541, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The development of thermokarst in ice-rich permafrost regions is a natural hazard, causing irreversible geomorphic changes. The formation of large depressions and lakes or swamps produced by thermokarst processes is observed in discontinuous and continuous permafrost zones, especially in Alaska and Northeastern Siberia. Despite the recognition of uncertainty about the fate of Arctic regions and global climate change due to permafrost degradation information about the spatial extent and rates of thermokarst processes are limited. We investigated thermokarst development triggered by the Anaktuvuk River Fire (ARF), which combusted a vast tundra area in 2007 in the North Slope, Alaska, using both optical and microwave remote sensing as well as in situ fieldwork measurements and observations. The two-pass differential InSAR technique using ALOS-PALSAR (L-band microwave) has been shown capable of capturing thermokarst subsidence at a spatial resolution of tens of meters, with supporting evidence from field data and optical satellite images. Significantly large amounts of subsidence (up to 6.2 cm/year spatial average) were measured by the InSAR within burned areas relative to unburned nearby in the first three years after the fire. Relatively small spatial variation (less than 0.5 cm in spatial average) was observed from two independent InSAR pairs during the pre-fire period. The obtained interferograms did not show sub-meter scale depressions along the troughs of the depression network developed by thermokarst, though they could distinguish small land areas with stable and subsiding land surface at smaller than tens of meters scale and smaller-scale detailed spatial variation of thermokarst subsidence. Post-fire interferograms were decorrelated along fire boundaries where rapid surface changes due to lateral erosion can be expected and clearly separated subsiding burned areas from stable areas of intact environment. Inside the burned areas there are some gradual changes in phase values (e.g. slopes changes) while there are relatively uniform phase values in unburned areas. Despite the topography of the studied area being flat or showing only gentle slopes (95% of the area shows slope angles of less than 5°), the magnitude of subsidence seems to depend on the slope. There was a tendency for areas with larger slopes to experience larger subsidence. It is also worth noting that large subsidence was calculated for fragmented unburned areas, as they were small patches (most of them smaller than 1 m²) surrounded by burned surfaces in which thermokarst had been active. This fact seems to show that thermokarst areas tend to propagate into adjacent areas by the lateral influence of thermal and/or hydrological regime shifts in the ground.

2019040637 Jacquemart, Mylene Fabienne (University of Colorado at Boulder, Boulder, CO); Loso, M.; Hansen, Jasmine S.; Sykes, J. and Tiampo, K. F. Instantaneous glacier loss through catastrophic collapse at Flat Creek Glacier; disentangling the roles of climate, geology and glacier dynamics in Wrangell-St. Elias National Park and Preserve, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C32A-03B, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In 2002, Kolka glacier, a surge-type glacier in the Russian Caucasus, detached catastrophically and turned into a destructive debris-flow of historical dimensions (Evans et al., 2009; Haberli et al., 2004). In 2016, two neighboring glaciers in the Aru range in Tibet catastrophically lost their tongues, revealing a similar, practically instantaneous mode of glacier loss (Kaab et al., 2018). Mostly unreported, to date, is a failure in Alaska's Wrangell-St. Elias National Park and Preserve (WRST), that, at first glance, shares some surprising similarities with the events in Russia and Tibet. Ice and debris deposits were first detected in the drainage known as Flat Creek during an overflight in 2015. Subsequently, a comparison of the DEMs, as well as corresponding Planet Labs optical images, revealed that a significant portion of the glacier had been lost in what appears to be two large mass failures. A first detachment tore away the front of the glacier tongue (roughly 1.3 million m³) in 2013. The slide ran out 12 km into the main river and deposited ice and debris many meters thick along almost 4 km of the runout. In July 2015, an even larger failure ran out equally far, spilling over the 2013 deposit onto a forested fan. Ice and debris were deposited over an area of roughly 7 km². The 2015 event removed approximately 20 million m³ of mass, an amount similar in magnitude to the 2016 events in Tibet (60 - 80 million m³). Sixty km away, a seismometer recorded all of these events, allowing us to pinpoint the exact timing. No earthquake activity was registered prior to any of the events, but all known failures occurred during peak melt season, and the 2013 event followed a large precipitation event. Permafrost in the source area further complicates the matter. Interestingly, and analogous to the Aru and Kazbek ranges, the area is home to numerous surging glaciers. A trace of the active right-lateral Totschunda Fault passes within 2 km of the Flat Creek glacier and slopes in the upper Flat Creek basin are composed mainly of weak, shattered shales and phyllites. We present results from a 2018 field and UAV mapping campaign as well as remote-sensing and modelling analyses to help understand what circumstances led to this catastrophic failure, and how it may relate to other, similar events around the globe and the potential for their occurrence in the future.

2019040657 Jafarov, E. E. (Los Alamos National Laboratory, Los Alamos, NM); Coon, E. T.; Harp, D. R.; Wilson, C. J.; Painter, S. L.; Atchley, A. L. and Romanovsky, V. E. Modeling the role of preferential snow accumulation in through talik development and hillslope groundwater flow in a transitional permafrost landscape [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Through taliks - thawed zones extending through the entire permafrost layer - represent a critical type of heterogeneity that affects water redistribution and heat transport, especially in sloping landscapes. The formation of through taliks as part of the transition from continuous to discontinuous permafrost creates new hydrologic pathways connecting the active layer to sub-permafrost regions, with significant hydrological and biogeochemical consequences. At hilly field sites in the southern Seward Peninsula, AK, patches of deep snow in tall shrubs are associated with higher winter ground temperatures and an anomalously deep active layer. To better understand the thermal-hydrologic controls and consequences of through taliks, we used the coupled surface/subsurface permafrost hydrology model ATS (Advanced Terrestrial Simulator) to model through taliks associated with preferentially distributing snow. We simulated a synthetic hillslope domain to explore the conditions under which large shrub patches would drive through-talik formation. The model was forced with detrended meteorological data with snow preferentially distributed at the midslope of the domain to investigate the potential role of vegetation-induced snow trapping in controlling through talik development under conditions typical of the current-day Seward Peninsula. We simulated thermal hydrology and talik development for five permafrost conditions ranging in thickness from 17m to 45m. For the three thinnest permafrost configurations, a through talik developed, which allowed water from the seasonally thawed layer into sub-permafrost waters, increasing sub-permafrost groundwater flow. These numerical experiments suggest that in the transition from continuous to discontinuous permafrost, through taliks may appear at locations that preferential trap snow and that the appearance of those through taliks may drive significant changes in permafrost hydrology.

2019040670 Jakosky, Bruce Martin (University of Colorado at Boulder, Laboratory for Atmospheric and Space Physics, Boulder, CO) and Brain, David. Atmospheric loss, climate change, and planetary habitability; Mars, the terrestrial planets, and exoplanets [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P31C-3732, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Our solar system has carried out three natural experiments (on Venus, Earth, and Mars) spanning a wide range of boundary conditions that can affect atmospheric loss to space and climate change. The Mars example is especially illuminating, given the compelling evidence for loss of a significant amount of gas to space; understanding those processes and how they transfer over to other planets will be particularly useful. Observations at Mars show ongoing loss of gas to space today due to the solar-EUV and solar-wind energy inputs, albeit at a relatively low level. Extrapolation into the past and interpretation of the ratio of stable isotopes of the light gases (H, C, O, N, Ar) strongly suggest that loss to space has been a major process in the evolution of the atmosphere through time. Other processes that can remove gas from the atmosphere (and which are seen to operate at Mars) include formation of carbonates, polar and ground ice, adsorbed gas, and possibly clathrates. While these processes all can operate, both intrinsic and extrinsic boundary conditions determine which will be most important. Implications for atmospheric loss from exoplanets provide important constraints on evolution of exoplanet habitability; in particular, climate on planets orbiting M-dwarf stars is subject to potentially more-dramatic change due to their exposure to likely greater stellar-wind interactions.

2019040680 James, Stephanie R. (U. S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center, Denver, CO); Minsley, Burke J.; Waldrop, Mark P. and Mcfarland, Jack W. Monitoring water and ice dynamics in degrading permafrost using ambient seismic noise [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract S41B-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The nature of how permafrost thaw will impact arctic and subarctic ecosystems - both physically and chemically - in response to a warming climate remains uncertain, as does the influence on the global carbon budget. This is in part due to limitations in subsurface measurement capabilities and the complex relationship between above and below ground processes. A one-year multidisciplinary field experiment began in April 2018 to improve the understanding of subsurface physical and mechanical controls on soil carbon losses and net ecosystem exchange at a degrading permafrost site near Fairbanks, AK. Geophysical and biogeochemical instrumentation are collocated along a transect between forested permafrost and two collapse-scar bogs. An array of nine seismic stations provide a continuous dataset for high-frequency ambient noise monitoring and characterization of the shallow subsurface dynamics through: 1) relative velocity variations (dv/v) for 3-D monitoring of subsurface freeze/thaw and water saturation changes, 2) inversion of group velocity dispersion curves from cross-correlations for vertical shear-wave velocity structure, and 3) horizontal-to-vertical spectral ratios (HVSR) for monitoring active-layer thaw. Initial results from April-July 2018 reveal decreases in relative velocity for all station pairs between -3% and -8% concurrent with snowmelt in mid-May, followed by continued velocity reduction though early July of up to -20%. Station pairs show significant variability which will be used to map the spatial patterns of thaw depth and moisture content across the study site. Preliminary dispersion analysis indicates group velocities between 100 and 1000 m/s, consistent with thawed and frozen soil, respectively, and higher modes are also observed. HVSR results contain a clear response to the development of a thawed active-layer starting in late May, seen as a strong amplitude increase and the emergence of peaks at higher frequencies (>10 Hz). Joint inversion of HVSR and dispersion curves will help constrain the velocity structure and provide insights into the vertical and spatial extent of permafrost. Overall, preliminary results show high-frequency ambient seismic noise contains great potential for high-temporal resolution monitoring and characterization of permafrost environments.

2019040651 Jan, Ahmad (Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN); Coon, E. T. and Painter, S. L. Impacts of microtopography on the evolution of polygonal tundra hydrology in a warming climate [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1811, 3 ref., December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The soil thermal hydrology in permafrost regions is characterized by strong coupling among thermal and hydrologic processes on the surface and in the subsurface, making it difficult to assess how hydrological condition will evolve in a warming climate. For polygonal tundra, microtopography (heterogeneities in the surface elevation below the scale of an ice wedge polygon) is an important factor influencing hydrological processes because it determines the flow direction, liquid storage, drainage networks and greatly affects surface/subsurface interactions. We explore the consequences of microtopographic features on the evolution of polygonal tundra using a recently developed integrated surface/subsurface permafrost thermal hydrology simulator, the Advanced Terrestrial Simulator (Painter et al. 2016). Our model is calibrated to field observations of soil temperature, soil moisture and evaporation, and can efficiently capture critical microtopographic features (Jan et al. 2018a) and thaw-induced subsidence in large-scale integrated models (Jan et al. 2018b). We present 100-year projections of the integrated thermal hydrology system in stochastically generated landscapes comprising high- and low-centered ice wedge polygons and explore how warming climate can affect surface flow and active layer evolution. This work was supported by the Interoperable Design of Extreme-scale Application Software (IDEAS) project and the Next-Generation Ecosystem Experiments-Arctic (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science. Painter SL, ET Coon, A Atchley, M Berndt, R Garimella, JD Moulton, D Svyatskiy, CJ Wilson (2016), Integrated surface/subsurface permafrost thermal hydrology: Model formulation and proof-of-concept simulations, Water Resources Research 52:6062-6077. Jan A, ET Coon, J Graham, SL Painter (2018a), A subgrid approach for modeling microtopography effects on overland flow. Accepted for publication in Water Resources Research. Jan A, ET Coon, SL Painter, R Garimella, and JD Moulton (2018b), An intermediate-scale model for thermal hydrology in low-relief permafrost-affected landscapes, Computational Geosciences 22:163-177.

2019037785 Jastrow, Julie D. (Argonne National Laboratory, Environmental Science Division, Argonne, IL); Matamala, Roser; Ping, Chen-Lu; Vugteveen, Timothy W.; Lederhouse, Jeremy S.; Hofmann, Scott M.; Michaelson, Gary J. and Mishra, Umakant. Potential decomposability of permafrost carbon stocks in ice-wedge polygons of the Alaskan Arctic Coastal Plain [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2498, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In the lowland permafrost soils of the Alaskan Arctic Coastal Plain, much of the organic matter exists in a poorly degraded state and is often weakly associated with soil minerals due to the cold, wet environment and cryoturbation. Thus, the impact of future increases in active layer thickness on mineralization rates are expected to be correlated, at least initially, to the level of organic matter decomposition and mineral association of existing permafrost carbon stocks. We are investigating particle size fractionation as an indicator of organic matter decomposition state for permafrost-region soils. Samples representing the soil horizons of flat-, low-, and high-centered ice-wedge polygons near Barrow (Utqiagvik), Alaska, were size-fractionated to isolate fibric (coarse; >250 mm) from more degraded (fine; 53-250 mm) particulate organic matter (POM) and to separate mineral-associated organic matter into silt- and clay-sized fractions. Data from over 160 samples were used to develop calibration models that can predict the amount of carbon associated with each size fraction from the mid-infrared (MIR) spectra of unfractionated bulk soils (organic carbon concentrations ranging from 0.8 to 47%). The MIR calibration models were then used to supplement measured data to estimate the size distribution of carbon stocks throughout entire 3-m deep profiles of the sampled ice-wedge polygons. We found that organic matter in both active layer and permafrost was relatively undecomposed, even in mineral horizons. High-centered polygons had greater carbon stocks than other polygon types, with most of this difference attributed to POM rather than mineral-associated organic matter. However, the carbon stocks that might be destabilized by model-projected increases in active layer thickness under future climate scenarios did not vary significantly among polygon types. On average, about 70% of these carbon stocks were composed of un-complexed POM, with about half of this POM characterized as lightly decomposed fibric materials. Our findings suggest that upper permafrost carbon stocks in ice-wedge polygons of the Alaskan Arctic Coastal Plain are likely to have intrinsically high mineralization potentials upon thawing.

2019040628 Jeong, S. (Seoul National University, Seoul, South Korea); Bloom, A. Anthony; Schimel, D.; Sweeney, C.; Parazoo, N.; Medvigy, D.; Schaepman-Strub, G.; Zheng, C.; Schwalm, Christopher R.; Huntzinger, D. N.; Michalak, Anna and Miller, C. E. Accelerating rates of Arctic carbon cycling revealed by long-term atmospheric CO2 measurements [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B51G-2010, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The contemporary Arctic carbon balance is uncertain, and the potential for a permafrost carbon feedback of anywhere from 50 to 200 petagrams of carbon (Schuur et al., 2015) compromises accurate 21st-century global climate system projections. The 42-year record of atmospheric CO2 measurements at Barrow, Alaska (71.29 N, 156.79 W), reveals significant trends in regional land-surface CO2 anomalies (DCO2), indicating long-term changes in seasonal carbon uptake and respiration. Using a carbon balance model constrained by DCO2, we find a 13.4% decrease in mean carbon residence time (50% confidence range = 9.2 to 17.6%) in North Slope tundra ecosystems during the past four decades, suggesting a transition toward a boreal carbon cycling regime. Temperature dependencies of respiration and carbon uptake suggest that increases in cold season Arctic labile carbon release will likely continue to exceed increases in net growing season carbon uptake under continued warming trends.

2019040650 Ji, F. (Harbin Institute of Technology, School of Environment, Harbin, China); Yao, Y. and Zheng, C. Variability of hydraulic conductivity in frozen ground zone; a case study [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1810, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost and seasonally frozen ground greatly affect the groundwater discharge, and this intensified discharge could facilitate the transport of dissolved solids, nutrients and carbon cycle in cold and arid regions. The seasonally frozen ground is regarded as an active layer near the surface land in which the ice-liquid water content is varied seasonally with temperature. The hydraulic conductivity (K) of the active layer, as a controlling factor to determine groundwater discharge, is varied by ice-liquid water content, and variations in the density of liquid water versus ice and hard to be quantified in regional scale. In this study, we use Qinghai-Tibet Plateau (QTP) as a representative case to quantify the seasonal variation of K of active layer driven by temperature. QTP is the source area of most major rivers of China including Yellow River, Yangtze River, Lancang River, Yarlung Zangbo River, which is covered with permafrost and seasonally frozen ground. The air temperature and ground temperature data and active layer thickness data from ten meteorological stations are used to construct a vertical temperature change model with multiple scenarios to calculate the K in active layers of Yarlung Zangbo River Basin in QTP. According to different freeze-thaw conditions, the whole period of the active layer is divided into four periods, including thawing period, all-thawed period, freezing period and all-frozen period. We obtain seasonal variation of K at a depth of 0-100 cm of the active layer at each meteorological station during four periods. Our results show that at freezing period and thawing period, the value of K ranges between 10 m/d and 10^-3 m/d. Our estimates provide the important basis for seasonal groundwater discharge evaluation, and these findings suggest the effects of climate change on hydrological processes in cold and arid regions.

2019037801 Jimmie, Jordan Andrew (University of Montana, Missoula, MT); Turner, Kelly; Mann, Paul James; Schade, John D.; Natali, Susan and Fiske, Greg. Investigating physical changes in tundra lakes and ponds in Alaska's Yukon-Kuskokwim Delta using remote sensing and stable isotopes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2546, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Surface air temperatures in the Arctic have been increasing at approximately twice the global average, contributing to myriad changes including shifting vegetation, thawing permafrost, and altered surface and groundwater hydrology. Wildfire frequency and intensity has also been increasing, and in summer 2015, more area burned in the Yukon-Kuskokwim Delta than in the previous 74 years combined. Our objectives were to investigate how wildfires affect the movement of water through tundra lakes and ponds, and to assess any associated patterns in lake expansion or drying. We investigated the origin of source water (i.e. rainwater, water from thawing permafrost, soil pore water) for lakes across a range in size by constructing a water stable isotope-mass balance model. The model quantifies d²H and d¹⁸O isotopic ratios in lake water and in potential source waters, then identifies the proportion of each source water entering each lake. These ratios also allow us to calculate an evaporation/inflow ("E/I") ratio, a local water balance tool useful in understanding if water bodies are expanding or drying. Further, in conjunction with lake water isotopic ratios, we identified changes in lake surface area through remote sensed imagery extracted from Google Earth Engine. We found that smaller ponds and lakes were more likely to be drying, and more ponds and lakes in watersheds that had recently burned experienced drying relative to unburned counterparts. We did not find any clear patterns between E/I ratio and burned and unburned water bodies. Our results support the notion that wildfires contribute to drying of smaller water bodies, suggesting potential profound changes in hydrology in tundra landscapes as fire frequencies increase in response to climate change.

2019038103 Jin Huijun (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Sheng Yu; Wen Jun; Zhou Jian; Luo Dongliang; Wang Qingfeng; Jin Xioayin; Ma Qiang; Gao Shuhui and Lan Yongshao. Hydrological impacts of permafrost degradation in the source area of Yellow River on the northeastern Qinghai-Tibet Plateau, southwest China [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC51B-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost degradation has resulted in evident hydrological consequences. In this study, hydrological impacts of permafrost degradation have been observed and modeled in the Source Area of Yellow River (SAYR) on the NE Qinghai-Tibet Plateau due to its representativeness for permafrost hydrology and its sensitivity to climate changes. Since 2013, four aspects of this program have been studied. First, the status quo and change trends of permafrost, hydrometeorology, terrestrial processes and water resources in the SAYR have been analyzed and evaluated on the basis of field surveys, mapping, observations and monitoring. Second, field experiments on permafrost hydrology in the SAYR have been conducted at various spatial scales via field monitoring on key geocryological and hydrometeorological parameters, isotope tracing, hydro-geophysical ground truthing and hydrogeological drilling, and numerical modeling on interactions of permafrost and talik. Third, elevational permafrost hydrological modeling, and model assessment of hydrological impacts of permafrost degradation have been achieved in the SAYR, with a focus on 1-dimensional hydrothermal transfer model, 2-dimensional heat transfer model with phase changes, runoff generation and outflow model, and the model for coupling groundwater and surface-waters. On the basis of these models, responses of stream-flows to climate changes have been predicted under different climate change scenarios taking into account of uncertainties in hydrometeorology and terrestrial processes, and sensitivity and uncertainty analysis. The results indicate by 2050, permafrost degradation will significantly impact stream-flow regimes, and by 2100 sharp reduction in permafrost extent may dramatically impact the hydrology in the SAYR and down-streams. In conclusion, significant progress have been made in understanding the hydrological impacts from permafrost degradation, but long-term field observations, systematic experiments on thermohydraulic properties of representative soils at frozen and thawed states in the SAYR, and improvement on hydrological modeling and predictions deem necessary.

2019037808 Jones, Eleanor Louise (University of Sheffield, Sheffield, United Kingdom); Hodson, Andrew J.; Thornton, Steven F.; Redeker, Kelly R.; Rogers, Jade C. and Wynn, Peter. More than methane; biogeochemical processes in High Arctic fjord valley infill sediments [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31G-2572, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Rising air temperatures in the High Arctic are predicted to increase permafrost active layer depths, releasing previously frozen organic carbon and nutrients for microbial metabolism. The quantities of methane and carbon dioxide produced from decomposition of this organic carbon are strongly influenced by environmental variables, such as hydrology and redox status. We studied the active layer and permafrost of High Arctic low-centred polygons formed on fjord valley infill sediments in Adventdalen, Svalbard, to ascertain the dominant biogeochemical processes leading to greenhouse gas production. We obtained replicate cores from two contrasting sites within the valley, extracted the porewaters of the cores, and measured the aqueous and solid phase chemistry. Our results suggest that consistent water saturation and high organic carbon content at one site facilitated the formation of pyrite and siderite via the reduction of iron and sulphate. The low redox conditions in this saturated zone are conducive to methanogenesis, with concentrations of dissolved methane in the porewaters reaching almost 300 mmol L^-1. Conversely, at the other, well-drained site, which also has lower organic carbon content, the biogeochemistry is dominated by pyrite oxidation, leading to high concentrations and covariance of aqueous iron and sulphate in the cores. Methanogenesis at this site appears to be negligible. Carbon dioxide concentrations in cores from both sites reach >6000 mmol L^-1, indicative of microbial respiration. It is predicted that permafrost thaw will cause poorly-drained, low-centred polygons to degrade to well-drained, high-centred polygons. We hypothesise that the water-saturated, high organic carbon content sites are more vulnerable in the long-term to altered hydrology by polygon degradation. These polygon sites are likely to transition from methanogenesis to aerobic respiration, leading to rapid decomposition of organic carbon, increased carbon dioxide emissions and major changes in the redox chemistry of iron and sulfur.

2019038075 Jull, Matthew G. (University of Virginia, Charlottesville, VA). Dynamic ground and design of the built evironment in the north [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is one of the defining features of the Arctic environment and poses one of the most difficult challenges for the design and construction of buildings and cities. Disruption of the thermal and rheological profile of the ground due to anthropogenic effects from either local disturbances or from climate change can destabilize an already delicate balance between annual freeze thaw cycles of the active layer and the underlying frozen substrate. Typically, buildings and heat-carrying infrastructure are elevated off of the ground in order to minimize this effect. In this paper I review techniques and strategies that are employed in the design and construction of buildings built on permafrost in the Arctic, outline some of the impacts that climate change related effects are having on destabilization of large industrial cities in Russia and smaller communities in North America, and highlight some of the design strategies we are developing in our research for the Arctic region. On the one hand, techniques and structural systems are being developed to overcome the increasing thermal destabilization of the ground. On the other, the impact of climate change throughout the Arctic is providing an opportunity to rethink the design of the built environment. One of the defining characteristics of most buildings and cities in the Arctic are models imported from southern latitudes and temperate climates, retrofitted and engineered with brute force to meet the demanding environmental conditions. The result is a long legacy of poorly designed buildings and cities, particularly for many of the smaller rural indigenous communities in North America. Reconsideration of the design of buildings and their relationship to underlying permafrost is one way we can begin to develop an architecture that is better suited for the dynamic Arctic environment and the people who live there, potentially serving as models for other regions in the world facing increasingly extreme environmental conditions due to climate change.

2019040623 Juncher, Jorgensen Christian (Aarhus University, Department of Bioscience, Roskilde, Denmark); Christiansen, Jesper Riis and Mariager, Tue. CH₄ sink capacity across the geodiversity of Arctic drylands and extreme soils [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43F-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Using atmospheric methane (CH₄), certain soil microbes are able to sustain their metabolism, and in turn remove this powerful greenhouse gas from the atmosphere. Recent studies have demonstrated the occurrence of CH₄ consumption in upland dry tundra soils in Arctic and High Arctic environments. Oxidation of CH₄ in these cold, dry soils in the Arctic region can counteract CH₄ emissions from Arctic wetlands and thereby play a potential important role for the net Arctic CH₄ exchange budget. Currently, knowledge gaps exist on the overall magnitude of the net CH₄ sink in these cold, dry systems as the spatial and environmental limits for CH₄ oxidation is unknown. In particular, the extent, magnitude and drivers of CH₄ oxidation in mountains and alpine landforms, which occupy large land areas in the Arctic and High Arctic has not yet been investigated leaving a potentially vast CH₄ sink unquantified with major potential implications for our conceptual view of Arctic CH₄ budget in both a past, present and future changing climate. To address this important knowledge gap and identify the most relevant spatial scaling parameters, we studied in situ CH₄ net exchange across several large landscape transects in West Greenland as well as in Alpine landscapes in the Yukon Territory, Arctic Canada. The aim of the research was to quantify the variation in flux magnitude and determine the spatial extent of net uptake of atmospheric CH₄ across a variety of previously unexplored dry tundra and post-glacial landforms in the Arctic. Our results show a persistent net uptake of CH₄ uptake in these dry, extreme environments that rival the sink strength observed in temperate forest soils, otherwise considered the primary global terrestrial sink of atmospheric CH₄. Quite surprisingly, we found high CH₄ sink rates in conditions when soils were both extremely thin (< 10 cm to bedrock), very dry (< 5-10% soil moisture), weakly developed and exposed to harsh environmental conditions such as mountain tops, alpine tundra and abrasion plateaus, which are historically overlooked "extreme soils" regarding CH₄ exchange. The results show that the physical areas and landforms where CH₄ oxidation and net CH₄ deposition occurs has not been delimited for the Arctic and calls for further studies of the spatiotemporal nature and occurrence of the CH₄ sink across the Arctic.

2019040666 Jung, Jinyoung (Korea Polar Research Institute, Incheon, South Korea); Ha, Sun-Yong; Lee, Youngju; Yang, Eun Jin; Shin, Kyung-Hoon and Kang, Sung-Ho. Dynamics of dissolved organic carbon in the Chukchi Sea [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS41B-2006, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Dissolved organic carbon (DOC) is an important component for understanding the regional carbon budget and the global carbon cycle. As the amount of river discharge continues to increase, along with increasing DOC export due to climatic warming and permafrost thawing, the remineralization of terrigenous organic marine-origin matter in the Arctic Ocean can reduce the Arctic Ocean's ability to absorb atmospheric carbon dioxide (CO₂). Thus, a complete understanding of the terrigenous and marine-origin DOC dynamics is required. To investigate behavior of DOC and sources of DOC, seawater sampling was carried out over in the Chukchi Sea, using a CTD/rosette sampler holding 24-10 L Niskin bottles during Korea research ice breaker R/V Araon cruises. d¹⁸O and salinity were used to estimate DOC inputs by river and sea ice melt, allowing the marine portion of the DOC pool. Concentration of DOC ranged from 34-116 mM. High DOC concentration was observed in the surface layer, suggesting the strong influence of terrigenous DOC derived from Arctic river. However, low-salinity water from ice melt diluted DOC concentration in the surface layer. The penetration depth of brine, rejected during sea ice formation, was observed from the surface layer to 200 m depth, where the contribution of riverine DOC was more than 50%. Our result revealed that sea ice formation, which injects brine into the underlying seawater, is a key mechanism for delivering riverine DOC into the deeper layer.

2019038114 Kholodov, Alexander L. (University of Alaska Fairbanks, Fairbanks, AK); Debolskiy, Matvey Vladimirovich and Nyland, Kelsey E. Cryoplanation terraces at the Seward Peninsula; mechanisms of origin and influence on subsurface hydrology on the local scale [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H21K-1809, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Slope terraces are widespread feature at the Seward Peninsula. Many researches identify these landforms as solifluction lobs. But in fact the solifluction is the process of the flowage of the soil of active (seasonally frozen) layer oversaturated with water down a steep slope. So it is strongly associated with permafrost. At the same time we notice these feathers not only on the north facing slopes, underlined by permafrost but as well on the south slopes where permafrost is detached from the seasonally frozen layer where surface soil layer is undersaturated. We assume that in this region within the areas where permafrost absence close to ground surface these features originated in result of solifluction during the cold epochs now days are subjectd to development of the neval processes i.e. influence of perannual or late-lying snow patches. These landforms control the redistribution of snow during winter seasons and, thus controls soil temperature and moisture regime. In September of 2017 we established the 70 meters long observation transects across one of the slope terraces at the milepost 28 of the Teller road. We installed temperature sensors at the ground surface and the depths of 20, 50 and 120 cm in three points located in the rear, central and front parts of the terrace. We also conducted vegetation, soil and snow surveys along the transect. In according to our results at the spring time of the 2018 snow thickness across the terrace decreases from the 1.8 m in the rear part to less than 30 cm at the front. It provides the conditions for permafrost preservation at the front part, while at the rear we observe only shallow (about 30 cm) seasonal freezing. This thin seasonally frozen layer thaws completely soon after the melting of snow cover that allows melted water and precipitation to infiltrate to deeper horizons during the summer. Presence of permafrost close to the ground surface at the frontal parts of these terraces creates series of "frozen dumbs" across the slope. These dumbs make longer the paths of downhill flow of ground water and sometimes can event create local water catchments.

2019038074 Kim, Yeonjoo (Yonsei University, Department of Civil and Environmental Engineering, Seoul, South Korea); Wang, Zhan; Seo, Hocheol and Mao, Jiafu. Surface temperature variation induced by the LAI change in Arctic tundra [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC21G-1193, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The permafrost response to the Arctic vegetation variation is controversial. We simulated the consequences of the Arctic vegetation variation in the recent three decades in the Community Earth System Model, and found the Arctic vegetation variation is too weak to directly affect the permafrost. However, it induces the air temperature perturbation, which is amplified by the snow cover variation, and finally leaves a footprint on the soil temperature. On the location of the maximum LAI increase, the soil temperature at 1 m depth is affected little, however, we found significant soil warming along the summer snowline between the Low and High Arctic, indicating the direct impact of the snow cover variation. In the Low Arctic, the winter snowpack insulates the soil from the colder air, and results in less permafrost; in the High Arctic, the snow persists in the summer and has a stronger opposite effect on the permafrost, by insulating the soil from the warmer summer air, and reflecting the solar radiation. Acknowledgments: This work was supported by the Korea Polar Research Institute (KOPRI, PN17081 and PE17900) and by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2015R1C1A2A01054800).

2019037811 Kinsman-Costello, Lauren E. (Kent State University, Kent, OH); Duroe, Kiersten; Mills, Jonathan; Barczok, Maximilian; Smith, Chelsea and Herndon, Elizabeth. Phosphate sorption to iron (oxy)hydroxides in organic tundra and boreal soils [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31G-2576, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

As the arctic continues to warm due to climate change, unprecedented permafrost thaw will release long-stored carbon as CO₂ into the atmosphere. This greenhouse gas release may be offset by plant growth, but this offset will in part be determined by nutrient availability. Phosphorus (P) availability can control numerous arctic ecosystem processes including primary production and organic matter mineralization rates. To assess P storage and bioavailability mechanisms in tundra and boreal soils, we measured P species, iron (Fe) species, and an indicator of phosphate sorption (phosphate sorption index, PSI). We found strong evidence for a substantial role of geochemical processes to control P storage and bioavailability, even in highly organic arctic soils. On average across all organic soils, over one-quarter (28±13%) of total extracted P and one-half of extracted P_i (46±2%) was present as iron oxide-bound P_i. Another 16±14% of P_i was water-soluble (8±8% of total P), while 30±22% was bound to non-reducible aluminum oxides. Organic P comprised 37±18% of extracted P, with acid-soluble P constituting the remaining 7±15%. Phosphate sorption was strongly related to extractable Fe, in particular poorly crystalline Fe oxides. Soils with greater poorly crystalline Fe oxides had the highest capacity to sorb phosphate, although the amount of P stored was similar, suggesting that high-Fe organic arctic soils have the capacity to sequester even more P. Water-soluble P_i, the most bioavailable of the P fractions, decreased with increasing soil PSI (r=0.52, p=0.002). That is, soils with a high capacity to bind phosphate had both low concentrations of water-soluble P_i and a low percentage of P_i in the water-soluble fraction. Prior work in arctic soils has emphasized the importance of biologically mediated processes in controlling P bioavailability and transport, yet our results reveal that inorganic P associated with metal oxides is a relevant and potentially dynamic pool of soil P, at times composing as much as half of stored soil P, even in highly organic soil horizons. Alterations to redox regime as climate change re-shapes the hydrology of tundra and boreal ecosystems may thus limit or enhance P bioavailability to plants and microbes.

2019037784 Kirkwood, Adam (Laurentian University, Living with Lakes Center, Sudbury, ON, Canada); Asemaninejad, Asma; Basiliko, Nathan; Roy-Léveillée, Pascale; Mykytczuk, Nadia C. S.; Packalen, Maara S. and McLaughlin, James. Microbial methane and carbon dioxide production in permafrost peatlands of Hudson Bay Lowlands [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2497, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Peatlands in the Hudson Bay Lowlands (HBL) constitute a sensitive and globally significant store of carbon, estimated at approximately 30 Pg, where much of this carbon is stored in permafrost, particularly in palsa fields. However permafrost degradation in HBL is proceeding at an accelerated pace as changing sea-ice dynamics in Hudson Bay amplify the regional effects of global warming. This research investigates the controls on carbon dioxide (CO₂) and methane (CH₄) production in degrading palsa fields. Soil cores were extracted from permafrost and thermokarst features in degrading and intact palsa fields near Peawanuck, Ontario. Peat C chemistry and bioavailability was assessed using Fourier-Transform Infrared (FTIR) Spectroscopy. Anaerobic microbial CH₄ and CO₂ production was assessed over 225 days at 4°C and 14°C to characterize thaw effects on permafrost horizons and the temperature sensitivity of C mineralization across permafrost, active layer, and thermokarst samples. Methanogen communities were characterized through high throughput sequencing of the mcrA functional gene. Production of CO₂ and CH₄ from thermokarst samples was much higher than from permafrost and active layer samples at the same depth horizons even after long-term stable incubation conditions at either temperature. This may suggest two things regarding microbial C mineralization in HBL peatlands: 1) thawing permafrost and the associated release of labile substrates to contemporary anaerobic decomposers is not as dominant a control as previously believed; and 2) carbon substrates derived from more recent net primary productivity (rather than older peat parent material) and increased graminoid plant cover increases C mineralization significantly. Further analyses of microbial community structure and carbon bioavailability data will help elucidate why anaerobic microbes in thermokarst features mineralize C faster and more broadly on the role of microorganisms in carbon cycling in permafrost peatlands. These results will allow for more accurate quantifications of CO₂ and CH₄ release in carbon rich permafrost landscapes, which is especially important where permafrost is threatened by rapid environmental change, as is the case in the HBL.

2019040671 Kling, Corbin L. (North Carolina State University, Department of Marine, Earth, and Atmospheric Sciences, Raleigh, NC); Byrne, Paul K.; Wyrick, Danielle Y. and Wegmann, Karl W. Investigating the formation of Noctis Labyrinthus, Mars [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P31I-3826, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Noctis Labyrinthus is a domical, highly faulted region on Mars situated west of Valles Marineris and southeast of the Tharsis Rise. The geomorphology of this region is complex, and the mechanism(s) responsible for the tectonic structures therein is not fully understood. Normal faults and graben complexes are widespread, and pit crater chains commonly coalesce and merge with the large troughs that dominate the central region of Noctis Labyrinthus. We combined detailed structural analysis with geophysical data to develop a relative formation sequence for this enigmatic region of Mars. We used fault displacement profile analyses as well as displacement-length scaling to characterize the populations of normal faults present. Our structural analyses show that there are two distinct populations of normal faults, one set with vertical displacements of »375-500 m, and a second set with displacements of »75-250 m. The geometric parameters of pit craters (major/minor axes, pit depth, and volume) were measured to determine their contribution to the geomorphology of the region. We find that individual pit crater chains increase in size, both in terms of diameter and volume, with increasing proximity to the central region of Noctis Labyrinthus. Importantly, we also find that the dimensions of the graben and pit crater systems within Noctis cannot be accounted for by tectonic deformation alone: they are simply too broad and too deep to have resulted solely from extensional tectonics. We propose that substantial volume loss has also occurred here, albeit perhaps enabled by crustal extension. For example, pit crater formation and normal faulting could expose subsurface volatiles (e.g., ground ice deposits) within the faulted sections, allowing for sublimation or melting and the opening of the troughs beyond that which is possible through faulting alone. Heat flux modeling for Mars shows that the Noctis Labyrinthus region has among the greatest present-day heat flux values, providing a basis by which volatile loss could have occurred here. The lack of large outflow channels in this region, however, suggests that sublimation, rather than large-volume melting, took place in this region. If so, then areas of comparatively little faulting with Noctis may still host substantial and as-yet unexposed deposits of subsurface ice.

2019040632 Kogutenko, Larissa (Institute of Geography of Kazakhstan, Almaty, Kazakhstan); Severskiy, I.; Shahgedanova, M.; Armstrong, R. L.; Kapitsa, Vassiliy; Kokarev, Alexander; Tokmagambetov, Turebek and Usmanova, Zamira. Changes in glaciers and glacial systems of transboundary basins in Central Asia over the past 60 years and their impact on runoff and water resources [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C21E-1385, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The changes of glacier systems of the Ile, Irtysh and Syrdariya transboundary river basins and its impact to the river runoff and water resources were analyzed based on the series of glacier inventories. Changes of glacial systems of the Balkhash-Alakol basin - the Ile-Kungei (6 inventories from 1955 to 2014), the Jungar (7 inventories in the same period) and the Upper-Ile glacial system on the Chinese part of Ile river basin (3 inventories from 1962/62 to 2012.) is the most studied. The glaciers of these three glacier systems decreased linearly with the average annual rate 0.73% for area and 1% for ice volume for the period 1955-2014. According to the results of research the share of glaciers area of particular basin relative to the total area of glacierization of the respective glacial system is stable in time. The error in calculation of glaciation area of the entire glacial system does not exceed ±5% when area of glaciers of particular basin is more 10 km². Glacier runoff and its impact to the regional water resources formation were investigated based on the data from a series of glacier catalogues of the Balkash-Alakol basin and data on rivers runoff, measured at the stations at the output of 16 rivers from the mountains for the period from 1955/56 to 2014. Based the analysis of data of Tuyuksu glacier mass balance monitoring for the last 14 years the method of separated evaluation of snow and ice components of glacier runoff depending on the ELA elevation was proposed. The share of runoff from melting of multiyear ice is small and with rare exception is less than 10% of the total annual river runoff. But the complete glacier runoff is up to 40-50% of the river runoff for the growing season, providing the possibility of existence of the irrigated agriculture system in Central Asia and become a kind of guarantor of water and food security in that region. Despite a significant reduction in glacial resources, there are no any negative trends in streamflow in any catchment or season, which allows to suggests the existence of some compensating mechanism. Such mechanisms have more significant participation in streamflow of melt water of ground ice: buried glaciers, rockglaciers and permafrost. This research was supported by Ministry of Education and Science of the Republic of Kazakhstan, Newton- al-Farabi fund and CHARIS project.

2019040620 Kolka, R. (U. S. Forest Service Grand Rapids, Grand Rapids, MN); Trettin, Carl; Tang, W.; Krauss, K.; Bansal, S.; Drexler, J. Z.; Wickland, K.; Chimner, Rodney; Hogan, D. M.; Pindilli, E.; Benscoter, B.; Tangen, B.; Kane, E. S.; Bridgham, S. D. and Richardson, C. J. State of the carbon cycle in terrestrial wetlands of North America [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43C-11, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Because carbon (C) density of terrestrial wetlands is much greater than that of upland ecosystems, consideration of C stocks and fluxes along with associated changes resulting from management or land-use change are of particular importance at local, regional and global scales. Through new analyses of recent available data bases and literature, C stocks, net ecosystem exchange (NEE) and methane (CH₄) fluxes were estimated for North American (US, Canada, Mexico and Puerto Rico) terrestrial wetlands (excluding tidal wetlands or permafrost areas). North America contains approximately 2.2 million km² of terrestrial wetlands (approximately 37% of the global wetland area) with an ecosystem C pool of approximately 161 Pg (approximately 36% of global wetland C stock). Canada has the greatest area of terrestrial wetlands (52%), followed by the US (47%), Mexico (1%) and Puerto Rico. Likewise, Canada has the largest C stocks, NEE, and CH₄ fluxes (80%, 51%, and 57%, respectfully) followed by the US (19%, 43%, and 39%, respectfully) and Mexico (1%, 7%, and 4%, respectfully). Forested wetlands comprise 55% of the total terrestrial wetland area, with the vast majority occurring in Canada. Organic-soil wetlands comprise 58% of the total terrestrial wetland area and contain 80% of the C stock. Overall, North American terrestrial wetlands currently are a CO₂ sink (i.e., negative NEE) of approximately 126 Tg of C per year, with approximately 53% occurring in forested- and 51% in mineral-soil wetlands. However, North American terrestrial wetlands are a natural source of CH₄, with mineral-soil wetlands emitting 56% and non-forested wetlands emitting 55% of the estimated total of 45 Tg CH₄-C per year. The current rate of terrestrial wetland loss is much less than historical rates (about 0.06% of the wetland area from 2004 to 2009), with restoration and creation nearly offsetting losses of natural wetlands. Although area losses are nearly offset, there is considerable uncertainty about the functional equivalence of disturbed, created, and restored wetlands compared to undisturbed, natural wetlands. For this reason, studies and monitoring systems are needed that compare C pools, rates of C accumulation and greenhouse gas fluxes across disturbance gradients, including restored and created wetlands.

2019040612 Kumpula, Timo (University of Eastern Finland, Joensuu, Finland); Verdonen, Mariana; Korpelainen, Pasi; Kolari, Tiina; Tuominen, S. and Tahvanainen, Teemu. Aerial photograph time series and UAS remote sensing application to study rapid ecosystem change of palsa mires in Fennoscandinavia [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33K-2816, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Palsas (peat-covered mounds with perennially frozen cores) occur in the narrow circumpolar zone of sporadic permafrost in the northern hemisphere. Previous studies have shown palsa mounds melting and collapsing as a result of warming climate and increasing precipitation. In Fennoscandia, palsas are likely to disappear almost completely by the middle of this century. Aerial photo time series allow tracking areal changes of palsas in Finnish Lapland from ca. 1960s. Aerial photos reveal that about 50% of palsas have disappeared in many locations in Finnish Lapland 1960-2016. Since 2016 we have collected data with Unmanned Aerial Systems (UAS) from 10 separate palsa mires twice annually (mid June and late August flying campaigns). The ultra-high spatial resolution of UAS orthophotos and Digital Elevation Models (DEM) allow accurate detection of boundaries between palsa mounds and surrounding mire, which is often hindered by shrubs and other vegetation. New data improves our knowledge about palsas' decay rate, extent and topographical heterogeneity. The UAS time series (2016-2018) from several study sites showed ca. 2-18% decrease in areal extent of many palsa mounds. In summer 2018 field work in two large palsa mire complexes were conducted, we collected 12 km² of multispectral UAS data acquired, several hundred active layer measurements, vegetation mapping and GHG measurements on different mire surfaces were collected (e.g. palsa, open mire, overgrown thermokarst ponds). One of the clearest sign of palsa disappearance are thermokarst ponds that appear as palsa's melts. Thermokarst ponds are rather fast overgrown by sphagnum moss and grass species ( mainly Sphagnum riparium and Eriophorum russeolum). These revegetated thermokarst ponds are clearly visible in new and old aerial photos as whitish and roundish objects. By investigating these forms from old and new aerial photos we can estimate distribution and amount of palsas about 50-100 years pre 1960's. All these remote sensing and field data indicate that decay of palsa mounds is faster than expected. Signs of decay are clear in most of palsas and just a few new palsa embryos have been detected.

2019040604 Kyzivat, Ethan D. (Brown University, Providence, RI); Smith, L. C.; Arvesen, John C.; Cooley, Sarah W.; Fayne, Jessica V.; Pavelsky, T. and Pitcher, Lincoln H. An ABoVE open water map at 1 m resolution from AirSWOT airborne camera imagery [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B13E-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In July and August 2017, NASA's AirSWOT sensor flew from southern Canada to Arctic Alaska and back again, as part of the multi-aircraft NASA ABoVE (Arctic-Boreal Vulnerability Experiment) field campaign. The aircraft mapped »30,000 km² of area, including hundreds of lakes underlain by spatially varying geologic and permafrost conditions. The AirSWOT instrument suite includes an experimental Ka-band interferometric synthetic aperture radar designed to map surface water elevations, and a Digital Cirrus Systems color infrared (CIR) camera. Open (non-vegetated) water is known to produce a distinct, dark radar return in under calm conditions and can be clearly identified in SAR imagery. However, wind roughening, radar distortions, and the presence of inundated vegetation can introduce challenges. Thus, the CIR product will improve the understanding of how different water surfaces appear to optical and SAR instruments and will provide a high-quality water mask for water surface elevation studies from AirSWOT. The water classification uses an object-based thresholding technique combined with a region growing algorithm. We validate our results using in-situ shoreline maps collected with GPS and manual delineation of imagery and find an overall accuracy and kappa coefficient exceeding 98% and 84%, respectively. These CIR image data and open-water masks are freely available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). Applications include improved interpretation of other NASA ABoVE remote sensing flight campaigns (UAVSAR, LVIS, AirMOSS, AVIRIS, CFIS) and high-resolution mapping of Arctic-Boreal landforms, vegetation, lakes, rivers, and wetlands.

2019037857 Lamontagne-Halle, Pierrick (McGill University, Montreal, QC, Canada); Kurylyk, Barret; McKenzie, Jeffrey M. and Zipper, Samuel C. How permafrost thaw will affect the groundwater contribution to streams and lakes? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1047, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The presence or absence of permafrost strongly influences the movement of groundwater in cold regions by confining groundwater flow to the active zone located above permafrost, to the sub-permafrost aquifer located below permafrost or through perennially unfrozen areas known as taliks. The thawing of permafrost increases hydraulic conductivity by several orders of magnitude and thereby enhances groundwater storage and hydrological connectivity between aquifers and surface water bodies. Previous studies have revealed an overall increase of Arctic river baseflow while some lakes and wetlands are drying. These complex patterns are poorly understood. We need to use groundwater models effectively to provide a better understanding of the processes involved. However, it remains a challenge partly due to choices in the design and parameterization of the surface boundary conditions. Herein, we develop an improved set of surface boundary conditions for a coupled heat and groundwater flow numerical model that includes dynamic freezing and thawing processes to simulate the impacts of climate warming and permafrost thaw on the spatial and seasonal patterns of groundwater discharge. We show a spatial shift in groundwater discharge from upslope to downslope and temporal shift towards the winter season due to the formation of a lateral supra-permafrost talik underlying the active layer. Our results suggest that the thickness of the lateral talik and the duration of the seasonally thawed ground are the mains drivers for the modelled changes. Parameters such as subsurface permeability, surface slope, recharge rate and snow thermal conductivity can influence the timing and the magnitude of the temporal and spatial groundwater discharge variations, but the trajectory of spatial and temporal shifts in groundwater discharge remain the same. These insights help explain observed changes in Arctic baseflow and wetland patterns and are important for water resources and ecosystem management.

2019040655 Lamoureux, S. F. (Queen's University, Department of Geography, Kingston, ON, Canada); McFadden, Sarah I.; Bevan, George; Rudy, Ashley; Paquette, Michel and Fortier, D. Localized ground ice subsidence and soil water dynamics as indicators of near-surface ice content in the High Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Thermokarst is a key issue in a changing permafrost environment in terms of hazards, hydrological and ecosystem impacts. Modeling and remote sensing offer the potential to advance understanding of the landscape-scale controls over thermokarst activity, but are often used with limited ground validation. Given the need for ice distribution data to assess thermokarst potential, improving the interpretation of remotely-sensed DInSAR analyses represents a key opportunity to improve available ice content information. We present a combined field and differential interferometric synthetic aperture radar (DInSAR) assessment of subsurface ice content and related hydrological conditions from the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian High Arctic. We compared DInSAR data with permafrost core and ground penetrating radar (GPR) data to aid in research focused on hydrological and thermokarst processes. An area of subsidence that was observed with DInSAR measurements was studied using GPR and permafrost core analysis. The GPR survey showed the proximity of massive, near-surface ice in a pattern consistent with the DInSAR subsidence. This area of substantial subsidence is associated with an older (>65 years) active layer detachment scar and indicates potential ongoing adjustment to this earlier disturbance. We have followed this work with detailed field survey and surface detection change approaches, as well as hydrological analysis of soil water and drainage. This research demonstrates the utility of integrated DInSAR, hydrological and field approaches for identifying localized ground ice conditions. It also provides a framework for developing site-specific investigations of thermokarst potential to link larger scale thermokarst indicators to physical processes. This approach is suitable for both downscaling landscape-scale remote sensing and localized hydrological data sets, and for improving interpretations of thermokarst potential.

2019037859 Langer, Moritz (Alfred Wegener Institute, Helmholtz-Center for Polar and Marine Research, Potsdam, Germany); Nitzbon, Jan; Schneider von Deimling, Thomas and Oehme, Alexander. Modeling trajectories of degradation of ice rich permafrost landscapes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1050, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Thawing of permafrost triggers a wide range of morphodynamic processes which magnitude and pace directly relate to the ground ice content. Already induced or completed degradation processes are visible as intriguing geomorphological features of permafrost landscapes such as thermokarst lakes, thermo erosion gullies, thaw slumps, and degraded ice wedged polygons. The formation of these features is, on the one hand, strongly controlled by the topographical and hydrological landscape properties. On the other hand, these landscape properties are explicitly modified by permafrost thaw and the accompanying morphodynamics. Consequently, a wide range of positive and negative feedback mechanisms can lead to either accelerated permafrost degradation (due to e.g. ponding water) or permafrost preservation (due to e.g. enhanced drainage and insulation). Based on different modeling exercises using the permafrost - land surface model CryoGrid, we demonstrate the high sensitivity of permafrost landscapes to small morphodynamic landscape changes on the one side and permafrost stability on the other side. Therefore, we present simulations of ice wedged polygons, thaw slumps, and thermokarst lakes and follow their different trajectories of degradation under a warming climate. Our preliminary results indicate that already minor changes in the lateral flow rates of water and/or matter can result in different pathways of permafrost degradation leading to different landscape morphologies. This finding may have strong implications for biogeochemical processes such as the decomposition of organic soil components.

2019038078 Larsen, Joan Nymand (University of Akureyri, Akureyri, Iceland); Ingimundarson, Jon Haukur; Schweitzer, Peter and Jungsberg, Leneisja. Permafrost thaw and socio-economic impacts in the Disco Bay region, West Greenland; youth voices and local stakeholders in developing adaptation and mitigation strategies [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

An overview of the methods and some of the early scoping results from the Nunataryuk project (EU-Horizon 2020), on the socio-economic and infrastructure impacts of permafrost thaw in the Disco Bay area of West Greenland is presented, with a focus on a series of preliminary highlights from interdisciplinary and field-based research that connects permafrost studies to policy and stakeholders. Specifically, with a main focus on the coastal town of Ilulissat highlights from early scoping and community consultation processes with local stakeholders are discussed. Also, brief reference is made to preliminary field based efforts to identify and further develop arctic specific physical and social indicators of human development and biophysical changes that are relevant for coastal settings and will help facilitate measurement and tracking of Arctic change in coastal regions. Overview of early highlights also include a series of supporting data from case study work and focus group interviews with local youth in the Disco Bay region with an emphasis on their future, the choices they make, their priorities in terms of culture and identities, where to study and where to live, and factors affecting their social and physical environment. These and other field-based research results will contribute to the identification and design of effective adaptation and mitigation strategies.

2019040606 Larson, E. (Harvard University, Cambridge, MA); Munger, J. William; Commane, R.; Schiferl, Luke D.; Euskirchen, E. S.; Zona, D.; Wofsy, S. C. and Moorcroft, Paul R. Seasonal carbon balance in Arctic tundra and boreal forests [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B13E-08B, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

A substantial amount of carbon is frozen in the arctic permafrost that could be released as greenhouse gases under a warmer climate. This carbon could potentially lead to a strong positive global warming feedback; however the fate of this carbon is unclear. A myriad of complicated processes affect the Arctic carbon budget on different spatial and temporal scales. Two of the most important processes predicted to affect the long-term carbon budget are increased heterotrophic respiration due to warmer soils and increased plant growth due to warmer air temperatures and carbon fertilization. These two processes oppose each other and previous modeling efforts have resulted in very different responses to these driving mechanisms. This suggests that a better understanding of these processes and their feedbacks is critical for advancing our understanding of the fate of arctic peat and its contribution to the carbon budget and ultimately global warming. Here we use a mechanistic terrestrial ecology model to simulate plant growth and heterotrophic respiration at eddy covariance tower sites in order to understand the processes that control the carbon budget including its seasonal cycle. Specifically, we use the Ecosystem Demography model v2.2 to simulate the growth of Black Spruce, Arctic grammanoids, and Deciduous and Evergreen Arctic shrubs. The model is able to simulate the zero-curtain period with preliminary results near Fairbanks indicating that over 20% of the total heterotrophic respiration in black spruce forests occurs between October and December. Ongoing analysis will focus on quantifying the sensitivity of GPP and heterotrophic respiration to physical drivers such as temperature, moisture, and light that lead to the observed interannual variability in the carbon flux.

2019038071 Lee, Jaeyong (University of Tokyo, Center for Spatial Information Science, Bunkyo-ku, Japan) and Oguchi, Takashi. Gully formation processes at Ny-Alesund and Longyearbyen, Spitsbergen, and applications to Martian gullies [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP53E-1907, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We investigated gully formation in Spitsbergen by field surveys and compared them with Martian gullies using a Martian DEM. Gullies on the earth are usually formed by rainfall or snowfall, but Mars does not have rainfall or snowfall due to low pressures and temperatures. Therefore various theories have been proposed to explain gullies on Mars (e.g. Malin and Edgett, 2000; Pilorget and Forget, 2016). We carried out field work at Ny-Alesund and Longyearbyen in Spitsbergen in July 2017. At Ny-Alesund, we focused on a gully associated with a pingo and patterned-ground. Below the pingo, striped patterned-ground of 40-100 m long is mixed with fluvial deposits. It forms a shallow gully (channel) subject to classification and rearrangement of debris due to water flow. Analysis of the slope below the pingo suggests that liquid water originated from the upper pingo caused the gully. Excavation of the ground indicated that the water was transported through the subsurface. We also excavated a section of a 200-m-long gully at Longyearbyen. The surface of the gully was mostly covered with debris of about 20 cm in diameter, but smaller particles occur in the lower part due to selective transport. We observed a small amount of constant subsurface flow. This water seems to be originated from permafrost located at the top of the gullies. The slope around the gully is unstable because its angle (39°) exceeds the angle of repose. We propose that flowing water is responsible for gully generation. By comparing the results of photogrammetric analysis with the Martian DEM, we conclude that the structural form of the Longyearbyen gully is similar to gullies on Mars. The above observations indicate that underground liquid water or permafrost may have contributed to gully formation on Mars as in Spitsbergen, although the activity of liquid water or permafrost in the subsurface of Mars has not yet been clearly observed. Future bore hole surveys on Mars will test this hypothesis.

2019037791 Leewis, Mary-Cathrine (U. S. Geological SUrvey, Menlo Park, CA); Srinivas, Archana J.; Mackelprang, Rachel; Blazewicz, Steven; McFarland, Jack W.; Podgorski, David C.; Zito, Phoebe; Spencer, Rob; Conaway, Christopher H. and Waldrop, Mark P. The cold shoulder; microbial carbon metabolism across an ancient permafrost chronosequence [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2506, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is an extreme habitat with low water and substrate availability, yet it hosts microbial populations that remain active over geologic timescales. Using permafrost collected from a Pleistocene permafrost chronosequence (19 ka to 33 ka), we hypothesized that increasing age and associated stressors drive adaptive changes in microbial community function and composition, and that functional changes in the metagenome would be related to changes in the chemistry of permafrost carbon (C). Examinations of water-soluble organic carbon (OC) by Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR-MS), quantification of total anions, and metagenomic sequencing were combined to better understand the relationships between microbial populations, the molecular-level composition of potentially bioavailable organic matter (OM), and age. We found that age had a marked effect on both the molecular composition of dissolved OM and the microbial community. Diversity of the total microbial community, the relative abundance of carbohydrate active enzyme families, and the nominal oxidation state of C (NOSC) all significantly decreased as soils became older. In contrast, the concentration of low molecular weight organic acids and ammonia significantly increased with age. Both our chemical data and functional gene data supported the hypothesis of a shift from sugar to amino acid metabolism over geologic time. To this end, we present a conceptual model of microbial metabolism in permafrost based on fermentation of OC, changing metabolic pathways, loss of methanogenic activity, and the buildup of organic acids that helps to explain the unique chemistry and high C lability of ancient permafrost soils. These data indicate permafrost may present an age-dependent response to thaw, with important implications for future warming scenarios.

2019037876 Levy, Joseph (Colgate University, Hamilton, NY); Fountain, Andrew G.; Obryk, Maciej; Telling, Jennifer W.; Glennie, Craig Len; Pettersson, Rickard; Gooseff, Michael N. and Van Horn, David J. Decadal topographic change in the McMurdo dry valleys; thermokarst subsidence and glacier thinning indicate transfer of water storage from the cryosphere to the hydrosphere in the terrestrial Antarctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1071, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Recent ground-based observations of glaciers, streams, and soil surfaces in the McMurdo Dry Valleys (MDV), the largest ice-sheet-free area in Antarctica, have documented evidence for rapid ground ice loss, glacial thinning, and ground surface subsidence. To evaluate the extent, magnitude, and location of decadal-scale landscape change in the MDV we collected airborne LiDAR elevation data over 3,300 km² of the MDV in 2014-2015 and compared this data to a 2001-2002 airborne LiDAR campaign. This regional assessment of elevation change spans the recent acceleration of warming and melting observed by long term meteorological and ecosystem response experiments, allowing us to assess the response of MDV surfaces to warming and potential thawing feedbacks. We find that locations of thermokarst subsidence are strongly associated with the presence of excess ground ice and with proximity to surface or shallow subsurface (active layer) water. Subsidence occurs across soil types and landforms, in both low-lying, low-slope areas with impeded drainage and also high on steep valley walls. Glacier thinning is widespread and is associated with the growth of fine-scale roughness on glacier toes. Pond levels are rising in most closed-basin lakes in the MDV, across all microclimate zones, from the coastal thaw zone to the upland frozen zone. These observations highlight the continued importance of insolation-driven melting in the MDV. The regional melt pattern is consistent with an overall transition of water storage from the local cryosphere (glaciers, permafrost) to the hydrosphere (closed basin lakes and ponds as well as the Ross Sea). We interpret this regional melting pattern to reflect the potential for a transition to Arctic and alpine-style, hydrologically mediated permafrost and glacial melt in the Antarctic cold desert.

2019037821 Li Ruichao (Chinese Academy of Sciences, Institute of Atmospheric Physics, Laboratory of Atmospheric Sciences and Geophysics, Beijing, China) and Xie Zhenghui. A new frozen soil parameterization including frost and thaw fronts in the land surface model [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2589, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is an important part of the cryosphere, not only widely distributed, but also has great influence on the process of water and energy during the phase change process.Obtaining accurate frost and thaw front depth information plays an important role in surface energy balance, alpine ecology, hydrological runoff, cold zone engineering and greenhouse gas emissions. In order to solve the above scientific problems, we have developed a parameterization scheme of frozen soil considering the dynamic change of frost and thaw front depth, and coupled it with land surface model, and then used the new model to estimate frost and thaw front depth, degradation of permafrost. Finally, we evaluated the effects of degradation of permafrost on global climate.

2019038102 Li Zhongqin (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Wang Feifeng and Zhou Xi. The response of glacial runoff at the headwaters of the Urumqi RTiver, eastern Tianshan, central Asia [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC51B-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Over the past few decades, global warming has resulted in substantial landscape changes, particularly through the loss of the mass and volume of most alpine glaciers. Located at the headwaters of the Urumqi River in eastern Tianshan, the core area of arid and semiarid central Asia, Urumqi glacier No. 1 (43°06'N, 86°49'E) has the longest observation record of all the glaciers in China, covering the period from 1958 to the present. Originating from the thawing of glaciers, glacial runoff is sensitive to climate warming. As an important water supply for Urumqi, the provincial capital city of Xinjiang Uyger Autonomous Region, glacial runoff from Urumqi glacier No. 1 and its change as well as its sustainability have drawn wide attention in recent years. The runoff records of streams draining basins with between 0 and approximately 54% glacier cover, located at the headwaters of the Urumqi River in eastern Tianshan, central Asia, have been examined for the purpose of assessing climatic and glacial influences on temporal patterns of streamflow for the period 1959 to 2015. Runoff in the highest glacierized basin is found to be inversely correlated with the glacier mass-balance data and increased by over 2 times on average from 1959 to 2015, whereas flow from a glacier-free basin reflects precipitation changes associated with temperature that may enable either ground ice formation or ice storage release. From the measurement at Urumqi glacier No. 1 gauging station and a simple water balance model, the glacial runoff during the period 1959 to 2015 was calculated and found to have increased a factor of 2 over the 56-year span. A significant amount of the increase occurred after 1987, particularly after 1995, and coincides with increases in both temperature and precipitation. For the basin with a glacier cover of 18.5%, the runoff increased approximately 30% on average from 1983 to 2015, which underscores expected results based on glacier melt and precipitation increase, especially after 2000. This is due to several possible reasons including enhanced evaporation, groundwater percolation, increased water consumption due to plant colonization, and runoff decrease from glacier basins subject to area reduction.

2019040624 Liang, R. (Princeton University, Department of Geosciences, Princeton, NJ); Lau, M.; Vishnivetskaya, T. A.; Lloyd, K. G.; Pfiffner, S. M.; Rivkina, E. and Onstott, T. C. Differential diversity and function of microbial communities along a salinity gradient in ancient Siberian permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43H-2950, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost sediments along coastlines of the Siberian Arctic Shelf and other regions are susceptible to rapid erosion and degradation due to arctic warming. Given the large pool of ancient organic carbon, it's important to understand the diversity and metabolic status of the indigenous microbial communities in frozen saline sediments. Geochemical characterization, aspartic acid (Asp) racemization assays and metagenomic sequencing were applied to permafrost sediments collected at various depths from a borehole (0.4 to 21.7m) on the East Siberian Sea coast (Cape Chukochii; 70°05'N, 159°55'E). While the salinity generally increased with depth, the concentrations of Asp and DNA decreased with depth. The D/L Asp in the bulk sediment increased from 0.12 to 0.29 with a linear relationship (R²=0.99). The lower ratio of D/L Asp in separated cells (0.06-0.15) suggested that many microbes survived over geological time and might be metabolically active. Metagenomic sequencing revealed that the microbial diversity in the top layer (3.4m) was much higher than the older sediments of higher salinity (5.8 and 14.8m). While most microbial lineages in extracellular DNA pool were the same as the intracellular fraction, the divergence of the microbial community between intracellular and extracellular fractions increased with depth. The microbial community at 3.4m was predominated by aerobic heterotrophs affiliated with Actinobacteria and Proteobacteria. By contrast, Spirochaetes and Firmicutes overwhelmingly dominated the middle-depth stratum. The metabolic capability of these anaerobic, fermentative microorganisms was supported by the enrichment of fermentation-related genes and the highest accumulation of acetate at 5.8m. Interestingly, archaeal lineages from the phyla Euryarchaeota, Thaumarchaeota, Bathyarchaeota and Lokiarchaeota were only abundant (»23%) in the deeper, older layer (14.8m). Despite the presence of potential fermentative metabolisms, genes involving different autotrophic CO₂ fixation pathways were highly enriched at 14.8m. As the accumulation of DNA damages in ancient DNA makes sequencing challenging, further sequencing after DNA repair is ongoing to better capture the diversity and function of indigenous microbiomes in permafrost marine sediments up to »120 kyr old.

2019040639 Lilly, M. R. (Geo-Watersheds Scientific, Fairbanks, AK); Brown, Jerry; Frauenfeld, O. W.; Levine, Kristina; Streletskiy, D. A. and Tahirkheli, Sharon T. Permafrost Monthly Alert (PMA); a program to promote, preserve and enhance frozen ground knowledge [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C33E-1616, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The U.S. Permafrost Association (USPA) and the American Geosciences Institute (AGI) have jointly provided a monthly catalog of the world-wide, permafrost literature since 2012. The Permafrost Monthly Alert (PMA) program produces professionally reviewed reference material on a regular monthly schedule and results are made available in multiple locations. The monthly-updates portion of the PMA program are available through the USPA web site (URL: http://uspermafrost.org). The current seven-year collection includes over 75 monthly updates with a total of 5,800 citations. The vast majority of the references have abstracts and are organized into four major categories: journals, conferences, theses and reports. The monthly accessions are uploaded by AGI to the Bibliography of Cold Regions Science and Technology (COLD), a searchable database that includes more than 29,000 permafrost references. Bibliographic references on the USPA website are easily searchable with internet search engines. An example using "Alaska" and "permafrost" as search terms produce 659 records. The number of different search engines that index the USPA website exceeded 20 for each of the last four years. For 2017, the total search engine hits exceeded 90,000. Google search routines exceeded 6,000 hits each year since 2012. Content matters as much as reference age. As an example, the March 2012 PMA monthly reference listing is in the top four viewed monthly pages over a five-year period. Average annual usage of the service exceeds 10,000 inquiries (views by readers) in the last three years, with over 55,000 views since 2012. In addition to serving academic communities, the PMA is a valuable resource to industry, private institutions, engineering firms, government agencies and K-12 education programs. By providing current and historical sources of information, the PMA program is a readily available mechanism for conveying scientific information to decision-makers and the public. Future improvements to the PMA program will include efforts to increase engineering topics and reference sources, evaluations for using various search engines and improving applications for K-12 education programs.

2019037786 Lindgren, Amelie (Stockholm University, Department of Physical Geography, Stockholm, Sweden); Hugelius, Gustaf; Kuhry, Peter; Overduin, Pier Paul; Holloway, Max and Lu, Zhengyao. Dynamic changes of soil carbon storage from the last glacial maximum until present [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2499, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The soil carbon (C) storage of permafrost soils has undergone massive changes during the deglaciation and the Holocene (Lindgren et al., 2018). Tracking these changes are of importance to understand the dynamics of carbon storage, emissions and uptake under changing climate conditions. The general warming both prior to and during the Holocene resulted in shifts of the permafrost area and possibly a redistribution of ca 1000 Pg soil C. However, the timing of this redistribution remains uncertain. Using modeled climate together with empirical data, we reconstruct these changes. We trace the development of permafrost, biomes, and sea level across the northern hemisphere. Areas of particular interest are the gradually inundated sea shelves, the extensive biome shifts in Siberia where tundra gave way to boreal forest, loss of permafrost in Eurasia, retreat of the ice sheets and the associated development of new soils, as well as the gradual build-up of peat. We also include deep soil C storage in loess and Yedoma. The empirical data consists of data already compiled in databases, such as: measured soil C inventories, peat basal dates, thermokarst development, biomized pollen assemblages, and ice sheet retreat patterns. To extend these observational data both in space and time, we use varying approaches with models which require input from climate models (CCSM3 TraCE-21 ka, HadCM3) that cover the full period from the Last Glacial Maximum until present. Lindgren, A. Hugelius, G. Kuhry, P. 2018 Nature DOI:10.1038/s41586-018-0371-0

2019038129 Lindsey, Nate (University of California, Earth and Planetary Science, Berkeley, Berkeley, CA); Martin, Eileen Rose; Lisabeth, Harrison P.; Wagner, Anna M.; Rodríguez Tribaldos, Veronica; Titov, Aleksei; Ekblaw, Ian; Ulrich, Craig; Dou, Shan; James, Stephanie R.; Gelvin, Arthur B.; Saari, Stephanie P. and Ajo Franklin, Jonathan Blair. Time-lapse imaging of a controlled permafrost thaw experiment with strongly non-stationary vehicle noise and a 4,000 component distributed acoustic sensing (DAS) array [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost degradation, triggered by increased air temperature or coupled hydrological processes, also alters the mechanical properties of near-surface sediments. Recent laboratory rock physics experiments have demonstrated that seismic wave speed and attenuation are exquisitely sensitive to thaw state and could be used to characterize or even monitor thaw interfaces in situ. In this study, we evaluate seismic measurements in this capacity in the field using dense observations at the decameter scale. In 2016, a 10.5 m´12.7 m area of discontinuous permafrost located in Fairbanks, AK was artificially warmed over 60 days, resulting in 10 cm of ground subsidence driven by thaw and thaw-related consolidation in the upper 5 m. A busy road 200 m away from the warming site generated time-varying ambient seismic noise (f=5-35 Hz). Vehicular noise was recorded continuously by a dense array of fiber-optic distributed acoustic sensors (4,000 DAS sensors @1 sensor/meter), and then processed in co-linear segments using standard ambient seismic methods. Resulting 6-hour noise correlation functions are found to be time-invariant, which enables time-lapse virtual source point to receiver line analysis. 2-D noise correlation wavefields are dominated by coherent refracted SH waves that arrive before dispersive Love waves with velocities that can be confirmed by hammer-geophone survey. Relative SH phase velocity changes (dv/v) during the experiment are as large as 10% and correlate with the timeline of warming and subsidence as measured with an array of temperature sensors (thermocouple/RTD) and weekly LiDAR scans. Tomographic inversion of this part of the wavefield provides time-lapse volume images of the degrading permafrost.

2019040643 Liu, C. (University of Arkansas, Fayetteville, AR); Feng, S. and Guo, H. Comparison of methods for calculating freezing/thawing index using monthly and annual climate data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1787, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Changes in soil thermal regimes in the cold regions have widespread impacts on hydrology, ecology, and carbon exchanges. The annual freezing and thawing index, which are generally calculated using daily temperature, have been widely used to estimate the freezing depth, active layer thickness, and the distribution of permafrost. However, long and reliable daily temperature data are scarce in the cold regions, while monthly and annual temperature data are more readily available for many locations. When the daily temperature is unavailable, it can be estimated based on monthly or annual temperature using statistical methods and weather generators. This study firstly used the Global Land Data Assimilation System (GLDAS) daily temperature data on quarter degree resolution over the Northern Hemisphere during 1901-2012 to calculate the freezing and thawing index. Then the monthly and annual temperature in the GLDAS were calculated and three different approaches were subsequently used to estimate the daily temperature and the freezing/thawing index. When monthly data is used, the weather generator produced the smallest relative error (RE) and root mean square error (RMSE) in estimating the two indices comparing to the other two methods. The annual temperature data usually underestimate the freezing/thawing index, but the RE and RMSE are still less than 5% over most of the high-latitude regions, especially when the weather generator is used. These results suggested that, if the daily temperature can be well estimated using statistical methods and weather generators, the thermal regimes of permafrost can be reliably estimated using modeled monthly temperature and/or reconstructed monthly/annual temperature.

2019040633 Liu, L. (Sichuan University, State Key Laboratory of Hydraulics and Mountain River, Chengdu, China); Zhang, W. and Lu, Q. The variations in near-surface temperature gradient and related impacts in the Tibetan Plateau [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C21E-1411, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Climate warming likely causes intensive changes in local hydrological processes and atmospheric circulation in the Tibetan Plateau (TP), but our understanding about their links was greatly limited by the sparse in-situ measurements. In the study, we used multi-layer soil temperatures of 45 weather sites to investigate regional near-surface soil warming in the TP (1981-2015), and the possible hydrological effects were examined in two typical alpine basins. Moreover, temperature gradient between air and ground surface was investigated with the observations of 76 weather sites in the TP. Our results showed the enhanced sensible heating indicated by the increasing land-air temperature gradient at rate of 0.026±0.012 °C a^-1 (62 of 76 sites, p<0.05). The consistent trends in temperature gradient of 0-5 cm soil layer during both warm (averagely 0.019±0.008 °C a^-1 at 30 of 45 sites, p<0.05) and cold (0.031±0.013 °C a^-1 at 34 of 45 sites, p<0.05) seasons, which implied increasingly more heat transferred downward from ground surface annually. The deeper layer (5-10 cm) also showed similar (though relatively weaker) trends in the vertical heat transfer. The warming caused marked freeze onset delay (0.368±0.158 day a^-1, p<0.05) and thaw onset advance (-0.417±0.146 day a^-1, p<0.05) of ground surface. Our study also reflected that the increasingly near-surface soil warming tended to result in baseflow rise and quicker groundwater recession in the permafrost-dominated basin. However, the hydrological effects of soil warming were likely overwhelmed by the impacts of precipitation variation in the basin with lower permafrost fraction. Our study implied that the fraction of permafrost coverage plays an important role in hydrological impacts of weakening soil freezing induced by the increasingly near-surface warming in alpine basins, and the increasing sensible heating would have complex influences on atmospheric circulation.

2019040616 Liu, X. (University of Massachusetts Lowell, Biological Science, Lowell, MA); Hines, M. E. and Zhang, L. The effects of pH, temperature, and DOM on anaerobic carbon mineralization and methanogenic efficiency in ombrotrophic and minerotrophic Alaskan peatlands [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B41G-2793, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane (CH4) production varies greatly at ombrotrophic (OP) and minerotrophic peatlands (MP), which have different sources of nutrients. These two trophic endmembers usually are found within a short distance in Alaska. The trophic status of peatlands is associated with distinguished surface vegetation and contrasting pH, which also regulates methanogenesis. Projected global warming and melting of permafrost could dramatically change the hydrology of Alaskan peatlands, which may turn ombrotrophic peatlands into minerotrophic ones. Such trophic status change would result in changes in porewater (PW) pH and the quantity and quality of dissolved organic matter (DOM), which in together with projected temperature (T) increase will affect the anaerobic carbon mineralization and methanogenic efficiency in Alaskan peatlands. To better understand how pH, T, and DOM affect fermentation and methanogenesis in OP and MP, laboratory mesocosm manipulation experiments were conducted using peats and PW collected from the minerotrophic Frozen Pond (FP) and ombrotrophic Goldencreek Bog (GB) in Fairbanks, Alaska. The manipulation includes increasing T, changing pH to the value of the reciprocal site, exchanging porewater, covarying two of the above three factors, and changing all three factors in parallel experiments, respectively. Results suggest increasing T increased methanogenesis in both sites. Changing the pH didn't affect primary fermentation in either sites. Lowering pH in FP to GB value (3.9) did diminish the methanogenesis but increasing pH in GB to 6.5 didn't lead to higher CH₄production. Although the PW from GB has higher [DOM] and more humic material, it didn't affect the methanogenesis when incubated with the peats from FP. However, it did inhibit syntrophy at FP compared to the control. The PW from FP brought methanogens to GB but only slightly increased CH4 production. A combination of the two-factor manipulation didn't bring much change compared to single factor manipulation. But when all three factors changed in GB, it increased methanogenesis and carbon remineralization rates dramatically. It seems pH is the only factor affecting these processes when incubate peat from FP.

2019038079 Liu Lin (Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, China); Rouyet, Line; Strozzi, Tazio; Lauknes, Tom Rune and Christiansen, Hanne H. Seasonal thaw settlement and frost heave in permafrost regions in the Arctic; a synthesis of InSAR observations using sentinel-1 SAR images [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Ground surface in permafrost regions undergoes regular thaw settlement and frost heave at annual basis due to phase changes of soil water in the active layer. Despite ubiquitously occurring in vast areas, such seasonal movements are difficult to quantify because (1) their magnitudes are small, usually less than 10 cm; (2) the spatial gradient is low, resulting in no obvious features on the ground surface that can be easily identified. In addition to repeat ground-based surveys, remote sensing Interferometric Synthetic Aperture Radar (InSAR) observations have been proven to be able to resolve such subtle movements at both high spatial (tens of meters) and temporal (weeks to months) resolutions. Here we present a synthesis of InSAR measurements of seasonal movements in flat permafrost areas across the Arctic. All taking advantages of the recent, frequent acquisitions by the Sentinel-1A/B satellites, three research groups carried out InSAR time series analysis in Adventdalen (Svalbard), Ilulissat (Greenland), and Sobo-Sise Island (Siberia), respectively. The ground movement time series obtained from these independent studies show three common characteristics. First, the magnitudes of seasonal movements range from 2 to 5 cm. Second, their spatial variability is largely related to surficial soil types and geomorphology. Third, they all show a gradual subsidence in thaw seasons, followed by a faster uplift in the freeze-back period. Such freeze-back uplift has not been reported in previous InSAR studies as they used longer-repeat images acquired in thaw seasons only. We show that, to the first order, each time series of ground movements can be well described by the Stefan equation with a composite index that combines both the thawing and freezing degree-day indices. Our synthesis confirms that the temporal evolution of surface elevation in permafrost regions is primarily controlled by the thermal response of the active layer to the atmospheric forcing.

2019037820 Lorenson, Thomas D. (U. S. Geological Survey, Santa Cruz, CA); Oberle, Ferdinand J.; Johnson, Cordell D.; Richmond, Bruce M.; Erikson, Li H.; Gibbs, Ann; Conaway, Christopher H.; Bull, Diana L. and Jones, Benjamin M. Cryopegs of northern Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2587, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Cryopegs are saline taliks that develop over time in shallow permafrost. The prevalence and distribution of cryopegs is not well known in northern Alaska. We have previously documented their existence at Barter Island, Alaska where they occur near and at the current shoreline. We first became aware of their existence on Barter Island by running electrical resistivity tomography (ERT) surveys of the coastal bluffs. Geochemical analysis of the porewater and sediment have shown that the cryopegs on Barter Island developed from the concentration of groundwater and surface water salts rather than from seawater. In an effort to understand the areal extent of cryopegs in the region, we recently completed ERT surveys on the coastal bluffs adjacent to Beaufort Lagoon, located about 50 km southeast of Barter Island. The results show the development of a saline cryopeg extending from the coast to at least 400 m inland and below about 4 m depth. The maximum conductivity (salinity) values occur around 13 m below ground. Additional confirmation of cryopegs in northern Alaska has come from recent shallow permafrost coring (7.5 m deep) at Drew Point, Alaska, where saline, unfrozen silty clay well below 0°C was recovered from multiple holes around 3 to 7.5 m below ground. Cryopegs also occur around Barrow, Alaska, however their origin has been attributed to be from seawater. We suggest cryopegs are a common, but unrecognized state in shallow permafrost on the coastal plains of northern Alaska. The subsurface unfrozen saline ground has many implications including affecting permafrost strength and its erosion and thawing, allowing shallow saline groundwater flow, and degradation of shallow freshwater lake water quality. Another aspect of interest is that cryopegs create an environment for novel microbes that may be analogs to possible extra-terrestrial microbes on Mars or planetary moons with low temperature saline water in the subsurface.

2019038090 Lu Ping (Tongji University, Shanghai, China). Monitoring active layer of permafrost along the Qinghai-Tibet railway through InSAR measurements [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1397, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is one of the largest elements of the terrestrial cryosphere and is extremely sensitive to climate change. Changes of permafrost not only affect regional and global water circulation, carbon deposit and climate warming, but also influence ground ecological, geophysical, and biogeochemical processes in cold regions. The permafrost region of the Qinghai-Tibet Plateau is the highest and largest permafrost area in the middle and low latitudes of the world. In particular, the Qinghai-Tibet railway, from Xining to Lhasa, is 1956 kilometers long, including a length of 550 kilometers over the permafrost region. In order to monitor the active layer along the Qinghai-Tibet Railway, the surface deformation pattern has been analyzed by the L-band SAR data of the ALOS satellite and the C-band SAR data of the Sentinel-1 satellite, with the help of the DInSAR and the PS-InSAR technique, respectively. The estimation results from the InSAR deformation observation were furthered cross-validated by the in-situ measurement of subsidence along the Qinghai-Tibet railway, which is part of the maintenance project by the railway company.

2019040601 Ludwig, S. (Woods Hole Research Center, Falmouth, MA); Mann, P. J.; Natali, S.; Schade, J. D.; Powell, M.; Peter, Darcy L.; Lehman, A.; Arvizu, Mia; Jimmie, Jordan Andrew; Bristol, Emily Mae; Dabrowski, Jessica S. and Reyes, Joshua Abimael. Arctic tundra fire promotes increased greenhouse gas emissions from freshwaters and changes methane hotspot locations across the landscape in the Yukon-Kuskokwim Delta [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B12C-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Fire frequency and severity are increasing in high latitudes as a result of global climate change. The last decade has seen unprecedented tundra fires, such as the 2015 fires that burned >700 km² in the Yukon-Kuskokwim Delta (YKD), an area that is more than the previous 50 years combined. The YKD is located in subarctic tundra with discontinuous carbon-rich permafrost. Wetlands dominate the YKD and atmospheric models suggest the region may be a CH₄ hotspot. A lack of ground-based measurements limits our current understanding of the influence of fires on YKD ecosystem processes. We surveyed dissolved organic matter (DOM) and greenhouse gas concentrations and emissions across the landscape to address the question: How do landscape connectivity and fire affect the production, transport, and emission of greenhouse gases? We measured gas concentrations and fluxes from 2015 to 2018. In unburned ecosystems, small ponds and pore water on elevated peat plateaus had the highest CH₄ and CO₂ concentrations, followed by fens, which border the peat plateaus, and lakes which the fens drain into, demonstrating loss as water moved downslope. Plateau ponds and lakes within burned regions had lower dissolved CH₄ and CO₂ than unburned, whereas burned fens had more dissolved CH₄ and CO₂ than unburned. Lakes had the highest rate of CH₄ flux compared to other water bodies in unburned ecosystems, averaging 70 mg C-CH₄/m²/d. The burned lakes had 50% lower CH₄ fluxes than the unburned. CH₄ fluxes from burned fens were an order of magnitude higher than the unburned fens, making fens the largest source of CH₄ across burned ecosystems. Across all landscape types, CO₂ fluxes were higher in burned than in unburned areas. The burn effect was greatest in fens, doubling flux rates to 1500 mg C-CO₂/m²/d. We found the highest CO₂ fluxes in unburned fens, followed by peat plateau surface water and ponds, and lowest in lakes. The change in CH₄ hotspots after the fire from lakes to fens was driven by changes in the composition of DOM. In contrast, CO₂ flux correlated with pH, temperature, and dissolved oxygen. Our results highlight the importance of terrestrial-aquatic transitions for regional carbon emissions, and demonstrate the need for a mechanistic understanding of the drivers of greenhouse gas emissions after fires in the context of landscape connectivity.

2019040614 Mack, M. C. (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ). Increasing disturbance in Arctic and boreal ecosystems; local mechanisms and global consequences [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B41B-10, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Disturbance is integral to most ecosystems on Earth, and their dynamics are largely shaped by patterns and processes of post-disturbance recovery. As climate changes, however, the nature of disturbance in many ecosystems is also changing, increasing uncertainty about how ecosystem and regional dynamics will play out in the future. In the Arctic, where average surface air temperatures are increasing at around twice the global average, physical disturbances are intensifying. Recent observations suggest that climate-sensitive disturbance events, such as wildfire and abrupt permafrost thaw, are increasing in frequency, intensity, and magnitude across many Arctic regions, driven by gradual climate warming, extreme weather events, and interactions between disturbances, such as those between abrupt thaw and wildfire or human activities. In the case of coastal ecosystems, increased wave action due to loss of shore-fast ice is an additional driver of increased erosion rates and, in the case of permafrost coastlines, abrupt thaw. Because these disturbances affect permafrost, hydrology, and vegetation composition, increased rates have the potential to catalyze rapid and persistent changes in the structure and function of Arctic ecosystems. Understanding the mechanisms that determine when and where climate-sensitive disturbances fundamentally alter ecosystem dynamics is critical for predicting the future state of the Arctic system, its ability to support the health and wellbeing of local stakeholders, and its changing impacts on global climate via cycling of carbon and flows of energy.

2019031997 Mackelprang, Rachel (California State University at Northridge, Northridge, CA). Frozen in time? Metabolic processes and survival strategies of microbial communities in ancient permafrost. [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

One quarter of the earth's terrestrial surface is underlain by permafrost. Permafrost soils contain approximately 25-50% of the total global soil C pool, nearly double the atmospheric C reservoir. The C is largely protected from microbial decomposition by frozen conditions, but climate change is threatening to induce large-scale permafrost thaw exposing it to degradation. The resulting production of globally significant quantities of greenhouse gasses (GHGs)-including CO₂, CH₄, and N₂O-is expected to result in a positive feedback loop thus amplifying the effects of global warming. Permafrost only defines the thermal state of soil. Thus, physicochemical properties can differ dramatically across sites. In this study, we compared how permafrost age, history, and chemistry drives microbial community survival strategies and metabolic processes. To do so, we combined deep metagenomic sequencing, FTICR-MS, stable isotope probing (SIP), analysis of dormancy markers, and soil chemical measurements in permafrost samples from across the Arctic and sub-Arctic ranging in age from ~5000 to 150,000 years before present. We found that age was a primary driver of microbial community composition and functional potential, demonstrating that microbial communities adapt to life in permafrost through geologic time. We identified genes and pathways important for survival in ancient permafrost including environmental sensing and response, horizontal gene transfer, and chemotaxis. However, the ability to degrade carbon was not primarily influenced by age. Instead, carbon processing genes were correlated with carbon composition, vegetation present at the time the permafrost formed, paleoclimate, and moisture content. SIP experiments, analysis of dormancy, and activity assays (enzyme, ATP, and respiratory) show clear evidence of metabolic activity, even in Pleistocene-aged sample. Here, we describe how survival strategies and metabolic capabilities are related to carbon content, age, physicochemistry, and the paleoenvironment. The ultimate fate of carbon from permafrost depends on the complex relationship between permafrost physiochemistry and microbial communities. Therefore, understanding how the two interact will be important for predicting greenhouse gas emissions from the thawing permafrost.

2019038081 Marchenko, Sergey S. (University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK); Fresco, Nancy L.; Kokelj, Steve; Lindgren, Michael; Sieben, Brian; Floyd, Angelica and Romanovsky, Vladimir E. Long-term permafrost change projections across the Northwest Territory (NWT), Canada; implications for ecosystem, infrastructure and socio-economic impacts. [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Most of the permafrost observatories in North America show substantial warming of permafrost since the 1980s. The magnitude of permafrost warming is typically between 0.5 and 2.5°C depending on location (Romanovsky et al., 2010, Smith, et al., 2010). Climate projections suggest that by the end of the 21st century increases in average global temperatures are expected to be within the range 1.5-4°C, with some Extended Concentration Pathways (ECPs) showing substantial continued warming out to 2300. The close proximity of the exceptionally ice-rich soil horizons to the ground surface makes tundra surfaces extremely sensitive to the natural and human-made changes that result in development of processes such as thermokarst, thermal erosion, and thaw slumps that strongly affect the stability of ecosystems and infrastructure. The overall goal of this study is to evaluate the vulnerability of permafrost under climate warming across the NWT with respect to ecosystems stability, infrastructure, and socioeconomic impact. This will provide stakeholders with information for better understanding the range of possible future changes, to help guide land management and decision-making, particularly with regard to mine reclamation planning. We applied the process-based permafrost dynamics model GIPL2 developed in Geophysical Institute Permafrost Lab, UAF, using a historical climate forcing CRU TS 3.22 data set for retrospective (1950-2013) and five top ranked global circulation models from the CMIP5/AR5 models and RPCs/ECPs (2014-2300) for analysis of permafrost dynamics in the future. The Scenarios Network for Alaska and Arctic Planning (SNAP, URL: http://www.snap.uaf.edu/) climate data were using for this particular simulation. Our projections according to the most extreme greenhouse gas emissions RCP/ECP 8.5 climate scenario indicate that despite the slower rate of soil warming and permafrost degradation in peatland and wetland areas, a considerable volume of peat (approximately 25% of the total volume) across the NWT could be thawed by the end of the current century. Assuming the response of soil temperature and near-surface permafrost area shrinkage (as modeled) to climate warming across the NWT permafrost domain, an additional 60% of unfrozen soils within the upper three meters could appear by 2300.

2019040595 Marcus, Tamara Sade (University of New Hampshire, Durham, NH); Evans, Paul N.; Rich, V. I.; Saleska, S. R.; Wik, M.; Emerson, Joanne B.; Crill, P. M.; Johnson, J. E.; Tyson, G. W. and Varner, R. K. Mitigation of methane emissions by anaerobic oxidizers in post-glacial lakes, Stordalen Mire, Sweden [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B11C-2164, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

High latitude ecosystems are warming at a rapid rate, increasing permafrost thaw and thereby providing new sources of C to existing post-glacial lakes. These lakes are a significant source of methane (CH₄) emissions into the atmosphere. To examine the role of microbial communities in C cycling in lake ecosystems, lake sediment community composition was assessed using 16S rRNA gene amplicon sequencing from three well studied lakes in the Stordalen Mire. Stordalen Mire is a 25-ha hydrologically connected system of lakes and wetlands in the discontinuous permafrost zone in northern Sweden. Cores were collected from three lakes in both shallow and deep zones and high and low emission areas. Sediment and porewater were sampled in 14 cores at every 5 cm and analyzed for dissolved inorganic carbon (DIC), sediment CHNS, ¹³C, ¹⁵N, grain size, and sediment methane. Microbial samples were collected and stored in Lifeguard at -80°C before DNA was extracted using the PowerSoil DNA extraction kit. From the DNA 16S rRNA gene fragments were PCR amplified using 926F-1392R primer pair and then sequenced using the Illumina MiSeq platform. The resulting community profiles were found to be distinct between lakes based on principal coordinates analysis using Bray-Curtis distances. Relative abundance of ANME-2d in one lake, Inre Harrsjon, was significantly higher in shallow areas than in deeper locations, and in low than in high emission areas (p= 0.01 and p= 0.03, respectively). Depth profiles of relative abundance of ANME-2d in cores from Inre Harrsjon show increasing abundance as sediments become more anoxic in shallow water core locations. Additionally, ^d13C-CH₄ was strongly correlated with ANME-2d relative abundance, particularly in shallow depths of Inre Harrsjon (R²=0.97). Comparisons of microbial community composition and C biogeochemistry can potentially allow for the prediction of C transformations and losses based on microbial community composition in cases where both may not be measured, while also improving our predictions of emissions from high latitude lakes.

2019040590 Marrone, Thomas A. (State University of New York College at Oneonta, Oneonta, NY); Alexeev, V. A.; Kholodov, A. L. and McKenzie, M. Snow as a driver for climate processes and its relevance for modeling [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A53I-2604, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Snow is an important driver in arctic and sub-arctic climate systems and has important implications on surface processes in these regions. This makes snow an important factor to include for future permafrost projections. Snow insulates soil temperature against air temperature, so changing winter precipitation quantities, snow cover extent (SCE), and snow cover duration (SCD) are important variables as winter precipitation values change with climate change. Snow is one of the most challenging measurements to accurately record, leading to questionable long and short term data trends making accurate model development challenging. GIPL, a model created to predict permafrost levels was used to compare results with changing snow features and with respect to previously modeled winter precipitation projections outlined in articles by (Callaghan et al. 2011, Park et al. 2015, Liston and Hiemstra, 2011, and Euskirchen et al. 2016). The potential impact of inaccurate snow measurements affecting permafrost models will also be evaluated to highlight snows importance for climate change and the necessity of continuing to refine measurement accuracy. Thermal diffusivity values of snow will also be calculated from various locations across Alaska to compare how these differ annually and amongst different ecotypes. This research was supported by the National Science Foundation as an REU Grant, NSF OPP 1560372.

2019040625 Martens, J. (Stockholm University, Bolin Centre for Climate Research, Stockholm, Sweden); Wild, B.; Andersson, A.; Semiletov, I. P.; Shakhova, N. E.; Dudarev, O.; Kosmach, D.; Charkin, A. N.; Romankevich, Evgeny; Vetrov, A.; Lobkovsky, L. I.; Belyaev, N. A. and Gustafsson, O. CASSCADE; the Circum-Arctic Shelf Sediment CArbon DatabasE [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43K-2981, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The circum-Arctic shelves are the main receptors of sediments and organic carbon (OC) from the surrounding circum-Arctic permafrost region, and hold information on the sources and dynamics of recent and historical permafrost OC remobilization. After many decades of OC cycle research in circum-Arctic shelf seas, a holistic Arctic Ocean wide assessment of terrigenous OC in shelf sediments is due. The Circum-Arctic Shelf Sediment CArbon DatabasE (CASSCADE) is an international collaboration that combines data on elemental, isotopic and molecular OC parameters (total OC, C/N ratios, d¹³C, D¹⁴C and plant biomarkers i.e. long chained n-alkanoic acids and n-alkanes, lignin phenols), along with sediment physical properties, from the published literature as well as from yet unpublished records. The CASSCADE focuses on areas that are within the margins of the circum-polar continental shelf break and includes sample data in four depth categories: i) surface sediments representing annual to decadal time scale; ii) shallow sediment cores of centennial time scale (e.g., multicores); iii) deeper soft sediments of millennial scale (piston and heavy gravity cores); and iv) orbital time scale (drillcores in subsea permafrost). The CASSCADE currently includes data on OC concentrations at more than 1900 locations, C/N ratios at 1200 locations, as well as stable carbon isotopes (d¹³C) at 1400 stations with good spatial coverage in most Arctic shelf seas. Regarded on an Ocean scale, the database already exhibits patterns and striking differences of terrigenous OC input between the various regions in the "Mediterranean" Arctic Ocean. Less geospatial data is available for D¹⁴C (140 stations) and biomarkers (100-180 stations for each compound class), stressing the need for gap-filling analyses by current and future partners, particularly in the Kara Sea, Barents Sea and the Canadian Arctic Archipelago. Combining the CASSCADE with isotope-based source and transport modelling will permit large-scale integration and quantification of OC stocks and fluxes to shelf sediments across the Arctic Ocean. This will help identifying past, current and future hot spots of permafrost OC release that reintroduces dormant biomass into the active cycle.

2019040654 Martin, L. (University of Oslo, Department of Geosciences, Oslo, Norway); Westermann, S.; Nitzbon, Jan; Aas, K. S.; Etzelmuller, B.; Scheer, Johanna; Obu, Jaroslav and Kristiansen, H. Monitoring and modelling the evolution of ice-rich peat plateaus and palsas in Northern Norway [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C54A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Peat plateaus are permafrost bearing morphologies distributed in the discontinuous permafrost zone, at the margin of permafrost areas. It is a warm type of permafrost, particularly sensitive to climate changes. In Northern Norway, peat plateaus have been degrading over the last 60 years (Borge et al., 2016), giving the opportunity for process studies that can shed light on the future of vast permafrost peatlands such as in Western Siberia. The large scale temperature signal that drives permafrost dynamics on the long run is largely modulated by local factors on the decadal time scale, such as the micro-topography that affects the snow distribution and the soil water balance. These local parameters create a high spatial variability of the ground surface temperatures, and, within a few meters, conditions can evolve from permafrost stability to permafrost incompatibility. We present a permafrost modelling work that is coupled to a monitoring data set of peat plateaus in Northern Norway. We use this dataset to identify key variables and processes driving the ground surface temperature and to benchmark the CryoGrid3 permafrost model (Westermann et al., 2016). The forcing data are derived from meso-scale atmospheric modelling (Aas et al. 2015). We investigate the impact of the winter and summer hydrology (snow distribution, precipitation and surface/subsurface water flow). We show how these parameters can locally create favorable conditions for permafrost stability. Based on a steady state sensitivity test, we confirm the crucial effect of the snow cover than can affect the 1 m deep Mean Annual Ground Temperature (1m-MAGT) by more than 3°C. Soil moisture is also critical, with a temperature offset reaching 2°C on the 1m-MAGT between drained and saturated conditions. In a second time, a new version of the model performing coupled realization is used to reproduce the lateral erosion of the peat plateau we observe on drone imagery. This version includes lateral fluxes of heat, snow and water between the realizations and account for the excess ice melt. This modelling work provides new insights on the timing of the expected degradation of the peat plateaus. It also gives the opportunity to investigate the feedback between the modification of the micro-topography, the temperature profile evolution and the lateral fluxes.

2019031991 Mastepanov, Mikhail (Aarhus University, Department of Bioscience, Denmark); Lund, Magnus and Christensen, Torben R. Five field seasons of d¹³C methane emission measurements enhancing the automatic chamber monitoring in an Arctic tundra [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-01B, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane emissions have been monitored by an automatic chamber method in Zackenberg valley, NE Greenland, since 2006 as a part of Greenland Ecosystem Monitoring (GEM) program. During most of the seasons the measurements were carried out from the time of snow melt (June-July) until freezing of the active layer (October-November). Several years of data, obtained by the same method, instrumentation and at exactly the same site, provided a unique opportunity for the analysis of interannual methane flux patterns and factors affecting their temporal variability. Such analysis (Mastepanov et al., Biogeosciences, 2013) led to hypotheses of different sources for the spring, summer and autumn methane emissions, and multiyear cycles of accumulation and release of these components to the atmosphere. For the further investigation of these hypotheses it was decided to complement the monitoring system with a methane carbon isotope analyzer (Los Gatos Research, USA). The instrument was brought to the field during 2013 and was more or less successfully operating during five measurement seasons (2013-2015 and 2017-2018). Detecting both ¹²C-CH₄ and ¹³C-CH₄ concentrations in real time (0.5 Hz) during automatic chamber closure (15 min), the instrument was providing data for determination of d¹³C of the emitting methane. Despite a large number of technical problems, related to operations of this novel laboratory-oriented instrument in harsh field conditions, and a number of limitations in its application to the existing automatic chamber monitoring routines, the recent data confirms the feasibility of the chosen method for the further understanding of patterns and mechanisms of methane production, storage, transport and oxidation in soils of the high arctic tundra.

2019040608 McCalley, C. K. (Rochester Institute of Technology, Rochester, NY); Lamit, Louis J.; Shorter, J. H.; Crill, P. M.; Juutinen, Sari; Larmola, Tuula; Palace, M. W.; Rich, V. I. and Varner, R. K. Integrating microbial and isotopic observations to characterize methane emissions from global high-latitude peatlands [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33A-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane (CH₄) emissions from high-latitude peatlands are both a critical component of the global CH₄ budget and highly sensitive to climate change. Gaps in our knowledge of the biological processes that underlie CH₄ fluxes from these ecosystems limit our abilities to scale flux estimates across heterogeneous landscapes and quantify future emissions. Incorporation of stable isotope dynamics and microbial community composition can better constrain CH₄ transformations in process-based models and help improve predictions of emitted d¹³C-CH₄. In order to apply this knowledge to understanding the Arctic as a whole, we need to characterize these relationships across the Pan-Arctic. Here we combine microbial CH₄ cycling community and isotopic datasets collected at high latitude peatlands in Scandinavia and North America, with the goal of identifying key patterns in the relative abundances of known acetoclastic and hydrogenotrophic methanogens and their relationship with the isotopic signature of porewater and emitted CH₄. Our results show that there are distinctive microbial and isotopic features of bog and fen habitats that span Pan-Arctic peatlands, with the obligate acetoclastic genera Methanosaeta appearing in fens and being strongly associated with Further, both the CH₄ cycling community and ¹³C-CH₄ shift with depth in bogs, but show more consistent depth profiles in fens, suggesting that hydrologic variability is a key driver of both structure and function in these wetlands. While broad microbial functional group and isotopic patterns track hydrologic and vegetation patterns across sites, there are also distinct regional differences in the identity of dominant methanogenic and methanotrophic lineages. For example, in Finnish fens, hydrogenotrophic methanogens are predominantly in an unidentified genera within the Methanomicrobia, whereas in Swedish fens and surface bog communities, hydrogenotrophs are predominantly in the genera Methanobacterium. These insights into CH₄ cycling in peatlands with differing hydrologic, permafrost and vegetation characteristics will be key for both understanding CH₄ emissions patterns and constraining simulated CH₄ emissions and d¹³C-CH₄ across the Pan-Arctic.

2019040615 McIntosh, H. (University of Maryland (UMCES CBL), Solomons, MD); Lapham, L.; Orcutt, B.; Wheat, C. G.; Fournier, T.; Lesack, Lance; Geeves, Kimberly and Bergstresser, Mitchell. Quantifying the bottom-up influence on methane dynamics in one Mackenzie River (Canada) Delta lake with time-series measurements over two years (2015-2017) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B41G-2789, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic lakes are known to emit large amounts of methane (CH₄) to the atmosphere and their importance to the global methane cycle has been shown. The Mackenzie River delta has over 45,000 freshwater lakes within its watershed, and it is an important representative of the great river deltas along the Arctic coast. However, the impact of such delta lakes on the Arctic methane cycle is not well known. Open questions remain on whether methane builds up under seasonally ice covered lakes, where this methane is coming from, and if it is escaping into the atmosphere. Our goal was to answer these questions using unique, high resolution temporal time-series. We address this in a small, thermokarst lake, with little/no connection to the Mackenzie River near Inuvik, Northwest Territories, Canada. We deployed osmotically powered pumps (OsmoSamplers), which autonomously and continuously collected lake bottom water over the course of a year, to test the hypothesis that methane is building up under the ice during the winter. OsmoSamplers collected water at multiple water depths from August 2015 through August 2017 in order to test the hypothesis that the source of methane is the sediments. From these time-series samples, dissolved methane concentration, stable isotope content of methane (d¹³C-CH₄), and dissolved sulfate concentrations in bottom water were measured. Methane concentrations and d¹³C-CH₄ values were also measured in the sediment porewater in three summers to feed into a diffusion controlled model of methane build-up from the sediments. In this presentation, we will also present data to calculate methane flux to the atmosphere from this Arctic Lake. Taken together, these results show methane builds up throughout the water column during ice-cover, but the timing of when methane is released from the sediments to the overlying water column is variable year to year. By using this lake as an example of thermokarst lakes worldwide, we predict how increases in air and water temperature, shorter periods of ice cover, and spring floods will effect methane dynamics in this changing Arctic environment.

2019038112 McKenzie, Jeffrey M. (McGill University, Earth and Planetary Sciences, Montreal, QC, Canada); Kurylyk, Barret; Walvoord, Michelle A.; Bense, Victor; Fortier, Daniel; Spence, Christopher and Grenier, C. François. Cryohydrogeology; is groundwater a catalyst for Arctic change? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H12C-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Much of our knowledge regarding how climate change is transforming Arctic hydrologic systems and water resources is based on data collected at or near the land surface from localized field studies or through remote sensing observations. While these studies yield extremely valuable information about shifts in surface water and ground ice distribution, river discharge, and soil moisture, the underpinnings of many of these water-related changes are linked to changing hydrogeologic conditions. Thawing of ancient permafrost is opening new subsurface pathways for groundwater flow, thereby altering fluxes and distribution of water, energy, and solutes. We identify different ways that these changes impact Northern society, including the potential for increased contaminant transport, modification to water resources, and enhanced rates of infrastructure (e.g. buildings and roads) damage. Further, as permafrost thaws it allows groundwater to transport carbon and nutrients from terrestrial to aquatic environments via progressively deeper subsurface flowpaths. Groundwater has the potential to catalyze a positive feedback on environmental change in the Arctic and is a critical component of the narrative of how the Arctic will respond to climate change, both physically and socially. Our presentation argues for the inclusion of cryohydrogeology, the study of groundwater in cold regions, within transdisciplinary Northern research initiatives.

2019037805 McLean, Josette Elena Trisha (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Drown, Devin and Kholodov, Alexander L. Investigating the methane producing and antibiotic resistant potential of microbes in Alaskan permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2564, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is perennially frozen ground that has been at or below 0°C for at least two consecutive years. It is mainly found in Arctic and Antarctic regions, and it contains almost half of the world's soil carbon content. Permafrost is also a naturally occurring reservoir for antibiotic resistant genes. Over the past 30 years, polar temperatures have risen significantly, which has led to rapid permafrost thaw. In turn, this has facilitated the release of methane gas which intensifies the impact of global warming. Additionally, permafrost thaw also exposes antibiotic resistant genes to the environment; which increases the potential for multi-drug resistance; furthermore, according to the World Health Organization, this is one of the leading global threats to human health. As part of a National Science Foundation (NSF) Research Experience for Undergraduate (REU) program, we designed this study to determine if there are methane producing and antibiotic resistant microbes within permafrost in the Alaskan Arctic. The sites used represent a latitudinal range of permafrost in Alaska: the northernmost point of Barrow, Alaska; the interior of Fairbanks, Alaska and along the Dalton Highway enroute from Fairbanks to the North Slope of Alaska. At each site, we collected cores using a rotary column coring technique with a core barrel that was 2" wide. To avoid contamination, we used a sterilized 1" hole saw to obtain subsamples from the central part of the cores. Then we extracted DNA from these subsamples using both the DNeasy Power Soil and Power Max Soil kits (QIAGEN). Finally, we used a MinION machine (Oxford Nanopore) to sequence the DNA. Our results identified a variety of microbes, but the most abundant types were methanogens and methanotrophs, antibiotic resistant microbes and some nitrogen fixing and denitrifying bacteria. However, the presence and abundance of these microbes varied among sites. Our study yields new information on the microbiome of Alaskan Arctic permafrost. This has not been well studied, with respect to methane producing and antibiotic resistant bacteria. Such insights are becoming increasingly important in the face of global warming as they highlight some of the unforeseen implications of climate change.

2019040629 McMillan, Cameron Kyle (University of Toledo, Environmental Sciences, Toledo, OH) and Weintraub, Michael N. Measurable disturbance effects from non-invasive soil sampling [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B53G-2152, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methods such as micro-lysimetery are becoming more popular to sample soil pore water without disturbing the soil matrix; however, there has yet to be a study assessing disturbance effects from lysimeter installation. Most studies assume that the 2.5 mm diameter hole in the soil created for installation is not enough disturbance to cause artificial increases in nutrient or dissolved organic carbon concentrations. However, multiple studies report their highest nutrient concentrations on the first sampling date, suggesting a possible installation effect. We tested this within a moist non-acidic tundra soil in the western Brooks Range, Alaska, by installing micro-lysimeters and collecting soil pore water from them for roughly one week, sampling once per day. We then installed clean lysimeters in new pilot holes and repeated sampling for another week. These results are compared to a much larger, "long-term" set of lysimeters, that were in the ground and regularly sampled for roughly one year prior to this experiment. We observed a clear increase in soil nutrient concentrations the first day of collection after lysimeter installation (order of magnitude increases), followed by sharp declines on day two or three to the concentrations from the "long-term" lysimeters. Thus, we recommend that the first set of samples collected from micro-lysimeters be considered contaminated by the installation process, as these samples may not accurately represent soil pore water concentrations. Given such a strong disturbance signal, we next attempted to determine the extent of micro-lysimeter installation disturbances using an already installed lysimeter. New pilot holes were created on several days 5 mm from existing lysimeters to induce high nutrient concentrations of pore water. We found little to no measurable disturbance within pore water collected from these existing lysimeters, indicating that the radius of the micro-lysimeter installation-disturbance is relatively narrow.

2019037873 Menio, Emma C. (University of Arkansas, Department of Geosciences, Fayetteville, AR); Marshall, Jill A. and Cothren, Jackson D. Discerning periglacial drainage evolution using historic satellite-imagery-derived digital elevation models [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1067, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Over the past several decades, geomorphic processes in the Arctic have been changing and intensifying due to region-wide warming and thawing of permafrost. Permafrost depth and extent control sediment and hydrologic pathways in Arctic landscapes, and, permafrost degradation by even modest temperature changes can severely alter tundra landscapes and ecosystems. Much is still unknown about the nature of feedbacks within Arctic landscapes, though the expansion and contraction of river networks is expected to be a first order control on the routing of water, sediment, nutrients, and carbon from headwaters to the ocean. This study investigates the propagation of channel heads in Imnavait Creek, the headwaters of the Kuparuk River, Alaska, over the last half century. Analysis of gradient versus contributing area at the pixel scale is often used to identify the transition from diffusive (hillslope) to advective (fluvial) transport. These slope-area plots demonstrate a threshold between transport regimes, which defines the channel head in a watershed. It has been argued that in periglacial watersheds, fluvial erosion is restricted by permafrost on the hillslope, and therefore the contributing area at the channel head represents the area in a watershed dominated by periglacial processes. The channel head location and contributing drainage area can be identified through time series analysis using historic 1960-1970's CORONA data and modern 2000's-present ArcticDEM and Alaska IFSAR elevation data. We expect that with the degradation of permafrost since the 1960's, the contributing area for the channel head will decrease due to an increase in fluvial erosion, enhanced by more mobile soil on the hillslope. Saturated zones on the hillslope will become connected to channels, and the drainage network will expand. Preliminary Google Earth Engine imagery time series analysis of Imnavait Creek shows an increase of hillslope-channel connectedness from 1990-2016. Slope-area results will identify the locations of channel heads, identify rates of expansion of the drainage network, and provide insight into areas at risk for erosion.

2019040634 Middleton, J. L. (Lamont-Doherty Earth Observatory, Palisades, NY); Mason, Zachary; Mukhopadhyay, S.; Putnam, A. E.; Ackert, R. P. and Campbell, S. W. Cosmogenic nuclides suggest long-term Pleistocene exposure of subglacial bedrock at the Ohio Range in the West Antarctic ice sheet [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C22B-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Knowledge of the long-term history of the marine-based West Antarctic Ice Sheet (WAIS) is important due to its potential instability in the face of increasing polar temperatures. With a total ice volume equivalent of »5m of sea level, even partial WAIS collapse will have disastrous consequences for global coastlines and coastal communities. However, the modern observational record is too short to determine if recent thinning and retreat of WAIS outlet glaciers falls within the natural centennial to millennial-scale WAIS variability or if these changes presage significant loss in WAIS volume. Geologic evidence of past ice elevation can provide critical constraints on long-term WAIS stability over a wide range of climatic conditions. However, geologic constraints on WAIS geometry prior to the Last Glacial Maximum are rare. We provide new cosmogenic constraints on interior WAIS behavior throughout the Pleistocene using multiple subglacial bedrock cores obtained from the Ohio Range in the Transantarctic Mountains. Rock cores recovered from 10-30 m under present-day ice levels contain cosmogenic ¹⁰Be, ²⁶Al, and ²¹Ne. Cosmogenic nuclide concentrations closely follow spallation dominated depth profiles, indicating buildup of cosmogenic nuclides during significant periods of ice-free exposure to cosmic irradiation. However, ²⁶Al/¹⁰Be ratios also indicate significant periods of burial by ice. A simple two-stage scenario provides limiting constraints on the duration of bedrock exposure and ice burial. The data indicate that bedrock surfaces 20-30 m below present-day ice levels experienced more ice-free exposure (250 kyr - 2 Myr) than ice cover (100 - 200 kyr) over the past »2 Myr. Thus, our new subglacial cosmogenic data imply that long-term Pleistocene WAIS elevations at the Ohio Range are typically >25 m lower than present-day, suggesting interior WAIS elevations during glacial periods were thinner than previously inferred.

2019040592 Miller, C. E. (Jet Propulsion Laboratory, Pasadena, CA); Griffith, Peter C.; Goetz, S. J.; Hodkinson, Daniel J.; Larson, Elisabeth K.; Kasischke, E. S.; Margolis, H. A. and Hoy, Elizabeth Embury. The Arctic Boreal Vulnerability Experiment (ABoVE) airborne campaign [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B11A-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Arctic Boreal Vulnerability Experiment (ABoVE) Science Team continued airborne activities in 2018 with the objective of creating interannual time series observations using NASA's L-band synthetic aperture radar (SAR) and the Next Generation Airborne Visible InfraRed Imaging Spectrometer (AVIRIS-NG) imaging spectrometer. These flights followed on the successful 2017 ABoVE Airborne Campaign, providing revisits of key locations and additional ground-truth calibration-validation data. AVIRIS-NG flights from mid-July to mid-August characterized Arctic-boreal vegetation near peak greenness, as well as wetlands and inland waters. Flights in early August targeted the Mackenzie Delta for characterization of its vegetation and methane emissions. L-band SAR flights occurred in late August and revisited key lines flown in 2017 to enable accurate interferometric differencing and comparisons of interannual variability in permafrost active layer thickness. Additionally, tomoSAR flights were coordinated with the German Space Agency's F-SAR over the Boreal Ecosystem Research and Monitoring Sites (BERMS) near Saskatoon, SK to capture boreal forest structure. We will present an overview of the 2018 ABoVE airborne flights and highlight some key preliminary results.

2019040674 Miller, Jamie (Johns Hopkins University, Applied Physics Laboratory, Laurel, MD); Mellon, Michael T. and Sizemore, Hanna. Salt migration in Mars-like permafrost soil [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P53F-3025, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Soluble salts and duricrust (weakly-cemented soils) are observed at every landing site on Mars. Indeed, global remote sensing indicates that salts and duricrust are globally widespread. However, the origin and hydrological history of duricrust is presently not understood. Modern Mars is cold and dry, yet salts can help stabilize liquid water. Below freezing, thin films of liquid-like water can persist, aided by the addition of salts. These thin films can move throughout the soil column, transporting salts with them. Salts can also diffuse through mobile layers driven by concentration gradients and thermodynamic forces, where precipitation may cement loose soil grains into duricrust. Our research investigates the possible mechanism of duricrust formation via migration of thin liquid films of water and associated salts. Likewise, we examine the effect of salts on water mobility and ice formation. In our study, we focus on chloride and sulfate salts, such as those found at the Viking and Phoenix sites. MgCl₂, MgSO₄, and CaSO₄ were individually added to Mars simulant soil (Birch Hill loess from Alaska, a silt-dominated soil with minimal organic and native salt contents) at concentrations consistent with those measured on Mars. The salt-doped soils were subjected to a temperature gradient: 0 °C at the surface extending to -5 or -10 °C at the base, at ~2 cm depth. A continuous flow of humidified nitrogen (frost point -1°C) was delivered to the headspace, a supply of water to condense and migrate within the soil column. After 2-4 weeks, we processed the soil samples by sectioning, observing textural changes and gravitimetric ice content. Salt concentrations were determined from measured electrical conductivity of sectioned samples in solution. Comparison of salt concentration across the column shows that MgCl₂ appeared to undergo the strongest degree of migration, in a direction toward the top of the soil column. The sulfate salts do not seem to migrate in this way. Chloride salts have higher solubility and lower eutectic compared to sulfate salts, which may explain this increased migration rate. The motion of chloride salt toward the surface is repeatable and not presently understood. Therefore, chloride salts are expected to be stronger drivers of thin film migration and duricrust formation in Mars regolith.

2019031984 Miller, John Houston (George Washington University, Department of Chemistry, Washington, DC) and Bailey, Diana Michelle. Development of optical sensors for assessment of greenhouse gas concentrations above thawing permafrost at the bonanza creek experimental forest near Fairbanks, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B21J-2457, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Beyond anthropogenic carbon emissions, the increase in atmospheric carbon from natural feedbacks, such as thawing permafrost, poses a risk to the global climate as global temperatures continue to increase. Permafrost, formally defined as soil that is continuously frozen for 24 consecutive months, comprises nearly twenty-five percent of the Earth's terrestrial surface and possesses twice the amount of carbon currently in the atmosphere. Continuous collection of carbon dioxide (CO₂) and methane (CH₄) concentrations is imperative in understanding seasonal and inter-annual variability of carbon feedbacks above thawing permafrost. A multi-year collaborative effort was undertaken to monitor these feedbacks near Fairbanks, Alaska. Open-path tunable diode laser absorption spectrometers were developed and deployed for measurement of CO₂ and CH₄ concentrations above thawing permafrost at a young thermokarst collapse scar bog and a rich fen site. The open-path instrument (OPI) is a relatively inexpensive, low-power sensor that collects spatially-integrated measurements of target molecules approximately 1.5 meters above ground level. The instrument sweeps across an absorption feature at 500 Hz and reports an averaged spectrum every 10 seconds. The OPI achieves ~6 ppm precision for measurements of CO₂, and 10s of ppb for CH₄, over a 2.5 minute reporting interval. Here we report on initial retrieval of diurnal cycles from each field site and compare our spatially-integrated measurements of CO₂ and CH₄. For CO₂, the magnitude of the diurnal cycles show a strong dependence on daily weather at both field sites. CH₄ diurnal cycles show short-term enhancements overnight compared to CO₂. We also present an auto-alignment scheme for the OPI to mitigate effects from ground-surface instability and hysteresis present in the alt-azi motor mount. These laser measurements are complemented by point measurements of CO₂ via non-dispersive infrared (NDIR) sensors combined with temperature, pressure, and humidity measurements along the laser's optical path. The point-based sensors (referred to as "LuftSinn" sensors) collect measurements approximately 0.6 meters above the surface. Reported CO₂ concentrations from LuftSinn sensors show good agreement with OPI measurements.

2019037789 Mishra, Umakant (Argonne National Laboratory, Environmental Science Division, Argonne, IL); Matamala, Roser and Jastrow, Julie D. Spatial heterogeneity and environmental controllers of organic carbon stocks of permafrost affected soils [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2503, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost affected soils are a key component of the global carbon cycle and play an important role in moderating the global climate system. Previous permafrost soil organic carbon (SOC) stock estimates used a variety of upscaling approaches and reported substantial uncertainties in the estimates. In this study, we used greater number of field observations (n=2703) and spatially referenced data of soil-forming factors (topographic attributes, land cover types, climate, and bedrock geology) in a regression kriging framework to predict the spatial and vertical heterogeneity of SOC stocks across the northern circumpolar and Tibetan permafrost regions. This approach allowed us to take into account both the correlation between SOC and environmental factors and the spatial autocorrelation among SOC observations to make separate estimates of SOC stocks and their spatial uncertainties (90% CI) for three depth intervals at 250-m spatial resolution. In the northern circumpolar region, we estimated 510 (449-572), 345 (297-397), and 355 (324-401) Pg C for 0-1, 1-2, and 2-3 m depth intervals, respectively. In the Tibetan region, our estimates were 11 (9-13), 3 (0.5-6), and 3 (1-5) Pg C at 0-1, 1-2, and 2-3 m depth intervals, respectively. We captured large spatial variability (coefficient of variation=13-127%) depending upon the study region and depth interval. We found the greatest uncertainty range at 1-2 m depth in both permafrost regions. Soil wetness index and elevation were significant controllers of SOC stocks in both regions. Surface air temperature and bedrock geology were significant controllers of permafrost SOC in the circumpolar region, whereas precipitation was a significant controller in the Tibetan region. Flat areas (<2% slope angle) stored the greatest amount of SOC in the northern circumpolar region, but hill toe-slope positions stored the largest SOC stocks in the Tibetan region. In the circumpolar region, the greatest topographic uncertainty in SOC stocks (27%) was in hill toe-slope positions. In the Tibetan region, however, the uncertainty was highest (62%) in flat areas. We hope our spatially explicit estimates of SOC stocks can be useful for initializing and benchmarking the representation of SOC stocks in regional and global land surface models.

2019040585 Mitchell, R. J. (Michigan State University, Department of Geography, Environment, and Spatial Sciences, East Lansing, MI); Nyland, K. E.; Klene, A. E.; Nelson, F. E.; Shiklomanov, N. I. and Streletskiy, D. A. A quarter century of CALM; recent developments in the Alaskan component of the Circumpolar Active Layer Monitoring program [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A23G-2935, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Circumpolar Active Layer Monitoring (CALM) program is focused on assessing the long-term responses of the active layer and near-surface permafrost to climate change. CALM recently marked its 25th anniversary and has been operating continuously at many sites in North America, Eurasia, Antarctica, and several midlatitude mountain regions. CALM sites now number approximately 250. This presentation discusses recent developments in the component of the program focused on northern Alaska. CALM sites in this region form two parallel north-south transects extending from (a) Prudhoe Bay and (b) the Barrow Peninsula, to the northern foothills of the Brooks Range. Both transects extend over pronounced temperature and continentality gradients. Data collection involves probed active layer thickness (ALT), air and shallow ground temperatures, soil moisture, and thaw subsidence at a series of 1 km² and 1 ha plots, using a spatially oriented sampling protocol developed early in the program's history. This presentation also discusses recent trends in ALT, as well as plans for new instrumentation and observation strategies over the 2019-2024 period.

2019040589 Moffett, Claire Elizabeth (Baylor University, Department of Environmental Science, Waco, TX); Barrett, Tate Edward; Yoon, S. and Sheesley, Rebecca J. Terrestrial biogenic source contribution to aerosol on the North Slope of Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A51P-2457, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Arctic ecosystem is undergoing rapid changes including warming, wetting, loss of sea ice, and thawing of permafrost. Over the last few decades it has warmed almost twice as fast as the rest of the planet, which has led to plant life on the tundra becoming greener and shrubbier. The biogenic emissions that result from these changes has the potential to affect the regional chemistry and climate through the production of secondary organic aerosol (SOA) from biogenic volatile organic compounds (BVOCs) emissions. Terrestrial sources of biogenic SOA have not been studied on the North Slope of Alaska (NSA). Previous biogenic studies have focused on the high Arctic and have generally been short campaigns. Results from emission studies have shown that BVOCs such as isoprene and pinene are emitted at higher concentrations during periods of warming and increased plant growth while short aerosol studies have measured SOA products. With conditions varying drastically from year to year, a long term study of these compounds is necessary to fully understand the impacts of warming and the potential future impacts. Filter based samples were collected at Utqiagvik (Barrow), AK, over several summers from 2012 - 2017. Utqiagvik is located on the northern most point of the United States with a population of 4,581. The site is 7.4 km north of the village of Utqiagvik. The ecosystems surrounding Utqiagvik is primarily sedge/grass, moss wetland. The primary focus of this study was to investigate the presence of isoprene and monoterpene SOA products including methyl tetrols and pinonic acid. Samples were analyzed utilizing gas chromatography - mass spectrometry for a wide suite of organic tracers in addition to the SOA products. Results show a median concentration of pinonic acid of 32.83 pg m^-3, while the sum of methyl tetrols have a median concentration of 2.27 pg m^-3. The concentration of these biogenic SOA tracers is highly variable by year; summers with higher average temperatures have overall higher concentrations of both pinonic acid and methyl tetrols. The results highlight a need to understand biogenic SOA in the Arctic, which may affect the formation of cloud condensation nuclei, ultimately leading to impacts on the radiative balance.

2019040602 Moghaddam, M. (University of Southern California, Electrical Engineering, Los Angeles, CA); Chen, R. H. and Tabatabaeenejad, Alireza. High-resolution distribution and interannual dynamics of permafrost active layer thickness in the Alaskan Arctic retrieved from P-band radar [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B13E-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

There is widespread evidence from ground-based in-situ observations that, as the temperatures have risen in the arctic, the permafrost active layer thickness (ALT) has increased in many locations. Ground observations are not dense, pervasive, or consistent enough to make definitive statements about regional distributions and year-to-year dynamics of ALT. However, using high-resolution (2 arcsec) P-band radar observations of the NASA Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS), we have developed an ALT retrieval algorithm that allows us to take important steps in systematic mapping of ALT in the Alaskan arctic. AirMOSS has acquired polarimetric P-band synthetic aperture radar (SAR) imagery across a roughly 2500-km long and 10-km wide circuit in northern Alaska eight times between August 2014 and October 2017. Two of the 3 data acquisitions in 2017 have been part of the more extensive Arctic Boreal Vulnerability Experiment (ABoVE) airborne campaigns. The ALT retrieval algorithm we have developed assumes a multi-layer soil structure above permafrost and uses a same-year multi-season time-series approach to estimate the maximum thaw depth in each year when data were acquired (2014, 2015, and 2017). We have thus produced ALT maps with spatial resolutions of 2 arcsec across the above-mentioned transect for 2014, 2015, and 2017. The radar-derived ALT maps have been validated against in-situ observations, primarily from the Circumpolar Active Layer Monitoring (CALM) network. In this presentation, we will describe the retrieval algorithm and will show maps of spatial patterns of ALT within each observation year, as well as an assessment of the interannual variability of ALT during the overall observation period. These are unprecedented ALT products resulting directly from radar remote sensing observations.

2019037780 Mu Cuicui (Lanzhou University, Lanzhou, China). Organic carbon accumulation in mountain permafrost regions; topography and permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2490, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Large amounts of soil organic carbon (SOC) have accumulated over thousands of years in permafrost regions; however, carbon accumulation rates in these regions remain largely unknown, which leads to large uncertainties in estimates of SOC pools and their response to warming. Here, we examined SOC densities and accumulation rates under different topographic conditions in the northern Qinghai-Tibetan Plateau. The results showed that SOC density increased with elevation on south-facing slopes but decreased with elevation on north-facing slopes. The carbon accumulation rates for the upper 6 m soils were highest (19.9 g C m^-2 y^-1) in the north-facing wet meadow and lowest (0.68 g C m^-2 y^-1) in the south-facing alpine steppe. Aspect and active layer thickness explained 26.5% and 36.5% of the total variance in SOC density. The study suggests that topography strongly affects the SOC distribution in mountainous permafrost regions and that topography should be incorporated into evaluations of carbon storage and permafrost carbon-climate feedback.

2019038120 Muster, Sina (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Laboor, Sebastian; Heim, Birgit; Haas, Antonie; Schaefer-Neth, Christian; Nitze, Ingmar; Bartsch, Annett and Grosse, Guido. The Arctic Permafrost Geospatial Center; a portal for high-quality open access scientific data related to permafrost in the Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract IN34B-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Thematic Open Access data portals foster and support an open data culture in order to reduce knowledge gaps and data uncertainty. We here present the Arctic Permafrost Geospatial Center (APGC), which provides open access, high quality geospatial data in the field of permafrost research. The APGC mission is (i) to provide data that is of high usability, significance and impact, and (ii) to facilitate data discovery, data view and supports metadata documentation and exchange via a data catalogue (URL: http://apgc.awi.de/). The Data Catalogue is based on the open source CKAN data catalogue architecture, which uses the metadata standard DCAT. The catalogue structure can host a variety of data models of varying themes, format, spatial and temporal extents. Data is documented according to the fair data principles. Each catalogue entry has a data abstract, data preview and extensive metadata that can be downloaded in RDF/XML-, JSON- or Turtle-format. Data can be searched by location--using spatial keywords or by interactively selection locations on a base map. Data can further be searched by product type, project, tags, keywords, license type, or data format. Data can be downloaded directly via link to the publishing data repository such as PANGAEA. APGC, initially supported by the ERC PETA-CARB and the ESA GlobPermafrost projects currently features over 100 selected datasets mainly from these projects. A WebGIS application is available for most of these data sets, which allows users to explore the data interactively (URL: http://maps.awi.de). Data provide information about surface and subsurface permafrost characteristics in the Arctic, Antarctica, or mountain permafrost areas, e.g., soil temperatures, soil carbon, ground ice, land cover, vegetation, periglacial landforms, subsidence and more. Data include in-situ measurements, earth observation, and modelling and are provided in vector or raster format. New data submissions to the catalogue are evaluated according to the following access criteria: permafrost focus, significance and impact, access, quality, and metadata. APGC invites submissions from both individual users as well as project consortiums.

2019038052 Muster, Sina (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Pit, Mare L.; Kaiser, Soraya; Schneider von Deimling, Thomas; Jacobi, Stephan and Langer, Moritz. Digital storytelling; using multi-media tools to explore transformation processes in Arctic permafrost landscapes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract ED51A-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

PermaRisk is a young investigator's research group that simulates erosion processes in permafrost landscapes under warming climate and conducts risk assessments for ecosystems and infrastructure within the Arctic. Diverse ecological, social, and financial risks are associated with potential damages to ecosystem functions and infrastructure caused by permafrost thaw. Communication with local stakeholders in the Arctic such as the Bureau of Land Management in Alaska or town communities in Canada are integral to the research of PermaRisk. Local indigenous knowledge will help researchers to better understand past and current landscape changes and their impact on local life and infrastructure. PermaRisk promotes a transparent and open communication between research and society. Here, we present the tool of digital storytelling and how it is used to portray both the stories of the research project and the scientists as well as the stories of the people affected by climate change in the Arctic. Digital storytelling allows the combination of photos, videos, sound bites, interviews, graphics, maps, and data into compelling, entertaining, and interactive stories. Research data and materials brought back from fieldwork are used to look into questions like: What drives these scientists to do what they do? How do they do it? Why does it matter? To whom does it matter? How are local communities affected by Arctic climate change? How do they perceive the change and the research? In the final product, the project's main research findings are translated into accessible storylines about erosion and permafrost and placed within the socio-ecological context of climate change in the Arctic and globally. Finished Stories will be used for community outreach and public relations to advocate science. Furthermore, they will be integrated into teaching at German universities and schools to invite interactive learning and situate the research in concrete, real-life situations and communities.

2019037880 Nelson, Frederick E. (Michigan State University, Department of Geography, Environment, and Spatial Sciences, East Lansing, MI) and Nyland, Kelsey E. A century-old geomorphic enigma; cryoplanation terraces and associated processes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1076, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Cryoplanation terraces (CTs) are a contentious topic within periglacial geomorphology. Many of the questions posed in landmark reviews (Demek 1969; Priestnitz 1988; Thorn and Hall 2002), have been at least partially addressed in subsequent literature. This presentation reviews existing literature relevant to cryoplanation and the controversies surrounding this concept. We address three closely related topics: 1) the diverse lexicon associated with cryoplanation; 2) the distribution of studies around the world and through time that report cryoplanation features and landscapes; and 3) the chronology of the numerous and diverse theories that have been advanced for the formation of CTs. An important aspect of the controversy surrounding CTs is the topic's plethoric lexicon and the wide distribution of study areas around the world. Many adjectival modifiers have been used in reference to elevated terraces of possible periglacial origin in geomorphic literature, despite the fact that they make reference to the same feature. Terms used in English-language literature have included cryoplanation (borrowed from Bryan 1946), altiplanation (Eakin 1916), equiplanation (Cairns 1912), nivation (Hopkins and Einarsson 1966), and Goletz (Boch and Krasnov 1951). Many different hypotheses for the formation of cryoplanation terraces have been proposed, including a modification to the Davisian cycle erosion (e.g. Moffit 1905; Prindle 1905; Peltier 1950), a special phase of solifluction (Eakin, 1916), complex sorting from mass-movement (Taber 1943), surface and permafrost table lowering (Krivolutskiy, 1965), and polygonal cracking (Popov 1960). Contemporary literature favors two interpretations: structural control (e.g., Hall and Andre, 2010; French 2016), and nivation (e.g. Demek 1969; Reger and Pewe 1976; Nelson and Nyland 2017). This presentation outlines the relative merits of these interpretations in light of new evidence from eastern Beringia.

2019038085 Nicolsky, Dmitry (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, Vladimir E.; Debolskiy, Matvey Vladimirovich; Cai, Lei; Bailey, Chris J.; Fisher, Laurin and Muskett, Reginald R. High-resolution permafrost modeling and mapping in Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1392, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We develop a series of ecotype-based permafrost dynamics models for the Alaska North Slope (30-m resolution), Seward Peninsula (500-m resolution) and Selawik National Wildlife Refuge (770-m resolution) regions. The developed models allow computations of the mean annual ground temperature (MAGT), active layer thickness (ALT) and talik thickness projections into the future for various climate scenarios. We demonstrated that the projections with the IPCC Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios will result in a drastic difference in the future near-surface ground temperature regimes in 2050s and 2090s. For the RCP 8.5 scenario, we find that ALT in the Alaska North Slope region, up to 0.5 m on average in 2000, increases by a factor of 2 by 2050. From 2050 to 2100, according to the RCP 8.5 scenario, ALT continues to increase and widespread taliks will start to form in the Alaska North Slope region. Development of the taliks will have serious implications for ecosystems, human activities (infrastructure and subsistence lifestyle), and potential feedbacks to climate change. On the other hand for the RCP 4.5 scenario, the current model predicts only a modest increase in the near-surface. We plan to increase the spatial resolution of all developed models to 30-m in order for the community planners and engineers to understand potential hazards related to the permafrost degradation on the local scale near the relevant infrastructure. In particular, using existing permafrost modeling capabilities for the community of Selawik, Alaska, we developed a stand-alone software package to compute and present various scenarios of permafrost degradation to local government agencies and to the local residents of Selawik. In order to conduct the public outreach more effectively, we designed a publicly-downloadable application for iPhone to show how permafrost temperature might response to changes in air temperature, snow thickness and ground moisture. The permafrost thaw projections and other related products are posted at the permamap.gi.alaska.edu in order to help to visualize results at the fine scale and transfer projection to the public.

2019040652 O'Connor, M. (University of Texas at Austin, Department of Geological Sciences, Jackson School of Geosciences, Austin, TX); Nicholaides, Kindra Diane; Cardenas, M. B.; Neilson, B. T. and Kling, G. W. Predictability of variable Arctic soil hydraulic and thermal properties, and implications of such variability on future thaw [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1812, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Global climate change is driving rapid increases in Arctic temperatures and the thawing of shallow permafrost. The amount of anticipated permafrost thaw has uncertainty because of the limited observations of hydraulic and thermal properties of Arctic soils. The spatial variability of these soil properties is especially unclear at landscape scales because few studies have collected the data necessary to establish predictive relationships at such scales. Here we present systematic measurements of hydraulic and thermal properties, including water retention, thermal conductivity, organic matter content, porosity, and permeability, across multiple watersheds with continuous permafrost. These measurements illustrate that Arctic soil stratigraphy and subsequent hydraulic and thermal properties vary predictably due to glacial age, location along a topographic transect, and microtopographic relief. Furthermore, simulations of freeze-thaw and groundwater flow across this distribution of properties indicate that the observed variability can exert a strong control on active layer development and groundwater fluxes. These findings can be used to inform landscape-scale Land Surface Models designed to predict changes in heat, water, and carbon fluxes in arctic watersheds due to increased thaw.

2019038122 Omisore, Busayo Oreoluwa (China University of Geosciences, School of Geophysics and Information Technology, Beijing, China); Jin Sheng and Fayemi, Olalekan. Assessing borehole-surface electromagnetic technique with vertical and horizontal sources as tool for gas-hydrate delineation using finite difference method [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS13A-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Introduction Submarine and permafrost gas hydrate deposits have been investigated as clean and sustainable energy sources. Yet, understanding of subsurface geology is important in resource assessment and exploitation of gas hydrates. Hence, we present simulated response from finite dipole sources in the subsurface with focus on delineating simplified structure of gas hydrate accumulation in a part of permafrost region of Qilian mountain, China, using borehole surface electromagnetic technique (BSEM). Method We used matlab code developed based on higher order FD approximate equation on x-z plane (Fig. 1; Eqns 1-3). Simplified model of subsurface geology (Fig 2) was designed using information from existing literature. 3 thin elongated resistive targets (GH1-3) with resistivity of 200 W m were placed in the subsurface. Finite line source was placed at 3 positions. 2D plot of the log of E fields are presented in figures 3 & 4. Interpretation It is observed that subsurface stratigraphic distribution is best detected by considering Ez field characteristics. Hence, response from gas hydrate accumulation is best seen on Ez measurement. The impact of resistive targets (gas hydrate) on total field is relatively small when source is shallower than anomaly (Fig. 3a). However, when source goes deeper than anomaly, amplitude of anomaly becomes bigger (Fig. 3b). The phenomenon of inadequate resistivity contrast between layer 1 and GH2 (Fig. 2) has been a major challenge for most surface electrical exploration techniques. However, by locating the source in the subsurface, a sudden bulging of target base with slight distortion in wave pattern can be indicative of gas hydrate accumulation (Fig. 3b). Conclusion Application of horizontal and vertical borehole sources were confirmed as solution to solving challenges with gas hydrate characterization. Changing the depth of vertical source enables BSEM to obtain information on subsurface medium from different angles. Also, results from horizontal source shows BSEM is very effective in gas hydrate delineation.

2019037858 O'Neill, Hugh (Natural Resources Canada, Ottawa, ON, Canada) and Wolfe, Stephen. Modelling ground ice in permafrost using a paleogeographic approach [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1049, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Ground ice is a key geomorphic agent in permafrost regions, and its melt influences geomorphology, water fluxes, and infrastructure stability. We present new models incorporating paleogeography of three ground ice types (massive, segregated, and wedge) for all of Canada. The models use an expert-system approach to calculate near-surface ground ice evolution over the last ca. 17,000 years in a geographic information system. Datasets of surficial geology, deglaciation, paleovegetation, glacial lake and marine limits, and modern permafrost distribution represent paleoclimatic shifts, tree line migration, marine and glacial lake inundation, and terrestrial emergence. The model outputs indicate abundant massive ice in the western Arctic, preserved since deglaciation in thick glacigenic sediments in continuous permafrost. Segregated ice is widely distributed in fine-grained deposits, occurring in highest abundance in frost-susceptible glacial lake and marine sediments. The modelled abundance of wedge ice largely reflects the exposure time of terrain to cold air temperatures in tundra following deglaciation or marine/glacial lake inundation, and is thus highest in the western Arctic. Holocene environmental changes reduce wedge and massive ice abundance where forest tundra and boreal forest advanced during warmer periods. Published observations of thaw slumps, segregated ice and associated landforms, and wedge ice allow a preliminary assessment of the models, and the outputs are broadly comparable with previous ground ice mapping of Canada. However, the presented models are more spatially explicit and better reflect observed ground ice conditions in some regions. The modelling exercise has highlighted that field-based volumetric ice estimates from more areas are required to calibrate and better validate small-scale ground ice models.

2019037865 Orejel Gonzalez, Mariana (University of Texas at El Paso, El Paso, TX); Villarreal, Sandra; Lara, Mark J.; Tweedie, Craig E.; Hollister, Robert D. and Webber, Patrick J. A half-century of biophysical change in polygonised tundra on the coastal plain of Northern Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1056, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Polygonized tundra landscapes are widespread in the Arctic. Within these landscapes, there is a tight coupling between surface microtopography, surface hydrology, vegetation, energy balance, and permafrost dynamics. A change in any one of these elements appears to cause cascading ecosystem structural and functional change. Models suggest such change could impact various elements of the Earth System. To date, few studies have examined the interaction between the biophysical elements controlling ecosystem structure and function in polygonized landscapes over decade to half century time scales. Nonetheless, there is a well-recognized urgency for advancing knowledge in this area. By rescuing and resampling a historic research site established in the early 1970's during the International Biological Programme (IBP) near Utqiagvik (formerly known as Barrow), Alaska, this Masters project is documenting how the vegetation cover, surface hydrology, and microtopography of this fragile polygonized tundra landscape has changed over the last 45 years. Observing and measuring these changes in small-scale transects can provide a larger insight into how landscape dynamics work. Resampling efforts have utilized the same sampling approaches first employed at the site and others that utilize modern technologies. Interpretation and discussion of results are focused on elements critical to the structure and function of polygonized tundra landscapes; preliminary analyses on active layer depth numbers show the most variation at ice-wedge features, which is known to have a direct impact in further defining the polygonal surface pattern. With this research, we continue to collect valuable long-term data that will continue to provide irreplaceable information for the next 45 years of polygonized tundra research in Utqiagvik, Alaska.

2019038051 Overeem, Irina (University of Colorado, Institute of Arctic and Alpine Research, Boulder, CO); Piper, Mark; Kettner, Albert; Hutton, Eric and Harris, Courtney Kay. Teaching with numerical models in the Earth surface processes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract ED44B-22, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Modeling is an integral part of modern geoscience. We advocate that any student in the geosciences should have opportunities to explore models and play with modeling through exercises to build efficacy with casting hypotheses, designing experiments, executing models and analyzing model results. The Community Surface Dynamics Modeling System (CSDMS) builds modeling tools to be used in advanced undergraduate and graduate classes on surface processes. The Web Modeling Tool, WMT, allows an instructor and students to set up and run models through a web-based graphical user interface. The actual simulations run on a remote supercomputer, so that there are no local installations of software necessary. With the migration to a new supercomputing system in 2018, instructors can now more easily apply for tutorial accounts to smooth this process. Once simulations are completed, output can be downloaded to a local machine for further analysis and visualization. There are now online teaching resources for stratigraphic modeling, landscape evolution modeling, hydrological and river delta processes, coastal and marine sediment transport modeling and finally permafrost modeling, each consisting of web material and tested experiments. In addition, CSDMS now is embarking on an effort to provide Jupyter notebooks of these same teaching resources. These specific notebooks are designed for those learners aiming to learn about surface processes but acquire basic scientific programming skills in Python. Documented model experiments are similar to WMT exercises, but intent to form a bridge to more independent and flexible model use in the more advanced Python Modeling Tool (PyMT). Here, we present details on the design and use of these teaching resources. We report on user experiences with graduate student classes on coastal processes modeling with a coupled model and with the Regional Ocean Modeling System (ROMS-Lite) over 2012-2018.

2019038069 Overeem, Irina (University of Colorado at Boulder, CSDMS/INSTAAR, Boulder, CO); Zheng Lai; Clow, Gary and Wang, Kang. How changing fluvio-deltaic systems affect permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP52B-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic climate warming impacts the terrestrial hydrological system by decreasing snow cover duration, melting glaciers and by permafrost thaw. Observations indicate river discharge is increasing and the timing of peak floods has shifted. How do these profound changes in river systems impact permafrost dynamics? And vice versa, how does thawing permafrost control river morphodynamics? To assess whether river flood dynamics impact permafrost temperature and active layer thickness evolution in floodplains and riverbanks, we combine remote-sensing data analysis and numerical models of permafrost dynamics with river and delta process models. We calculate permafrost temperature evolution with the Control Volume Permafrost Model (CVPM), which implements the non-linear heat transfer equations in multiple dimensions. CVPM is designed to account for a large variety of materials, a.o. organic rich material, fine-grained material, sand and gravel--and thus allows for experiments with varying floodplain stratigraphy. We define hypothetical floodplain cross sections in the upstream and downstream regions. Analyses of remotely-sensed Landsat8 imagery is used in combination with a river discharge and temperature model, driven by annual relationships of solar radiation and cloudiness. This river model provides the permafrost model with varying river flood extents, depths, durations and temperature. Simulations are set to be representative for conditions in the continuous permafrost zone, such as rivers and deltas on the Arctic coastal plain of Alaska. Our simulations show that permafrost active layer thickness deepens significantly in response to prolonged flood inundation. Consequently, the lowest-lying sections in the floodplain that experience the longest flood durations would consistently have deeper active layers. The thawing effect is more pronounced for early season floods, whereas it takes time for heat to transfer into already thawed soils if floods occur later in the summer. We hypothesize these effects on permafrost dynamics could potentially have ramifications for permafrost bank erosion as well. Enhancing our understanding of how permafrost thaw is impacted by rivers ultimately improves predictions of release of old stocks of carbon, which is one of great questions about the changing Arctic.

2019037878 Pain, Andrea (University of Florida, Department of Geological Sciences, Ft. Walton Beach, FL); Martin, Jonathan B.; Martin, Ellen E. and Rahman, Shaily. Shifts in the quantity and quality of dissolved organic carbon delivered to the ocean as continental ice sheets retreat [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1073, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Retreat of continental ice sheets following the Last Glacial Maximum (LGM) exposed nearly 20% of Earth's land surface and simultaneously supplied large volumes of melt water to the oceans. The transition from ice-covered to deglaciated landscapes may have altered the relative quantity and quality of organic carbon (OC) delivered to the ocean via proglacial streams transporting glacial melt water and non-glacial streams that drain watersheds exposed following ice sheet retreat. Here, we compare proglacial and non-glacial streams in western (Kangerlussuaq and Sisimiut) and southern (Narsarsuaq) Greenland to study how OC delivery to the ocean may have shifted as the proportion of proglacial to non-glacial drainage varied with ice sheet retreat. We use dissolved OC (DOC) concentrations and UV spectroscopy (specific UV absorbance at 254 nm, SUVA₂₅₄ and spectral slope ratios, S_R) to compare the quantity and quality of DOC in samples collected early and late in the 2017 melt season. Both the quantity and quality of DOC differ between proglacial and non-glacial streams and seasonal variations occur in the non-glacial, but not proglacial, streams. Molar organic C:N ratios suggest DOC originates primarily from vascular plant tissue and soil organic matter in non-glacial streams, and from microbial sources in proglacial streams. Non-glacial watersheds have higher DOC concentrations than proglacial watersheds, likely due to increased contributions of active layer melt and lake discharge. Lower SUVA₂₅₄ and higher S_R suggest that non-glacial stream DOC is less aromatic and more microbially degraded than proglacial stream DOC. Non-glacial streams have higher DOC concentrations in the spring than the fall, and UV indices suggest that spring DOC is more aromatic and microbially processed. These changes reflect winter accumulation of degraded DOC when stream discharge is low. Our results suggest that since the LGM, the quantity and quality of DOC fluxes to the ocean may exhibit greater seasonal variability, and the quality of DOC may have shifted to become less aromatic and more degraded. As ice sheets continue to retreat, DOC delivered from non-glacial streams is likely to increase due to permafrost melt, expansion of the active layer, and formation of lakes, further altering the quality and quantity of DOC delivered to the oceans.

2019031994 Parmentier, Frans-Jan W. (Lund University, Department of Physical Geography and Ecosystem Science, Lund, Sweden); Nilsen, Lennart; Tommervik, Hans A.; Meisel, Ove; Bröder, Lisa; Vonk, Jorien; Semenchuk, Philipp R. and Cooper, Elisabeth. Thicker snow cover triggers lateral permafrost carbon loss both through enhanced warming and surface runoff [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Large parts of the Arctic have experienced increases in maximum winter snow depth, despite ongoing warming, and this may amplify the loss of permafrost carbon. Thicker snow packs insulate the ground from the coldest winter temperatures, effectively warming the soil. This deepens active layers, causes surface subsidence, and modifies pathways of permafrost carbon loss. However, our understanding of the effect of snow cover on the mobilization of carbon from permafrost soils is severely limited, and not included in the latest generation of Earth system models.In this presentation, we present results from a snow fence experiment in Adventdalen on Svalbard and show that thicker snow cover not only causes permafrost degradation through warming, but also extensive erosion and mobilization of sediment due to increased surface drainage and runoff. These two processes amplified each other and triggered a dramatic change in the landscape. In less than a decade, increased snow cover and runoff led to the collapse of a 50 m long ice wedge network, forming a deep gully. Through high-resolution remote sensing and carbon-isotope analysis of water samples we reveal the timeline of the ice wedge collapse and magnitude of lateral permafrost carbon loss - continuing for years after the initial collapse. Surface hydrology can be an important driver of permafrost carbon loss and should be considered in future projections of the permafrost carbon feedback.

2019040673 Pavlov, Alexander (NASA, Goddard Space Flight Center, Greenbelt, MD); Davis, Jeffrey; Johnson, James; Johnson, Chris and Trainer, Melissa G. Pockets of methane in the shallow Martian subsurface; implications for rapid and seasonal changes of the atmospheric methane on Mars [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P43K-3877, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Martian atmospheric methane remains a mystery. Recent discoveries of the abrupt and seasonal changes in the atmospheric methane (Webster et al., 2015,2018) require presence of some local methane sources which have not been identified. Such sources should be able to release significant amounts of methane on a short timescale. We propose that the pockets of methane can form just several cm below Martian surface. The mechanism of gas pockets formation involve migration of salts in the Martian soil due to sublimation of shallow subsurface ice or evaporation of briny water during RSL events. As water evaporates and ice sublimates from the top of the soil, salts remains in the top layer of soil causing soil cementation and formation of the gas diffusion barrier in the soil. We conducted laboratory studies of the Mars analogues soils mixed with various amounts of salts and water exposed to a broad range of temperatures and pressures in the Mars simulation chamber. We injected neon as a proxy of methane at the bottom of the soil sample and monitored neon gas permeability through the soil sample by measuring gas pressure differential above and below the soil sample. We also monitored the neon flux through the soil using a RGA mass spectrometer. We found that under Martian-like atmospheric pressures, a mixture of JSC-Mars-1A and 5-10% of Mg perchlorate or sodium chloride produce gas impermeable soil caps capable to withstand an excess of 5 mbars of neon under the cap at the soil temperatures of up to +9 C. The layer of cemented soil is only ~2 cm thick. Caps remain gas impermeable after subsequent cooling of the sample soil sample to the subzero temperatures. Gas permeability of the soil caps under various temperatures and atmospheric pressures will be reported at the conference. Our results suggest that regardless of the nature of the methane source on Mars (e.g. biology, serpentinization, methane clathrates etc.), it is possible to accumulate methane in the gas pockets in the areas of shallow permafrost and abundant salts or on the RSL slopes. Gas pockets formed so close to the surface can be activated by either motion of the MSL rover itself, by impacts of small meteorites, or annual climate oscillations and therefore cause abrupt changes in the atmospheric methane abundance detected by MSL's Curiosity rover.

2019037792 Pedron, Shawn (University of California Irvine, Irvine, CA); Xu, Xiaomei; Walker, Jennifer Clare; Welker, Jeffrey M.; Klein, Eric S.; Euskirchen, Eugenie Susanne and Czimczik, Claudia I. Apportioning seasonality of soil respiration sources; a passive, quasi-continuous ¹⁴CO₂ sampler [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2507, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Today, the Arctic is warming (0.48°C decade^-1) and degradation of permafrost may subject permafrost C to microbial mineralization and fluxes to the atmosphere. Loss of permafrost C can be quantified in situ by measuring the radiocarbon (¹⁴C) content of soil and ecosystem respiration, because permafrost C is older (depleted in ¹⁴C) than current plant products and soil C cycling operates on timescales of years to centuries. Here, we use ¹⁴C analysis of CO₂ respired from graminoid tundra in Arctic Alaska to apportion how contributions of plant and microbial respiration to ecosystem respiration vary seasonally. We used a novel, passive sampling system, capable of trapping diffusive CO₂ within the active layer of tussock sedge tundra (n=4, from mineral soil to air) over periods of 2-6 weeks. CO₂ was sorbed to 13X zeolite molecular sieve in the field, and thermally desorbed and analyzed for its ¹⁴C content at UC Irvine's KCCAMS lab. To evaluate the system's efficiency and quantify the temporal and spatial variability of respiration sources, we co-deployed Vaisala Carbocap [CO₂] and temperature probes and Decagon 5TM volumetric water content (VWC) probes at equivalent depths to the gas inlets, and traditional chambers (n=6, ~10 m away) for sampling of ecosystem- and soil-respired ¹⁴CO₂ over 15 min-24 hour periods. A comparison of common predictors of soil CO₂ flux with yields obtained by our new sampler indicates that the system operates in a consistent and reproducible manner in the field. Type II Anova (R, car package) was used to correlate CO₂ sampling rate (4.4-41 mg CO₂-C_* day^-1, n=26) to mean VWC (p=0.009) and temperature (p=0.018) at the inlet positions, as well as local barometric pressure (p=0.016). ¹⁴C analysis yielded values ranging from 0.723-1.095 Fraction Modern, with a peak in old C observed at the deepest inlet (mineral soil, -36 cm) in late winter. These traps will next be deployed in tandem with traditional ecosystem respiration techniques (eddy covariance, soil surface chambers) with the purpose of resolving the net isotopic flux into contributions from unique depths. A goal of the sampler is to elucidate the temporal dynamics of microbial C sources, specifically the decomposition of older permafrost C in winter, using ¹³C IRMS and NMR spectroscopy.

2019037781 Pegoraro, Elaine (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Mauritz, Marguerite; Crummer, Kathryn G.; Ebert, Christopher; Hicks Pries, Caitlin and Schuur, Edward. Inter-annual variation in radiocarbon age of ecosystem respiration exceeds permafrost warming effects [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2492, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost carbon (C) has accumulated in northern latitudes throughout the Holocene because of frozen and waterlogged conditions. As air temperatures increase with climate warming, we expect to see an increase in permafrost thaw and a decrease in environmental constraints on microbial decomposition. Over decadal timescales, highly thawed permafrost areas can release more old C than minimally thawed areas. Since the bulk of permafrost C is old, we anticipate that long-term C losses will largely originate from both old and slowly decomposing C pools. Our study was conducted in a moist acidic tundra site near Eight Mile Lake, Alaska where we have experimentally warmed permafrost for almost a decade and tripled the rate of thaw relative to control. We utilized natural abundance D¹⁴C as a tool to estimate the age of ecosystem respiration (Reco) during the peak of growing season, from 2010 to 2016. We found that from 2011 to 2016, Reco D¹⁴C decreased at a rate of 4 ppm per year (-7 to 0 ppm year^-1) in both slowly and rapidly thawing plots. This decline in Reco D¹⁴C over time approximates the ~5 ppm annual decline in atmospheric D¹⁴C. Long-term soil warming did not change the annual rate of decrease in Reco D¹⁴C that might be expected with greater decomposition of old soil C. However, previous studies have shown that in rapidly thawing areas, an increase in plant activity and C input to soil with contemporary D¹⁴C values can dilute the isotopic signal of old C, even when its contribution to Reco increases. In some years, we observed substantially more negative Reco D¹⁴C values across all treatments, suggesting that environmental conditions can promote higher rates of old C loss to the atmosphere. Our results illustrate that our ability to detect old soil C loss may be highly dependent on interannual variation associated with environmental drivers, rather than small-scale spatial variation and increased rates of permafrost thaw.

2019040682 Perryman, Clarice R. (University of New Hampshire, Department of Earth Sciences and Earth Systems Research Center, Durham, NH); Palace, Michael W.; DelGreco, Jessica; Malhotra, Avni and Varner, Ruth K. Rapid permafrost collapse spurs changes in methane oxidation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract U13B-21, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw in subarctic peatlands liberates a globally significant fraction of the soil organic carbon pool to decomposition and release to the atmosphere. In thawed sites within northern wetlands, submerged conditions promote methane (CH₄) production and emissions. Methane oxidizing bacteria can mitigate a significant fraction (20-60%) of CH₄ emissions by oxidizing CH₄ to CO₂ as CH₄ diffuses through the peat column and in submerged sites where aerenchymous vegetation deliver oxygen to the rhizosphere. It is uncertain how the fraction of CH₄ oxidized to CO₂ changes with permafrost thaw. Previous studies have investigated how rates of CH₄ oxidation change with permafrost thaw by thawing soils during incubation experiments or measuring CH₄ oxidation rates across a spatial gradient of permafrost thaw, yet few have investigated how rates of CH₄ oxidation change over time in a rapidly degrading permafrost peatland. We extracted peat cores from a collapsing permafrost palsa in Stordalen Mire (68°21'N, 18°49'E), a rapidly thawing peatland complex in northernmost Sweden, in 2015, 2017, and 2018 and incubated them at in situ temperatures and uniform CH₄ concentrations to measure CH₄ oxidation rates. Over the study period the seasonally thawed depth at this site increased from 25 ± 2.5cm to 77 ± 6.9 cm, and the site transitioned from a dry palsa mound to a submerged site with emergent aerenchymous vegetation under 10cm of standing water. Methane consumption rates in the 0-10cm and 10-20cm sections of the peat column differed between years as thaw progressed at this site. Methane oxidation rates were highest in 2015 before the palsa collapsed; however, in 2018 CH₄ consumption rates in the upper 10cm of peat where roots of aerenchymous vegetation were present were not significantly different from CH₄ uptake rates measured in 2015. These results suggest that communities of CH₄ oxidizing microbes adapt quickly to changing hydrology and vegetation associated with permafrost thaw and will affect CH₄ emissions rates from rapidly thawing peatlands.

2019040647 Pietroniro, A. (Environment and Climate Change Canada, National Hydrology Research Center, Saskatoon, SK, Canada); Pomeroy, J. W.; Razavi, S. and Wheater, H. S. The global water futures core modelling strategy [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1797, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Climate warming and human actions are altering precipitation, reducing snowpacks, accelerating glacier melt, intensifying floods, and increasing drought risk, while pollution from population growth and industrialization is degrading water systems. With such change, it is clear that the historical patterns of water availability are no longer a reliable. This is particularly evident in the cold regions that cover much of Canada and provide a large proportion of the world's freshwater supply. An integral part of the Global Water Futures Programme dictates that new, connected climate, hydrological, water quality and water management modeling tools that precisely capture these interconnected forces and their societal implications are necessary. Given this need, a core modelling team was formed to deliver the new modeling tools tied with the new monitoring systems for Canada and the cold regions of the world that were identified as programme deliverables. The systems being developed by the core modeling team are designed to support improved disaster warning and long term prediction of water futures. The modelling strategy is based on a sequence of atmospheric driving models, linked to terrestrial, riverine and management models, with a hierarchy of time horizons and objectives that scale from short term/real time operations to medium term predictions at weekly to seasonal scales to long term predictions at seasonal to decadal time scales. The strategy and models being evaluated and tested as part of the larger Global Water Futures programme are outlined. This includes scaling strategies, new basin segmentation approaches, data assimilation approaches, the role of hydrological observatories in model development and the multi-objective calibration strategies being examined. A multi-model approach is being used to quantify predictive uncertainty and show rapid advances over the 5 million km2 modelling domain. Examples of new models include hydrochemistry models suitable for Canadian agriculture and great lakes, glacier, river ice and permafrost hydrology models, multi-physics multi-scale modular models and coupled atmospheric land surface hydrology schemes. The modelling systems being developed may have application outside of Canada and have particular merit in cold and data-sparse regions of the world.

2019038064 Piliouras, Anastasia (Los Alamos National Laboratory, Earth and Environmental Sciences, Los Alamos, NM); Lauzon, Rebecca and Rowland, Joel C. Effects of ice and permafrost on delta channel dynamics and morphology [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP31D-2376, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

All deltas are influenced to varying degrees by rivers, waves, and tides. Arctic deltas, however, are also affected by permafrost and ice cover. The lack of direct observations of how ice and permafrost influence coastal sediment transport, channel dynamics, and delta morphology limits our ability to understand Arctic delta dynamics and potential response to climate change. Permafrost alters sediment erodibility and fast-ice cover constricts flow underneath the ice, introducing friction and resistance to flow. Previous research incorporating these effects into a reduced complexity model of delta formation (DeltaRCM) suggests that ice or permafrost presence reduces channel mobility, altering deltaic sediment retention and depositional patterns. While this research considered ice and permafrost separately, results suggested that ice might have a greater effect on delta morphology and dynamics than permafrost. Building on this research, we use DeltaRCM to explore the combined effects of ice thickness and permafrost erodibility on delta dynamics and morphology. Delta characteristics change with increasing ice thickness, regardless of permafrost erodibility. Shoreline roughness and offshore deposition increase with ice thickness, and delta area decreases. Similarly, delta morphodynamics change with with permafrost erodibility regardless of ice thickness. Shoreline rugosity and area of open water on the delta (e.g. lakes, abandoned channels) decreases with increasing permafrost erodibility. Both ice and permafrost decrease channel mobility to a comparable degree. However, ice thickness appears to have a stronger effect on depositional patterns such as progradation rate, shoreline rugosity, and offshore and overbank deposition. These results suggest that permafrost thaw and ice retreat in a warming climate may result in deltas with more dynamic channel networks. Ice retreat may have additional implications for storage and fluxes of water and sediment through Arctic deltas.

2019038063 Piliouras, Anastasia (Los Alamos National Laboratory, Earth and Environmental Sciences, Los Alamos, NM) and Rowland, Joel C. Changing Arctic river deltas [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP31D-2375, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Deltas connect rivers to the coastal ocean and buffer or filter the delivery of water, sediment, and nutrients to the coast. The potential filtering effect of deltas depends on the spatial patterns of channels and lakes, which is likely to change as Arctic deltas respond to sea level rise, changing hydrology, permafrost thaw, and retreating sea ice. We conducted an analysis of Landsat imagery for six high-latitude deltas (Colville, Kolyma, Lena, Mackenzie, Yenisei, Yukon) to determine the change in patterns and types of water bodies on decadal timescales. We utilized the oldest available cloud-free Landsat image(s) for each delta and a modern-day image (ca. 2014). Image classifications were done using eCognition and image objects were classified as either channel, land, lake, or other small water (≤&eq;4 pixels in width). Change on each delta was determined using two methods: (1) detecting change in the classification type of each individual pixel and (2) using the Spatially Continuous Riverbank Erosion and Accretion Measurements program to detect shifts in the planform channel network. Results suggest drying of the Yenisei delta over the period measured, while the other deltas have become wetter. The most notable change on the Yenisei was the disappearance or shrinking of small water bodies and lakes, as many seem to have dried up or contracted between 1990 and 2013, indicating a possible decrease in water storage on the delta plain over time. The Yukon and the Kolyma, on the other hand, showed many areas of lake expansion and new lake development, suggesting that these systems may be able to store more fine sediment and/or increase the residence time of water traveling through the deltas. Channels on the Yukon delta had the lowest erosion rates and some of the highest accretion rates overall, which may be due to the more rapid colonization of in-channel bars in the warmer climate of the Yukon compared to the other deltas. Channel erosion rates were highest on the Lena and Kolyma deltas, while channel accretion rates were highest on the Lena and Yukon. Future work aims to unravel the influences of local climate, hydrology, ice, and marine forcings on rates of channel bank migration and landscape change in Arctic river deltas.

2019038104 Potter, Stefano (Woods Hole Research Center, Falmouth, MA); Rogers, Brendan M.; Walker, Xanthe J.; Veraverbeke, Sander; Hoy, Elizabeth Embury; Baltzer, Jennifer Lynn; Goetz, Scott J.; Jenkins, Liza K.; Johnstone, Jill F.; Kane, Evan S.; Mack, Michelle C.; Turetsky, Merritt R.; Bourgeau-Chavez, Laura L. and French, Nancy H. F. Above and belowground carbon emissions from historical fires across Alaska and Canada [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC51E-0835, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Although boreal forests comprise about a third of the world's forests, they store approximately 40% of all terrestrial carbon and are estimated to be a carbon sink. Fire is considered a dominant disturbance mechanism in boreal ecosystems, and as a result of recent climate warming and drying there has been an increase in fire intensity across the North American boreal which has the potential to transition boreal forests from a carbon sink to a carbon source. Due to the large amount of fuel in boreal forest floors, belowground carbon emissions are often greater than aboveground. Therefore, understanding the most important controls on below and aboveground combustion, and how these vary over space and time, could improve predictions of disturbance effects and feedbacks to climate change. Here we built statistical models of both below and aboveground combustion based on 700 field observations representing a major synthesis effort sponsored by the NASA ABoVE program from 5 different research groups. Combustion measurements from these field plots were related to a variety of predictors including topography, soils, climate and vegetation. We compared various statistical approaches and types of models (e.g., a global model covering all of Canada and Alaska to region-specific models) to determine an optimal approach. Preliminary results indicate that a global model is more robust for both above and belowground consumption with R² values of 0.75 (0.25 cross-validated) and 0.67 (0.18 cross-validated) respectively. We also find differences in the important drivers of combustion between belowground and aboveground, with pre-fire tree cover, dNBR and day of burn more important for aboveground combustion while permafrost and soil characteristics are more important for belowground. The approach we present here represents a significant advance over prior research efforts in terms of the scope of training data as well as robustness of model fits which can be used to inform broader-scale fire carbon emissions modeling.

2019040635 Putkonen, J. (University of North Dakota, Harold Hamm School of Geology and Geological Engineering, Grand Forks, ND); Morgan, D. J.; Balco, G.; Bergelin, Marie and Grant, A. Age and history of a buried glacier ice mass, Ong Valley, southern Transantarctic Mountains [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C22B-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

A large body of ice that is buried beneath approximately a meter of debris occurs in the Ong Valley of the Transantarctic Mountains of East Antarctica. Our prior measurements of cosmogenic 10Be, 26Al, and 21Ne obtained from the meter thick layer of till covering the ice show that the till has resided at its current location for more than 1.1 Ma. By inference we expect the ice below to have the same residence age as the till that is sublimating off the ice. The idea of long, slow sublimation of the buried is supported by the lateral moraines that are mapped flanking the ice body, and perched above the current ice level on the valley walls. We drilled the ice body at two locations and retrieved two approximately 10 meter long cores of mixed ice and mineral matter in January 2018. The desire to find and date the ancient ice is motivated by the archives of information such ice may harbor of past environments and geological processes. In addition, similar buried ice bodies are found in other areas of Antarctica as well as in Mars. Most glacial ice contains tiny air bubbles that have trapped the atmospheric gases that existed at the time that the bubbles closed-off from the atmosphere. Such samples can contain not only the concentration of atmospheric greenhouse gases that existed at the time the bubbles formed, but also can contain plant pollen, microbes, and particles of mineral dust. We are currently measuring the cosmogenic nuclide concentrations both in the overlying debris and in the till encased in the ice. This site may contain some of the oldest ice on Earth and studies of the material contained within it could help us to better understand the processes involved in its survival for such long periods of time. This work will also help inform scientists about the processes involved in the development of landforms here on earth as well as those on Mars where similar dirt covered glaciers are found today.

2019038080 Ratsimbazafy, Tahiana (Institut National de la Recherche Scientifique-Eau Terre Environnement INRS-ETE, Quebec City, QC, Canada); Touati, Chaima; Poulin, Jimmy; Bernier, Monique and Ludwig, Ralf. New SMAP data brightness temperature approaches for water dampening removal [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Boreal and Arctic regions form a land cover mosaic where vegetation structure, conditions and distribution are strongly regulated by the environmental factors such as soil moisture and permafrost status. In these seasonally frozen environments, the growing season is determined primarily by the length of the non-frozen period which also has an impact on permafrost melt, construction of infrastructures, and traditional ways of life of the inhabitants. The Brightness Temperature (Tb) data from L-band passive microwave radiometer (1.20-1.41 GHz) onboard the Soil Moisture Active Passive (SMAP) satellite of the National Aeronautics and Space Administration (NASA) is able to sense the soil conditions through moderate land cover and to map the soil Freeze/Thaw (FT) status. The landscapes of Canadian boreal and arctic regions are shaped by many small lakes, ponds and rivers. Monitoring the soil FT dynamic in these regions is challenging because of the dampened effects of water surfaces on Tb values. The main purpose of this study is to validate SMAP related FT products. To overcome the effect of water bodies on Tb, normalization techniques applied to SMAP Level-1 Tb products are proposed in this communication. Two linear-based approaches are presented to normalize the Tb; one depends only on local water fraction (WF) and the other on both WF and land cover type (LCT) (Trees, Tundra, Wetland, and Mixed vegetation cover). The WF were extracted from Landsat-8 images and the land cover was recovered by combining classes of MODIS land cover product. The corrected Tb are then used to calculate Normalized Polarization Ratio (NPR) indices, a parameter used in FT mapping. The produced FT map is validated with in situ soil FT status derived from soil temperature measurements (at 5 cm) measured with installed probes near Umiujaq (Latitude: 56.5427; Longitude: -76.4477). The validation was done within the pixel housing the probes. Results shows an agreement up to 90% when both the WF and LCT are included in the Tb normalization process versus 74% when only WF is considered.

2019038106 Ravens, Thomas M. (University of Alaska Anchorage, Civil Enegineering, Anchorage, AK). Collaborative development of coastal hazards scenarios in Arctic Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC52A-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The University of Alaska Anchorage (UAA) is developing a Research Coordination Network (RCN) in the area of Arctic Coastal Hazards, considering both physical science / engineering issues as well as social / economic science issues. The RCN will emphasize community engagement and collaboration. As a backdrop for the RCN, the UAA research team is engaging with communities in the Yukon-Kuskokwim Delta, Norton Sound, and on North Slope coast to develop community-based coastal monitoring programs. For example, programs are being developed to monitor beach profiles, storm surge height, and wave run-up. Data from the monitoring effort is used to calibrate and validate coastal hazards models including models of coastal erosion and coastal flooding, and models quantifying coastal infrastructure vulnerability. Once the models are validated, they will be used to develop coastal hazards scenarios and risk maps for the next 50 years, including scenarios of coastal erosion and flooding. These scenarios will be discussed with coastal communities who will be use them to plan their futures. Throughout this process, we will be reflecting on how best to quantify community risks such as risks associated with permafrost thaw, coastal erosion, and coastal flooding - as well as quantify coastal infrastructure vulnerability. Can we develop a rubric that allows us to compare community vulnerability and resilience? The presentation/poster will present the coastal monitoring data and coastal hazards models, and communicate the vision of the Arctic Coastal Hazards RCN.

2019038126 Rey, David (Colorado School of Mines, Golden, CO); Walvoord, Michelle A.; Minsley, Burke J.; Rover, Jennifer and Singha, Kamini. Investigating lake-area dynamics across a permafrost-thaw spectrum using airborne electromagnetic surveys and remote sensing time-series data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Lakes in boreal lowlands influence carbon cycling and supply an important source of freshwater for wildlife and migratory waterfowl. The abundance and distribution of these lakes are supported, in part, by permafrost distribution, which is subject to change. Relationships between permafrost thaw and lake dynamics remain poorly known in most boreal regions. Here, new airborne electromagnetic (AEM) data were used to constrain deep permafrost distribution. AEM data were coupled with Landsat-derived lake surface-area data to inform temporal lake behavior changes in the Yukon Flats of Alaska. Together, these data were used to elucidate processes that drive lake dynamics across a variety of permafrost thaw states not possible in studies conducted with satellite imagery or field measurements alone. Clustered time-series data identified lakes with similar temporal dynamics. Clusters possessed similarities in lake permanence (i.e. ephemeral vs. perennial), subsurface permafrost distribution, and proximity to rivers and streams. Of the clustered lakes, ~66% are inferred to have at least intermittent connectivity with other surface-water features, ~19% are inferred to have shallow subsurface connectivity to other surface water features that served as a low-pass filter for hydroclimatic fluctuations, and ~15% appear to be isolated by surrounding permafrost (i.e. no connectivity). Observed lake dynamics exhibit the greatest degree of spatially uniformity in continuous, thick permafrost areas, largely characterized by disconnected lakes. In nearby regions of progressively thawed permafrost as inferred from the AEM data, lake dynamics exhibit spatiotemporal heterogeneity, which can be explained by high variability in shallow subsurface connectivity through thawed permeable gravel that provides pathways for lateral water redistribution in this area. This study suggests that permafrost distribution influences lake-area dynamics in the Yukon Flats and provides some insight on future trajectories.

2019038058 Richmond, Bruce M. (U. S. Geological Survey, Santa Cruz, CA); Erikson, Li H.; Gibbs, Ann; Lorenson, Thomas D.; Oberle, Ferdinand J. and Harrison, Shawn R. Multidisciplinary studies of permafrost coast processes, NE Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2363, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Recent trends of warming air, land and sea temperatures in the Arctic are resulting in longer periods of permafrost thaw and ice-free conditions during summer which can lead to increased exposure to coastal storm inundation, wave impacts, and heightened erosion which threatens local communities, diverse habitats and critical infrastructure. To better understand permafrost coast geologic history and the driving forces of coastal change an ongoing multidisciplinary study is being conducted in, NE Alaska. Methodologies employed and brief highlights include: 1) Characterize historical coastal change from maps, imagery, and DEMs using the digital shoreline analysis system (DSAS). Most of the northern coast of Alaska is undergoing severe erosion with a mean long-term shoreline change rate of -1.4±0.1 m/yr. Coastal rates can be highly variable, ranging from -25 m/yr to +20 m/yr. 2) Document permafrost bluff subsurface geologic structure using electrical resistivity tomography (ERT) surveys, targeted coring, and geochemical analysis. There is widespread occurrence of subsurface cryopegs (porewater brine) underlying most of Barter Island. Geochemical analyses of the porewater and sediment show that the cryopegs on Barter Island are old and developed from the concentration of groundwater and surface water salts rather than from seawater. 3) Conduct daily morphological monitoring with time lapse camera systems and permafrost thermistor arrays. Primary mechanisms of bluff failure include thermal sloughing when temperatures are elevated and thermal-erosional undercutting during storms. 4) Determine spatial distribution of methane gas detection and bluff thermal regime from unmanned aerial systems (UAS). We identify methane pathways through thawing coastal permafrost. These pathways represent hotspots that release significantly higher levels of methane than the surrounding areas, suggesting that point sampling is inadequate in characterizing methane release. 5) Measure nearshore water levels and wave characteristics from seabed-mounted pressure transducers and bluff-mounted mini seismometers. Wave characteristics derived from the pressure transducers and seismometers are coupled with the camera systems to document the timing, rates, and processes of bluff failure.

2019037806 Rick, Brianna (Colorado State University, Geosciences, Fort Collins, CO); Klene, Anna E. and Shiklomanov, Nikolay I. Plot-scale analysis of interactions between climate, vegetation, and permafrost at Toolik Lake, Alaska (1995-2018) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2566, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Air temperatures across the Arctic have increased in recent decades, and through complex feedbacks, vegetation and permafrost (frozen ground) are responding as climate warming continues. This study investigates the trends and interactions of observed air, soil-surface temperature (SST), and active-layer thickness (ALT) at Toolik Lake on the Alaskan North Slope between 1995 and 2017, as well as vegetation change over time. Time series between 1995 and 2017 at CALM site U12B, a 1 ha plot near Toolik Lake, reveal an increase in mean summer (Jun-Aug) air temperatures and a slight decrease in mean summer SST. In winter (Dec-Feb), the plot experienced an overall increase in SST and a slight increase in air temperatures. Deepening mean maximum ALT reflects the annual warming air and SST. Using aerial photographs, normalized difference vegetation index (NDVI) maps were produced for peak greenness in 1995 and 2017 within the 1 ha plot. A water track located within the study site, dominated by low shrubs, had the highest NDVI values compared to the surrounding tussock tundra. An increase in greenness along the edges of the water track in 2017 relative to 1995, as well as a visual comparison of the orthomosaics and photo-derived digital elevation models (DEMs), reveals the water track widening by nearly 4.5 m and growth of the shrubs adjacent to it. In nearly every year during the 23-yr observation period, mean winter SST at sensors positioned along the water track remained above -6°C, introducing the possibility of overwinter decomposition and nutrient mineralization. Since 2009, sensors in non-water track areas have recorded mean winter SST consistently above -8°C, signifying an increase in mean winter SST throughout the plot that could have important implications for winter microbial activity. Incorporating air and soil-surface temperatures, ALT, and vegetation dynamics into a time series demonstrates the complexity of feedbacks in a changing Arctic environment. These results may have strong implications for biogeochemical feedbacks and ecosystem processes.

2019038133 Riley, David Christophe (University of Southampton, Southampton, United Kingdom); Marin-Moreno, Hector; Minshull, Timothy A. and Schaafsma, Marije. A multi-criteria approach to social, economic and environmental assessment of gas hydrate development projects [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS11B-1416, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

To meet growing energy demand research has continued towards commercialisation of natural gas hydrates as a source of natural gas in permafrost and continental slope regions worldwide. While gas hydrate production technology continues to be refined, and the geoscientific challenges of hydrate production continue to be explored, the potential social, environmental and economic effects of pursuing this resource remain poorly understood. We have created a structured protocol for assessing gas hydrate developments encompassing a suite of social, economic and environmental factors. Our protocol is a form of multi-criteria analysis where different alternatives of gas hydrate development are appraised according to a series of criteria. Each alternative is defined by the change it would cause in the social, economic and natural spheres from the current condition. The protocol also involves the collection of stakeholder weighting information to establish the considerations of the different groups potentially impacted by gas hydrate development. Impacts of developing hydrates commercially have been hypothesised from literature review, comparison with analogous conventional projects, and conversation with experts. Stakeholders are found in production industry, governance, the local community, environmental organisations and the scientific community. Comparing the priorities of different stakeholders illustrates what elements should be the main considerations when hydrate production is being designed, and how different groups discriminate between forms of development. Our protocol has been tested and refined using the North Slope of Alaska as an example site where gas hydrate could be commercially developed. The compared alternatives are different scales of hydrate development with different target markets. This is the first attempt to broadly appraise commercial gas hydrate development projects and aims to provide a structured format underpinning future assessment. Future testing of the protocol on other sites will ensure that the method is robust and versatile.

2019037794 Riley, William J. (Lawrence Berkeley National Laboratory, Climate Sciences Department, Climate and Ecosystem Sciences Division, Berkeley, CA); Grant, Robert F.; Mekonnen, Zezalem Amdie; Arora, Bhavna and Torn, Margaret S. Modelling climate change impacts on an Arctic polygonal tundra; Changes in CO₂ and CH₄ exchange depend on rates of permafrost thaw as affected by changes in vegetation and drainage [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2512, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Model projections of CO₂ and CH₄ exchange in Arctic tundra during the next century diverge widely. Here we used ecosys to examine how climate change will affect CO₂ and CH₄ exchange in troughs, rims and centers of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO₂ and CH₄ fluxes associated with those in air and soil temperatures (T_a and T_s) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising T_a, atmospheric CO₂ concentrations (C_a) and precipitation (P) increased NPP from 50-150 g C m^-2 y^-1, consistent with current biometric estimates, to 200-250 g C m^-2 y^-1. Concurrent increases in R_h were slightly smaller, so that net CO₂ exchange rose from values of -25 (net emission) to +50 (net uptake) g C m^-2 y^-1 to ones of -10 to +65 g C m^-2 y^-1. Large increases in R_h with thawing permafrost were not modelled. Increases in net CO₂ uptake were largely offset by increases in CH₄ emissions from 0-6 g C m^-2 y^-1 to 1-20 g C m^-2 y^-1, reducing gains in NEP. These increases in net CO₂ uptake and CH₄ emissions were modelled with hydrological boundary conditions that were assumed not to change with climate. Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change.

2019037783 Rodenhizer, Heidi (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Mauritz, Marguerite; Taylor, Meghan and Schuur, Edward. Using the relationship between active layer thickness and subsidence to constrain permafrost thaw [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2494, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost soils have very high carbon content, and this carbon is vulnerable to release to the atmosphere as soils thaw and microbial activity increases. Active layer thickness, the depth to which soils thaw seasonally, is an important indicator of this permafrost carbon feedback, as it is a measure of the quantity of thawed carbon-rich soils available for microbial use. Permafrost soils also often have very high ice content, which can cause surface subsidence, the slumping of the ground surface as permafrost thaws and ice volume is lost. Subsidence masks increases in active layer thickness because it changes the location of the ground surface, which serves as the reference point of active layer thickness measurements. Tracking subsidence is therefore important but can be quite difficult. In this study, GPS derived subsidence was constrained by satisfying the condition that the relationship between active layer thickness and subsidence is constant across a permafrost warming experiment where soils are uniform. At this site, half of the plots have received a soil warming treatment by increasing snow depth for the past 10 years, causing visibly dramatic subsidence, while the other half have been exposed to ambient conditions and appear to have subsided relatively little. Previous analysis resulted in a lower bound estimate of no subsidence in control plots and 27 cm subsidence across warming plots over the course of 8 years, and an upper bound estimate of 63 cm in control plots and 89 cm in warming plots. By setting the relationship between active layer thickness and subsidence equal in warming and control plots, we were able to determine subsidence values of 8 cm in control plots and 34 cm in warming plots over 8 years. Accounting for subsidence increased average 2017 active layer thickness in control plots from 64 cm to 72 cm and in warming plots from 94 cm to 128 cm. Over the course of the experiment, the uncorrected ALT data suggested an increase of 4 kg C/m² within the active layer in control plots and 33 kg C/m² in the warming plots, but with the corrected ALT data there was an increase of 6 kg C/m² in the control plots and 38 kg C/m² in the warming plots. This shows that permafrost thaw could be having a greater effect on the quantity of available carbon at this site than previously realized.

2019038131 Rodríguez Tribaldos, Veronica (Lawrence Berkeley National Laboratory, Berkeley, CA); Lindsey, Nate; Titov, Aleksei; Wagner, Anna M.; Gelvin, Arthur B.; Ekblaw, Ian; Ulrich, Craig; Freifeld, Barry M. and Ajo Franklin, Jonathan Blair. Observations of long-term subsidence in an induced permafrost warming experiment using distributed acoustic sensing (DAS) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS43B-0845, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Increasingly warming trends are causing degradation of permafrost landscapes. This alteration induces surface deformation that can pose a threat to civil infrastructure such as roads, pipelines and buildings. Hence, it is crucial to understand timescales and mechanisms involved in ground deformation related to permafrost thaw. The aim is to provide an observational basis that could be used to detect critical areas and develop early warning systems. Here, we focus on the feasibility of Distributed Acoustic Sensing (DAS) to detect and monitor subsidence as a result of permafrost thaw at depth. DAS is typically used to detect dynamic strain in the seismic bandwidth. However, recent studies successfully apply DAS to monitor quasi-static strain variations at very low frequencies and long periods (>1000 s). By temporally integrating strain rates measured by DAS to strain, we can derive the ground's long-term response to deformation. In this way, DAS provides a unique means of continuously recording subsidence with high spatial resolution (1 m) over large distances (10s of km). With that goal, a continuous, 4000 m long 2D DAS array was deployed in 9 crossing profiles across a permafrost region undergoing a controlled thaw experiment at the Fairbanks Permafrost Experiment Station in Alaska. Data was acquired for the entire duration of thawing, from August 5th to October 4th, 2016. The experiment, with dimensions of 10.5 m ´ 12.7 m, accelerated permafrost degradation by ca. two decades, deepening the permafrost table from 4 to 5.5 m. Analysis of the temporal variation of strain shows that DAS recorded the onset and long-term evolution of subsidence related to permafrost alteration. Subsidence initiates ca. 20 days after start of thawing, manifest in the DAS dataset as an abrupt decrease in strain. A rapid decrease occurs for a period of another 20 days after which deformation slows down and stabilizes. Results are validated against two-point Electronic Distance Measurements (EDM) and terrestrial based LiDAR images. They also correlate with data acquired using other fiber optics sensing techniques such as Distributed Strain Sensing (DSS). Our study shows the feasibility of DAS to detect subsidence related to permafrost degradation and how it could constitute a powerful tool for long-term monitoring of environmental processes.

2019038083 Romanov, Eduard M. (Republican Social Movement "SIR", Yakutsk, Russian Federation); Fedorov, Aleksandr N.; Zheleznyak, Mikhail N. and Prokopiev, Vladimir M. Geographical basis of the law "On the Protection of Permafrost" of the Republic of Sakha (Yakutia), Russian Federation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1390, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Law "On the protection of permafrost" of the Republic of Sakha (Yakutia) was developed and adopted on May 22, 2018 in order to strengthen state, municipal and public supervision over the rational use and protection of permafrost. The necessity of preparing the law "On the protection of permafrost" was dictated due to the activation of cryogenic processes in the conditions of the recent climate warming. At the same time, the landscapes created and transformed by human, representing the economic basis of life, such as residential areas, agricultural lands, engineering structures and communications, react most strongly to climate warming which rapidly degrade, "badlands", thermokarst depressions and lakes, ravines are formed. Economic and social development and exploration of mineral resources of the cryolithozone need environmentally sound technologies, primarily aimed at permafrost protection. Preservation of permafrost taking into account the ecological ties and modern technologies, irreproachable transformation of permafrost landscapes into non-permafrost landscapes, should become the basis for the interrelation between human and nature of the North at the present time. The population adaptation to modern climate changes in the permafrost zone is the most acute problem. There is a threat of losing of the identity of North people, their language, culture and traditional economic activities. However, not all permafrost landscapes strongly react to the warming process, many of them can easily adapt to new conditions. The use of such lands and the protection of unsustainable permafrost landscapes should become the basis of life in areas with the permafrost. Adoption of the law "On the protection of permafrost" of the Republic of Sakha (Yakutia) was based on the results of the long-term studies of Russian and foreign permafrost scientists and geographers. The law presupposes the strengthening of the scientific basis for permafrost studying and monitoring. The active participation of public organizations, mass media and individual politicians in explaining the consequences of the change in permafrost became the basis for the adoption of law in the State Assembly of the Republic of Sakha (Yakutia), in order to rational use of permafrost landscapes, and preserve it for future generation in its original form.

2019038068 Rowland, Joel C. (Los Alamos National Laboratory, Earth and Environmental Sciences, Los Alamos, NM); Schwenk, Jon; Shelef, Eitan; Mishra, Umakant; Muss, Jordan D. and Stauffer, Sophie J. Pan-Arctic flux of soil organic carbon to rivers by river bank erosion [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP51B-26, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The migration of river channels simultaneously erodes and creates floodplain deposits. These deposits consist of both mineral and organic materials. While river bank erosion is recognized as a potential source for older carbon inputs to Arctic rivers its contribution to the cycling of carbon in permafrost regions has been unquantified to date. To constrain this contribution, we assessed bank erosion rates for >5,000 km of channels along 14 sections of 13 Arctic and sub-Arctic rivers with permafrost extent ranging from minimal to continuous. The analyzed rivers range in drainage area from 1,300 (Selawik) to 2.5±10⁶ (Yenisei) km², and in width from 50 (Selawik) to 6,500 m (Lena). Using our newly developed Python-based River and Basin Profiler (RaBPro) tool, we estimated channel slopes, delineated watersheds, and computed contributing basin statistics to develop an empirical model for river bank erosion rates in permafrost systems. This model, together with a pan-Arctic delineation of alluvial floodplains, and the Northern Circumpolar Soil Carbon Database, were used to estimate the pan-Arctic flux of soil organic carbon (SOC) into rivers due to bank erosion. Preliminary estimates suggest that the bank erosion flux of SOC may be as high as 38 Tg/yr--as large as the estimated flux of pan-Arctic riverine-transported carbon to the ocean. What fraction of eroded floodplain carbon reaches the ocean is unknown; significant fractions of the carbon may be redeposited downstream or released to the atmosphere.

2019038134 Sain, Kalachand (CSIR-National Geophysical Research Institute, Gas Hydrates Group, Hyderabad, India). Characterization and quantification of gas-hydrates along the Krishna-Godavari and Mahanadi basins, eastern Indian margin [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS11B-1424, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Gas-hydrates are important due to their abundant occurrences along the outer continental margins and permafrost regions and their huge potential as major energy resources. Successful test productions of gas-hydrates in McKenzie delta, Alaska, Japan continental margin and South China Sea provide great hopes for viable production, and have prompted many countries including India to pursue exploration and exploitation towards the energy security. The bathymetry, seafloor temperature, total organic carbon content, sediment-thickness, rate of sedimentation, geothermal gradient imply that the shallow sediments in the Krishna-Godavari (KG) and Mahanadi basins along the eastern Indian margin are good hosts for gas-hydrates. The methane within gas-hydrates has been prognosticated to be more than 1500 times of India's present natural gas reserve, which can make India energy self-sufficient. Thus, it was felt necessary to map the prospective zones and evaluate the resource potential of gas-hydrates. The gas-hydrates stability thickness map has been prepared in both these basins. This provides the maximum depth of gas-hydrates occurrences, and helps to identify the bottom simulating reflectors or BSRs, main marker for gas-hydrates, from seismic data. Different attributes such as seismic reflection strength, blanking, attenuation, sweetness and instantaneous frequency have been computed to characterize the gas-hydrate reservoirs. Several approaches based on traveltime tomography, full-waveform inversion, amplitude versus offset modeling, impedance inversion, coupled with rock-physics modeling have been applied to field seismic data. All these will be presented systematically for the delineation and assessment of gas-hydrates in both the KG and Mahanadi basins.

2019038072 Samsonov, Sergey V. (Natural Resources Canada, Canada Centre for Remote Sensing, Ottawa, ON, Canada). High-performance system for monitoring ground deformation from RCM SAR data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract G41B-0688, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Differential Interferometric Synthetic Aperture Radar (DInSAR) based mapping of surface deformation has proven valuable in a variety of geoscience applications. Conventional approaches to DInSAR analysis require significant expertise and are not suited to addressing the opportunities and challenges presented by the large multi-temporal SAR datasets generated by future radar constellations. As a result, the Canada Centre for Mapping and Earth Observation (CCMEO) developed, in support of Natural Resources Canada and Government of Canada priorities, a system for automatic generation of standard and advanced deformation products based on DInSAR technology from RADARSAT Constellation Mission (RCM) Synthetic Aperture Radar (SAR) data. Existing RADARSAT-2 processing algorithms were adapted to RCM specifications and novel advanced processing algorithms were developed to address the large data sets resulting from the constellation's four-day rapid revisit cycle. This permitted expanding the DInSAR functionality across a wide-range of spatial and temporal scales. The system architecture is scalable and can be expanded to serve a large number of clients; it can simultaneously address multiple application areas including natural and anthropogenic hazards, natural resource development, permafrost and glacier monitoring, coastal and environmental change and wetlands mapping.

2019038137 Sayedi, Sayedeh Sara (Brigham Young University, Department of Plant and Wildlife Science, Provo, UT); Abbott, Benjamin; Frederick, Jennifer Mary; Thornton, Brett F.; Vonk, Jorien; Overduin, Pier Paul; Zhang Tingjun; Jafarov, Elchin E. and Schaefer, Kevin M. Expert assessment of organic carbon stocks and vulnerability in subsea permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS11C-1430, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The continental shelves of the Arctic Ocean and surrounding seas contain large stocks of particulate organic matter and greenhouse gases in dissolved, free, and hydrate forms. The quantity of these carbon deposits and their vulnerability to climate change are highly uncertain, though it has been hypothesized that they may influence the global climate system on decadal to centennial timescales. To capture current views on the size and stability of Arctic subsea carbon, we performed an expert assessment of the size, location, and potential responses of subsea carbon to two warming scenarios. While an expert assessment does not provide definitive projections of future system responses, it complements modeling and empirical approaches by synthesizing formal and informal knowledge about the system to inform decision makers and future research priorities. Because such an expert assessment's experimental unit is an individual researcher, each data point represents an integration of quantitative knowledge (e.g. modeling, field, or laboratory data) as well as qualitative information based on professional opinion and personal experience. Participating experts provided qualitative 95% confidence intervals of: 1. Past and current extent of subsea permafrost, 2. Past and current shelf sediment organic matter and greenhouse gas stocks, and 3. Emissions trajectories for two IPCC warming scenarios (RCP2.6 and RCP8.5). They ranked major sources of uncertainty and identified specific research activities that could improve estimates. We compare this assessment with recent empirical and modelled estimates of subsea carbon stocks and vulnerability.

2019040677 Schaedel, Christina (Northern Arizona University, Flagstaff, AZ) and Schuur, Edward. Permafrost carbon network; synthesis science and outreach [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract PA23F-1050, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Permafrost Carbon Network (PCN, URL: http://www.permafrostcarbon.org) is a US sponsored but international network that produces new knowledge through research synthesis quantifying the role of permafrost carbon in driving future climate change. Established in 2010 with initial funding from the National Science Foundation (NSF) Research Coordination Network program, the PCN is a hub for synthesizing emerging data from individual projects, across a range of new measurement programs, and providing updated parameters in support of model assessment and development. PCN activities continued with the same focus in 2015 under the umbrella of the NSF Study of Environmental Arctic Change Program, which itself has a broader focus of the Arctic as a system. Within eight years, the network has grown from 45 scientists to 380 members from 155 institutions and 24 countries. One of the key elements for the high success rate in producing high profile publications within the activities of the PCN is the pairing of early career scientists with more senior scientists. This model creates career opportunities for early career scientists that are motivated for the detail oriented work such as data mining and analysis and provides the expertise from senior scientists that is necessary for the big picture understanding. Member interaction and opportunities for brainstorming occur during a one day open science meeting organized by the PCN the day before the fall meeting of the American Geophysical Union, which has attracted over 100 scientists interested and engaged in synthesis activities. Synthesis science results are published in peer-reviewed literature, presented at national and international meetings and incorporated into global scale reports such as the Intergovernmental Panel on Climate Change in order to disseminate results to a non-export audience. Synthesis information created by the PCN also provides a platform for communicating science results to society via news articles, blog posts, and via online communication, which are all meant to increase science impact to non-experts.

2019040669 Schmidt, Bitney E. (Georgia Institute of Technology, Atlanta, GA); Sizemore, Hanna G.; Duarte, Kayla; Burgess, Isobel; Romero, Vivian; Schenk, Paul; Scully, Jennifer E. C.; Buczkowski, Debra; Hughson, Kynan; Nathues, Andreas; Castillo, Julie C.; Russell, Christopher T. and Raymond, Carol A. The possible role of water and ice in the geology of Ceres' Occator crater [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P24A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Enigmatic Occator crater is the target of the second extended mission (XM2) of NASA's Dawn mission. During XM2 , Dawn reached 35km altitude, permitting the highest resolution Framing Camera images yet of the crater floor. These provide the chance to observe previously identified putative ground ice features in detail, and resolve new ones. Across the floor we observe features morphologically consistent with frost heave, including candidate pingos, potentially effusive ridges, extensional fractures, mounds, and quasi-polygonal hills. Examining regional placement of these features within Occator will improve our understanding of the potential interaction of ice and water within the subsurface of Ceres' regolith. Preliminary analysis shows small mounds present in clusters, many near Occator's central dome, with diameters ranging from 40 to 500m. Many of these domical features possess small pits at their apexes, potentially consistent with collapse or devolatilization. In some places, flows of bright material are sourced from low, asymmetric mounds and candidate pingos, potentially arising from the freezing of ground water within the melt sheet emplaced during Occator's formation. Fractures and ridges are in some cases associated with the presence of these mounds. The fracture systems may be indicative of inflation of the central portion of the crater, as fractures transition into ridges, sometimes topped by irregularly shaped "cap rocks" and putative flows. Further, there is a potential association of a bright mesa with such an "effusive" ridge that may indicate a relationship between deep sources and the cap material. Among the hypotheses these new data can address is the potential role of the freezing and volume expansion in facilitating cracking of the surface and allowing pathways for hydrothermally processed material to reach the surface, creating the diverse morphology we observe. These features within Occator point to the interplay of ground ice and impact processes on Ceres. The emplacement of impact melt consisting of unconsolidated silicates and liquid water or brines in cerean craters creates a unique environment in which 'periglacial' processes driven by freezing and sublimation may co-occur orhybridize with 'cryovolcanic' processes, blurring the conventional usage of these terms.

2019040619 Schuur, E. (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); McGuire, A. D. and Romanovsky, V. E. Arctic and boreal carbon; key findings from the state of the carbon cycle report [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B43C-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Factors that control terrestrial carbon storage in unmanaged arctic and boreal ecosystems are changing. Surface air temperature change is amplified in high-latitude regions, as seen in the Arctic where temperature rise is about 2.5 times faster than that for the whole Earth. Permafrost temperatures have been increasing over the last 40 years. Disturbance by fire (particularly fire frequency and extreme fire years) is higher now than in the middle of the last century. Soils in the northern circumpolar permafrost zone store 1,460 to 1,600 petagrams of organic carbon (Pg C), almost twice the amount contained in the atmosphere and about an order of magnitude more carbon than contained in plant biomass (55 Pg C), woody debris (16 Pg C), and litter (29 Pg C) in the boreal forest and tundra biome combined. This large permafrost zone soil carbon pool has accumulated over hundreds to thousands of years, and there are additional reservoirs in subsea permafrost and regions of deep sediments that are not added to this estimate because of data scarcity. Following the current trajectory of global and Arctic warming, 5% to 15% of the organic soil carbon stored in the northern circumpolar permafrost zone (mean 10% value equal to 146 to 160 Pg C) is considered vulnerable to release to the atmosphere by the year 2100. However, a recent model intercomparison project suggested that additional plant carbon uptake, growth, and deposition of new carbon into soil would together completely offset any soil carbon loss this century, and that it would take several centuries before cumulative losses from soils would overwhelm new carbon uptake. However, model projections do not always match current empirical measurements or other assessments, suggesting that structural features of many models are still limited in representing Arctic and boreal zone processes. At the same time, the intercomparison indicated that future scenarios with limited human greenhouse gas emissions would reduce changes to high latitude ecosystems. Together, the loss of carbon from thawing permafrost soils and disturbance by fire in combination with offsetting plant uptake response determines the net effect of high latitudes on the carbon cycle of both North America and the globe.

2019040667 Senger, Kim (University Centre in Svalbard, Department of Arctic Geology, Longyearbyen, Norway); Betlem, Peter and Hodson, Andrew J. 3D thermo-baric modeling of the gas hydrate stability zone of central Spitsbergen, Arctic Norway [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS51F-1314, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Dissociation of onshore natural gas hydrates could lead to the release of methane directly to the atmosphere. This is particularly alarming in the Arctic that experiences enhanced warming compared to more temperate latitudes. The Norwegian high-Arctic Svalbard archipelago offers 1) the presence of relatively thick permafrost giving suitable thermo-baric conditions within the gas hydrate stability zone (GHSZ) and 2) an active petroleum system. The recent discovery of natural gas in direct association with permafrost in Adventdalen provides clear evidence for recent gas migration, and motivated us to consider whether some of this gas could also occur as natural gas hydrates. We thus present a comprehensive assessment of the GHSZ in central Spitsbergen spanning the onshore and near-shore (fjords) settings. We utilize a novel approach incorporating 3-dimensional parameterization of temperature, pressure and the gas hydrate phase boundary. Our base case model employed a constant geothermal gradient of 33°C km^-1 with a laterally varying surface temperature, a 93:7 methane-ethane mixture and a pore water salinity equivalent to sea water. This resulted in an up to 650 m thick (mean: 308 m) GHSZ covering 74.8% of the study area and thickening significantly to the east where the climate is colder. We quantify the uncertainty range of the GHSZ maps by perturbing base case parameters with data-driven constraints. The largest changes in the GHSZ were observed when either the ethane content or the regional pore water over-pressure were increased (to 20% and to 125% hydrostatic pressure, respectively), or when the geothermal gradient was reduced to 26°C km^-1. The GHSZ was almost completely inhibited (by ca. 98%) in the presence of a dry gas (100% methane), greater salinity (50 ppt), or an increase in subsurface temperatures relative to the mean annual air temperature (e.g. by 2°C). While deep burial greatly reduced overall reservoir properties, fractured sandstones of Paleogene, Cretaceous and Late Triassic-Middle Jurassic age all lie partly within the GHSZ and may represent possible reservoirs. We conclude that there is high potential for natural gas hydrate in central Spitsbergen and a dedicated exploration effort is needed to find and characterize natural hydrate deposits onshore Spitsbergen.

2019037803 Shi, Hao (Auburn University, School of Forestry and Wildlife Sciences, Auburn, AL); Tian, Hanqin; Yao, Yuanzhi and Pan, Shufen. Effects of cyclic freezing-thawing on greenhouse gas emissions in permafrost regions [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2555, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Global warming has been profoundly affecting ecosystem processes, particularly accelerating the greenhouse gas emissions (CO₂ and CH₄) from the permafrost regions. Considering the substantial quantities of the frozen carbon pool, it is critical to quantify the timing and the rate of permafrost carbon release to the atmosphere. Accurate capturing the cyclic freezing-thawing (F-T) process is a key step. Within the framework of the Dynamic Land Ecosystem Model (DLEM), we introduce a subroutine for disaggregating daily temperature and radiation into an hourly time-step, to simulate sub-daily F-T cycles. Soil surface temperature, as the boundary condition for heat transfer and phase change processes along the soil profile, is estimated based on air temperature, leaf area index, litter and snow depth. A perched water table is then built above the permafrost layer. The soil organic carbon stored in the active thawing layer is calculated using a vertical distribution function with the loss of fine roots during previous freezing accounted. The CO₂ and CH₄ fluxes are then estimated as a function of soil water content and temperature. At the site level, filed observations of soil moisture, biomass, CO₂ and methane fluxes collected in the Arctic-Boreal Vulnerability Experiment (ABoVE) project are used to calibrate and validate the model. At a regional scale, satellite retrievals of land surface temperature, soil moisture, snow cover, snow depth and surface F-T status are used to compare with the model. Our work could effectively contribute to the understanding of the permafrost carbon dynamics and their feedback to climate change.

2019037872 Shirley, Ian (Lawrence Berkeley National Laboratory, Berkeley, CA); Dafflon, Baptiste; Chafe, Oriana; Akins, Hunter; Biraud, Sebastien; Hanson, Chad V.; Torn, Margaret S. and Hubbard, Susan. Linking surface and subsurface behaviors; UAV-based multi-spectral imagery as predictor of soil wetness, thaw depth and soil respiration in an Arctic watershed [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1065, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic ecosystems are characterized by fine-scale heterogeneity of surface and subsurface structure, with differences in hydrological conditions, soil physical properties, and vegetation cover that strongly influence the distribution of soil carbon content and fluxes across a watershed. This spatial variation poses a unique challenge to upscale soil carbon content and flux measurements from the sub-watershed scale to the regional scales that are used in full-scale climate models. This study links surface and subsurface properties at a discontinuous permafrost site in a Seward Peninsula watershed near Council, AK. We performed a vegetation classification and hydrological stream flow analysis from, respectively, a multi-spectral mosaic and Digital Surface Model (DSM), both inferred from data obtained by a low-altitude Unmanned Aerial Vehicle (UAV). We also performed ground-based measurements of soil temperature using a Distributed Temperature Profiling (DTP) system, soil electrical conductivity (as a proxy for soil wetness) using an electromagnetic sensor, and of soil respiration using gas flux chambers at points across the site. Correlations between these ground-based and aerial measurements were explored with an emphasis on understanding linkages that will be useful for upscaling. We found that the remotely sensed products could be effectively used to distinguish between areas of significantly different subsurface and biogeochemical characteristics. Topography, plant type, and surface wetness are linked and can be used to predict significant differences in active layer depth, carbon dioxide, and methane emissions. The observed connections between surface and subsurface properties at this intermediate scale will be critical in future attempts to characterize entire watersheds in the Seward Peninsula with remotely sensed data products.

2019040584 Shupe, M. (NOAA, Cooperative Institute for Research in Environmental Sciences, Boulder, CO) and Persson, Ola P. G. The impacts of Arctic liquid water clouds on surface and sub-surface fluxes in northern Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A23B-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The surface energy budget over Arctic terrestrial surfaces largely controls the state of soil temperatures and permafrost below. Atmospheric drivers are primarily responsible for variability in the surface energy budget, with one of the strongest contributors being clouds. In recent years, Arctic stratiform, liquid-containing clouds have been shown to form and persist over long periods via a complex web of interactions and feedbacks within the climate system. Moreover, these clouds are known to have particularly strong interactions with atmospheric radiation that can elicit other energetic responses in the atmosphere-surface system. This presentation examines the specific role that liquid water clouds at Barrow, Alaska play in determining the local surface energy budget and sub-surface heat fluxes. Ground-based sensors are used to derive the surface radiative, turbulent, and sub-surface heat fluxes. Clouds are identified using a combination of active and passive remote sensors at the surface, while liquid water clouds are identified using microwave radiometer retrievals. The cloud forcing for each energy flux term is examined by comparing the flux at times when liquid clouds are present versus times when they are not, while scaling by the fractional occurrence of liquid clouds. Annual cycle statistics reveal seasonally varying responses to cloud radiative forcing that are dependent on factors such as the solar input, snow on the surface, and soil temperature. All of these processes are essential to represent for models to accurately capture the myriad ways in which clouds impact the changing Arctic system.

2019038061 Singh, Deepali (Jawaharlal Nehru University, School of Environmental Sciences, New Delhi, India); Singh, Priyadarshni; Roy, Nidhi and Mukherjee, Saumitra. Identification of potential desiccated polygons in the equatorial region of Mars; hints of recent liquid water activities [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23F-2386, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Desiccation of lake sediments, repeated freezing and thawing of the soil in periglacial environments, thermal contraction of permafrost and tectonic stress have been known to produce polygonal patterned grounds on Earth. Presence of these patterned grounds on Mars is indicative of liquid water activities, ice distribution, recent events of thawing and its climate, in general. Although similar structures have been found in abundance at the poles and higher latitudes, there have been fewer occurrences at lower latitudes. In this study, we report four different kinds of polygonal patterns in the equatorial region. High resolution HiRISE images (0.3 m/pix) were used to study their morphology. Fractured terrain within the Huygens basin is around 10-15 m with polygonal to rectangular appearance. It is distributed with numerous Martian 'blueberries' or hematite concretions similar to the polygonal cracks found in Endurance crater. Three types of polygonal cracks were identified in the inter-crater depression towards the north of Huygens. These structures ranged between 10-30 m and in proximity with valley networks and gullies. They resembled the polygonal desiccated polygons (PDPs) previously reported in Nili Fossae and Libya Montes. PDPs are typically found in dried lake beds on Earth when water evaporates leaving behind minerals known as evaporites. The three types of polygonal cracks showed different salt encrustation patterns and thermal signatures in THEMIS IR-Day image. This along with their stratigraphic positioning of hints towards their different origin. CRISM data analysis shows signatures of phyllosilicates and water ice in the area. The presence of clay minerals in a depression signifies a long standing body of water which could be of interest for future exploration missions. Studies interpret Mars to be generally cold and dry with episodic melting events. Presence of different PDPs in close vicinity suggests different formation times. This further implies presence of liquid water in the equatorial region in the recent past and microclimate fluctuations.

2019040668 Singhroha, Sunny (University of Tromso-Arctic University of Norway, Department of Geosciences, Tromso, Norway); Bünz, Stefan; Chapman, Mark; Wu, Xiaoyang; Chand, Shyam and Plaza-Faverola, Andreia Aletia. Analysis of fracture/fault filled gas hydrate deposits in the Vestnesa Ridge [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS51F-1322, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Gas hydrates, crystalline ice-like solids that trap gases, mainly methane, form under suitable temperature and pressure conditions in continental margins and permafrost settings. Shallow marine sediments (up to 190-195m depth below the seafloor) of the Vestnesa Ridge on the western Svalbard margin fulfill the requirements for the formation of gas hydrates. Previous studies in the region hint towards the presence of gas hydrates in fractures/faults. We perform azimuthal seismic velocity analysis using multicomponent ocean bottom seismic (OBS) data to study the occurrence of gas hydrates in fractures and faults. Analysis of azimuthal seismic velocities at two OBS sites show seismic anomalies along fault azimuths and changes in the seismic velocities across the fault, thus, potentially suggesting the presence of gas hydrates in fractures and faults and their potential role in the distribution of gas hydrates and free gas. Furthermore, we study the effect of the presence of gas hydrates in fractures and faults on seismic velocities using Hudson's model and model the sensitivity of seismic velocities to the orientation of gas hydrate filled fractures and faults. We also evaluate uncertainties in gas hydrate saturation estimates due to uncertainties in the gas hydrate distribution (gas hydrates in pore spaces or fractures and faults under different orientations) and morphology (pore filling or load bearing). Results from this analysis suggest strong structural control on the presence of gas hydrates along the Vestnesa Ridge.

2019038101 Song Chunlin (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China) and Wang Genxu. Variations of pCO₂, DIC and d¹³C-DIC in the Yangtze River headwater catchments [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC43K-1722, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

It's well known that riverine dissolved inorganic carbon (DIC) exports accompanied by CO₂ evasion play central roles in the regional and global carbon cycle, yet the processes remain poorly understand. In this study we examined the partial pressure of CO₂ (pCO₂), DIC export and stable carbon isotope composition of DIC (d¹³C-DIC) in the Yangtze River headwater catchments of the Tibetan Plateau. The Yangtze river source region (Zhimenda station upstream) export 0.485 Tg C of DIC annually, which account for 91% of total dissolved carbon. Enriched average d¹³C-DIC values (-4.485 ppm to 1.027 ppm) indicated the DIC in this region is dominated by geogenic source. We found that all the studied catchments were characterized with supersaturated CO₂, with average pCO₂ values from 640 to 1418 matm. The highest pCO₂ values were found in the baseflow-dominant period, indicating the impact of flow path on pCO₂ value. The spatial variability in pCO₂ across streams was positively related to permafrost cover, along with depleted d¹³C-DIC in the high permafrost cover catchments. Enhanced negative correlations between pCO₂ and d¹³C-DIC along the downstream gradients suggesting carbon dioxide evasion caused the stable carbon isotope fractionation of DIC and processing of DIC along river channel. These results provide new understanding of the carbon transport mechanisms of the Yangtze River headwaters.

2019040642 Steiner, N. (City University of New York City College of New York, New York, NY); Podest, E.; Davitt, Aaron Walter Darwin; Brown, M. G. and McDonald, K. C. Monitoring seasonal soil frost dynamics in boreal-Alaska ecosystems with multi-frequency radiometer observations [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1786, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The seasonal landscape Freeze/Thaw (F/T) cycle profoundly affects surface meteorological conditions, ecological trace gas dynamics, energy exchange and hydrologic activity. Satellite products that estimate F/T state often provide a binary representation of the bulk landscape as observed in the sensor footprint- i.e. the integrated soil-snow-vegetation continuum. A more detailed F/T product is needed to interpret complex seasonal ecosystem processes such as net primary production and net ecosystem CO2 exchange whose dynamics are controlled by F/T transitional processes in individual landscape components (e.g. soil, vegetation). We present initial results for a radiometer-based satellite product that that delineates the primary F/T state of the landscape condition as well as individual states of the snow, soil, and bulk land surface. We demonstrate the utility of the Soil Moisture Active Passive (SMAP) radiometer data to characterize soil frost depth (i.e. depth of thaw) for cold soils in boreal-Alaska ecosystems. We present SMAP (L-Band) brightness temperature observations alone and together with higher frequency radiometer data from Advanced Microwave Scanning Radiometer (AMSR2), enabling use of microwave frequency spectral gradients (SG) near L-band. Microwave emission modeling is used to interpret and provide physical basis for satellite observations. Our modelling efforts consider a multilayer soil and snowpack that snowmelt in the snow and dielectric changes related to soil F/T with depth. Modeling results illustrate the expected changes in brightness temperatures that occur during seasonal transitional changes in the state of water (e.g. snowmelt and soil thaw). Distinct temporal and frequency signatures, or transitions, in observations are linked to physical hydrologic processes at the surface, namely, freeze/thaw transition, snowmelt, soil-thaw, soil-refreeze and the establishment of a seasonal snowpack. Ground measurements from the SnoTEL station network and our unique biophysical datasets of land surface component temperature collected along our Alaska Ecological Transect (ALECTRA) are used to support our approach and to assess and validate the derived frost dynamics datasets. In particular we highlight the sensitivity of SG to seasonal refreeze of the active layer for permafrost soils for ALECTRA sites, including sensitivities and relative accuracy of this approach. Portions of this work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

2019037777 Strauss, Jens (Alfred Wegener Institute, Center for Polar and Marine Research, Permafrost Research Section, Potsdam, Germany); Mann, Paul James; Bedington, Michael; Grosse, Guido; Mollenhauer, Gesine; Ogneva, Olga; Overduin, Pier Paul; Polimene, Luca and Torres, Ricardo. Changing Arctic Carbon cycle in the Coastal Ocean Near-shore (CACOON); a new project on the changing Arctic coast [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2487, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

No other region has warmed as much or as rapidly in the past decades as the Arctic. A new project, CACOON, will investigate how the ecosystems are influenced by this warming. Funded by the British Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF), CACOON will also help to better predict changes to the Arctic coastal-marine environment. Arctic rivers annually carry around 13% of all dissolved organic carbon transported globally from land to ocean, despite the Arctic Ocean making up only approximately 1% of the Earth's ocean volume. Arctic shelf waters are therefore dominated by terrestrial carbon pools, so that shelf ecosystems are intimately linked to freshwater supplies. Arctic ecosystems also contain perennially frozen carbon that may be released by further warming. Climate change already thaws permafrost, reduces sea-ice and increases riverine discharge over much of the pan-Arctic, triggering important feedbacks. The importance of the near-shore region, consisting of several tightly connected ecosystems that include rivers, deltas, estuaries and the continental shelf, is however often overlooked. We need year-round studies to be able to predict the impact of shifting seasonality, fresher water, changing nutrient supply and greater proportions of permafrost-derived carbon on coastal waters CACOON addresses this knowledge gap by investigating the near-shore regions of the two major Arctic rivers, the Lena and Kolyma, which together drain 19% of the pan-Arctic watershed area. CACOON will quantify the effect of changing freshwater export and terrestrial permafrost thaw on the type and fate of river-borne organic matter delivered to Arctic coastal waters, and the resultant changes to ecosystem functioning in the coastal Arctic Ocean. We will achieve this though a combined observational, experimental and modelling study. We will conduct laboratory experiments to parameterize the susceptibility of terrigenous carbon to abiotic and biotic transformation and losses, then use the results from these to deliver a marine ecosystem model of the major biogeochemical cycles of carbon, nutrients and organic matter cycling in these regions.

2019038091 Streletskaya, Irina D. (Lomonosov Moscow State University, Geography, Moscow, Russian Federation); Kizyakov, Alexander I.; Günther, Frank; Zimin, Mikhail V.; Sonyushkin, Anton V. and Wetterich, Sebastian. Rates of coastal destruction in areas of tabular ground ice occurrence in the western Russian Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1398, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Tabular ground ice bodies are widely spread on Eurasian and North American Arctic plains. Exposed tabular ground ice in coastal bluffs favors the activation of thermal abrasion and thermal denudation, which in turn causes increasing coastal destruction rates. Thermo-denudation under conditions of ground ice exposures includes thawing of ice and frozen sediments along retreating headwalls of retrogressive thaw slumps and their constant enlargement. Thermo-cirques and thermo-terraces are two basic landform types that either feature channelized or broad open outlets, depending on the initial ice body outcrop by the denudation processes inland or in the retreating coastal bluffs. We study key-sites on Kolguev Island (Barents Sea) and on Yugorsky Peninsula (Kara Sea), continuing and extending earlier research efforts on coastal dynamics in the region. New data on thermo-denudation and thermo-abrasion rates for these key-sites have been obtained using a set of multi-temporal satellite images of high and very-high spatial resolution covering the period from 2002 to 2016. For orthorectification purposes of imagery collected prior to TanDEM-X acquisitions, we used an edited version of the 12 m TanDEM-X DEM. Along erosive coastline segments the former relief situation was reconstructed through extrapolation of coastal bluff edge elevation values and restoration of the coastal plain relief towards the sea. On the western coast of Kolguev Island, average coastal bluff retreat rates between 2002 and 2012 varied from 1.7 to 2.4 m/year, while averaged rates of thermo-cirques headwalls retreat were 2.6 m/year. Maximum rates at some sections increased up to 14.5-15.1 m/year in the recent past. High rates of thermo-denudation increase were not only observed on western Kolguev Island, but also on the Yugorsky Peninsula, were rates raised up to 13 m/year in recent years. Activation of thermo-denudation is also noted in other parts of Kara Sea coasts and were generally correlated with changing environmental factors, particularly expressed in an increase on the thaw index during recent years. Supported by RFBR grants # 18-05-60080 (coastal destruction rates estimation), 18-05-60221 (method of satellite images orthorectification, based on reconstructed DEM) and DFG grant # WE 4390/7-1.

2019038094 Streletskaya, Irina D. (Lomonosov Moscow State University, Geography, Moscow, Russian Federation); Leibman, Marina O.; Vasiliev, Alexander and Kizyakov, Alexander I. Permafrost gas emission craters as a result of methane release from the massive tabular ground ice, Northwest Siberia [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1402, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Massive Tabular Ground Ice (MTGI) is widely present in West Siberia lowlands north of 68N. The MTGI deposits were formed as a result of rapid freezing of exposed marine sediments of fast retreating Pleistocene sea basin and preserved mineral, marine salts, ice, water, organic and gas components. The MTGI are found at the -30 to +50 m asl and overlain by the terrestrial ice rich sediments with syngeneic ground ice wedges or marine ice-rich deposits. The lower boundary of ice within the permafrost profile corresponds with the lower boundary of MTGI. Methane of bacterial genesis is the major gas component within the MTGI. Due to permafrost degradation from below, the ice is melting allowing gas and saline water (cryopegs) to occupy the newly developed pockets within the permafrost. The pressure conditions in such pockets depend on ground composition, and relative ratio of various components, including water, gas, and cryopegs. Under warming climatic conditions, increase of permafrost temperature decreases the mechanical ability of permafrost to effectively support the pressure. This can lead to pressure release in locations where the sediments have the least resistance leading to formation of so-called permafrost gas emission craters. Permafrost gas emission craters can be hazardous to engineering explorations, as variability of localized conditions limits predictions of areas where they may form. The only indicative characteristic, which is not usually easy to determine, is near-surface presence of MTGI. Under projected climatic conditions, we expect to see an increase of number on permafrost gas emission craters in the northern permafrost regions of Siberia, while the southern regions, where MTGI will degrade will have decreasing number of occurrences. This work was funded by the RFBR grants 18-05-60080 and 18-05-60004.

2019038095 Streletskiy, Dmitry A. (George Washington University, Geography, Washington, DC); Suter, Luis and Shiklomanov, Nikolay I. The direct cost of terrestrial permafrost degradation to the Arctic countries by mid-21 century [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33E-1403, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost plays an important role in functioning of natural ecosystems and is critical for construction in maintenance of the infrastructure in the Arctic regions. Observations show that following rapidly changing climatic conditions, the near surface permafrost temperature is increasing across the circumpolar Arctic. The active layer, the layer of soil just above the permafrost, which is subjected to seasonal freezing and thawing, is also increasing. These rapid climate-induced changes in thermal and physical properties of terrestrial permafrost may result in additional direct costs associated with maintaining the present level of infrastructure. These costs are expected to adversely affect local, regional and state budgets of the Arctic countries. This study uses publicly available inventories of six major types of infrastructure to estimate potential costs of replacing permafrost infrastructure at risk of damaged due to climatic changes projected by the mid-21 century over the circumpolar Arctic. Outputs form six CMIP5 models were used as forcing to permafrost-geotechnical GIS-based model to estimate climate-induced changes in permafrost properties between present decade (2005-2015) and mid-21 century (2050-2059) under RCP8.5 scenario. The lifecycle replacement and stressor-response models were used to assess potential damages associated with specific environmental stressors, such as increase in precipitation, decrease of foundation bearing capacity, and ground subsidence as well as to estimate costs associated with these damages. According to our estimates the projected combined cost to the Arctic economy was found to be USD ~40 bil, but there is substantial regional variability of types of infrastructure affected as well as the ability of regional budgets to absorb these costs.

2019038055 Strzelecki, Matt C. (University of Wroclaw, Institute of Geography and Regional Development, Wroclaw, Poland); Lim, Michael; Kasprzek, Marek and Swirad, Zuzanna M. Arctic rocky coastal zone responses under a rapidly changing climate [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2354, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The warming of Arctic transformed circumpolar coastal zone with major impacts on the acceleration of coastal erosion and destabilization of coastal permafrost directly affecting safety of Arctic communities. Recent years have brought major advances in our understanding of Arctic coastal processes operating in longer ice-free periods and adapting to accelerated sediment supply from degrading Arctic landscape. However, the major progress in Arctic coastal research was achieved along ice-rich permafrost coasts of Siberian, Alaskan and NW Canadian seas with only limited progress in rocky coastal environments typical of numerous still glaciated Arctic islands such as Canadian Arctic Archipelago, Greenland or Svalbard. This is a significant research gap as over a third of Arctic coastlines are rock dominated and it is expected that future Arctic infrastructure development will concentrate on rocky coasts recognised as more stable than unlithified permafrost shores. Here we revisit a rare, well-constrained quantitative study of Arctic rocky coastal zone evolution conducted in the late 1950s in south-western Svalbard with new multiscale, high-resolution surveys over a 4 year monitoring period. Our data indicate that small (<1´10^-6 m³) changes respond distinctly from those of larger, more readily detected cliff failures, potentially altering geomorphic responses. Contrary to an expected acceleration in erosion rates, we establish a reduction in rock cliff recession (ranging from 37% to 80%) over the 60 year timeframe. We propose that this reduction is indicative of a change from cryogenic processes to marine dominated behaviour, more akin to lower latitude environments. We support this through novel thermographic characterisation, geophysical surveying, geotechnical tests and thermodynamic monitoring, noting rock surface layer sensitivity to both global and local influences and exploring regional variations in coastal process zones of Svalbard, an area of unique climate sensitivity within the High Arctic region. Acknowledgements: This is a key contribution to the National Science Centre in Poland project 'POROCO - Mechanisms controlling the evolution and geomorphology of rock coasts in polar climates' (UMO2013/11/B/ST10/00283) awarded to M.C.S.

2019040636 Sturm, M. (University of Alaska Fairbanks, Fairbanks, AK). Cold roots; the emergence of cryospheric science from the Heroic Age of polar exploration [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C24A-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The first cryospheric scientists may have been the indigenous people of the Arctic. By 1500 Western explorers were pushing into the Arctic, and by 1770 into the Antarctic. Both groups found that survival and success depended on an innate understanding of the snow, ice, permafrost and glaciers that characterized the polar regions. Eventually, societal norms required that these geographic exploration efforts should include scientific studies as well, and with that formal cryospheric studies began. This will be a selective retrospective of how polar exploration (and high-altitude mountaineering) led to today's world of cryospheric studies, with some comment about how those roots still manifest in our science efforts today.

2019038121 Sudakov, Ivan (University of Dayton, Dayton, OH). Spatiotemporal dynamics of lakes/ponds in the Arctic; a statistical physics perspective [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NG41B-0945, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

During the summer melt season, lakes and ponds in the Arctic (melt ponds on sea ice, thermokarst lakes in tundra etc.) display a complex geometry. Casual inspection of remote sensing images shows that the lake/pond phase of Arctic landscape undergoes a transition where disconnected lakes evolve into much larger scale connected networks with complex boundaries. Spatiotemporal dynamics of lakes and ponds is crucial for the stability of the Arctic climate system and its positive feedback. Here, we will explore how the models and approaches arising in statistical physics can be used to efficiently characterize spatiotemporal dynamics of lakes and ponds and quantify their contribution to climate feedback. First, we will discuss a machine learning technique for segmentation of lakes observed in historical maps and satellite imagery. The proposed technique combines color thresholding, Mahalanobis Distance measuring, region growing and support vector machine classifier. It allows us to detect and segment the lakes, compute area and perimeter values and fractal dimension that characterized the complex lake geometry. Next, we will consider how the percolation and Ising-like models can be employed to describe spatiotemporal dynamics of lakes/ponds. The models reveal that such lake/pond patterns exhibit metastable states of the system, where the binary variable assigned as frozen state or thaw state. Finally, we will show how to parametrize simple climate models taking into account spatiotemporal dynamics of lakes/ponds.

2019038125 Sullivan, Taylor D. (University of Wyoming, Laramie, WY); Parsekian, Andy; Schaefer, Kevin M.; Michaelides, Roger J.; Westenhoff, John H.; Schaefer, Sean and Douglas, Thomas A. Geophysical investigation of soil moisture distribution and behavior in permafrost soils from interior Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Temperatures in Arctic regions are increasing at twice the rate of those in equatorial regions; this merits concern because the thawing and release of carbon contained in permafrost can influence climate, and permafrost projection models vary greatly in their predictions of permafrost extent and the amount of carbon that will be released during future thaw. Active Layer Thickness (ALT)-a measure of the seasonal thaw depth in the upper-portion of permafrost-serves as a climate variable to monitor permafrost conditions. This study considers the seasonal development of soil moisture distribution within ALT to help constrain permafrost predictions that will inform carbon cycle response to changing global climate. To address the question of how soil moisture distribution within the soil column evolves throughout a thaw season and influences ALT, we utilize geophysical techniques including time domain reflectometry (TDR) and nuclear magnetic resonance (NMR). TDR methods-including Ground Penetrating Radar (GPR) and hand-held soil moisture probes (HSIIs)-yield information about electromagnetic wave propagation velocity which can be used to calculate the dielectric constant of a medium (indicative of soil moisture). Borehole NMR (BNMR) measurements reveal information about water content and relative pore sizes distributions of bound versus unbound water throughout the soil column. Lab-NMR measurements on synthesized- and field- soil samples with varying degrees of saturation and thaw serve as a basis of comparison for BNMR field data from five boreholes in the Alaskan interior. Results from lab-NMR suggest that, in Fairbanks silt, water resides in differing pore spaces throughout freeze/thaw processes. In the field, higher water contents are apparent in organic soils compared to mineral soils. Additionally, S_w information from borehole core samples, BNMR, and HSII measurements aids in interpretation of GPR-derived S_w measurements along survey lines across interior Alaska. Results from this investigation constrain key parameters of soil-freezing- and remote-sensing- models of S_w and ALT, which in turn inform the response of permafrost processes to warming global temperatures.

2019038113 Tang, Weigang (McMaster University, School of Geography and Earth Sciences, Hamilton, ON, Canada) and Carey, Sean. Detection of shifting flow regimes for watersheds in western North America using deep learning techniques [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H21J-1775, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Changes in the flow regimes of rivers driven by climate change has considerable implications for aquatic organisms and water security, and is a major hydrological challenge this century. Whereas changes in temperature and precipitation patterns will strongly influence flow volume and timing, in cold regions watersheds, these changes are enhanced due to the existence of cryosphere features (e.g. snow, permafrost and glaciers). Changes to cryosphere extent over time will result in numerous possible changes in flow regimes as the rain/snow transition changes, snowpacks diminish, glaciers recede and permafrost thaws. Traditionally, shifts in flow regime are identified and quantified using the Mann-Kendall test, a widespread statistical approach for trend analysis, with a selection of hydrometrics derived from long-term, continuous hydrographs (i.e. mean flows, peak flows) tested for change. However, it is difficult to design a set of hydrometric indices that are capable of fully characterizing the overall shift of flow regimes, which requires considerable domain expertise. Deep Learning (DL), a state-of-art machine learning algorithm, is able to self-learn and self-design a set of features from raw flow data to effectively characterize, differentiate, and classify flow regime in an optimal manner. In this work, a DL model is trained with a selection of Annual Daily Hydrographs (ADHs) aiming to accurately recognize the primary flow regimes in western North America. In addition to gauged flow data, a large number of artificially-generated ADHs that resemble the natural flow regimes are included to expand the size of training dataset, consequently boosting the DL's performance. The ADHs of the watersheds in this region are classified using this trained DL, and the class membership of ADHs are arranged in yearly order for every watershed. Class transition of ADHs explicitly indicates the shift in flow regime. This new approach provides an alternative way to examine changes of watershed hydrology that is subject to overall shift of flow regime and is not contingent upon a selected flow parameter. Furthermore, this intensively-trained DL model provides a powerful and convenient tool to recognize and classify the flow regime type of any given hydrograph.

2019032002 Tank, Suzanne E. (University of Alberta, Edmonton, AB, Canada); Zolkos, Scott; Shakil, Sarah; MacDonald, Erin; Lung, Liyung Joanna; Hutchins, Ryan H. S.; Bonsal, Barrie; Holmes, Robert Max; Kokelj, Steve; McClelland, James W.; Olefeldt, David; Quinton, William L.; Spence, Chris; Striegl, Robert G. and Yang, Daqing. Landscape legacies and the biogeochemistry of surface waters in permafrost affected terrains [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23C-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw is increasingly causing materials locked in frozen soils to enter contemporary biogeochemical cycles, while also fundamentally altering how water flows across landscapes. From a carbon cycle perspective, this means that we expect greater opportunity for both organic matter mineralization and chemical weathering as organic carbon and minerals from permafrost soils are able to enter the aquatic continuum. However, although these changes in biogeochemical function are agreed upon in a general sense, we have a much weaker understanding of how they might vary regionally, particularly in the systematic fashion necessary for large-scale modelling efforts. Ultimately, it is the interaction between local factors such as the chemical composition of permafrost soils, landscape attributes including topography, ground ice content, and surficial geology, and connections between terrestrial and hydrologic systems that will determine region-to-region variation in the biogeochemical effects of thaw. This talk will use compositional measures of stream and permafrost thaw waters from across the Canadian north to consider landscape drivers of surface water biogeochemistry in permafrost-affected terrains. In the ice-rich, till-dominated western Canadian Arctic, substantial hillslope thermokarst is altering sediment regimes and causing particles to dominate and mediate the biogeochemical response, while also enabling a switch in carbon cycle function towards one that is governed by inorganic processes. Throughout the Canadian north, ecoregion attributes fundamentally regulate the abundance, and relative importance of the species participating in carbon cycle reactions, and this region-to-region variation appears to also control whether various carbon species increase or decrease as permafrost extent declines. Moving towards a systematic understanding of how permafrost thaw will play out across aquatic systems requires research efforts that span scales from pore waters to watersheds, and encompass broad geographic variability. Only with multi-disciplinary collaborative efforts will we begin to be able to bridge this gap.

2019037818 Tansey, Peter (University of New Hampshire, Durham, NH); Persson, Andreas; Spry, Erin; Chanton, Jeff; Johnson, Joel E. and Varner, Ruth K. Carbon transport in a subarctic permafrost peatland catchment area [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2585, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic and subarctic regions are experiencing the effects of a warming climate faster than other regions around the globe. As circumarctic regions warm the annual freeze-thaw cycles of permafrost areas are changing, causing an increase of the annually thawed active layer depth (ALD). As the ALD increases previously inaccessible terrestrial carbon (C) stores become hydrologically active. The C from these stores is transported in the forms: dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC). A fraction of the transported C is consumed by microbial organisms, then transformed into the greenhouse gases carbon dioxide (CO₂) or methane (CH₄). C transport through arctic watersheds has been demonstrated to be an understudied, yet important link to the global C budget. Stordalen Mire is a permafrost peatland area located in the discontinuous permafrost zone. The hydrology of Stordalen Mire is comprised of streams, ombrotrophic bogs, minerotrophic fens, and lakes. As the permafrost thaws and the landscape changes the total C budget for the system is also impacted. Net C export from the mire is expected to increase as the ALD increases, permafrost formations collapse, and connectivity between previously hydrologically isolated areas increase. This study monitors stream parameters and samples DOC from nine nested catchment areas around Stordalen Mire, and samples POC at the Mire and the surrounding lakes. Physical factors such as pH, specific conductivity, and temperature were also sampled at each site of water collection. In addition to water sampling, remote sensing data was collected at a sub-set of the sampling sites in an attempt to relate vegetation cover types to the concentration of DOC sampled. The POC collected from these sites will be C dated to determine the age of accessible C stores. This will help to improve understanding of what factors drive the increased C export. Such as whether old C stores are now accessible due to thawing permafrost or if the increased hydrologic connectivity of the area is transporting recently deposited C. The data collected during this study will be compared to samples taken a decade ago. This comparison will give insight on the timescale for which change occurs in sub-arctic regions.

2019037854 Tao, Jing (University of Maryland at College Park, College Park, MD); Koster, Randal D.; Reichle, Rolf H.; Forman, Barton A.; Xue, Yuan; Chen, Richard H. and Moghaddam, Mahta. Permafrost variability over the Northern Hemisphere based on the MERRA-2 reanalysis [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51B-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

This study introduces and evaluates a comprehensive, model-generated dataset of Northern Hemisphere permafrost conditions. Surface meteorological forcing fields from the Modern-Era Retrospective Analysis for Research and Applications-2 (MERRA-2) reanalysis data were used to drive an improved version of the land component of MERRA-2 in middle-to-high northern latitudes from 1980 to 2017. The resulting simulated permafrost distribution across the Northern Hemisphere captures well the observed extent of continuous permafrost except in Western Siberia, which is permafrost-free in the simulation. Noticeable discrepancies also appear along the southern edge of the permafrost region where sporadic and isolated permafrost types dominate. The evaluation of the simulated active layer thickness (ALT) climatology against in-situ measurements demonstrates reasonable skill except in Mongolia. In northern Alaska, both ALT retrievals from airborne remote sensing for 2015 and the corresponding simulated ALT exhibit reasonable accuracy vs. in-situ measurements. However, the remotely sensed ALT retrievals generally demonstrate lower levels of spatial variability than both the observed and simulated ALT. Controls on the spatial variability of ALT are examined with idealized numerical experiments focusing on northern Alaska; meteorological forcing and soil type are found to have dominant impacts on the spatial variability of ALT, with vegetation also playing a role through its modulation of snow accumulation. A correlation analysis further reveals that accumulated air temperature and maximum snow water equivalent (SWE) explain most of the year-to-year variability of ALT nearly everywhere over the model-simulated permafrost regions. Simulated ALT trends from 1980 to 2017 indicate that some permafrost areas are experiencing significant degradation, with ALT increasing up to 0.5 cm/year.

2019031993 Taylor, Meghan (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Mauritz, Marguerite; Salmon, Verity G.; Trochim, Erin; Natali, Susan; Ledman, Justin and Schuur, Edward. Effects of permafrost thaw and changes in soil moisture on CH₄ and CO₂ fluxes in Alaskan upland tundra [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The magnitude and rate of greenhouse gas emissions (methane (CH₄) or carbon dioxide (CO₂)) are highly uncertain in Arctic ecosystems. The fraction of C released as CH₄ may increase with ground subsidence from thawing permafrost, where newly waterlogged areas may shift even relatively well-drained upland tundra areas to stronger CH₄ sources. To examine how total C emissions change with variable thaw depth and soil moisture conditions, measurements were made from the Carbon in Permafrost Experimental Heating Research (CiPEHR) project located in Interior Alaska. This site has undergone experimental soil warming from 2009 - 2018 and water table manipulation since 2011. Methane and CO₂ fluxes were measured in 2017 across a gradient of active layer thickness (ALT) and water table depths (WTD) that fell into 3 categories: control (WTD -21 cm; ALT -70 cm), wetter + deeper thaw (WTD -11 cm; ALT -75 cm) to reflect sites where increased drainage would result in drier, warmer soil conditions, and inundated + deeply thawed (WTD +1 cm; ALT -108 cm) as a result of ground subsidence and resulting in warmer, wetter soils. The wetter + deeper thaw treatment experienced highest ecosystem respiration rates (532.0 ± 79.6 g C m^-2) relative to inundated + deeply thawed (327.5 ± 38.2 g C m^-2) and control (399.5 ± 33.9 g C m^-2). Methane emissions were highest in the inundated + deeply thawed treatment (1050.1 ± 433.5 mg C m^-2) relative to control (82.6 ± 15.4 mg C m^-2), or wetter + deeper thaw conditions (164.8 ± 57.5 mg C m^-2). Methane emissions response to soil warming was variable, with fluxes ranging from net uptake of CH₄ to relatively strong emissions rates. Plots with strongest CH₄ emissions were inundated and had high graminoid biomass (Eriophorum vaginatum). Total C respiration rates (CO₂ + CO₂ equivalent of CH₄) were calculated by accounting for the mass difference between the gases and multiplying CH₄ by its 100 year sustained emissions global warming potential. Highest total C respiration rates occur with wetter + deeper thaw (539.4 g C m^-2), relative to respiration rates in inundated + deeply thawed (374.7 g C m^-2) or control (403.2 g C m^-2). These results highlight the effects of warming on C cycling in permafrost regions, where increased thaw and thaw-driven hydrologic changes play a substantial role in determining the form and magnitude of C release.

2019038135 Thornton, Brett F. (Stockholm University, Stockholm, Sweden); Prytherch, John; Geibel, Marc C.; Andersson, Kristian; Brooks, Ian M.; Tjernstrom, Michael K. H.; Humborg, Christoph; Salisbury, Dominic J. and Crill, Patrick M. What can measurements near the sea surface tell us about subsea permafrost methane emissions? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS11C-1428, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Seafloor seeps of methane (CH₄) gas are found globally, but the existence of subsea permafrost beneath some Arctic seas complicates understanding of CH₄ emissions in these regions. Subsea permafrost may act as both a cap on deeper CH₄ sources, and the frozen sediments themselves can be a source of CH₄ after thawing. Ultimately, much of the interest in subsea permafrost is on potential effects on the modern carbon cycle-in particular related to CH₄'s high global warming potential on sub-century timescales. Whether any released CH₄ from subsea permafrost areas reaches the atmosphere is a critical question to address, and one that must be examined against the backdrop of a multitude of Arctic CH₄ sources to the atmosphere, many of which are presently growing. During the 2014, 2015, 2016, and 2018 Arctic summers we made measurements of near-surface seawater and atmospheric CH₄, and CH₄ isotopologues, as well as CH₄ sea-air fluxes, from the Swedish icebreaker Oden. These measurements were obtained across broad regions of the Arctic Ocean, above regions of suspected subsea permafrost, and regions where subsea permafrost was not expected. Large but localized positive sea-air fluxes, likely attributable to CH₄ bubbles, were observed in small areas of the Laptev and East Siberian Seas, reaching 170 mg m^-2 d^-1 and 600 mg m^-2 d^-1, respectively. However, the area-average emissions on a larger scale were much smaller, <5 and <2 mg m^-2 d^-1, respectively. In regions of the Chukchi Sea not believed to include subsea permafrost, fluxes were <0.2 mg m^-2 d^-1. Distinguishing subsea permafrost emissions from other oceanic and land-based sources of CH₄ based on observed isotopologues in the water and air is presently frustrated by lack of suitable methane source signature data. Subsea permafrost slowly thaws once submerged; the effect of submerged duration on potential CH₄ emission remains to be understood. Combining sediment porewater studies with sea surface and tropospheric boundary layer studies may help understand the stability and/or efficiency of the transfer of CH₄ from old carbon stores to the atmosphere.

2019038132 Titov, Aleksei (Lawrence Berkeley National Laboratory, Berkeley, CA); Lindsey, Nate; Rodríguez Tribaldos, Veronica; Wagner, Anna M.; Gelvin, Arthur B.; Ekblaw, Ian; Ulrich, Craig; Freifeld, Barry M. and Ajo Franklin, Jonathan Blair. Permafrost monitoring with brillouin based fiber optic distributed strain and temperature sensing; findings from a controlled thaw experiment [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS43B-0846, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permanently frozen ground or permafrost covers vast areas of the earth's polar regions. Global warming has led to increased rates and areas of permafrost thaw; this process can lead to damage of infrastructure due to the soil subsidence as well as promote the release of greenhouse gases into atmosphere. Novel techniques are needed to monitor the state of the permafrost over long distances, especially near infrastructure. In this study, we present the results of monitoring mechanical and thermal changes due to permafrost thaw with a fiber optics sensing technique based on Brillion optical time domain analysis (BOTDA), also known as distributed strain sensing (DSS). Using this technique, one can measure axial strain and temperature distribution along the fiber over tens of kilometers with one-meter spatial resolution. In 2016, Lawrence Berkley National Laboratory in collaboration with Cold Regions Research Engineering Laboratory conducted a unique artificial permafrost warming experiment in Fairbanks, Alaska. 121 heaters warmed the subsurface at a depth of ~3 m, perturbing a soil volume of 10.5´12.7´1.5 m³ for three months. Permafrost thawed in the heated area, leading to a measured surface subsidence of 10 cm. Commercial fiber optic cable was buried in a shallow trench directly above the heater array. 2700 m of the cable were used as a sensor for DSS measurements. We clearly observe the subsidence process in the DSS data. In the center of the subsidence zone we see the negative shift in Brillion frequency, which corresponds to compression along the fiber, while on the perimeter of the subsidence zone we observe the positive shift, which indicates tension. The measured response is similar to prior DSS observations in sinkhole studies. Besides the strain measurements, we also estimated the soil temperature using the BOTDA data from the unstrained parts of the fiber (outside the subsidence zone). The soil temperature inverted from BOTDA data is in good comparison with the temperature measured by thermocouples installed in the experiment area. We believe that our study Is the first experiment which demonstrates successful usage of DSS as an early detection system for permafrost thaw processes. We believe that this technique can be widely applied for monitoring critical infrastructure in permafrost regions.

2019038067 Toby, Stephan (University of Liverpool, Liverpool, United Kingdom); Duller, Robert; De Angelis, Silvio and Straub, Kyle M. Transferring periodic sediment supply signals to the stratigraphic record [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP43D-2743, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The stratigraphic record is a unique physical archive for paleo-environmental records on Earth and other planetary bodies. This includes information on the rate and volume of sediment delivered to sedimentary basins. However, for sediment supply signals to be stored in long-time scale stratigraphy, they must produce depositional products that are not significantly reworked prior to burial beneath the active layer of the Earth's surface. Within this active layer, morphodynamics, influenced by autogenic processes, govern sediment storage and release, which can distort or even destroy environmental signals. To address this, we develop a new theoretical regime diagram that defines when supply signals influence surface dynamics and stratigraphic products. This novel framework is specifically designed to assess the ability of depositional landscapes to store sediment supply signals emanating from catchments by predicting how combinations of signal amplitude and duration influence transport systems and their stratigraphy. We hypothesize that a time scale set by topographic roughness and long-term aggradation rate sets a minimum temporal threshold for signal transfer to stratigraphy. In addition, we hypothesize that the maximum autogenic variation in deposition rate (Q_SA) sets the minimum change in supply rate necessary for stratigraphic storage. Interestingly, we identify that Q_SA decreases as a function of the time window of measurement, i.e. the minimum amplitude to store a signal of 1 ky should be higher than for supply change taking place over 10 ky. We test our framework with a suite of aggrading physical delta experiments forced with sinusoidal sediment supply rate cycles, each with a unique combination of signal period and amplitude. Results show that signals of supply cycles exceeding Q_SA are stored in stratigraphy. Interestingly, we find that low amplitude, but high frequency signals do have a capacity to influence surface processes, but their products get reworked before long-term stratigraphic storage, while low amplitude and long period signals do not influence either surface processes or the stratigraphy. It is anticipated that this approach can be applied to field stratigraphy and can guide more reliable diagnosis of ancient environmental signals.

2019040675 Tognetti, Laurence (Arizona State University, Tempe, AZ); Harrison, Tanya; Bell, James F., III and Stuurman, Cassie M. Investigating a link between scalloped depressions and topography in Utopia Planitia on Mars [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract P53F-3033, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Western Utopia Planitia, located in the northern plains of Mars, is home to a myriad of periglacial landforms. One of these is scalloped depressions-also known as Scalloped-Depression-Bearing Terrain (SDBT) in Harrison (2016)-are defined primarily by their oval-shape and north-south asymmetry, including both pole-facing "steps" and an equator-facing slope. Scalloped depressions are thought to have formed through sublimation of ground ice in the late Amazonian, consistent with the hypothesis that Mars is presently in an interglacial period marked by the poleward retreat of mid-latitudinal ice. Here, we successfully map the directional growth of scalloped depressions within the region, and present a correlation between a high density of scalloped depressions and the location of a large deposit of buried water ice within southwestern Utopia Planitia, previously identified using Mars Reconnaissance Orbiter (MRO) SHAllow RADar (SHARAD) data by Stuurman et al. (2016). Our study area encompasses a region spanning from approximately 39° to 54°N and 70° to 117° E. We determined that a large majority of scallops maintain a north-south asymmetry with the exception of some craters that cause scallop formation to demonstrate east-west asymmetry. We observed changes in geomorphology that range from predominantly smoother terrain in the northern latitudes to very hummocky terrain dominated by more known periglacial features as latitude decreases. We primarily used MRO Context Camera (CTX) images, with a few images coming from the MRO High Resolution Imaging Science Experiment (HiRISE). Our observations are consistent with previous studies showing the overall density of scalloped depressions decreases with increasing latitude, with the majority having their "steps" facing in a poleward direction. The scallops observed to have "steps" in a non-poleward direction were found in various craters throughout the study area, as well as where the underlying unit-beneath the SDBT-is exposed in the southern latitudes of the study area.

2019038097 Tolmanov, Vasiliy Andreevich (Lomonosov Moscow State University, Moscow, Russian Federation) and Grebenets, Valery I. Negative influence of thermoerosion processes on the Arctic infrastructure [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33E-1407, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The reliability of the northern infrastructure is associated with cryogenic processes that can be activated by climate change and technogenic impact. Particular danger for objects is the process of thermoerosion. Thermoerosion is the process of destruction of the banks or ground massives constructed by the permafrost and ground ice by thermal and mechanical influence of the running water. Special studies were conducted on the Tazovskiy Peninsula, which is the "kingdom" of thermoerosion. These studies included field measurements, the study of archival engineering and geocryological surveys and databases, the analysis of aerial and satellite imagery and modeling. The landscapes of the peninsula are tundra on the plains. The depth of permafrost is 300-400 m. Many surface areas are occupied by polygonal peat bogs. Since the late 1980s, intensive gas production has been underway, which creates a "new reality" for the heat and mass exchange in the permafrost-atmosphere system. An increase in the average annual air temperature and the increase in snowiness over the last 30-40 years contribute to the activation of thermoerosion. The maximum of summer precipitation is confined to August-September, the period of the maximal active layer depth. The weak root system of tundra vegetation does not provide soil consolidation and does not prevent erosion. Dusty sands and sandy loams, iced, fluidizing when thawed, and easily erodible, are the ideal material for the development of thermoerosion. Often, system of polygonal veins are the "routes" for the development of thermoerosion. The change in the conditions of the waterflow during exploitation of roads and pipelines activates thermoerosion. For the first time, a "contribution" to the thermal erosion of block caving of frozen soils was studied at the end of snowmelt period; the lateral erosion rates can be 20-30 cm per day, the width of individual blocks can reach 1.5-2 m. Over the past 40 years, areas with active development of thermoerosion on the Tazovskiy Peninsula have increased by 15-20%, which is due to climatic changes and active exploitation of technogenic systems. The effectivity of applied engineering-geocryological measures for controlling thermo-erosion was estimated

2019032001 Toohey, Ryan (U. S. Geological Survey, Alaska Climate Adaptation Science Center, Anchorage, AK); Mutter, Edda Andrea; Herman-Mercer, Nicole Michelle and Schuster, Paul F. Hydrological interactions of biogeochemical and active layer dynamics within a large-scale heterogeneous permafrost environment, the Yukon River Basin. [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23C-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In this presentation, we discuss the hydrological interactions between active layer and surface water biogeochemical dynamics at multiple sites from the headwaters to the mouth of the Yukon River Basin (YRB). Hydrological analysis indicates that the Yukon River has been changing over the last several decades with increasing groundwater contributions that dampen variability of annual discharge. Large scale permafrost degradation, within the predominantly discontinuous permafrost YRB, has been hypothesized as one of the reasons for increasing groundwater contributions. At the same time, multi-decadal increases of annual fluxes of weathering ions have also been observed within the Yukon to support the hypothesis of increasing groundwater as the result of permafrost degradation. Seasonally, biogeochemical changes present a more complex picture with results showing large increases of weathering ions during an earlier break up and longer freeze up seasons. Over the past decade, throughout the Yukon River Basin, the active layer appears to be thickening with seasonal correlation between weathering ions, DOC and O¹⁸ dynamics and longer periods of unfrozen soil moisture and increased temperatures within the active layer. Important regional differences in geochemistry and active layer parameters linked to permafrost continuity and tributaries will be highlighted. Changing biogeochemistry and active layer dynamics of the YRB may have important implications for the global effort to characterize arctic river fluxes as they relate to permafrost dynamics, the carbon cycle, aquatic ecosystems, and contaminant transport.

2019040594 Toyoda, J. (North Pacific Research Board Anchorage, Anchorage, AK); Chu, Rosalie Kae; Tolic, Nikola; Robinson, E. R.; Hess, N. J. and Tfaily, M. Extraction efficiency and molecular characterization of organic matter from soils and sediments using high resolution mass spectrometry [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B11C-2163, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Soil organic matter (SOM) represents a key reservoir for carbon (C) and is comprised of a heterogeneous mixture of plant, animal and microbial detritus. To study SOM and gain a better understanding of microbial communities, rhizosphere interactions, and biogeochemical processes, protocols have been developed using different solvents to extract this OM. Most of these extraction protocols use an aqueous solvent to extract the water soluble OM from the soil. In this study, we calculate the extraction efficiency and compare the molecular composition of the soil after repeated extractions with water. Three soil types; peat, Alaska permafrost, and river sediment, with varying percentages of organic C content were extracted sequentially with water up to 15 times. The organic matter in the extracts was characterized at the molecular level using high resolution mass spectrometry. We found that repeated extractions with smaller volumes of water extracts a higher percentage of dissolved organic carbon (DOC) compared to using one large volume of water. The DOC concentration measured in soil water extracts decreased with extraction number, regardless of soil type. The molecular composition of the OM in the extracts however didn't change with repeated extraction for each soil type, suggesting that with each extraction we are extracting the same type of compounds. Interestingly, the repeated sequential extractions were able to extract only 4% of total SOM regardless of soil type. These results are important as they suggest that water extractable organic matter (WEOM) accounts for only a small proportion of the total organic matter in the soil. However, even with this small percentage of WEOM, it is very diverse in chemical composition, with thousands of compounds resolved by high resolution mass spectrometry.

2019038076 Trochim, Erin (University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK); Schuur, Edward; Rupp, Scott T. and Bennett, Alec. Connecting people, infrastructure and permafrost information in Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC31B-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Infrastructure planning and design currently incorporates the concept of permafrost as ground that is frozen continuously for two or more years, using many different techniques and types of data. However, this basic definition does not include ice content or the roles water, surface topography and vegetation play in modifying the ground thermal regimes governing permafrost. For example, surface water in permafrost areas covered a total area of 1,066,643±144,582 km² in the northern hemisphere where lands approximately size of the state of New York converted from land to water or vice versa between 1985 and 2015. Planning and building infrastructure on permafrost requires synthesizing data including this type of information on surface water to better understand the pre-disturbance conditions, impacts the infrastructure will have, and how to best mitigate potential issues. Data supporting this analysis is produced through a variety of different lenses, with features including spatial (building site vs. community vs. regional vs. statewide vs. global), temporal (long-term monitoring vs. project based), accessibility (data collected by a public agency that should be open and easily accessible vs. data collected by private parties and industry), type (point collection vs. distributed grids). The data collection process is already well-established for conducting site-level analysis using historical data products for planning and building some types of infrastructure. However, this often fails to consider future changes or data sparseness. This project examines theoretical vs actual data availability for permafrost and infrastructure information critical for planning and development in Alaska. We explore proof-of-concept methods of quantifying environmental change related to permafrost conditions around infrastructure. We also identify key areas which contain critical information gaps for assessing permafrost related impacts to infrastructure. This analysis will highlight the development of a framework that connects permafrost specific information to infrastructure risks within the context of project planning and decision making. It will enable the research community to better position their products to fit the needs of stakeholders and improve interfaces for dissemination.

2019040681 Tsereteli, Nino Sidamon (Tbilisi State University Geophysics Institute, Georgian Republic); Varazanashvili, Otar and Gogoladze, Zurab. Seismic hazard estimation based on active faults data for Georgia (Sakartvelo) [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract S41D-0587, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The present work show the efforts towards evaluation of basic steps in PSH analysis in the frame of Project N 216758 supported by Shota Rustaveli National Science Foundation. As usual PSH were estimated by seismic sources characterization of which were made by seismic data. This work is first attempt to estimate PSH based on active fault data. Active fault were divide by segments and section. Fault Geometry were built using geological field data as well seismic data: fault plane solution, distribution of aftershocks, macroseismic data. For some faults seismic reflection profiles were available. Slip rate were estimated for each sections/ segments from geological field data. Correlation equation between slip rates, fault length and magnitude were used for those active fault for that we know length from seismological and geological data. Each sections/segments were assigned Maximum magnitude by the geological methods or historical data. PSH were estimated also for seismic sources. The procedure for building SS is based on the allocation of a certain width along the active fault. In this case, the width of SS plays a decisive role in creating the SS models of the region. The width of SS depends on the information about the width of the fault, the slope of the fault plane, the thickness of the seismically active layer, and the geometric dimensions of the source of the maximum possible earthquake. The asymmetry of SS with respect to the axial line of the inclined fault is a characteristic feature of this construction. For each SSZ in the source model determined the following parameters: the maximum magnitude; the magnitude-frequency parameters of the seismicity; the parameters of depth distribution. Estimations of Mmax are made on the basis of compilation of several methods of Mmax determination. Five methods have been used to estimate Mmax within individual SS. Three of them are seismological methods and two other are geological ones. Finally results of PSH obtained from different source data (active faults, deidmicsource zoe) were compared and analyzed.

2019031996 Turetsky, Merritt R. (University of Guelph, Department of Integrative Biology, Guelph, ON, Canada); Jones, Miriam; Olefeldt, David; Waldrop, Mark P.; Euskirchen, Eugenie Susanne; Kane, Evan S.; Douglas, Thomas A.; Hugelius, Gustaf; Manies, Kristen; Moorberg, Colby and Neumann, Rebecca. New insights test our fundamental understanding of how thermokarst influences permafrost peatlands [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw and release of greenhouse gases through enhanced microbial activity is considered one of the most likely biogeochemical feedbacks to the future climate system. Most 'permafrost-enabled' Earth System models agree that permafrost carbon release is likely to be significant enough to include in emissions negotiations. Yet to date most models simulate only top-down thaw and do not represent lateral or abrupt thaw processes that can lead to subsidence and ecosystem state changes. Recent empirical and modeling studies have revealed surprising insights into how thermokarst develops in permafrost peatlands and what this means for carbon storage. Regional-scale sampling (100+ km) across gradients of time-since-thaw shows that permafrost ontogeny (epigenetic versus syngenetic permafrost) influences the vulnerability of thawing permafrost carbon to mineralization and release. At a landscape scale (10+ km), we tested whether there are predictable relationships between initiation date (age of a thermokarst feature) and surface area in several ecoregions of Alaska. We found no consistent size-age relationships, complicating our ability to simulate thermokarst development through space and time. We further tested subsurface and geomorphic properties as predictors of permafrost vulnerability or resistance to abrupt thaw. At local scales (10-50 m), our results have previously shown that methane hotspots occur at the edges of thermokarst bogs due to rapid turnover of newly thawed permafrost carbon. However, our recent results show that these patterns of methane emissions are controlled more by the timing of rainfall and its influence on hydrology and deep soil temperatures than the timing of permafrost thaw. Overall, our results are testing our fundamental understanding of thermokarst initiation, development, and behavior, which is relevant for how models might start to incorporate abrupt thaw into their frameworks.

2019040676 Turetsky, Merritt R. (University of Guelph, Department of Integrative Biology, Guelph, ON, Canada). Collaborations with the Royal Society of Canada to develop national-scale engagement tools for Arctic sustainability in Canada [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract PA13D-0884, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

With Canada leading the G7, there is increasing focus on Arctic sustainability from scientific, economic, and political perspectives. Timed to contribute to the deliberations of the G7 political summit, the Royal Society of Canada (RSC) drafted a document articulating the challenges and opportunities related to northern sustainability. In collaboration with the RSC and the AAAS Leshner Leadership Institute, my work builds on these activities with a diverse communication platform aimed at improving public awareness about Arctic sustainability. For example, permafrost or frozen ground underlies as much as 50% of the Canadian land surface. Most of this area will experience persistent loss of subsurface ice during the 21^st century, leading to irreversible transformations in land stability and infrastructure. Despite being a "permafrost nation", the majority of Canadian citizens are unfamiliar with permafrost and its sensitivity to climate change. Using a series of public events, we are 1) connecting the Canadian public with stories of change from Arctic scientists and community leaders, and 2) promoting dialogue and debate from a variety of public perspectives on Arctic challenges at local, regional, and global levels, and 3) serving as a model project for national-scale science engagement in Canada, with the hopes of initiating institutional change within the RSC to meet its stated objectives on public engagement. Responsible development and monitoring in the Arctic requires new tools to prepare Arctic communities for change, and this work is intended to use public engagement to enrich the public's interest and investment in climate adaptation.

2019037802 Turner, Kelly (Northumbria University, Newcastle-Upon-Tyne, United Kingdom); Jimmie, Jordan Andrew; McElvein, Ann; Arvizu, Mia; Natali, Susan; Fiske, Greg; Biester, Harald U. and Mann, Paul James. Mercury in freshwaters of the Yukon-Kuskokwim Delta, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2553, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Tundra regions store globally significant quantities of mercury (Hg) in active layer and permafrost soils, and are experiencing greater rates of atmospheric Hg deposition since industrialization. Freshwater environments act as critical intermediaries between upland soil organic Carbon loss and methylmercury uptake by freshwater organisms, which is a critical vector for biological exposure to humans. Despite this, little information is available on freshwater mercury concentrations and its spatial variability in Arctic environments. To address these knowledge gaps, we measured Hg concentrations in freshwaters across the Yukon-Kuskokwim delta, Alaska during July 2018. We collected 58 waters from lakes spanning 12 m2 to 0.36 km2 in surface area across the landscape. We found a significant negative linear relationship between water body size and dissolved organic carbon concentrations, demonstrating a greater transfer of Carbon (C) between terrestrial stocks and smaller water bodies. Using pre-existing C to Hg relationships (1), we initially estimate average Hg concentrations to vary between 3.5-5.8 ng Hg L-1 within lakes and total Hg freshwater stocks to range from 1.6 to 9.7 Tg Hg over our 274 km2 study area. We also present direct Hg measurements from waters and examine dissolved C:Hg ratios across the delta to investigate how differences in lake environmental conditions (e.g. pH, oxygen availability) may alter the relative amount of Hg in C stocks. These results highlight the importance of incorporating freshwaters stocks of Hg into our understanding of Arctic ecosystems and provide crucial information on the potential mobilization of terrestrial Hg stocks to the aquatic environment with important ramifications for human health. (1) Driscoll, C. T. et al., 1995. The role of dissolved organic carbon in the chemistry and bioavailability of mercury in remote Adirondack lakes. Water, Air, and Soil Pollution, 80(1-4), pp.499-508.

2019038116 Valentin, Melissa McShea (2100 Consulting PBC, Denver, CO). Calculation of the Palmer drought severity index (PDSI) in cold region watersheds with glaciers and permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H51H-1402, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The presence of permafrost, delayed runoff from snow and ice, and sparse data complicate the calculation of drought indices in cold regions. As glaciers, snow, and permafrost respond to a changing climate, the effects of drought on high-latitude and high-elevation forests is important but uncertain. A new method to calculate the Palmer drought severity index (PDSI) in cold regions is demonstrated here in the Copper River, an ecologically unique watershed in Southcentral Alaska that is home to world-renowned salmon fisheries, hundreds of mountain glaciers, and vast boreal forests. The cold region PDSI uses output from a USGS monthly water balance model enhanced to simulate glaciers and the permafrost active layer. The monthly, 2-km resolution model of the Copper River was calibrated and evaluated to 8 stream gages, glacier mass balance, GRACE total water storage, CALM active layer measurements, MODIS snow cover, and MODIS evapotranspiration. Future water balance and PDSI calculations are based on five CMIP5 model projections. This presentation will explore the seasonal sensitivity of the PDSI and the Z-index to active layer depth, delayed runoff from snow and ice, Pacific Decadal Oscillation teleconnections, alternative methods of PET estimation, and future climate.

2019038056 Vulis, Lawrence M. (University of California Irvine, Department of Civil and Environmental Engineering, Irvine, CA); Tejedor, Alejandro; Schwenk, Jon and Foufoula-Georgiou, Efi. Channel-lake connectivity in Arctic deltas [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP23D-2356, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Arctic deltas (ADs) are ecogeomorphologically complex systems that are at risk due to climate and human forcings, e.g. warming temperatures and permafrost thaw. This will have impacts on natural and human systems since ADs have stores of permafrost carbon on the order of 90 Pg carbon, which can be mobilized into the atmosphere and ocean. Arctic lakes are estimated to be the source of two-thirds of the natural methane emissions in the Arctic and increasing methane emissions are predicted due to permafrost thaw. The potential climate change impacts and incomplete process knowledge in ADs behoove further study. For instance, observational studies and numerical experiments have indicated higher permafrost thaw rates in the presence of suprapermafrost and subpermafrost aquifers due to increased heat advection from liquid water. Here, we hypothesize that delta channel networks also contribute to more rapid permafrost thaw from this same mechanism, and that this leads to increased subsurface connectivity between the channel network and lakes located close to the channel network. We test this hypothesis by analyzing the lake drainage rates in ADs as a function of their proximity to the channel network during the active season (June - August) from 2000 to 2015 in the Yukon and Colville deltas in Alaska. We used python-based RivGraph for delta channel network extraction and for channel-lake distance computation. We controlled for interannual variability in the total seasonal streamflow and associated flooding over the delta top. We find that there are faster drainage rates of surface water with smaller distances from the channel network, indicating a higher degree of subsurface connectivity near the channel network, and supporting our hypothesis. Further analysis of connectivity in the delta will help uncover dynamical processes and predict critical transition points, which can nonlinearly accelerate permafrost thaw under climate change with unexpected consequences for the hydrology, ecology, and geomorphology of ADs.

2019040610 Wacha, Kenneth (U. S. Department of Agriculture-Agricultural Research Service, National Laboratory for Agriculture and the Environment, Ames, IA); Hatfield, J.; Cambardella, Cindy; Papanicolaou, T.; Huang, C. H. and Dold, Christian. How changes in management impact size distribution and stability of soil aggregates [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33G-2764, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Within agricultural soils, the active layer (top 5cm) is by far the most dynamic in response to management practices. Tillage events break apart the structure of the soil, weakening soil aggregates and reduce their resilience to mechanical and hydrological forces. During storm events, raindrops impact the soil surface, dislodging soil fractions that can be swept up and transported across the landscape by overland flow. These erosion processes can become amplified without the presence of surface residue cover or cover crops, which absorb raindrop energy and break up flowpath connectivity. Therefore, looking the distribution and stability of aggregate size fractions within the active layer may indicative to changes in management or dynamicity of landscape processes. In this rare study we capture changes in soil aggregate dynamics during the conversion of long-term conventional tillage systems to reduced till w/ cover crop systems. We implemented a 50m x 50m grid where topsoil samples were collected. Soil samples were air dried and broken into 9 size fractions to determine dry size distribution, and then analyzed for water stable aggregates, and stability against raindrops using kinetic energy supplied by rainfall simulator. Results found a 20% increase in dry mean weight diameter upon conversion to cover crops as well as a 5% increase in stability. LiDAR data was used to determine flowpath networks within the fields and overlaying the sampling grid uncovered landscape processes impacting aggregate dynamics. Data from this study is currently being used to build upon a hillslope transport model to simulate size fraction redistribution in intensely managed landscapes.

2019038127 Wagner, Florian M. (University of Bonn, Department of Geophysics, Bonn, Germany); Uhlemann, Sebastian; Dafflon, Baptiste; Ulrich, Craig; Peterson, John; Akins, Hunter; Kemna, Andreas and Hubbard, Susan. Permafrost characterization near Teller, Alaska, using petrophysical joint inversion of seismic and geoelectrical data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Imaging the spatiotemporal distribution of liquid water and ice is needed to improve our understanding of hydrological processes in permafrost systems and the parameterization of numerical models that simulate the dynamics and evolution of permafrost environments. Seismic and geoelectrical techniques are sensitive to the phase change of water between its liquid, frozen, and gaseous states and are therefore widely used in cryospheric geophysical applications. The combination of both methods offers opportunities for non-invasive and quantitative imaging of permafrost characteristics. Based on a recently developed joint inversion approach, we combine electrical resistivity and seismic refraction data acquired in a watershed near Teller, Alaska, during the summer of 2018. The complementary sensitivities of both methods are exploited by means of petrophysical coupling, enabling simultaneous inversion of both data sets for the volumetric fractions of liquid water, ice, and air. Due to the small contrasts between ice and bedrock in both acoustic and electrical properties as well as uncertainties in porosity, quantitative estimates of the pore-filling constituents remain ambiguous. Based on field data and analogous synthetic investigations, we demonstrate the value of adding non-tomographic ground truth data as constraints to the joint inversion framework (e.g., point measurements of soil water content), discuss the resulting uncertainty reduction, and give recommendations for future measurement strategies.

2019037774 Wagner, Julia (Stockholm University, Department of Physical Geography, Stockholm, Sweden) and Hugelius, Gustaf. Mapping of permafrost landforms and soils of coastal catchments along the Yukon coast, Northwest Canada [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2483, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Climate change in arctic permafrost regions leads to alterations in biochemistry, a redistribution of soil organic carbon (SOC), contaminants, sediment and other nutrients. Arctic permafrost coasts make up 34% of the Earth's coastlines. Along the Yukon coast near Herschel Island, 80% of the landforms are erosional landforms. Climate change induced temperature alterations lead to thermal erosion of ice-rich cliffs and high retreating rates. Recent studies show erosion rates of up to 25 m yr^-1 at specific locations. In the context with coastal erosion, a release into the ocean is likely. Whereas terrestrial permafrost is widely investigated, the aim of the EU project Nunataryuk is to improve knowledge in the context of land ocean interactions of these vulnerable coastal environments. Environmental changes such as rising sea level and longer and warmer thawing seasons necessitate investigations on processes and interconnections of parameters of arctic coastal systems. The aim of the PhD project is to investigate soil parameters such as soil organic carbon, nitrogen, bulk density, nutrients, contaminants and further potential thaw impacts of terrestrial permafrost soils in small coastal catchments on the Canadian Beaufort coast. One task is to create landcover and geomorphological maps using different types of high-resolution remote sensing data. These will be further used to apply digital soil mapping methods to model the spatial distribution of different soil parameters. Previous work has shown that the application of machine learning methods, e.g. Random Forest, can gain promising results. Therefore, machine learning methods of digital soil mapping will be used to improve the understanding of Arctic soils in the context of climate change, the influence of environmental variables and to create data sets supporting local to regional applications of permafrost models.

2019040607 Wagner, R. (San Diego State University, Department of Biology, San Diego, CA); Storey, Emanuel; Arndt, Kyle Andreas; Lipson, D. and Oechel, W. C. Eighty-five percent of terrestrial methane emissions arise from a single landscape feature type during spring thaw in Barrow, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33A-01, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane emissions from Arctic polygonal tundra dramatically increase during the annual transitional period from the initiation of polar day through the spring thaw. This narrow period is characterized by a rapid thawing of the soil active layer, the waking up of anoxic soil microbial communities (and consequent biogenic methane production), and the release of methane trapped from the previous year. Methane emissions vary significantly with landscape microtopography, vegetation and soil moisture. Here, we combine eddy covariance and soil chamber techniques to determine the proportional contribution of landscape microtopography feature types to total methane emissions from polygonal tundra during the spring thaw. We show that the vast majority of methane emissions (»85%) during the spring thaw come from low center polygons, and that emissions from polygon troughs are lower than would be expected given their moisture characteristics. These data provide an opportunity to better tune landscape methane emissions models (and to avoid overestimating emissions from polygon troughs) during the spring thaw period. We further investigate the biogeochemical differences between landscape microtopography feature types, and the mechanisms by which methane emissions might be suppressed in polygon troughs.

2019037790 Waldrop, Mark P. (U. S. Geologican Survey, Menlo Park, CA); McFarland, Jack W.; James, Stephanie R.; Minsley, Burke J. and Leewis, Mary-Cathrine. Greenhouse gases from intact permafrost nearing collapse; a result of increased microbial activity? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2505, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Widespread permafrost thaw is expected to occur this century with potentially large increases in carbon dioxide (CO₂) and methane (CH₄) release post-thaw. Already, much of the permafrost in interior Alaska is hovering just below zero degrees C, allowing for a significant fraction of the permafrost volume to be liquid water. As such, microorganisms inhabiting permafrost have the capacity to be active and produce greenhouse gases. Lab-based incubations of frozen permafrost indicate strong temperature sensitivities of microbial activities, but there are few measurements of permafrost microbial activity in situ. In the field, as permafrost temperatures approach zero, we expect concomitant increases in permafrost liquid water content and microbial activities, and the implication of these fluxes on ecosystem carbon balance is as yet unknown. We examined in situ permafrost greenhouse gases across a gradient from colder intact permafrost to warmer degrading permafrost at the edge of a thermokarst bog. This experiment took place at the Alaska Peatland Experiment (APEX) which is a lowland thermokarst fen/bog complex surrounded by lowland black spruce in Interior Alaska near Fairbanks. Along this gradient we installed gas probes and thermistors at 1.2, 1.8 and 2.4 m depths, and co-located boreholes for downhole nuclear magnetic resonance (NMR) to quantify liquid water content with depth to 2 m. Liquid water content of intact permafrost ranged from near zero to 20% while greenhouse gas concentrations in the permafrost range from 0.2-37% CO₂, 0-30% ppm CH₄, and <1-300 ppm N₂0. ¹³C-CO₂ and ¹³C-CH₄ suggest that methane is largely derived from methane fermentation. Along the thaw gradient we observed higher concentrations of greenhouse gases (particularly CH₄) associated with increasing temperature and liquid water content. To translate gas concentrations to flux, we are conducting a permafrost tracer study in which ¹³C-CO₂ is injected at 1.8 m and detected in a separate borehole at 1.2 m. Preliminary estimates of flux based upon Fick's Laws of Diffusion indicates that permafrost contributions of greenhouse gas to ecosystem flux is minor, but increases as permafrost nears collapse.

2019031992 Walter Anthony, Katey M. (University of Alaska at Fairbanks, Fairbanks, AK); Schneider von Deimling, Thomas; Nitze, Ingmar; Frolking, Steve E.; Emond, Abraham; Daanen, Ronald P.; Anthony, Peter; Regmi, Prajna and Grosse, Guido. Climate warming accelerated by abrupt permafrost thaw beneath lakes [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B22D-02, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Until now permafrost carbon feedback modeling has focused on gradual thaw of near-surface permafrost in terrestrial environments, which leads to enhanced carbon dioxide (CO₂) and methane (CH₄) emissions that accelerate global climate warming. The state-of-the-art land models do not simulate emissions from deeper permafrost thaw beneath thermokarst lakes or other abrupt-thaw processes, and so have not quantified the impact of abrupt thaw on the permafrost carbon feedback. We reanalyzed output from the Community Land Model (CLM4.5BGC), to quantify carbon emissions originating from gradual permafrost thaw in the terrestrial environment, and added to this box-model-projected permafrost carbon emissions from abrupt thaw beneath thermokarst lakes. Simulations spanned 2010 to 2100 under moderate and high Representative Concentration Pathways (RCP4.5 and RCP8.5). Supported by field observations, radiocarbon dating, and remote sensing, this re-analysis of model data leads to four striking conclusions. First, accounting for abrupt permafrost thaw beneath lakes more than doubles the radiative effect of circumpolar permafrost carbon release in the 21^st century beyond that of gradual thaw alone. Second, permafrost carbon emissions from lakes are similar under RCP4.5 and RCP8.5, but their contribution to the circumpolar permafrost carbon radiative effect (CPCRE) is much larger under the moderate warming scenario. Third, CH₄, not CO₂, is the dominant driver of the CPCRE, responsible for up to ~70% of circumpolar permafrost-carbon radiative forcing this century. Finally, including abrupt thaw beneath lakes, a process that accelerates mobilization of ancient, deeply frozen carbon, increases old permafrost soil carbon (C-CO_2e) emissions by ~125% to 190% compared to gradual thaw alone. Since abrupt thaw has not been considered in earth system models, these findings have important implications for climate change scientists and policy makers, who will now need to account for a >100% larger radiative effect from permafrost carbon loss this century.

2019031999 Walvoord, Michelle A. (U. S. Geological Survey, Earth System Processes Division, Boulder, CO); Wickland, Kimberly; Minsley, Burke J. and Striegl, Robert G. Hydrologic and biogeochemical significance of perennial thaw zones in degrading permafrost [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23C-03, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Studies spanning arctic and boreal regions provide observations and physically-based models describing the deepening of the active layer in response to climate warming. A growing number of data and model-based studies document the development of perennial thaw zones, or supra-permafrost taliks, below the depths of seasonal ice as the next stage in top-down permafrost thaw evolution. Discerning the presence and movement of water (or lack thereof) in these actively thawing zones and their hydraulic connectivity are of high interest as these hydrologic characteristics affect biogeochemical cycling and the lateral transport of dissolved constituents, including organic carbon, released from permafrost. The strength of the permafrost-carbon feedback, for example, is critically dependent on coupled hydrologic and biogeochemical processes in shallow thawed zones. Our recent examination of soils in interior Alaska, USA, reveals a larger potential yield of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) from near-surface Holocene permafrost soils upon thaw than previously recognized. In parallel, cryohydrogeologic modeling and geophysical observations in these settings suggest that perennial thaw zones may be more prevalent than previously thought. All lines of evidence suggest that more attention toward lateral hydrologic transport of permafrost DOC and TDN is warranted in expanding the typical one-dimension view of the permafrost-carbon feedback. While side-by-side comparison of hydrology and biogeochemistry studies in permafrost systems help construct critical conceptual building blocks, more fully integrated approaches are needed toward quantitatively constraining current and projected lateral hydrologic export of aqueous constituents, including DOC and TDN, influenced by thawing permafrost. Material presented here from site-based research in Alaska describes necessary steps toward such advances.

2019040641 Wang, K. (University of Colorado, Institute of Arctic and Alpine Research, Boulder, CO); Overeem, I.; Zhang, T. and Jafarov, E. E. High spatial resolution soil temperatures simulation over the Northern Hemisphere [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C33F-1631, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Soil temperatures are comprehensive indicators of energy, mass, and biogeochemical exchanges in the atmosphere-ground interaction. Their spatial variation provides catch-all information for better understanding climate, ecological, hydrological processes, and the critical indicator for permafrost mapping. Although almost every land surface models simulated ground thermal regime and mostly used parameterization scheme or simplified formulas, together with coarse vertical resolution, shallow bottom boundary, and without unfrozen water. We present a high resolution simulation with a more detailed soil heat transfer model. Here, we utilized GIPL-2.0 model to simulate long-term mean (1971-2000) monthly soil temperatures up to 50 m below the ground surface over the Northern Hemisphere. WorldClimate v2.0 was used to provide a long-term monthly mean air temperature over 1971-2000. Long-term monthly mean snow depth (only averaged over 1998-2017) was obtained from the Canadian Meteorological Centre dataset. A new high-resolution soil database, SoilGrids, was used for soil parameterization for seven soil layers (0-0.05, 0.05-0.15, 0.15-0.30, 0.30-0.60, 0.60-1.00, 1.00-2.00, 2.00-50.0 m) with an assumption of uniform soil properties below 2 m. Thermal properties were estimated from soil texture, bulk density, and water content. Mean annual air temperature was used as a first guess of initial soil temperature conditions. To reduce the influence of initial conditions, the model was run for 100 years to achieve approximate steady state, and only the last year's outputs were used for validation. We compared the simulated soil temperatures with the long-term (1971-2000) monthly mean soil temperatures measurements up to 3.2 m (including 0.20, 0.40, 0.80, 1.60, 3.20 m) from approximately 1000 meteorological stations. Simulated soil temperatures were well correlated with the observations (R²=0.96, p<<0.01), although there was a cool bias of about 1.13 °C from simulated soil temperatures. We compared mean annual ground temperature at 15 m with the measurements from 592 boreholes in GTN-P network. Measurements at this depth were also indicating a good correlation (R²=0.62, p<<0.01). These validations suggested that the soil thermal parameterization is valid for simulation of ground thermal statues. This study provides a snapshot of current high-resolution monthly soil temperatures over the Northern Hemisphere, which serves as a reliable initial condition for the dynamic simulation. Future works aims to use high-resolution climatic data (e.g., TerraClimate since 1958) for tracking or reconstructing historical soil temperatures evolution over the Northern Hemisphere.

2019038100 Wang Taihua (Tsinghua University, Department of Hydraulic Engineering, Beijing, China) and Yang Dawen. Spatial distribution and potential changes of frozen ground on the Tibetan Plateau; analysis based on statistics and machine learning algorithms [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC43K-1703, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Frozen ground degradation resulting from climate warming on the Tibetan Plateau (TP) has aroused wide concern in recent years. In this study, the permafrost and maximum thickness of seasonally frozen ground (MTSFG) distribution in the baseline period (2003-2010) and in the future (2040s and 2090s) with 1-km resolution are estimated using statistics and machine learning algorithms. Three algorithms including support vector machine (SVM), random forest (RF), and logistic regression (LR) are adopted to estimate the permafrost distribution and validated using the survey-based maps at three investigated regions (IRs). According to the ensemble results of the three algorithms, 44.5% area of the TP is underlain by permafrost in the baseline period, and respectively 27.2% and 47.2% of the current permafrost will disappear by the 2040s and the 2090s projected by 5 General Circulation Models (GCMs) under the Representative Concentration Pathway (RCP) 4.5 scenario. SVM has better spatial generalization ability according to nested cross validation thus selected to estimate the MTSFG distribution. According to the results derived from SVM, the most dramatic decrease in MTSFG will occur in the southwestern TP, which is projected to exceed 50 cm in the 2090s compared with the baseline period projected by the 5 GCMs under RCP 4.5 scenario. The estimates of frozen ground changes could provide a scientific basis for water resource management and ecological protection under the projected future climate changes in headwater regions on the TP.

2019040678 Wehner, Michael F. (Lawrence Berkeley National Laboratory, Berkeley, CA); Hayhoe, Katharine; Wuebbles, Donald J.; Easterling, David R.; Fahey, David W.; Doherty, Sarah J.; Kossin, James P.; Sweet, William; Vose, Russell S. and Kunkel, Kenneth. Our changing climate; national climate assessment; NCA4 vol. 2, chapter 2 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract PA31D-1151, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Global climate is changing rapidly compared to the pace of natural variations in climate that have occurred throughout history. Global average temperature has increased by about 1.7°F from 1901 to 2016. Observational evidence does not support any credible natural explanations for this amount of warming. The evidence consistently points to the emissions of greenhouse gases by humans as the dominant cause. How much more the climate changes will depend primarily on global emissions of greenhouse gases and on the response of the climate system to human-induced warming. With significant emission reductions, global temperature increase could be limited to 3.6°F or less. Without significant reductions, global temperatures could increase by 9°F or more by the end of this century. Global average sea level has risen by about 7-8 inches since 1900, with almost half this rise occurring since 1993 as oceans have warmed and land-based ice has melted. Sea levels are very likely to continue to rise by at least 1-4 feet by 2100 relative to 2000 levels. Emerging science regarding Antarctic ice sheet stability suggests that for higher scenarios a rise exceeding 8 feet is physically possible. In the Arctic, average temperatures have increased more than twice as fast as the global average, accompanied by thawing permafrost, loss of sea ice and glacier mass. By mid-century, it is very likely that the Arctic will nearly free of sea ice in late summer. Permafrost is expected to continue to thaw and methane released from thawing permafrost has potential to amplify human-induced warming. Human-induced change is contributing to the poleward expansion of the tropics and a northward shift in Northern Hemisphere winter storm tracks since 1950. Increases in greenhouse gases and decreases in air pollution have contributed to increases in Atlantic hurricane activity. Hurricane rainfall and intensity are projected to increase, as are the frequency and severity of landfalling atmospheric rivers on the West Coast. Climate change resulting from human activities will persist for millennia. Future changes above the range projected by climate models cannot be ruled out and due to their systematic tendency to underestimate temperature change during past warm periods, models may be more likely to underestimate than to overestimate long-term future change.

2019040627 Wehr, R. A. (University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ); McCalley, C. K.; Logan, Tyler A.; Chanton, J.; Crill, P. M.; Rich, V. I. and Saleska, S. R. Depth-resolved methane chemistry and transport in an Arctic peatland retrieved from isotopic porewater gas profiles [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B44D-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Emission of methane from wetlands is a major factor in the prediction of climate change - especially emission associated with thawing permafrost, which may drive a positive feedback loop of emission and warming. In addition to the biochemistry of methane production and consumption, wetland methane emission depends critically on the transport mechanisms by which methane moves through and out of the ecosystem, but it is difficult to disentangle the various chemical and transport processes involved. We therefore developed the Peat Isotopic Depth-resolved Gas Emission (PIDGE) model for retrieving vertical profiles of methane biochemistry and transport from porewater isotopic gas measurements, and we applied PIDGE to a sphagnum bog and an eriophorum-dominated fen (putatively representing successive permafrost thaw stages) in Stordalen Mire, Sweden. PIDGE includes 5 chemical reactions (hydrogenotrophic and acetoclastic methanogenesis, methanotrophy, homoacetogenesis, and aerobic respiration) and 4 transport processes (aqueous diffusion, aerenchymal diffusion, ebullition, and advection). A Differential Evolution algorithm was used to efficiently search the model's 25-dimensional parameter space for solutions consistent with our observations of: (a) vertical profiles of the concentrations and isotopic compositions of methane and carbon dioxide in the peat porewater, (b) the magnitude and isotopic composition of the surface methane efflux, and (c) the anaerobic CO₂:CH₄production ratio. PIDGE has revealed that: (1) realistic retrievals require accounting for the chemistry and transport of not only the measured, carbon-containing gases (CH₄and CO₂) but also the principal unmeasured gases (O₂and N₂); (2) our observations cannot be reproduced without advection (i.e. xylem flow/lateral water flow); and (3) the presence/absence of homoacetogenesis is uncertain due to large uncertainty in the associated isotopic fractionation. The biochemical and transport profiles retrieved from PIDGE give us a window into subsurface methane dynamics and can be used to train or test ecosystem models designed to predict peatland methane emissions.

2019040638 Westermann, S. (University of Oslo, Department of Geosciences, Oslo, Norway); Strozzi, T.; Wiesmann, A.; Aalstad, Kristoffer; Fiddes, J.; Kaab, A.; Obu, Jaroslav; Seifert, F. M.; Grosse, G.; Heim, B.; Matthes, H.; Nitze, Ingmar; Rinke, A.; Hugelius, G.; Palmtag, J.; Barboux, C.; Delaloye, R.; Kroisleitner, Christine and Bartsch, A. Circumpolar mapping of permafrost temperature and thaw depth in the ESA permafrost CCI project [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C32B-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is an Essential Climate Variable (ECV) within the Global Climate Observing System (GCOS), which is characterized by subsurface temperatures and the depth of the seasonal thaw layer. Complementing ground-based monitoring networks, the Permafrost CCI project funded by the European Space Agency (ESA) 2018-2021 will establish Earth Observation (EO) based products for the permafrost ECV spanning the last two decades. Since ground temperature and thaw depth cannot be directly observed from space-borne sensors, we will ingest a variety of satellite and reanalysis data in a ground thermal model, which allows to quantitatively characterize the changing permafrost systems in Arctic and High-Mountain areas. As recently demonstrated for the Lena River Delta in Northern Siberia, the algorithm uses remotely sensed data sets of Land Surface Temperature (LST), Snow Water Equivalent (SWE) and landcover to drive the transient permafrost model CryoGrid 2, which yields ground temperature at various depths, in addition to thaw depth. For the circumpolar CCI product, we aim for a spatial resolution between 10 and 1km, but ensemble runs will be performed for each pixel to represent the subgrid variability of snow and land cover. The performance of the transient algorithm crucially depends on the correct representation of ground properties, in particular ice and organic contents. Therefore, the project will compile a new subsurface stratigraphy product which also holds great potential for improving Earth System Model results in permafrost environments. We report on simulation runs for various permafrost regions and characterize the accuracy and ability to reproduce trends against ground-based data. Finally, we evaluate the feasibility of future "permafrost reanalysis" products, exploiting the information content of various satellite products to deliver the best possible estimate for the permafrost thermal state over a range of spatial scales.

2019038136 Westermann, Sebastian (University of Oslo, Department of Geosciences, Oslo, Norway); Angelopolous, Michael; Schneider von Deimling, Thomas; Miesner, Frederieke; Grigoriev, Mikhail; Juhls, Bennet; Lantuit, Hugues and Overduin, Pier Paul. Modelling submarine permafrost extent and development at the circum-Arctic scale [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS11C-1429, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Submarine permafrost is likely a key component of the permafrost-carbon climate feedback, but its current state and distribution on the Arctic shelves are largely unknown, aside from regions for which industry data are available. We present recent advances in modeling the dynamics of submarine permafrost on a range of spatial and temporal scales conducted within the EU H2020 Project "Nunataryuk -Permafrost thaw and the changing arctic coast: science for socio-economic adaptation". We modelled the thermal regime of present-day submarine permafrost for the past 450 ka using distributed reconstructions of air temperature and ice sheet dynamics (from the CLIMBER 2 model), geothermal heat fluxes and sea level histories combined with modern bathymetry. The numerical model is a branch of the 1D heat flow CryoGrid 2 model, with repeated cycles of inundation driving surface temperatures at the upper boundary. The resulting map provides a first order estimate of submarine permafrost distribution and state that implies that much of the shelf can function as a cap on potential greenhouse gas stocks. We examine the evolution of permafrost in the Laptev, East Siberian, Beaufort and Barents seas, and in the Canadian Arctic Archipelago. The circum-Arctic dataset includes a map of the extent of cryotic sediment and the depth of cryotic sediment below the land or seabed. Relevant parameters such as ice saturation, which controls gas permeability and the thermal inertia of permafrost, and the enthalpy required to degrade permafrost completely, are also produced. Validation of the model includes comparison to existing sets of borehole and geophysical data. The applied method holds potential to investigate the following questions: How resilient is submarine permafrost to shelf water warming and freshening and shifting sediment dynamics? What are the implications for energy and mass fluxes from submarine permafrost under future changing conditions?

2019040660 White, Mark D. (Pacific Northwest National Laboratory, Richland, WA); Kneafsey, Timothy J. and Seol, Yongkoo. Modeling of coupled thermal, hydrologic, and geomechanical processes in gas hydrate bearing porous media; the 2^nd international gas hydrate code comparison study [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS31F-1850, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Realizing the vast energy potential of natural gas hydrates stored in geologic deposits requires developing and demonstrating production technologies at the commercial scale. Numerical simulation historically has played a key role in understanding the coupled thermal, hydrologic, thermodynamic, and geomechanical processes associated with producing natural gas from hydrate bearing deposits, such as those found beneath the Arctic permafrost within suboceanic sediments. Analytical capabilities for modeling gas hydrate systems in geologic media have advanced steadily over the last two decades, and the number of computer codes designed to model the production of natural gas hydrates has grown internationally, with computer codes being developed at universities and research institutes. An effective means for advancing and verifying these scientific computer codes, beyond comparing simulation results against experimental observations, is to compare simulation results from multiple computer codes on well-defined problems. An alternative option to verify gas hydrate computer codes is to compare simulation results against analytical solutions, however, the complexity of gas hydrate systems makes such analytical solutions scarce. The first international gas hydrate code comparison study, organized by the U.S. Department of Energy, National Energy Technology Laboratory about one decade ago, considered a series of problems involving the coupled thermal, hydrologic, and thermodynamic processes associated with natural gas hydrates in geologic media. Since that time, advances in natural gas hydrate simulators have made the inclusion of coupled geomechanical processes more common, which spurred a second code comparison study, focused on coupled processes with geomechanics. To understand the state of these reservoir simulators and contribute to their advancement, a second international gas hydrate code comparison study has started. The study is anticipated to span two years, with the first year being focused on benchmark type problems. Four benchmark problems were developed with the guidance of problem champions, and solutions submitted and compared during regularly scheduled teleconferences, involving 24 international research teams.

2019040593 Whitley, Matthew Allen (Michigan Technological University, Houghton, MI); Frost, G. V., Jr.; Macander, M. J.; Jorgenson, T. and Dissing, Dorte. Permafrost degradation on Alaska's Yukon-Kuskokwim Delta; bellwether of the future Arctic, or black sheep? [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B11A-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Yukon-Kuskokwim Delta (YKD) is among the most biologically productive areas of the tundra biome, but the YKD's comparatively warm climate, proximity to the coast, and low elevation make it highly vulnerable to rapid and persistent change following shifts about basic physical and thermal thresholds. Here we exploit disparate high-resolution datasets from long-established and newly developed remote sensing technologies to examine degradation of permafrost on the YKD using a retrospective approach. Traditional optical datasets (airphotos, commercial satellite imagery) provide the longest period-of-record for examining landscape change. We photo-interpreted ecotypes using a time-series of airphotos from circa 1953 and 1980, IKONOS satellite images from c. 2007, and WorldView satellite images from c. 2015. We found that ecotype classes changed 16.2% (342 km²) overall during the »62-year timespan. Permafrost degradation was a dominant driver of ecotype changes since 1953, and rates of permafrost degradation increased dramatically during 2007-2015 (from 0.06 to 0.26%/yr), coinciding with increasing storm frequency and air temperatures. Emerging technologies such as LiDAR now provide a means of mapping permafrost extent extremely well on the flat landscapes of the YKD, where ground-ice is the chief mechanism producing topography. Integrating field data with a high-resolution digital elevation model (DEM) from 2009 LiDAR supported a probabilistic mapping approach based on local surface elevation. Using a 0.9 predicted probability threshold yielded a permafrost map with 95% accuracy. Recent "repeat" LiDAR acquisition in 2016 permits precise three-dimensional modeling of changes in near-surface permafrost. Ongoing operation of legacy instruments, coupled with maturation of emerging remote technologies provide a powerful toolkit for detailed studies of high-latitude environmental change. We conclude with discussion of whether current dynamics on the YKD foretell changes likely to be seen in the future Arctic, or are unique to this corner of Beringia.

2019038088 Whitley, Matthew Allen (University of Alaska Fairbanks, Department of Geology and Geosciences, Fairbanks, AK); Frost, Gerald V., Jr.; Jorgenson, Torre; Macander, Matthew J.; Maio, Chris and Winder, Samantha G. Creating high-resolution permafrost maps using LiDAR as baseline datasets for landscape change on the Yukon-Kuskokwim delta, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1395, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Alaska's Yukon-Kuskokwim (YK) Delta spans nearly 67,200 km² and is among the largest and most productive coastal wetland ecosystems in the pan-Arctic. Permafrost currently forms extensive elevated plateaus on abandoned floodplain deposits of the outer delta, but is vulnerable to disturbance from rising temperatures, inland storm surges, and salt-kill of vegetation. This ecosystem-protected permafrost is expected to disappear within the coming century, which will profoundly affect local communities reliant on services provided by the permafrost plateaus. Thus, accurate baseline maps of permafrost extent are critical for a variety of applications including long-term monitoring, understanding the scale and pace of permafrost degradation processes, and estimating resultant greenhouse gas dynamics. This study shows that high-resolution LiDAR data in tandem with field-based parameterization and validation can yield permafrost maps with 95% overall accuracy. This region is a good case study for mapping permafrost with LiDAR alone, as the majority of the topography on the coastal plain comes from permafrost aggradation, where non-permafrost areas are extremely flat. The resultant maps serve as an important baseline for tracking change in the region, and monitoring permafrost--and by proxy community--health in the region.

2019032003 Wickland, Kimberly (U. S. Geological Survey, Wisconsin Water Science Center, Middleton, WI); Tate, Michael and Krabbenhoft, David P. Impacts of permafrost thaw on mercury dynamics [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B23C-07, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost soils retain a large, globally important, reservoir of mercury (Hg) originating from atmospheric deposition of natural and anthropogenic sources. Upon thaw, permafrost Hg becomes potentially vulnerable to mobilization by gaseous emission of elemental Hg (Hg⁰) to the atmosphere and by aqueous transport of dissolved inorganic Hg(II) to downstream ecosystems. Thaw also impacts near-surface Hg cycling rates and pathways by dramatically changing the distribution of water across the landscape. Ground subsidence following thaw of ice-rich permafrost soils (thermokarst) commonly creates mosaics of saturated collapsed areas and drier uncollapsed areas. We conducted a multi-year field study near Denali National Park, Alaska focused on understanding the effects of permafrost thaw and thermokarst formation on Hg⁰ emission at a site characterized by high spatial heterogeneity in depth to permafrost, soil moisture, and dominant vegetation. Total gaseous Hg (TGM) flux was continuously measured at paired contrasting locations during multi-day field campaigns using a Tekran 2500 elemental Hg analyzer and dynamic chambers, along with environmental and meteorological conditions. High spatial and temporal variability in TGM flux was observed, dominated by net Hg⁰ deposition at all sites over hours to days but interspersed with distinct periods of net Hg⁰ emission. TGM flux positively correlated with air temperature, solar radiation, and soil temperature. Results from paired locations revealed that while hourly variation in meteorological conditions influenced short-term TGM flux, spatial heterogeneity in soil temperature was an underlying control on TGM flux across the landscape. In areas where thaw led to ground collapse and increased soil moisture, soil temperature and TGM fluxes were less compared to uncollapsed ground. In contrast, where thaw led to deeper permafrost and improved drainage, soil temperatures and TGM fluxes were greater than in adjacent areas having shallower permafrost. The complex spatial variability in TGM fluxes and the relationships with soil temperature and moisture indicate the role of soil microbes in Hg⁰ generation and dynamics with permafrost thaw and suggest increased Hg⁰ emission with soil warming and increased soil water drainage in high latitude ecosystems.

2019031979 Wild, Birgit (Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden); Andersson, August; Bröder, Lisa; Vonk, Jorien; Tesi, Tommaso; Hugelius, Gustaf; McClelland, Jim W.; Song, Wenjun; Raymond, Peter A.; Pipko, I.; Dudarev, O.; Semiletov, I. P.; Shakhova, N. E. and Gustafsson, Orjan. Carbon remobilization from permafrost and peatlands along Siberian rivers [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B21I-2433, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost and peat deposits of northern high latitudes hold large organic carbon stocks that may be thawed and remobilized upon climate warming. Part of the carbon will degrade to CO₂ and CH₄ at point of thaw to amplify climate warming, and part will be released into aquatic systems, degraded during transport or again removed from active cycling by sediment sequestration. This lateral carbon transfer is difficult to constrain, but represents an important component of the high latitude carbon cycle; it is also an opportunity to monitor permafrost thaw in a warming climate. Here, we present results from several related studies. First, we combined a decadal, high temporal resolution record of ¹⁴C in dissolved and particulate organic carbon (DOC, POC) at one monitoring station in each of the four largest Siberian rivers (Ob, Yenisey, Lena, and Kolyma) with a ¹⁴C fingerprint database of potential organic carbon sources in a statistical source apportionment approach. In spite of the vast extent of old permafrost and peat deposits in the river catchments, organic carbon from recent primary production accounted for 85 ± 9% of the annual fluvial organic carbon transport in the lower reaches of the rivers. These findings might indicate rapid loss of permafrost and peat carbon during river transport. In follow-up studies, we employ a high spatial resolution dataset of dissolved inorganic carbon (DIC), DOC, and POC, as well as atmospheric CO₂ sampled along the Ob and Lena rivers in late summers of 2016 and 2017, respectively, to assess the contribution of different organic carbon sources to the rivers across their heterogeneous catchments, and its fate during transport. Systematically higher concentrations of DIC and DOC in the Ob than in the Lena coincide with a lower extent of permafrost and higher extent of peatlands in the Ob catchment; both are expected to facilitate soil carbon leaching. An increasing offset in ¹³C content between POC and potential carbon sources towards both river mouths further points at degradation or sedimentation of a large POC fraction during river transport. We will apply ¹⁴C source apportionment to quantify the contribution of different organic carbon sources to DOC and POC at multiple locations along the rivers, thereby assessing the fate of terrestrial carbon during transport.

2019031987 Wilkerson, Jordan Patrick (Harvard University, Cambridge, MA); Dobosy, Ronald; Sayres, David S. and Anderson, James G. Significant permafrost nitrous oxide emissions observed on a regional scale [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B21K-2480, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw induced by climate change sparks concern about increased carbon emissions. However, Arctic emissions of N₂O, a more potent greenhouse gas, are assumed to be negligible. Some recent studies have questioned this view, but they were severely limited in spatial scope. In August 2013, we used the airborne Eddy Covariance technique to measure N₂O emissions from a low-flying aircraft covering a permafrost area spanning 310 km². We observed an average N₂O emission that is 0.07 g N m^-2, when extrapolated over the month of August. This is higher than the maximum yearly emissions typically assumed for these regions. These results demonstrate that N₂O fluxes can be measured on a much larger scale than in previous studies, and they question the assumption of negligible permafrost N₂O emissions. Furthermore, laboratory studies have shown elevated soil N₂O production with increasing permafrost soil temperature. Therefore, these observed fluxes may be expected to increase in response to climate change, constituting a significant non-carbon climate feedback.

2019040588 Wilson, E. L. (NASA, Goddard Space Flight Center, Greenbelt, MD); DiGregorio, A.; Villanueva, G. L.; Floyd, M.; Menendez, Arsenio R.; Cutlip, Lauren R.; Miletti, Karla and Souders, Zachary. Portable, low-cost, column carbon dioxide and methane measurements for validating satellite observations in remote locations [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract A31L-3080, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

We present a low-cost (»$10K per instrument), portable solution to ground-based validation of satellite observations for difficult to reach locations with precisions of 1 ppm XCO₂ and 10 ppb XCH₄ for hourly data products. While Total Carbon Column Observing Network (TCCON) is the gold-standard for ground validation, there are locations where a ground column validation data point would be useful but conditions are not conducive to a permanent station. Examples include wetlands, thawing permafrost, the tropics, the Amazon, sub-Saharan Africa, as well as locations without a power grid or with geopolitical conflict. In addition, the low-cost and portability mean a geographical region can be studied in depth with multiple instruments. This passive, sun-pointing instrument is a miniaturized, laser heterodyne radiometer (mini-LHR) that has been under development by our team since 2009. It can be operated either in tandem with AERONET (a global network of 500 instruments that measure aerosol optical depth), or as a stand-alone instrument with a low-cost (»$3K), light-weight sun tracker. One of the main benefits of the mini-LHR is that it can quickly reach remote locations and provide a validation measurement even if there is limited or no infrastructure at the site. The instrument weighs »10 lbs, fits into a backpack, and is powered by two folding solar panels and a battery pack. In clear conditions, the instrument can be set-up in under an hour. Portability means that mini-LHRs can be easily moved for side-by-side comparisons with other mini-LHRs and with TCCON which simplifies assessing instrument bias as well as accuracy. Like TCCON, the mini-LHR points directly at the sun with a narrow field-of-view and is its insensitivity to cloud and aerosol scattering that is common to nadir-pointing passive satellite approaches. Here we present a collection of sample data sets to demonstrate performance from locations that vary in climate, altitude, solar zenith angle, hours of sun per day, etc., as well as data from side-by-side TCCON comparisons. Retrievals of CO₂ and CH₄ were completed using the NASA/Goddard's Planetary Spectrum Generator (PSG) that incorporates meteorological inputs from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data set.

2019038086 Witharana, Chandi (University of Connecticut, Natural Resources and the Environment, Storrs, CT); Liljedahl, Anna K. and Zhang, Weixing. From ice-wedge polygons to pan-Arctic landscapes; intensive mapping of ice-wedge polygons at extensive spatial scales using very high-resolution remote sensing imagery [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1393, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

A multitude of field measurements across the Arctic have documented ice-wedge degradation resulting in low-centered (LC) polygons transforming into high-centered (HC) polygons in less than a decade. The microtopography associated with ice-wedge polygon types governs many aspects of Arctic ecosystem, permafrost, and hydrologic dynamics from local to regional scales owing to the role of polygon type on the flow and storage of water. Despite the availability of sub-meter remote sensing imagery for Arctic research, the spatial distribution of ice-wedge polygons and their successional characteristics at pan-Arctic scale are largely unknown. The geographical extent and the sheer data volumes hamper both manual and semi-automated mapping approaches. Transforming big imagery into 'Arctic science ready' analytics demands for computationally efficient and scalable 'image-to-assessment' pipelines. There are currently no automated methods to map ice-wedge polygonal ecosystems, including polygon type (LC and HC), ice-wedge degradation/stabilization stage, and wedge-ice content that can operate at the pan-Arctic scale. We aim to develop computationally efficient workflows to automatically characterize ice-wedge polygons and address methodological and implementation challenges in deploying large-scale image resources now available for the Arctic from the Polar Geospatial Center. Our combined approach of automated mapping, local field measurements and numerical modeling will allow us to capture the spatial patterns and temporal dynamics of polygonal tundra processes from the individual polygon to pan-Arctic scales. Overall, our research will provide an extensible framework for imagery-enabled intense mapping of ice-wedge polygons and their fate at extensive spatial scales.

2019038070 Wondolowski, Nicholas Aksel (University of Pittsburgh, Pittsburgh, PA); Shelef, Eitan and Abbott, Mark B. A sedimentary record from Burial Lake, AK, reveals a covariance between erosion rate, permafrost thaw, and climate [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP53E-1904, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The interaction between permafrost thaw and soil erosion may meaningfully influence the Arctic ecosystem through re-distribution of sediment and soil organic carbon, which may also influence global climate. Although permafrost thaw generally increases soil erosion, the relations between permafrost thaw, soil erosion, and climate are yet to be quantified. To quantify these relations, we analyzed sediments from Burial Lake, an Arctic lake with a small watershed nested in the Brooks Range, AK. Erosion rates for the lake's watershed were reconstructed from sedimentation rate, lake area, and watershed area. Additionally, age offsets (difference between a bulk sediment age and the sediment's depositional age approximated from macro-fossils), which indicates the presence of old carbon sourced from thawed permafrost, were calculated from the lake's sedimentary record of 36 ka. Results show a rough correlation between age-offset and erosion rate, both of which appear to respond to local and regional climatic changes. This correlation likely reflects increased erosion rate and sediment flux in warm periods when the active layer thickens. Both erosion rate and age-offset are high during the mid-Wisconsin interstadial (past interglacial period) and erosion rate is low during the Last Glacial Maximum. During the recent interglacial period erosion rate shows long term increase with short term fluctuations, while age-offset only shows short term fluctuations similar to those observed in erosion rate. A particularly large peak in age-offset occurs during the mid-Wisconsin interstadial. We find that paleo-erosion rate, age-offset, and summer temperature generally covary, where age-offset responds differently to the mid-Wisconsin interstadial compared to the recent interglacial. This suggests that erosion and transport of old carbon from thawed permafrost is not only a function of climate and may dependent on additional factors such as vegetation cover, changes in sediment sources, or the erosional history of the watershed.

2019038073 Wu, Yue (University of Texas at Austin, Department of Aerospace Engineering & Engineering Mechanics, Austin, TX); O'Connor, Michael; Chen, Jingyi; Kling, George W.; Cardenas, M. Bayani and Ferencz, Stephen B. Determining the link between hydraulic properties of Arctic tundra soils and interferometric synthetic aperture radar deformation measurements [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract G41B-0701, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The North Slope of Alaska is covered with continuous permafrost. Permafrost thawing affects delivery of water and carbon from the landscape to surface waters, which has further influences on the global C cycle. Remotely sensed measurements are especially useful for studies of thaw processes over the Arctic region due to inaccessibility for ground-based measurements. In this study, we use spaceborne Interferometric Synthetic Aperture Radar (InSAR) data acquired from ALOS and Sentinel-1 missions to estimate Active Layer Thickness (ALT) near Toolik Lake, Alaska. We show the magnitude of land surface seasonal uplifting and subsidence when permafrost soil undergoes thaw-freeze processes, due to the density difference between liquid water and ice. Compared with ground-based techniques such as probing and thaw tubes, InSAR monitors the hydrologic state of the permafrost over larger areas at relatively high spatial resolution. To understand the link between hydraulic properties of the suprapermafrost zone and InSAR deformation signals, we analyzed soil samples and ALT data from Imnavait Creek. Based on field measurements of soil porosity and soil moisture content of different types of soils, we developed algorithms to translate InSAR deformation signals to soil moisture content and ALT. This is the first step toward our over-all goal of regional, real-time estimation of hydrological C transport through overland and groundwater flow in the Arctic region and examine how it will affect Arctic climate.

2019038066 Wu, Zi (University of California Irvine, Department of Civil and Environmental Engineering, Irvine, CA); Foufoula-Georgiou, Efi; Parker, Gary; Singh, Arvind; Fu Xudong and Wang Guangqian. Super diffusion of bedload tracer transport at intermediate time scales explained via a new analytical formulation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract EP41B-2674, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Anomalous diffusion of bedload transport is typically inferred from the tail characteristics of step length and/or waiting time distributions. However, since this approach is valid only for the long term asymptotic transport process, the mechanism of anomalous diffusion observed at intermediate time scales in field and numerical simulations remains unclear. Here we propose a modified active layer formulation by incorporating a slow process of tracer burial from the active layer into the substrate layer underneath, to account for a simplified form of vertical exchange of tracers during the streamwise transport. We demonstrate, by the obtained analytical solutions, that this formulation can capture the key characteristics of the tracer transport in terms of the advective slowdown and super-diffusion observed in field and numerical studies. By the solution for the variance of the tracer population, we find that the burial effect corresponds to an advection-induced scaling term (??? t³) at the intermediate time scale, explaining the super diffusion as an accelerated streamwise separation between two distinct groups of tracers consisting of travelling and buried (immobile) particles, respectively.

2019037816 Wu Xiaodong (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Cryosphere Research Station on Qinghai-Xizang Plateau, Lanzhou, China); Ma Xiaoliang; Liu Guiming and Zhao Lin. Seasonal changes in the riverine dissolved organic carbon in the permafrost regions on the Qinghai-Tibetan plateau [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31H-2583, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost degradation can thaw previously frozen organic matter, which can result in decomposition or trans-regional export along with runoff. So far, little is known about the water quality in the permafrost regions on the Qinghai-Tibetan Plateau. We investigated the temporal variation of dissolved organic carbon (DOC) in the rivers of the Three Rivers' headwater region. The results showed that the average monthly DOC concentrations of 47 rivers in the Three Rivers' headwater regions ranged from 2.92 mg/L to 6.82 mg/L, with an average of 4.39 mg/L. From the spring to the beginning of summer, DOC concentrations increased sharply. During this period, the monthly mean temperature raised from -11°C to 2°C, and reached the maximum value. Then, DOC concentrations decreased rapidly as the temperature rising the highest temperature from 2°C to 13°C. From summer to winter, the average DOC concentrations decreased gradually during the temperatures decreasing from 13°C to -11°C, and the lowest value was recorded in November. There were a great variance in the seasonal DOC export fluxes, ranging from 0.406 kg/(km²·d) to 11.022 kg/(km²·d) among the rivers under different land cover types. DOC export fluxes were positively correlated with average runoffs in the watersheds. The highest DOC export was recorded in the spring snowmelt period and the rainy summer.

2019038092 Yanagiya, Kazuki (Hokkaido University, Sapporo, Japan) and Furuya, Masato. Post-wildfire ground deformation in eastern Siberian permafrost areas detected by InSAR [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1399, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw by recent global warming can liberate the frozen organic carbon, which is decomposed into greenhouse gasses. As the released greenhouse gasses may lead to a positive feedback of global warming, it is important to monitor where and how permafrost thawing has been occurring. However, it is infeasible to perform direct field observations over such wide areas where permafrost is distributed. Instead, it is technically possible to monitor the subsidence and uplift of the ground over the wide areas, which could make a significant contribution to monitoring thawing processes of permafrost. In this study, we observe quantitatively the amount of ground deformation in the vast permafrost area with InSAR (Interferometric Synthetic Aperture Radar) image analysis. In particular, we focus on post-wildfire areas where remarkable deformation is occurred and reveal the spatiotemporal change of that.

2019038123 Yang Bo (China University of Geosciences, Wuhan, China); Hu Xiangyun; Lin Wule and Liu Shuang. Exploration for gas hydrate with audio-magnetotelluric data in the Juhugeng Mine of Qilian Mountain permafrost, China [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS23A-0686, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Gas hydrate in onshore permafrost area of China only occurs in the Juhugeng mine of Qilian Mountain until now. However, its subsurface distribution remains unclear. Electrical resistivity logs reveal the resistivity of zones containing gas hydrate is high than that of surrounding zones, which makes the electromagnetic (EM) methods available to detect the gas hydrate deposits. We deployed a natural-source audio-magnetotelluric (AMT) survey at the Juhugeng mine. AMT data were collected at 176 sites along five profiles and the resistivity models were derived from two-dimensional (2D) inversions after detailed data analysis. The resistivity model from profile 1 yielded good agreements with the gas hydrate inferred from the drill holes information. We found that the permafrost near surface with high-resistivity and high-thickness is also essential to the existence of underlying gas hydrate besides gas source, migration pathways, and reservoir rocks. The decrease in the resistivity and/or thickness of the permafrost caused by climate warming may lead to the gas hydrate dissociation. The other four AMT transects without logging data suggest three gas hydrate prospects, and one of them correlates well with previous geochemical observations. Our study can also provide useful reference for AMT exploration on gas hydrate in other potential regions.

2019037775 Yang Yuanhe (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Yang Guibiao; Peng Yunfeng and Olefeldt, David. Changes in methane flux along a permafrost thaw sequence on the Tibetan Plateau [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31E-2484, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost thaw alters the physical and environmental conditions of soil and may thus cause a positive feedback to climate warming through increased methane emissions. However, the current knowledge of methane emissions following thermokarst development is primarily based on expanding lakes and wetlands, with upland thermokarst being studied less often. In this study, we monitored the methane emissions during the peak growing seasons of two consecutive years along a thaw sequence within a thermo-erosion gully in a Tibetan swamp meadow. Both years had consistent results, with the early and mid-thaw stages (3 to 12 years since thaw) exhibiting low methane emissions that were similar to those in the undisturbed meadow, while the emissions from the late thaw stage (20 years since thaw) were 3.5 times higher. Our results also showed that the soil water-filled pore space, rather than the soil moisture per se, in combination with the sand content, were the main factors that caused increased methane emissions. These findings differ from the traditional view that upland thermokarst could reduce methane emissions owing to the improvement of drainage conditions, suggesting that upland thermokarst development does not always result in a decrease in methane emissions.

2019038115 Yao Yingying (Xi'an Jiaotong University, Department of Earth and Environmental Science, Xi'an, China); Andrews, Charles; Wu Yiping and Zheng Chunmiao. Contribution of groundwater system on the streamflow of Yarlung Zangbo River and implications for the water-energy nexus [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H34I-10, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In the high Qinghai-Tibet Plateau, precipitation, ice and snow are sources of streamflow of the large rivers, which provide water resources particularly for food production and hydropower. Groundwater systems with seasonally frozen ground (SFG) and permafrost regulate the seasonal discharge through separating the baseflow from precipitation and melted ice and snow. The questions of how groundwater systems considering SFG and permafrost contribute to streamflow, what spatial variability of this contribution represents in regional-scale and to what extent this spatial contribution impacts the hydropower are lacking. In this study, we access these scientific gaps in the Yarlung Zangbo River Basin, which is one of the largest rivers originated from the Himalaya region. A hydrological model was used to simulate the spatial streamflow variation and groundwater recharge, then a coupled groundwater and heat transport model was used to simulate the flow pattern of groundwater system and seasonal discharge under freeze-thaw conditions. Multiple model scenarios were made to evaluate the sensitivity of groundwater discharge on hydropower. Our preliminary results show that the groundwater discharge from melted ice and snow contributes roughly less half of the annual streamflow in the upper and part of lower stream areas and less 20% in the middle stream. Groundwater discharge in dry season contributes hydropower generation in the upper stream. Our study not only bridges the quantification gap for the role of groundwater in the Himalaya region but also provides the implications for water-energy nexus and water engineering planning in the headwater regions.

2019040640 Yi, Y. (Jet Propulsion Laboratory, Pasadena, CA); Chen, R. H.; Miller, C. E.; Moghaddam, M. and Kimball, J. S. Developing a modelling framework to characterize sensitivity of soil freezing processes to snow cover changes and active layer dynamics in Arctic Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C33F-1628, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Contribution of cold season soil respiration to boreal-arctic carbon cycle and its potential feedbacks to climate change remain poorly quantified, largely attributed to a poor understanding of changes in soil thermal regime and unfrozen water content during soil freezing/thaw (F/T) period. Here we developed a modelling framework integrating in-situ observations, airborne longwave radar data and a remote sensing based permafrost model to investigate underlying processes controlling soil F/T in Arctic Alaska. To better capture the regional variability of snow cover changes, we developed a new algorithm to downscale a global coarse-resolution (»0.5°) reanalysis snow dataset using the cloud filtered MODIS snow cover extent data to drive the permafrost model. The downscaled 1-km snow depth data showed fine-scale variability closely associated with local topography, and compared well with in-situ SNOTEL observations across Alaska, with a mean RMSE of 0.16 m and bias of -0.01 m in Arctic Alaska. We also used the in-situ soil dielectric constant ((open e)) measurements within the soil active layer to guide model parameterization of soil organic carbon profile and unfrozen water content curve. This will lay the foundation for a joint radar-soil modeling framework currently under developing. The model simulated zero-curtain period was generally consistent with the in-situ observations across a 2° latitudinal transect in Alaska North Slope; both the observed and model simulated zero-curtain period are positively correlated (R>0.55, p<0.01) with MODIS SCE during early snow season. Analysis using the Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) P-band radar data along the same transect showed a larger reduction in radar retrieved surface (open e) in early October in areas with lower SCE, indicating earlier frozen conditions in those areas. Across regional scale, model simulated zero-curtain period at the top soils (< 0.4 m) from 2001 to 2016 was significantly correlated with MODIS snow onset, with earlier snow onset areas generally associated with longer zero-curtain period. However, active layer dynamics becomes more important in controlling deep soil freezing process; therefore, warming induced deepening active layer will potentially result in large carbon loss and permafrost carbon feedback.

2019040662 Yoon, Hyun Chui (Texas A&M University, College Station, TX); Kim, Jihoon and Lee, Joo Yong. Rigorous field-wide simulation of the gas hydrate deposit located in Ulleung Basin and the geomechanical responses during depressurization. [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS31F-1861, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Gas hydrate deposits are located in deep oceanic and permafrost areas, being considered as one of the potentially substantial future energy resources. Depressurization is a conventional method to extract methane from the gas hydrates, but it may cause geomechanical problems. Geological instability due to dissociation of hydrates also causes problems in production facilities and well stability, and thus coupled flow and geomechanics are necessary for accurate modeling of behaviors of hydrate deposits. However, the gas hydrate deposits exhibit complex physical processes including flow, geomechanics and chemistry. In particular, the Ulleung Basin gas hydrate deposits are located below in the deep sea, and large deformation followed by geomechanical instability might be possible. Yet, field-wide simulation is still less investigated due to complexity of the coupling between flow and geomechanics as well as of mathematics. Large scale simulation is required for accurate prediction for long term production. We have developed a reliable coupled flow-geomechanics simulator for large-scale field-wide simulation of gas hydrate deposits, named T+M. This simulator is based on the fixed-stress sequential method that can provide unconditional stability and convergence in two-way coupling, combining TOUGH+Hydrate (flow simulator) with ROCMECH (geomechanics simulator). Then, by using T+M, we can perform rigorous large-scale simulation with computational accuracy and efficiency. In this study, we first focus on the early-time behavior of geomechanics and well stability, for example, during 14-day production with various levels of depressurization. We then analyze geomechanics responses and productivity of gas for long-term production.

2019038110 Yoshida, Natsuki (Tokyo Institute of Technology, Civil and Environmental Engineering, Tokyo, Japan); Oki, Taikan and Kanae, Shinjiro. How equilibrium state of soil moisture and groundwater table is influenced by climate on global scale [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract H11O-1644, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Groundwater and soil moisture are key components of the terrestrial water cycle. The equilibrium state of soil moisture and water table is important to understand water balance and has been investigated on regional scales and a global scale. However, the equilibrium state of soil moisture and water table interaction has never been investigated on a global scale. Hence, this study focuses on explaining the equilibrium state of soil moisture and water table as influenced by climate on a global scale. The concept of 'climatological equilibrium state' in hydrology was proposed and define it as the situation when a similar pattern of climate continues for a long time. Within the modeling framework of one dimensional coupled land surface and water table dynamics, a 30 years climate forcing has been repeated to create a 1020 year-long synthetic climate dataset. The offline simulations under wet and dry initial condition and with and without effect of frozen soil are conducted. The simulated water table depth, soil moisture and runoff are compared with observations. The relationship between soil moisture, water table depth and climate (precipitation, evapotranspiration, budyko's dryness index) were analyzed. The results revealed that ~20% of land surface area does not reach the climatological equilibrium state, mostly in arid and semi-arid regions while ~80% of land surface area reach the climatological equilibrium state. The 'climatological e-folding time'( simulation years to reach the equilibrium) is ~300 from 600 years at arid and semi-arid regions and ten times longer than assumed 30 years as climate. It suggests that response of water table is slow to climate change and water table is transient at those regions under the current climate because in reality, climate will change before water table reach the equilibrium. The initial condition (existence of ice, water table depth, soil moisture) remain for a long time at permafrost area and it is important to know past climate and hydrological state for understanding current state at permafrost area. The analysis showed shallow groundwater table is controlled by E/P (evapotranspiration divided by precipitation) and it depends on land use type. In conclusion, soil moisture and water table are found to be transient in arid and semi-arid regions under the current climate.

2019040664 Yuan, Yilong (Jilin University, Changchun, China); Xu and Xin Xin. Prospects of gas production from the sedimentary complex hydrate reservoir using conventional technology [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS31F-1860, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane hydrate is expected to be an alternative energy source with extensive distribution in nature in permafrost and in marine sediments. As shown in Fig. 1, a few short-term production tests focusing on reservoir depressurization have been conducted in recent years. As more field data from logging-while-drilling, seismic interpretation, and core sample analysis became available to characterize the actual hydrate deposits, more realistic reservoir models can be developed. In this work, we extensively used the well-logging data and core samples analyses results at the Eastern Nankai Trough of Japan. A more realistic reservoir model was constructed, which considers the vertically varying lithofacies, porosity, permeability, and hydrate saturation. The reservoir model was validated by comparing the fluid flow rates at production well and temperature changes at a monitoring well. Based on the validated reservoir model, we investigate (1) the multiphase flow behavior, and (2) the long-term gas production potential from the sedimentary complex hydrate reservoir. Additionally, the systematic comparison of gas production between heterogeneous reservoir and homogeneous one was performed to clarify the essential mechanism that results in the difference caused by the vertical heterogeneity. This is very important to guarantee the effective productivity forecast in the future. The modeling results indicate that the hydrate dissociation zone is strongly affected by the reservoir heterogeneity and shows a unique dissociation front. Gas production rate is expected to increase with time and reaches the considerable value of 3.6 ´ 10⁴ ST m³/d, owing to the significant expansion of the dissociation zone. The numerical model using a simplified description of porosity, permeability, and hydrate saturation leads to significant underestimation of gas productivity from the sedimentary complex hydrate reservoir. The most advanced dissociation front exceeds 500 m from the production well after one year production. This emphasizes the field faults system should be carefully considered when conducting the long-term field production test in the future. The results also suggest that the interbedded hydrate occurrence systems might be the better candidate for methane gas extraction than the massive hydrate reservoirs.

2019040661 Yuan Yilong (Jilin University, Jilin, China); Xu Tianfu and Xin Xin. Prospects of gas production from the sedimentary complex hydrate reservoir using conventional technology [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS31F-1860, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Methane hydrate is expected to be an alternative energy source with extensive distribution in nature in permafrost and in marine sediments. As shown in Fig. 1, a few short-term production tests focusing on reservoir depressurization have been conducted in recent years. As more field data from logging-while-drilling, seismic interpretation, and core sample analysis became available to characterize the actual hydrate deposits, more realistic reservoir models can be developed. In this work, we extensively used the well-logging data and core samples analyses results at the Eastern Nankai Trough of Japan. A more realistic reservoir model was constructed, which considers the vertically varying lithofacies, porosity, permeability, and hydrate saturation. The reservoir model was validated by comparing the fluid flow rates at production well and temperature changes at a monitoring well. Based on the validated reservoir model, we investigate (1) the multiphase flow behavior, and (2) the long-term gas production potential from the sedimentary complex hydrate reservoir. Additionally, the systematic comparison of gas production between heterogeneous reservoir and homogeneous one was performed to clarify the essential mechanism that results in the difference caused by the vertical heterogeneity. This is very important to guarantee the effective productivity forecast in the future. The modeling results indicate that the hydrate dissociation zone is strongly affected by the reservoir heterogeneity and shows a unique dissociation front. Gas production rate is expected to increase with time and reaches the considerable value of 3.6 ´ 10⁴ ST m³/d, owing to the significant expansion of the dissociation zone. The numerical model using a simplified description of porosity, permeability, and hydrate saturation leads to significant underestimation of gas productivity from the sedimentary complex hydrate reservoir. The most advanced dissociation front exceeds 500 m from the production well after one year production. This emphasizes the field faults system should be carefully considered when conducting the long-term field production test in the future. The results also suggest that the interbedded hydrate occurrence systems might be the better candidate for methane gas extraction than the massive hydrate reservoirs.

2019040665 Zhang, Xin (Chinese Academy of Sciences, Institute of Oceanology, Qingdao, China); Du, Zengfeng; Xi, Shichuan; Li, Lianfu; Luan, Zhendong; Wang, Bing; Cao, Lei; Lian, Chao and Yan, Jun. Gas hydrates associated with hydrothermal vents [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract OS41A-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Normally, the gas hydrates are distributed throughout permafrost regions and continental margin sediments. The necessary conditions for the formation of gas hydrates are low temperature and high pressure. Therefore, it is generally believed that the gas hydrates cannot be formed nearby the high temperature hydrothermal vents. Here, we report the first discovery of the gas hydrates exposed on the seafloor around the high-temperature deep-sea hydrothermal vents. The minimum distance between the gas hydrates and the high-temperature hydrothermal vents up to 364°C is less that 30 cm. The gas hydrates have been found at three hydrothermal fields of the Okinawa trough during two cruises of RV Kexue at 2016 and 2018. The in situ chemical compositions and cage structures of these gas hydrates were measured by a Raman insertion probe for gas hydrate (RiP-Gh) that was carried and controlled by the remotely operated vehicle (ROV) Faxian at the depth down to 2190 m. The in situ Raman data indicated that all these three locations are the mixed hydrates of CO₂ and CH₄, and the composition of CH₄ hydrate is much higher than that of CO₂ hydrate, which is opposite to the composition of CH₄ and CO₂ in the surrounding hydrothermal vent fluids. The gaseous and dissolved gas spectra of CH₄, CO₂ and H₂S with seawater were also observed at these gas hydrates sites. It indicated that these hydrates are not monolithic single structures but can instead record significant small-scale heterogeneities due to inclusions of free gas and surrounding seawater. We also fund S₈ Raman peaks at some of the gas hydrates, which can act as nucleation particles for the formation of these gas hydrates. Deep-sea hydrothermal activities are widely developed in the mid-ocean ridges and back-arc basins. Our results indicated that the global hydrothermal fields may also bury a large amount of gas hydrates and play a significant impact on future energy supplies and climate change.

2019038087 Zhang, Yu (Natural Resources Canada, Canada Centre for Remote Sensing, Ottawa, ON, Canada); Sherstiukov, Artem; Qian, Budong; Kokelj, Steve and Lantz, Trevor C. Impacts of snow on soil temperature observed across the circumpolar north [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1394, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost temperature observations are sparse, which limits our understanding and mapping permafrost at landscape scale. From August 2016 to August 2017, we measured near-surface (about 5 inch or 13 cm depth) soil temperatures (Ts) at 107 sites around Inuvik and Tuktoyaktuk in northwestern Canada. They are in northern boreal area and low-arctic tundra, respectively. These multi-site observations show strong variations within each study area. The site variation of Ts mainly occurs in snow-cover period, indicating the importance of snow. Ecotypes are effective for stratifying Ts in snow-cover period and annual mean Ts, but not for Ts in thawing months. Ecotypes are useful to stratify organic layer thickness and active-layer thickness (ALT) in low-arctic tundra, but not in northern boreal area. The site variation of ALT does not correlate with thawing season Ts but is determined by the edaphic factor. There is a significant and positive correlation between ALT and Ts in snow-cover period in both areas. The soil near the highway is warmer due to snow accumulation near the embankment and changes of land cover during highway construction. These results are useful for understanding and mapping permafrost at landscape scale and for assessing the impacts of highway on permafrost.

2019038107 Zhang Fan (Chinese Academy of Sciences, ITP Institute of Tibetan Plateau Research, Beijing, China) and Wang Guanxing. Response of sediment transport in the up- and midstream of the Heihe River to the climate change and human activities [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC52C-05, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Heihe River originated in the Qilian Mountain on the northeast margin of the Tibetan Plateau is the second largest inland river in northwestern China. The river is divided into the up-, mid- and downstream segments by the Yingluoxia (YLX) and Zhengyixia (ZYX) hydrological stations, respectively. There are two major tributaries in the upstream segment, i.e., the Yeniugou river in the west and the Babao river in the east controlled by the Zhamashike (ZMSK) and Qilian (QL) hydrological stations, respectively. These two tributaries join together at the Huangzangsi (HZS), which is 95 km upstream from YLX. River runoff is mostly generated in the upstream segment where the land use is mainly grassland (69.1%), unused land (24.0%) and built-up land (0.2%). In contrast, the river runoff is largely consumed in the midstream segment where the land use is mainly unused land (40.2%), grassland (36.0%), cropland (17.3%) and built-up land (0.8%), indicating noteworthy human activities. To recover the degraded eco-environment in the downstream segment due to the large water consumption in the midstream, cascade reservoirs were constructed between HZS and YLX through the Ecological Water Diversion Project (EWDP) and started to retain water since 2001. To evaluate the impact of climate change and human activities, e.g., irrigation and EWDP on sediment transport in the up- and midstream, Kendall trend analysis, double mass curve (DMC) and elastic coefficient method were applied to analyze the observation data at the four hydrological stations. The results showed that climate change controlled the sediment transport in the upstream of both ZMSK and QL. Because the glacier and permafrost area in the upstream of ZMSK was almost 4 times of that in the upstream of QL, sediment transport at ZMSK adventured more drastic increase than QL under the background of significant warming. At YLX, the climate change resulted in 36.7% increase of sediment load while human activities introduced 136.7% reduction comparing 2001-2017 to 1960-1995. At ZYX, climate change and human activities contributed 84.5% and 15.5% of the sediment load decrease during 1991-2000, but 8.3% increase and 108.3% decrease during 1991-2000, respectively.

2019038089 Zhang Jiahua (Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, China); Liu Lin and Hu Yufeng. Investigating the changes in surface elevation of permafrost terrain in the Canadian Arctic measured by GPS interferometric reflectometry [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1396, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The Canadian Arctic is one of the most sensitive areas to the warming climate. Borehole temperatures have shown that the permafrost in this region has been warming since the mid-1970s. The ground surface in permafrost terrain undergoes subsidence or uplift, due to seasonal thawing or freezing of the active layer and decadal degradation or aggradation of the permafrost. Recent studies have shown the capability of GPS Interferometric Reflectometry (GPS-IR) of obtaining such vertical deformation of ground surface. In this study, we screen the Canadian Active Control System (CACS) and identify five GPS stations (ALRT, RESO, REPL, BAKE, and IQAL). All of these stations are located in continuous permafrost areas and suitable for GPS-IR studies. At each site, we apply the GPS-IR and then construct continuous time series of surface elevation changes. We find that the ground surface subsided at ALRT by 0.79±0.04 cm/year during 2012-2017 and RESO by 0.68±0.02 cm/year during 2003-2014. By contrast, we find uplift trends at the other three sites: 0.03±0.09 cm/year at REPL during 2014-2017, 0.02±0.02 cm/year at BAKE during 2010-2017, and 0.34±0.02 cm/year at IQAL during 2010-2017. We choose the records at RESO for detailed investigation as they are the longest among the five. From 2003 to 2014, the seasonal surface elevation changes were irregular and inconsistent. And significant summer heave could be observed in 2003 and 2007. Moreover, end-of-thaw-season surface elevations exhibited large interannual variability, and they were highly negatively correlated with the thawing indices represented by the square root of degree days of thawing (²ÖDDT) (see Fig 1). However, after 2011, the end-of-thaw-season surface elevations were low even with the low ²ÖDDT. Such phenomenon indicates the Markovian behavior of active layer. In the extremely warm thawing season of 2011, the ice loss near the permafrost table or the changes in soil moisture within the active layer reset the response of the active layer to the atmospheric forcing. This study shows that five GPS stations from CACS can be used to investigate the surface elevation changes of the permafrost areas in the Canadian Arctic by GPS-IR, and also demonstrates that the end-of-thaw-season surface elevations are independent measurements to investigate the changes in frozen ground.

2019038105 Zhang Tingjun (Lanzhou University, College of Earth and Environmental Sciences, Laboratory of West China's Environment, Lanzhou, China) and Wang, Kang. Enhanced cold-region/cold-season warming and its implications to permafrost degradation [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC51O-0975, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

It has been well documented that climate warming was greater in the Arctic than elsewhere. Observed evidence also shows that increase of permafrost temperatures was outpaced the increase in air temperature over the past decades in the Arctic, especially for cold permafrost. Meanwhile, changes in active layer thickness provided mixed signals with increase in some places, no change or even decrease in the other sites. In this study, we investigated changes in air temperatures, especially seasonal air temperatures, over different permafrost regions in the Northern Hemisphere using the Climate Research Unit (CRU) gridded datasets from 1976-2016. The primary results indicated that permafrost regions as a whole experienced a warming at 0.36, 0.41, and 0.46°C/decade in mean annual maximum, mean, and minimum air temperature, respectively, which are 16%, 32%, and 44% higher than the corresponding trend in non-permafrost regions. More importantly, strong increases occurred in cold months and nighttime over continuous permafrost zone, exceeding 0.72°C/decade in Spring and Autumn; while summer air temperature had a relatively small increase or no statistically significant trends. As a result, the decrease of air freezing index by 529°C-day would result in permafrost temperature increase by 1.43°C in continuous permafrost zone over the past four decades. This may explain the observed evidence that increase of cold permafrost temperature was greater than that of warm permafrost, while active layer thickness had little or no change during the past several decades. These results suggest that permafrost thawing may not be as fast as the global climate models predicted.

2019038084 Zhao Lin (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Lanzhou, China); Sun Zhe; Hu Guojie and Qiao Yongping. Modeling permafrost temperature development on the Qinghai-Tibetan Plateau from 1966 to 2100 [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract GC33D-1391, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Great amount of literatures indicated that the permafrost on the Qinghai-Tibet Plateau (QTP) is degrading obviously due to the climate warming in the last several decades, and it have taken its effects on the local engineering, hydrological and environmental conditions. Ground temperature field, considered as a key indicator of permafrost evolution, can not only represent the thermal regime of active layer, but also reflect historical climate changes in a certain extent and the evolution trend of permafrost in the future. Based on high-resolution active layer hydrothermal data and boreholes ground temperature data from the Cryosphere Research Station on Qinghai-Xizang Plateau of Chinese Academy of Sciences, a numerical model of ground heat conduction was used to simulate the past and future permafrost temperature development on the Qinghai-Tibetan Plateau. First, the model was forced with a reconstructed historical ground surface temperature series reaching back to 1966. Second, the measured ground temperature series was used to validate the mode. Third, the impact of future climate change on permafrost temperature until 2100 was predicted by the model under the different RCP scenarios. The results show that the model is able to describe the heat transfer process in permafrost accurately; during 1966 to 2012, the declines of the permafrost table were slight, but the permafrost thickness obviously decreased because of the rise of the permafrost base at Xidatan located in the island permafrost zone near the northern limit of permafrost region; under the RCP 2.6, the permafrost mainly degrades upwards at Xidatan, while the permafrost degradation is not remarkable at Tanggula located at the hinterland of the continuous permafrost zone; under the RCP 6.0 and RCP 8.0, with the significant permafrost degradation at both Xidatan and Tanggula, the permafrost degradation mode changes from upwards to bidirectional when the gradient is closed to zero grads in the permafrost at Xidatan, while downwards is the main permafrost degradation mode at Tanggula throughout; during 2012 to 2100, under the different RCP scenarios, the permafrost table declines by 0.3-13.6 m at Xidatan and 0.85-15.2 m at Tanggula respectively, and the permafrost base rises by 9-11.5 m at Xidatan and <2 m at Tanggula respectively.

2019037800 Zheng, Aiyu (Princeton University, Ecology and Evolutionary Biology, Princeton, NJ); Natali, Susan; Schade, John D.; Sistla, Seeta; Ludwig, Sarah and Mann, Paul James. The impact of fire on energy balance in tundra soils in the Yukon-Kuskokwim Delta, AK; implications for permafrost thaw under climate change [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2544, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Rapid climate change in the Arctic is thawing permafrost and exposing carbon stored there to microbial processing and loss to the atmosphere as greenhouse gases. Climate change is also increasing fire frequency and intensity in Arctic tundra. These changes may be significantly impacting energy balance by altering heat transfer between air and the ground, within the soil profile, and heat associated with phase change of water. To understand the impact of fire on heat transport along topographic gradients from highland peat plateaus to lowland soils in the Yukon-Kuskokwim (YK) Delta, AK, this study collected soil moisture, soil temperature, surface temperature, air temperature, and evapotranspiration data from nine burned and nine unburned sites. Experiments on burned and unburned soil along the topographic gradients were conducted to assess soil thermal inertia. Results show that temperature differences between air and soil surface on burned peat plateaus decreased due to changes in soil structure and moisture. After removal of vegetation cover by fire, burned soil lost the capacity to shed heat through evapotranspiration, resulting in higher soil temperature. Patterns in soil temperature along topographic gradients following rain events suggest that higher soil bulk density on highland peat plateaus after fire contributed to greater runoff. Overall, the 2015 fire in the YK Delta altered energy balance along the topographic gradient and increased soil temperatures, which is likely to contribute to accelerating permafrost thaw.

2019040649 Zheng, L. (Wuhan University, Chinese Antarctic Center of Surveying and Mapping, Wuhan, China); Clow, G.; Overeem, I. and Wang, K. Enhanced degradation of permafrost under increasing inundation in the Kuparuk delta, Alaska [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C43C-1809, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost in the Alaskan Arctic may be degrading in response to continuous amplified warming. Advanced degradation of ice-rich permafrost could significantly alter the water balance by increasing runoff and standing water. How do the hydrological changes, in turn, affect the permafrost conditions? Here, we present an investigation into the effect of river dynamics on the permafrost thermal state in Kuparuk delta, Alaska. Flood water occurrence was retrieved based on the river discharge and the ArcticDEM with a spatial resolution of 2 m. Driven by ground and river water temperature, permafrost temperatures and active layer thickness (ALT) along a cross-section in the Kuparuk floodplain were simulated with the Control Volume Permafrost Model (CVPM). The results indicate that permafrost warms during flood conditions, and ALT can increase for about 40 cm with sustained inundation in the floodplain. Water bodies in the Kuparuk delta extended since the 1980s according to the satellite observations, which may contribute to the degradation of local permafrost conditions. More generally, Alaskan permafrost is vulnerable to future changes in timing and magnitude of freshwater flooding as a result of earlier spring snowmelt, ice-wedge degradation, glacier recession and thinning. Degradation of permafrost in floodplains could potentially lead to the release of old carbon.

2019038128 Zheng Guanheng (Tsinghua University, Department of Hydraulic Engineering, Beijing, China) and Yang Dawen. Spatiotemporal changes of frozen soils in the Tibetan Plateau estimated by a processes-based model and satellite data [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract NS42A-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Frozen soils are widely spread in the Tibetan Plateau (TP) and the seasonally freezing-thawing processes of near-surface ground is important for the runoff regime of many large Asian rivers originated there. During the past several decades, global warming has been the most significant aspect of climate change and TP is among the most sensitive regions. A limited number of field observations in TP have shown the serious degradation of frozen soils on the local scale. In order to acquire the changes of frozen soils in regional scale, previous studies relied on the simulated results from processes-based models. And, these models always needed the spatially distributed meteorological data as inputs. However, the meteorological observations are very sparse in the TP and there is even no station in the western or high-altitude (>5000 m) regions. In contrast, the satellite sensors can monitor the land surface condition in much higher spatial resolutions and it is possible to use the satellite remote sensing data to drive the processes-based model to estimate the spatiotemporal changes of frozen soils in the TP. In this study, all the satellite remote sensing datasets are publically available and the processes-based model used is the geomorphology-based eco-hydrology model (GBEHM). The satellite remote sensed land surface temperature, precipitation, cloud fraction, air temperature, air pressure, relative humidity, and surface albedo are used to force the GBEHM to simulate the soil freezing-thawing processes over the TP from 2002 to 2015. The model simulation is validated using the synchronous ground measured frozen depths and soil temperature at 135 China Meteorological Administration stations. Based on the simulated results, the spatiotemporal variabilities of frozen soil types, maximum thickness of seasonally frozen ground, and active layer thickness of the permafrost land are analyzed.

2019037871 Zhou Zhiwei (Chinese Academy of Sciences, Institute of Geodesy and Geophysics, Wuhan, China); Jiang Liming; Liu Lin; Wang Hansheng and Zhang Tingjun. Rapid development of thermokarst terrains detected by repeated UAV images in the northeastern Qinghai-Tibetan Plateau, China [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51C-1064, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

The widespread and rapid permafrost degradation on the Qinghai-Tibet (QT) Plateau since 1950s can be mainly attributed to climatic warming. In this study, we aim to detect and quantify the development of hillslope process thermokarst through repeat UAV images, mainly focus on sinkhole, thermal erosion gully and thaw slump-gully complex. Two high resolution DSMs obtained by UAV in July 2016 and June 2017 is used to calculate the difference. The results showed that the headwall of sinkhole was withdrawn by nearly 7 meters, the decrease in thickness is up to -5 m. The retrogression of boundary of erosion gully mainly happened in the initial and end zone, and up to 15 m. Obvious subsidence zones are observed in the middle and the end of gullies. The subsidence rate is up to -1.7 m/year, which is much lower than that of sinkhole. Clear decrease signals in depth can be observed in the headwall, middle and end zone. The highest subsidence rate of slump-gully complex is up to -2.9 m/year. The boundary changes less, it retreats about 5 m/year in maximum and mainly happens in headwall and end zone. Under the same climate conditions, the changes of the three types of thermokarst terrain show different change pattern in topography and geomorphology. Compared with the other regions, the change rates in thickness and boundary are faster. This study also presents UAV has great potential in detecting and monitoring the rapid permafrost thermokarst changes in topography and geomorphology.

2019040609 Zimov, N. (Russian Academy of Sciences, North-East Scientific Station, Pacific Institute of Geography, Cherskii, Russian Federation); Zimova, G.; Gabaidulin, Alexandr; Shipilov, Konstantin; Sleptsov, Valeriy and Zimov, S. A. Pleistocene Park experiment; effect of grazing on the accumulation of soil carbon in the Arctic [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B33B-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

In the late Pleistocene Mammoth Steppe was the world largest ecosystem. It was a highly productive steppe ecosystem with numerous herbivores that maintained the dominance of grasslands. Over tens of thousands of years this ecosystem was accumulating carbon in the soil. Portion of this storage still persist in the permafrost of Siberia and Alaska. With the end of the Pleistocene, and human expansion this ecosystem vanished. Mosses, shrubs and larch forest soon replaced grasses and herbs. Pleistocene Park is an experiment conducted in the far north of Siberia; its main goal is to restore the high productive steppe ecosystems in the Arctic similar to the Mammoth Steppe. This would increase the richness of the northern ecosystems and bioproductivity, and through a series of ecological mechanisms help to mitigate climate change. To conduct the experiment, we fenced 2000 hectares of land, and continue the ongoing process of introducing animals that either lived on this territory in the past or that can adapt to the modern northern environment. Through grazing, animals slowly transform the vegetation, replacing mosses, shrubs, and trees with grasses and herbs. Here we present detailed carbon inventory map of the Pleistocene Park territory, which been the subject of the active grazing in the last 20 years. Analyses are based on 300 frozen soil cores drilled in April-May 2018 within the oldest fenced area and territories outside of the Pleistocene Park with no grazing effect. Data indicates substantially higher carbon storage within entire soil profile (0 to 1 meter) for the grazed pastures. Based on 1200 samples taken at various depths average carbon content within the fenced area is 7.7% from dry weight. We attribute higher carbon soil content at the actively grazed pastures to the following mechanisms: Increased turnover of nutrients on the pastures compared with the modern Arctic ecosystems. Grasses root system is penetrating to the deeper soil horizons where decomposition of organic matter is very slow. More active photosynthesis dries soil through evapotranspiration and creates a more developed root system is required. Grasses adapt to high grazing pressure by dedicating a higher portion of productivity to the root system. Restoration of high productive steppes will create a soil carbon sink in the Arctic.

2019037798 Zimov, Nikita (Russian Academy of Sciences, Pacific Institute for Geography, Northeast Scientific Stations, Cherskiy, Russian Federation) and Zimov, Sergey A. Climate warming causes carbon rich permafrost in the North of Siberia to degrade [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract B31F-2538, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Permafrost is the biggest organic carbon reservoir. It stores 1672 Gt of carbon, twice the amount stored in the atmosphere. Siberian yedoma is the most carbon-rich of all permafrost. Because of thickness of the strata it can store up to 1000 kg C/m². The largest area of yedoma is located in the lowlands of Kolyma and Indigirka rivers. If this permafrost thaws, region can become largest greenhouse gas emitter. On the other hand, this region is one of the coldest, suggesting that yedoma degradation will not occur soon. However, in recent years average annual air temperature on the Kolyma river lowland increased by 3°C, and the amount of snow doubled. Both these parameters increased temperature of soils on 8°C. This caused permafrost degradation during winter of 2017-2018 when deep active layers did not re-freeze throughout cold season. At the most sites where moss-organic layer is thin or absent less than a half of thawed layer froze. Historically at these sites the active layer freezes entirely in November-January. Similar doubled snow depth was observed at all meteorological stations in Kolyma and Indigirka river watersheds. If permafrost started to thaw in the coldest region then soon it can start to thaw everywhere. Most organic matter in permafrost is preserved in the top 2-3 meters. This layer may take only several years to thaw. This means there is a risk hundreds of gigatons of organic carbon will become available for decomposition within a few years. In this case, CO₂ emission to the atmosphere can exceed anthropogenic emission.

2019037856 Zwieback, Simon (University of Guelph, Guelph, ON, Canada); Westermann, Sebastian; Langer, Moritz; Boike, Julia; Marsh, Philip and Berg, Aaron A. The importance of soil moisture for permafrost modeling [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C51B-04, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.

Soil temperatures are closely coupled with soil moisture in permafrost environments. However, dynamic changes in soil moisture have not been given much attention in permafrost modeling, e.g. in long-term predictions. We illustrate the importance of surface soil moisture for permafrost modeling using the Cryogrid-3 model (a permafrost model with surface energy balance boundary condition) coupled with a dynamic soil moisture module. We explore the two key processes by which surface soil moisture affects soil temperature profiles: evapotranspiration and changing thermal properties. These two have partially opposing tendencies; evaporation cools moist soils; the larger thermal conductivity leads to increased heat flux to deeper layers and thus warmer deeper soil temperatures. The magnitude of the effect depends on the depth at which the temperature is measured, the environmental conditions and soil type in complex ways that are difficult to capture with traditional but widely used schemes such as those based on n-factors. We then show how permafrost modeling can benefit from soil moisture information by assimilating satellite soil moisture observations from Radarsat-2 into the Cryogrid-3 model. The assimilation exploits the dynamic coupling between surface soil moisture and the soil temperature profile to update the soil temperatures given a (noisy) soil moisture observation. The soil temperature estimates improve most for thick organic soils in our subarctic tundra site (Trail Valley Creek, NWT, Canada), but improvements are also found for mineral soil hummocks with thinner organic soil covers. The results highlight the importance of accurate soil moisture information for understanding and predicting soil temperatures in permafrost regions.

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