2019072187 Gyalay, Szilard (University of California, Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA); Noe Dobrea, Eldar Z.; Chu, Kathryn and Pitman, Karly M. Nonlinear spectral mixture modeling to estimate water-ice abundance of Martian regolith: Icarus, 329, p. 79-87, illus. incl. 3 tables, 37 ref., September 2019.
We present a new technique to estimate the abundance of water-ice in the Martian permafrost using Phoenix Lander Surface Stereo Imager (SSI) multispectral data. Past work estimated this abundance by employing radiative transfer methods to model the spectra of ice and regolith mixtures using the optical constants of water-ice and a Martian-analogue soil. Our technique removed the uncertainty of using an analogue (or of estimating a regolith composition) by deriving the optical constants directly from observations of icy regolith acquired before and after sublimation of the ice at similar viewing geometries. Laboratory spectral measurements of known mixtures of water-ice and dry soil at controlled viewing geometries allowed us to constrain the uncertainty in our technique. We found that model fits across the observational uncertainty will contain the actual water-ice fraction. We then applied the technique to Phoenix SSI observations of Snow White Trench and Dodo-Goldilocks Trench. For the Snow White Trench, we estimated water-ice abundances consistent with pore-fill in the near-surface ice, consistent with atmospheric diffusion. For the Dodo-Goldilocks Trench, we estimate water-ice abundances larger than pore-fill would allow. These results have implications to our understanding of the history of water-ice on Mars and the role of the regolith at high latitudes as a reservoir of atmospheric H2O.
2019070470 Gibbs, Ann E. (U. S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA); Nolan, Matt; Richmond, Bruce M.; Snyder, Alexander G. and Erikson, Li H. Assessing patterns of annual change to permafrost bluffs along the North Slope coast of Alaska using high-resolution imagery and elevation models: Geomorphology, 336, p. 152-164, illus. incl. 4 tables, sketch maps, 62 ref., July 2019.
Coastal permafrost bluffs at Barter Island, on the North Slope, Beaufort Sea Coast of Alaska are among the most rapidly eroding along Alaska's coast, having retreated up to 132 m between 1955 and 2015. Here we quantify rates and patterns of change over a single year using very-high resolution orthophotomosaics and co-registered surface elevation models derived from a survey-grade form of structure-from-motion photogrammetry from a fixed-wing, manned aircraft. The resulting elevation models were validated with over 10,000 ground check points and found that 95% agreed to within 20 cm, before accounting for real differences in the ground surface due to seasonality, vegetation, and checkpoint acquisition errors. This data set provides the most detailed and accurate measurements of coastal change to date along the Alaskan coast and the method is scalable to more extensive coastlines. Between July 2014 and July 2015, the bluffs retreated an average of 1.3 m, and a maximum of 8.1 m, with an associated net volume loss of 38,100±300 m3 (1.3 m3/m). This average retreat over this single year was slightly less than the 60-year mean rate of change of -1.5±0.1 m/yr, suggesting the 2014-2015 year represented relatively typical to slightly below average conditions. Most of the bluff material (70%) was lost during the 3 summer months (July to Sept) of 2014 and the remaining 30% between the late-summer and following winter-spring. The pattern of change was predominantly landward retreat of the top of the bluffs, removal of the debris apron and subsequent niching at the base of the bluffs during mid to late summer (July to Sept) followed by erosion of the bluff face and deposition of debris at the base of the bluff through the remainder of the year (Sept to the following July). Drivers of the observed change are likely a combination of thermal erosion on the bluff face throughout the summer and episodic thermo-mechanical removal of material, niching, and undercutting of the base associated with high-water levels driven by low-pressure storms and westerly winds. These patterns and high rates of change are believed to be broadly representative of coastal permafrost bluffs found along many high-latitude coastlines worldwide.
2019070465 Rodrigues, William Fortes (Universidade Federal de Ouro Preto, Departamento de Geologia, Ouro Preto, Brazil); Oliveira, Fabio S.; Schaefer, Carlos E. G. R.; Leite, Mariangela G. P.; Gauzzi, Teodoro; Bockheim, James G. and Putzke, Jair. Soil-landscape interplays at Harmony Point, Nelson Island, Maritime Antarctica; chemistry, mineralogy and classification: Geomorphology, 336, p. 77-94, illus. incl. sect., 3 tables, geol. sketch maps, 102 ref., July 2019.
Soils and landforms of Nelson Island remain one of the least studied in the South Shetlands Archipelago, despite that it is one of the oldest ice-free areas and is strongly vegetated. In this paper, we examine the main processes and factors of soil formation at Harmony Point and the relation of soils to landforms, vegetation and lithology.To achieve the goals, 26 pedons were collected and studied from a 4 km2 ice-free area at Harmony Point (S62°18'; W059°10') on the southern area of Nelson Island (Maritime Antarctica). The soils were sampled on all representative local landforms, including three levels of uplifted marine terraces up to cryoplanated plateau, waterlogged depressions, rock felsenmeer, debris slopes and patterned ground, and a paraglacial border of the ice cap (270 m a.s.l). Sampling along the cryoplanated plateau was carried out along a gradient extending inland from the margins of the Ice Cap; and sampling of the marine terraces was performed along a chronosequence under varying bird-nesting influence and age. The main pedogenetic processes observed in this area are marked phosphatization, melanization from the accumulation of organic matter, and cryoturbation. Soil development varies from weakly developed, shallow, stony and cryoturbated to well-developed and organic-rich, phosphate soils with colors ranging from grayish to brown. The mineralogical composition of the clay fraction contains secondary minerals, indicating the active role of chemical weathering. Ornithogenic soils have mature phosphate minerals such as vivianite and taranakite, as well as poorly crystalline leucophosphite. Intensively cryoturbated soils are underlain by permafrost and are classified as Typic Haploturbels; polygonal soils are widespread on the cryoplanated plateau. Areas without permafrost were classified as Typic Gelorthents. Phosphatization is a dominant soil-forming process in this area and is associated with past and present-day guano accumulation by bird nesting and has led to the the development of deeper Ornithogenic Haplorthels. The ornithogenic soils occur at different topographic levels on the cryplanated platform and marine terraces. High P concentrations can be used as a proxy of the past nesting birds' activities, with far-reaching implications, especially with regards to vegetation growth and microbial activity and diversity.
2019070462 Swanger, Kate M. (University of Massachusetts at Lowell, Department of Environmental, Earth and Atmospheric Sciences, Lowell, MA); Babcock, Esther; Winsor, Kelsey and Valletta, Rachel D. Rock glaciers in Pearse Valley, Antarctica record outlet and alpine glacier advance from MIS 5 through the Holocene: Geomorphology, 336, p. 40-51, illus. incl. 3 tables, sketch maps, 39 ref., July 2019.
Rock glaciers and buried ice are common in the McMurdo Dry Valleys, Antarctica. In central Taylor and Pearse valleys rock glaciers cover at least 10% of the valley walls and occur at elevations of 300-800 m above sea level. We investigate the origin and geomorphology of a ~1.5 km2 rock glacier in northern Pearse Valley, the westernmost extension of Taylor Valley. The rock glacier is cored by sporadic deposits of clean ice that are covered by sand-rich, stratified sediments and dissected by five glacial meltwater streams. Ground-penetrating radar data indicate that the clean buried ice ranges from 1 to 14 m thick and contains dipping sediment-rich bands. Water stable isotopes from five cores extracted from the buried ice support multiple ice sources: (1) recent ice from alpine glaciers and (2) ancient, stagnant ice from East Antarctic outlet Taylor Glacier. The eastern half of the rock glacier lies directly downslope from alpine Fountain Glacier, which is actively feeding ice, sediments and water to the rock glacier via ~1 km-long ice falls. The buried ice in this section of the rock glacier is relatively heavy isotopically and similar to Fountain Glacier (d18O of -36 ppm to -32 ppm). The ice that cores the western half of the rock glacier is isotopically light and similar to Taylor Glacier (d18O of -43 ppm to -40 ppm). The last documented advance of Taylor Glacier that was sufficient to reach the rock glacier position occurred during Marine Isotope Stage 5 (70-125 ka), implying long-term preservation of the ice. The age and origin of buried ice in Pearse Valley has implications for rock glaciers throughout the Antarctic. Rock glaciers (1) are potentially long-term archives of glacial ice with complex depositional histories and (2) could be used to map previous advances of both outlet and alpine glaciers.
2019072359 Zhang Dongming (Tongji University, Department of Geotechnical Engineering, Shanghai, China); Huang Hongwei; Zhang Dongmei; Li Zhihong; Zhou Qingzin and Zhang Kairui. Centrifuge modelling of shallow and large sectional tunnel under full pipe-jacked ring: Tunnelling and Underground Space Technology, 89, p. 189-204, illus. incl. 5 tables, 43 ref., July 2019.
2019072074 Iizuka, Yoshinori (Hokkaido University, Institute of Low Temperature Science, Sapporo, Japan); Miyamoto, Chihiro; Matoba, Sumito; Iwahana, Go; Horiuchi, Kazuho; Takahashi, Yoshio; Kanna, Naoya; Suzuki, Koji and Ohno, Hiroshi. Ion concentrations in ice wedges; an innovative approach to reconstruct past climate variability: Earth and Planetary Science Letters, 515, p. 58-66, illus. incl. sketch map, 49 ref., June 2019.
For atmospheric gases and aerosols, snow and ice provide a useful archive of paleoenvironmental history. In the northern hemisphere, this archive has been largely limited to Greenland ice, but promising pioneering work has been done recently using chronology of an ice wedge in Barrow, northern Alaska. Here, we investigate past aerosols at the same ice-wedge sampling site, reconstructing the sea-ice fluctuations in the adjacent Beaufort Sea during the Bolling/Allerod (BA) and Younger Dryas (YD) periods. We confirm the integrity of methanesulfonate ion (MS-) concentrations in the BIWS as marine proxies, and then find that the ice wedge has a high MS- concentration through the beginning (coldest) YD periods. The high MS- concentration indicates that even during the coldest YD periods (12,900-12,700 yrBP), the near-shore region in the Alaskan Beaufort Sea near Barrow may not have been completely filled by permanent sea ice.
2019072139 Morino, Costanza (Open University, School of Environment, Earth & Ecosystem Sciences, Milton Keynes, United Kingdom); Conway, Susan J.; Saemundsson, Thorsteinn; Helgason, Jon Kristinn; Hillier, John; Butcher, Frances E. G.; Balme, Matthew R.; Jordan, Colm and Argles, Tom. Molards as an indicator of permafrost degradation and landslide processes: Earth and Planetary Science Letters, 516, p. 136-147, illus. incl. sketch maps, 90 ref., June 15, 2019. Includes appendix.
Molards have been defined in the past as conical mounds of debris that can form part of a landslide's deposits. We present the first conclusive evidence that molards in permafrost terrains are cones of loose debris that result from thawing of frozen blocks of ice-rich sediments mobilised by a landslide, and hence propose a rigorous definition of this landform in permafrost environments. We show that molards can be used as an indicator of permafrost degradation, and that their morphometry and spatial distribution give valuable insights into landslide dynamics in permafrost environments. We demonstrate that molards are readily recognisable not only in the field, but also in remote sensing data; surveys of historic aerial imagery allow the recognition of relict molards, which can be used as an indicator of current and past permafrost conditions. The triggering of landslides as a result of permafrost degradation will arguably occur more often as global atmospheric temperatures increase, so molards should be added to our armoury for tracking climate change, as well as helping us to understand landslide-related hazards. Finally, we have also identified candidate molards on Mars, so molards can inform about landscape evolution on Earth and other planetary bodies.
2019071948 Dalla Santa, Giorgia (Universita di Padova, Department of Geosciences, Padua, Italy); Farina, Zeno; Anbergen, Hauke; Rühaak, Wolfram and Galgaro, Antonio. Relevance of computing freeze-thaw effects for borehole heat exchanger modelling; a comparative case study: Geothermics, 79, p. 164-175, illus., 51 ref., May 2019.
In closed-loop geothermal systems the underground may freeze and thaw due to intensive heat extraction. Phase change alters the sediments' mechanical and hydraulic properties and their thermal behaviour, thus affecting the thermal plume propagation and the area of potential changes. By means of a finite element model, this paper evaluates the thermal plume in a particular case study in several conditions, comparing the results obtained when considering or disregarding the freeze-thaw processes by applying a benchmarked plug-in. The model is based on experimental input data. The results show that the frost front propagates significantly faster when phase change occurs.
2019075878 Scheideger, Johanna M. (British Geological Survey, Environmental Science Centre, Keyworth, United Kingdom); Jackson, Christopher R.; McEvoy, Fiona M. and Norris, Simon. Modelling permafrost thickness in Great Britain over glacial cycles: The Science of the Total Environment, 666, p. 928-943, illus. incl. 6 tables, 60 ref., May 20, 2019. Includes appendix.
Like other countries, the UK has opted for deep geological disposal for the long-term, safe management of higher-activity radioactive waste. However, a site and a geological environment have yet to be identified to host a geological disposal facility. In considering its long-term safety functionality, it is necessary to consider natural processes, such as permafrost development, that have the potential to alter the geological environment over the time-scale of glacial-interglacial cycles. We applied a numerical model to simulate the impact of long-term climatic variability on groundwater flow and permafrost dynamics in two contrasting geological settings in Great Britain: (i) higher strength rocks (HSR) overlain by higher permeability sandstones with a high topographic gradient (GS1); (ii) a mixed sedimentary sequence of high and low permeability rocks resting on igneous HSR with a very low topographic gradient (GS2). We evaluated the sensitivity of simulated permafrost thickness to a variety of climatic and subsurface conditions. Uncertainty in the scaling of the surface temperature time-series, 10-25 °C below present day temperature, has the largest impact on maximum permafrost thickness, PFmax, compared to other variables. However, considering plausible parameter ranges for UK settings, PFmax is up to twice as sensitive to changes in thermal conductivity and geothermal heat flux than to changes in porosity. Heat advection only affects modelled PFmax for high hydraulic conductivity rocks and if permafrost is considered to be relatively permeable. Whilst local differences in permafrost thickness of tens of meters, caused by variations in heat advection, are of minor importance over glacial-interglacial cycles, heat advection can be important in the development of taliks and the maintenance of a more active groundwater flow system. We conclude that it is likely to be important to simulate the effect of heat advection on coupled permafrost and groundwater flow systems in settings containing higher permeability lithological sequences.
2019075870 Sun Aili (Hohai University, State Key Laboratory of Hydrology-Water Resource and Hydraulic Engineering, Nanjing, China); Zhou Jian; Yu Zhongbo; Jin Huijun and Yang Chuanguo. Three-dimensional distribution of permafrost and responses to increasing air temperatures in the head waters of the Yellow River in high Asia: The Science of the Total Environment, 666, p. 321-336, illus. incl. 3 tables, sketch maps, May 20, 2019. Based on Publisher-supplied data.
Fine-scale three-dimensional (3D) permafrost distributions at the basin scale are currently lacking. They are needed to monitor climate and ecosystem change and for the maintenance of infrastructure in cold regions. This paper determined the horizontal and vertical distributions of permafrost and its quantitative responses to climate warming in the High Asia region by constructing a quasi-3D model that couples heat transfer and water movement and is forced by spatially-interpolated air temperatures using an elevation-dependent regression method. Four air temperature scenarios were considered: the present state and air temperature increases of 1, 2 and 3°C. A fine-scale permafrost map was constructed. The map considered taliks and local factors including elevation, slope and aspect, and agreed well with field observations. Permafrost will experience severe degradation with climate warming, with decreases in area of 36% per degree increase in air temperature, increases in the depth-to-permafrost table of 2.67 m per degree increase in air temperature, and increases in 15 m-depth ground temperatures of 1.25 °C per degree increase in air temperature. Permafrost is more vulnerable in and beside river valleys than in high mountains, and on sunny rather than shady slopes. These results provide an effective reference for permafrost prediction and infrastructure and ecosystem management in cold regions affected by global warming.
2019071884 Bernhardt, Hannes (Arizona State University, School of Earth and Space Exploration, Tempe, AZ); Reiss, Dennis; Ivanov, Mikhail; Hauber, Ernst; Hiesinger, Harald; Clark, Jaclyn D. and Orosei, Roberto. The banded terrain on northwestern Hellas Planitia; new observations and insights into its possible formation: Icarus, 321, p. 171-188, illus. incl. 1 table, sketch maps, 76 ref., March 15, 2019. Includes appendix.
Northwestern Hellas Planitia hosts landforms that are unique on Mars, e.g., the so called honeycomb and banded (aka "taffy pull") terrains. Recently, robust formation models for the ~6 km large honeycomb depressions involving salt or ice diapirism have been formulated. However, the nature of the banded terrain, a ~30,000 km2 area characterized by a decameter- to kilometer-scale pattern of curvilinear troughs, has remained elusive. While previous interpretations range from deep-seated, honeycomb-related outcrops to a younger veneer, recent reports of putative periglacial features (e.g., potential thermokarst) strongly indicate it to be a relatively thin, volatile-related surface unit. In order to further constrain the origin and nature of the banded terrain, we investigated the northwestern Hellas basin floor employing various datasets. We mapped the banded terrain's extent at high precision, showing that it partially superposes the honeycomb terrain, but also occurs up to ~240 km away from it. Via stratigraphic analyses and crater size-frequency measurements, we bracketed the age of the banded terrain between ~1.9 and ~3.7 Ga. Furthermore, the banded terrain can be differentiated into two types, ridged and creviced, with the former predominantly occurring among the lowest reaches of the terrain's ~2 km topographic extent. We also produced a grid map (2´2 km box size) of the entire banded terrain and identified no large-scale (>25 km) band pattern and no correlation between local slope and band orientation. Because of this, we submit that regional tectonics or gravity-driven flow down modern topography are unlikely to have played decisive roles for banded terrain formation. Instead, we observed numerous locations, where band slabs appear to have broken off and subsequently rotated, as well as "cusps" that seem to have resulted from buckling. Based on this, we suggest that the banded terrain experienced both, ductile deformation as well as brittle failure on or near the surface. Despite certain similarities, neither salt (as salt glaciers), lava sheets, or land-based glaciers are in agreement with the extensive curvilinear texture and topographic/geologic setting of the banded terrain. Ice shelf margins, on the other hand, can produce surface textures akin to the banded terrain in both form and scale, even including cusps and broken off, rotated blocks. However, an ice-covered sea between 1.9 and 3.7 Ga ago is not indicated by the geologic inventory of the Hellas basin, which previous investigations found to lack any landforms indicative of a standing body of water. Instead, we identified several sinuous ridges terminating at plains covered by smaller, braiding ridges, which we interpret as eskers and glacial sandurs, respectively. As both are embayed and partially covered by the banded terrain, we tentatively propose an alternative, subglacial model of the banded terrain having formed as wet till that was viscously deformed according to the stress fields created by the ice overburden pressure in conjunction with bed topography. Although this formation model remains inconclusive, it is in agreement with climate models suggesting obliquity excursions and a denser, early Amazonian atmosphere to have caused ice accumulation in the adjacent northwestern Hellas basin rim, thus potentially enabling flow onto the floor entailing subglacial banded terrain formation.
2019071887 Cassanelli, James P. (Brown University, Department of Earth, Environmental, and Planetary Sciences, Providence, RI) and Head, James W. Assessing the formation of valley networks on a cold early Mars; predictions for erosion rates and channel morphology: Icarus, 321, p. 216-231, illus. incl. 1 table, sketch maps, 89 ref., March 15, 2019. Includes appendix.
The ancient Noachian highlands of Mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet. Morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation-derived fluvial activity and therefore as evidence for a relatively warm and wet Noachian Mars climate. However, these interpretations conflict with the results of sophisticated global climate modeling studies, which suggest that early Mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands. Difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate. Here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice-free, desiccated surface regolith and subjacent ice-cemented regolith, similar to that found in the Antarctic McMurdo Dry Valleys on Earth. We implement numerical thermal models, quantitative erosion and transport estimates, and morphometric analyses in order to outline and test predictions for: (1) the nature and structure of the cold and icy Noachian substrate, (2) valley network fluvial erosion and incision rates, and (3) resulting channel/valley morphology. Morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate. Through this approach we present and develop the underlying conceptual model, identify and generate the fundamental data inputs required to evaluate it, and perform a preliminary first-order assessment to serve as a basis for further investigation. While these analyses have been performed over a broad parameter space to address relative uncertainties, we report findings with a specific emphasis on the nominal results. We find that under cold conditions, the substrate is characterized by a kilometers-thick, globally-continuous cryosphere with a ~50-100 m thick ice-free surface layer in diffusive equilibrium with the atmosphere and underlying ice-cemented regolith, the top of which forms the ice-table. Estimates of the potential infiltration capacity of the ice-free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates, and thus does not preclude fluvial activity sourced by rainfall. Additionally, due to the predicted thicknesses of the ice-free surface regolith, any transient period of warming would need to be sustained in duration (~2 kyr) to induce melting of ground ice to initiate solifluction/gelifluction activity. The predicted range of ice-table depths is exceeded by the incised depths of a majority of the valley network population, therefore suggesting interactions were possible. Evaluation of the rates of mechanical substrate erosion and thermal ice-cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters (i.e. the substrate erodibility factor and the valley network fluvial water temperature) but generally indicate that at low water temperatures, consistent with a cold and icy surface environment, thermal erosion of the ice-cement can be outpaced by mechanical erosion of the substrate. In this scenario, the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice-table, causing preferential channel/valley widening and increased width-to-depth ratios. Assessment of this prediction through a morphometric analysis of valley network width-to-depth ratios and occurrence of U-shaped cross sections indicates no significant correlation to ice-table depths. This result suggests that either: (1) permafrost was not present in the Noachian Mars substrate, indicating a warmer climate, (2) the permafrost ice-table did not significantly influence valley network width-to-depth ratios, possibly owing to more rapid thermal erosion rates than mechanical, or (3) additional factors not accounted for in this analysis are involved. Potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux, substrate thermal conductivity, substrate composition and physical state as well as valley network preservation state, and morphometric sampling biases (due to data availability constraints). These factors represent areas for future investigation to refine assessments of valley network formation under cold early Mars conditions.
2019075662 Kenner, Robert (WSL Institute for Snow and Avalanche Research, Permafrost and Snow Climatology, Davos, Switzerland). Geomorphological analysis on the interaction of alpine glaciers and rock glaciers since the Little Ice Age: Land Degradation & Development, 30(5), p. 580-591, illus., 55 ref., March 2019.
The interaction of glaciers and rock glaciers and the associated development and degradation of permafrost landforms are intensely discussed fields of periglacial geomorphology. This study presents examples of glacier-rock glacier interactions since the Little Ice Age in the Swiss and French Alps, based on sequences of current and historical maps and orthophotos as well as field observations. It is concluded from these examples that many creeping permafrost features, which were widely specified as 'glacier derived' in the literature, appear to be much older than the glacier itself and constitute the remains of rock glaciers, which were disrupted by glaciers. Furthermore, the environmental conditions causing an alternation of glaciers and rock glaciers at the same location are analysed here, and the processes leading to a transition from one landform to the other are identified in the examples given. The influence of climate change on rock glacier development appears to be ambiguous and partly contradictory. The examples show how rock glacier development can benefit from increased rock fall activity and deglaciation in warming periods. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019072037 King, Tyler V. (Utah State University, Department of Civil and Environmental Engineering, Logan, UT) and Neilson, Bethany T. Quantifying reach-average effects of hyporheic exchange on arctic river temperatures in an area of continuous permafrost: Water Resources Research, 55(3), p. 1951-1971, illus. incl. 3 tables, sketch map, 95 ref., March 2019.
Hyporheic exchange has the potential to significantly influence river temperatures in regions of continuous permafrost under low-flow conditions given the strong thermal gradients that exist in river bed sediments. However, there is limited understanding of the impacts of hyporheic exchange on Arctic river temperatures. To address this knowledge gap, heat fluxes associated with hyporheic exchange were estimated in a fourth-order Arctic river using field observations coupled with a river temperature model that accounts for hyporheic exchange influences. Temperature time series and tracer study solute breakthrough curves were measured in the main channel and river bed at multiple locations and depths to characterize hyporheic exchange and provide parameter bounds for model calibration. Model results for low-flow periods from 3 years indicated that hyporheic exchange contributed up to 27% of the total river energy balance, reduced the main channel diel temperature range by up to 1.7 °C, and reduced mean daily temperatures by up to 0.21 °C over a 13.1-km study reach. These influences are due to main channel heat loss during the day and gain at night via hyporheic exchange and heat loss from the hyporheic zone to the ground below via conduction. Main channel temperatures were found to be sensitive to simulated changes in ground temperatures due to changes in hyporheic exchange heat flux and deeper ground conduction. These results suggest that the moderating influence of hyporheic exchange could be reduced if ground temperatures warm in response to projected increases in permafrost thaw below rivers. Abstract Copyright (2019), . American Geophysical Union. All Rights Reserved.
2019075661 Wei Xia (Lanzhou University, College of Earth and Environmental Sciences, Laboratory of Western China's Environmental Systems, Lanzhou, China); Huang, Chihua; Wei Ning; Zhao Hengce; He Yan and Wu Xiaodong. The impact of freeze-thaw cycles and soil moisture content at freezing on runoff and soil loss: Land Degradation & Development, 30(5), p. 515-523, illus. incl. 3 tables, 58 ref., March 2019.
The freeze-thaw (F-T) cycles play an important role in soil erosion, although quantitative description of this effect is challenging due to the complicated interactions of soil moisture content (SMC), surface hydrology, and flow hydraulics involved in processes of erosion. In this study, we investigated the influences of F-T cycles and SMC at freezing on runoff and soil loss under simulated rainfall in the U.S. Department of Agriculture Agricultural Research Service National Soil Erosion Research Lab. The SMCs at the start of freezing were adjusted to 10% and 20%, undergone 1, 3, and 6 F-T cycles with freezing at -12°C for 24 hr and followed by thawing at 4°C for 24 hr. After designed F-T cycle, the air-dried soils were packed into the 0.5-m-long, 0.2-m-wide, 0.1-m-deep soil boxes and subjected to simulated rainfall. The results showed that the impact of 20% SMC was greater than that of 10% SMC under the same F-T cycles and rainfall intensities. The impact of F-T cycles on runoff and soil loss increased with the number of F-T cycles at 10% SMC. However, at 20% SMC, the impact on runoff and soil loss increased after 1 and 3 F-T cycles and declined after 6 F-T cycles. Furthermore, the impact of SMC on runoff and soil loss was greater than the impact from different F-T cycles. This research fills a gap in the current literature on Alfisols affected by the F-T processes, and results are useful in the assessment of runoff and soil loss in regions where winter processes are significant. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019072030 Zwieback, S. (University of Guelph, Department of Geography, Guelph, Canada); Westermann, S.; Langer, M.; Boike, J.; Marsh, P. and Berg, A. Improving permafrost modeling by assimilating remotely sensed soil moisture: Water Resources Research, 55(3), p. 1814-1832, illus. incl. 2 tables, 50 ref., March 2019. Includes appendices.
Knowledge of soil moisture conditions is important for modeling soil temperatures, as soil moisture influences the thermal dynamics in multiple ways. However, in permafrost regions, soil moisture is highly heterogeneous and difficult to model. Satellite soil moisture data may fill this gap, but the degree to which they can improve permafrost modeling is unknown. To explore their added value for modeling soil temperatures, we assimilate fine-scale satellite surface soil moisture into the CryoGrid-3 permafrost model, which accounts for the soil moisture's influence on the soil thermal properties and the surface energy balance. At our study site in the Canadian Arctic, the assimilation improves the estimates of deeper (>10 cm) soil temperatures during summer but not consistently those of the near-surface temperatures. The improvements in the deeper temperatures are strongly contingent on soil type: They are largest for porous organic soils (30%), smaller for thin organic soil covers (20%), and they essentially vanish for mineral soils (only synthetic data available). That the improvements are greatest over organic soils reflects the strong coupling between soil moisture and deeper temperatures. The coupling arises largely from the diminishing soil thermal conductivity with increasing desiccation thanks to which the deeper soil is kept cool. It is this association of dry organic soils being cool at depth that lets the assimilation revise the simulated soil temperatures toward the actually measured ones. In the future, the increasing availability of satellite soil moisture data holds promise for the operational monitoring of soil temperatures, hydrology, and biogeochemistry. Abstract Copyright (2019), . American Geophysical Union. All Rights Reserved.
2019071986 Pitcher, Lincoln H. (University of California at Los Angeles, Department of Geography, Los Angeles, CA); Pavelsky, Tamlin M.; Smith, Laurence C.; Moller, Delwyn K.; Altenau, Elizabeth H.; Allen, George H.; Lion, Christine; Butman, David; Cooley, Sarah W.; Fayne, Jessica V. and Bertram, Mark. AirSWOT InSAR mapping of surface water elevations and hydraulic gradients across the Yukon Flats basin, Alaska: Water Resources Research, 55(2), p. 937-953, illus. incl. 2 tables, sketch map, 60 ref., February 2019.
AirSWOT, an experimental airborne Ka-band interferometric synthetic aperture radar, was developed for hydrologic research and validation of the forthcoming Surface Water and Ocean Topography (SWOT) satellite mission (to be launched in 2021). AirSWOT and SWOT aim to improve understanding of surface water processes by mapping water surface elevation (WSE) and water surface slope (WSS) in rivers, lakes, and wetlands. However, the utility of AirSWOT for these purposes remains largely unexamined. We present the first investigation of AirSWOT WSE and WSS surveys over complex, low-relief, wetland-river hydrologic environments, including (1) a field-validated assessment of AirSWOT WSE and WSS precisions for lakes and rivers in the Yukon Flats Basin, an Arctic-Boreal wetland complex in eastern interior Alaska; (2) improved scientific understanding of surface water flow gradients and the influence of subsurface permafrost; and (3) recommendations for improving AirSWOT precisions in future scientific and SWOT validation campaigns. AirSWOT quantifies WSE with an RMSE of 8 and 15 cm in 1 and 0.0625 km2 river reaches, respectively, and 21 cm in lakes. This indicates good utility for studying hydrologic flux, WSS, geomorphic processes, and coupled surface/subsurface hydrology in permafrost environments. This also suggests that AirSWOT supplies sufficient precision for validating SWOT WSE and WSS over rivers, but not lakes. However, improvements in sensor calibration and flight experiment design may improve precisions in future deployments as may modifications to data processing. We conclude that AirSWOT is a useful tool for bridging the gap between field observations and forthcoming global SWOT satellite products. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
2019075384 Gao Xiaofeng (China Agricultural University, College of Water Resources and Civil Engineering, Beijing, China); Li Fahu; Chen Chao; Ban Yunyun and Gao Yuan. Effects of thawed depth on the sediment transport capacity by melt water on partially thawed black soil slope: Land Degradation & Development, 30(1), p. 84-93, illus., 45 ref., January 15, 2019. WWW.
This study proposed an apparatus for measuring the sediment transport capacity, which is an important parameter for rill erosion prediction and modeling. Laboratory experiments were conducted to measure the sediment transport capacity of partially thawed black soil slope under different hydraulic conditions and thawed depths (five slope gradients of 5°, 10°, 15°, 20°, and 25°; three flow discharges of 1, 2, and 4 dm3 min-1; and four thawed depths of 1, 2, 5, and 10 cm). The effect of thawed depth on sediment transport capacity was quantified with experimental data under different slope gradients and flow discharges. A quadratic model was used to relate sediment transport capacity to thawed depth, slope gradient, and flow discharge, and its key factors that influenced sediment transport capacity were determined by using stepwise regression. Results showed that sediment transport capacity decreased with the increase of thawed depth from 1 to 5 cm, but it tended to be steady when the thawed depth was greater than 5 cm. Model-fitting results showed that sediment transport capacity was positively correlated with slope gradient and flow discharge but negatively correlated with thawed depth. The proposed method and experimental device solved the difficulties of insufficient sediment supply on the measurement of sediment transport capability, and it can be used to measure the sediment transport capacity of concentrated water flow under different conditions of slope gradient, thawed depth, and flow discharge. The method is helpful to the research of erosion process of partially thawed soil under concentrated water. Abstract Copyright (2019), John Wiley & Sons, Ltd.
2019075979 Göckede, Mathias (Max Planck Institute for Biogeochemistry, Jena, Germany); Kwon, Min Jung; Kittler, Fanny; Heimann, Martin; Zimov, Nikita and Zimov, Sergey. Negative feedback processes following drainage slow down permafrost degradation: Global Change Biology, 25(10), p. 3254-3266, illus., 72 ref., 2019.
The sustainability of the vast Arctic permafrost carbon pool under climate change is of paramount importance for global climate trajectories. Accurate climate change forecasts, therefore, depend on a reliable representation of mechanisms governing Arctic carbon cycle processes, but this task is complicated by the complex interaction of multiple controls on Arctic ecosystem changes, linked through both positive and negative feedbacks. As a primary example, predicted Arctic warming can be substantially influenced by shifts in hydrologic regimes, linked to, for example, altered precipitation patterns or changes in topography following permafrost degradation. This study presents observational evidence how severe drainage, a scenario that may affect large Arctic areas with ice-rich permafrost soils under future climate change, affects biogeochemical and biogeophysical processes within an Arctic floodplain. Our in situ data demonstrate reduced carbon losses and transfer of sensible heat to the atmosphere, and effects linked to drainage-induced long-term shifts in vegetation communities and soil thermal regimes largely counterbalanced the immediate drainage impact. Moreover, higher surface albedo in combination with low thermal conductivity cooled the permafrost soils. Accordingly, long-term drainage effects linked to warming-induced permafrost degradation hold the potential to alleviate positive feedbacks between permafrost carbon and Arctic warming, and to slow down permafrost degradation. Self-stabilizing effects associated with ecosystem disturbance such as these drainage impacts are a key factor for predicting future feedbacks between Arctic permafrost and climate change, and, thus, neglect of these mechanisms will exaggerate the impacts of Arctic change on future global climate projections.
2019073276 Ashastina, Kseniia (Senckenberg Research Institute and Natural History Museum, Research Station of Quaternary Palaeontology, Weimar, Germany); Kuzmina, Svetlana; Rudaya, Natalia; Troeva, Elena; Schoch, Werner H.; Römermann, Christine; Reinecke, Jennifer; Otte, Volker; Savvinov, Grigoriy; Wesche, Karsten and Kienast, Frank. Woodlands and steppes; Pleistocene vegetation in Yakutia's most continental part recorded in the Batagay permafrost sequence: Quaternary Science Reviews, 196, p. 38-61, illus. incl. 2 tables, sketch map, 116 ref., September 15, 2018.
Based on fossil organism remains including plant macrofossils, charcoal, pollen, and invertebrates preserved in syngenetic deposits of the Batagay permafrost sequence in the Siberian Yana Highlands, we reconstructed the environmental history during marine isotope stages (MIS) 6 to 2. Two fossil assemblages, exceptionally rich in plant remains, allowed for a detailed description of the palaeo-vegetation during two climate extremes of the Late Pleistocene, the onset of the last glacial maximum (LGM) and the last interglacial. In addition, altogether 41 assemblages were used to outline the vegetation history since the penultimate cold stage of MIS 6. Accordingly, meadow steppes analogue to modern communities of the phytosociological order Festucetalia lenensis formed the primary vegetation during the Saalian and Weichselian cold stages. Cold-resistant tundra-steppe communities (Carici rupestris-Kobresietea bellardii) as they occur above the treeline today were, in contrast to more northern locations, mostly lacking. During the last interglacial, open coniferous woodland similar to modern larch taiga was the primary vegetation at the site. Abundant charcoal indicates wildfire events during the last interglacial. Zoogenic disturbances of the local vegetation were indicated by the presence of ruderal plants, especially by abundant Urtica dioica, suggesting that the area was an interglacial refugium for large herbivores. Meadow steppes, which formed the primary vegetation during cold stages and provided potentially suitable pastures for herbivores, were a significant constituent of the plant cover in the Yana Highlands also under the full warm stage conditions of the last interglacial. Consequently, meadow steppes occurred in the Yana Highlands during the entire investigated timespan from MIS 6 to MIS 2 documenting a remarkable environmental stability. Thus, the proportion of meadow steppe vegetation merely shifted in response to the respectively prevailing climatic conditions. Their persistence indicates low precipitation and a relatively warm growing season throughout and beyond the late Pleistocene. The studied fossil record also proves that modern steppe occurrences in the Yana Highlands did not establish as late as in the Holocene but instead are relicts of a formerly continuous steppe belt extending from Central Siberia to Northeast Yakutia during the Pleistocene. The persistence of plants and invertebrates characteristic of meadow steppe vegetation in interior Yakutia throughout the late Quaternary indicates climatic continuity and documents the suitability of this region as a refugium also for other organisms of the Pleistocene mammoth steppe including the iconic large herbivores.
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2019075973 Bilodeau, Jean-Pascal; Nadeau, Daniel F.; Fortier, Daniel and Conciatori, David, editors. Cold regions engineering 2019; proceedings of the 18th international conference on Cold regions engineering and the 8th Canadian permafrost conference: Proceedings of the International Symposium on Cold Regions Engineering, 18, 697 p., illus., 2019. ISBN: 978-0-7844-8259-9. Meeting: 18th international conference on Cold regions engineering and the 8th Canadian permafrost conference, Aug. 18-22, 2019, Quebec City, QC, Canada.
This conference was sponsored by the Canadian Geotechnical Society (Eastern Quebec and National), the Canadian Permafrost Association, the Canadian National Committee for the International Permafrost Association, and the Cold Regions Engineering Division of the American Society of Civil Engineers. The volume includes 79 peer-reviewed papers on topics including snow and ice, structures, foundations, pavements and permafrost. The volume is available from the American Society of Civil Engineers.
2019072459 Kirpotin, S. N., prefacer (Tomsk State University, "Bio-Clim-Land" Center of Excellence, Tomsk, Russian Federation). 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate": IOP Conference Series. Earth and Environmental Science, 232(1), January 2019. Meeting: 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate", July 7-21, 2018, Tomsk, Russian Federation. Individual papers within scope are cited separately.
2019072460 Prokushkin, A. S. (Russian Academy of Sciences, Siberian Branch, V. N. Sukachev Institute of Forest, Krasnoyarsk, Russian Federation); Korets, M. A.; Panov, A. V.; Prokushkina, M. P.; Tokareva, I. V.; Vorobyev, S. N. and Pokrovsky, O. S. Carbon and nutrients in the Yenisei River tributaries draining the Western Siberia peatlands: in 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate" (Kirpotin, S. N., prefacer), IOP Conference Series. Earth and Environmental Science, 232(1), Paper no. 012010, illus. incl. 1 table, sketch map, 14 ref., January 2019. Meeting: 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate", July 7-21, 2018, Tomsk, Russian Federation.
The study is focused on carbon and nutrient behaviour in tributaries of the Yenisei River draining the Western Siberian Plain. The previous studies showed that dissolved organic carbon (DOC) concentrations in riverine systems are influenced by wetland cover within a watershed and modulating effect of permafrost. Our data point out more complex interactions within the south-north transect of the Yenisei River basin including a partitioning of sources at different seasons and in-river metabolic processing of DOC involving utilization of nutrients and production of DIC. On the other hand, DOC concentration in rivers is driven by available stock of labile carbon and, thus, is a function of total organic matter stored in soils. Terrigenic C and nutrient fluxes to rivers are enhanced in colder environments of northern Western Siberia, contradicting the earlier observations and respective future projections of permafrost degradation effects on riverine C release. Copyright Published under license by IOP Publishing Ltd
2019072462 Suslyaev, V. I. (Tomsk State University, Laboratory of Radiophysical and Optical Methods of Studying the Environment, Tomsk, Russian Federation); Kolesnichenko, L. G.; Dorozhkin, K. V.; Machnov, A. Yu.; Sorochynskiy, A. V.; Pavlova, A. A.; Nikitkin, V. A.; Kirpotin, S. N. and Pokrovsky, O. S. Investigation of the earth roof through the combined method; mechanical way and ground penetrating radar in the Yamalo-Nenets Autonomous Okrug: in 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate" (Kirpotin, S. N., prefacer), IOP Conference Series. Earth and Environmental Science, 232(1), Paper no. 012015, illus. incl. sects., 20 ref., January 2019. Meeting: 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate", July 7-21, 2018, Tomsk, Russian Federation.
The paper presents the results of the multidisciplinary experimental investigation of the soils in the sporadic permafrost Northern-taiga subzone (Yamalo-Nenets Autonomous Okrug, Western Siberia) based on the combination of the methods of radiophysical GPR investigation and classical methods of soil science. The aim is to develop the methods of objective identification of soils during the decoding of radarograms when monitoring the state of permafrost soils. Copyright Published under license by IOP Publishing Ltd
2019072463 Volkova, I. I. (Tomsk State University, Tomsk, Russian Federation); Kolesnichenko, L. G.; Kirpotin, S. N.; Pokrovsky, O. S. and Vorobyev, S. N. Peat deposits and peat-forming plants in the mires of the West Siberian northern taiga (based on studies of the Khanymei site): in 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate" (Kirpotin, S. N., prefacer), IOP Conference Series. Earth and Environmental Science, 232(1), Paper no. 012018, illus. incl. sketch map, 34 ref., January 2019. Meeting: 5th International summer school for students and young scientists "Natural and human environment of arctic and alpine areas; relief, soils, permafrost, glaciers, biota life style of native ethnic groups in a rapidly changing climate", July 7-21, 2018, Tomsk, Russian Federation.
The botanical composition of peat from upper (over-permafrost) layers of the peatland, a part of the peat-podzol soil profile, was analysed. It was discovered that peat deposits in the Khanymei site are characterised by large-scale diversity, and mosaic structure and composition of peats constituting them. Copyright Published under license by IOP Publishing Ltd
2019071838 Aas, Kjetil S. (University of Oslo, Department of Geosciences, Oslo, Norway); Nitzbon, Jan; Martin, Leo; Berntsen, Terje and Westermann, Sebastian. Simulating ice-rich permafrost landscapes under climate change with laterally coupled tiles in a land surface model [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C53A-08, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.
Ice-rich permafrost landscapes represent an important, but complex component of the Earth's climate system. As a major reservoir of soil carbon which can potentially be activated by enhanced permafrost thaw, these regions are important to represent in future climate projections. However, the complex interplay between changing micro-topography due to melting excess ground ice and lateral fluxes of snow, water and energy makes these regions particularly challenging to represent in large scale models. In order to improve model representation of these regions, we have developed a version of the NoahMP land surface model (LSM) with two laterally coupled tiles. Previous work with an earlier version of this model has shown that sub-grid heterogeneities in snow accumulation can be well represented with tiles, resulting in improved representation of local meteorology and land surface conditions during the snow-melt season in high-mountain Norway. Building upon this work, we have now developed a model version which includes lateral subsurface water and energy fluxes, as well as the previous snow redistribution. Additionally, the model has been augmented with excess ice representation to dynamically represent changing microtopography. The model is applied to a palsa mire location in Northern Norway and an ice-wedge, low-centered polygons location in northern Siberia, representing two very different ice-rich permafrost landscapes. Our results show that both the transition from stable to degrading palsas and from low-centered to high-centered polygons, under current and warming climate conditions respectively, can be represented with this two-tile approach. Furthermore, we find that lateral fluxes of snow, water and energy are all important in order to represent these very different locations and their response to climate change, which highlights the need for improved representation of lateral processes in future development of LSMs in Earth System Models.
2019071837 Douglas, Madison (California Institute of Technology, Pasadena, CA); Rowland, Joel C.; Li, Gen; Kemeny, Preston C.; West, A. Joshua; Piliouras, Anastasia; Schwenk, Jon; Chadwick, Austin J.; Lamb, Michael P. and Fischer, Woodward W. Quantifying organic carbon mobilization and storage in permafrost river floodplains [abstr.]: in AGU 2018 fall meeting, American Geophysical Union Fall Meeting, 2018, Abstract C53A-06, December 2018. Meeting: American Geophysical Union 2018 fall meeting, Dec. 10-14, 2018, Washington, DC.
Arctic permafrost soils store approximately twice the carbon currently present in Earth's atmosphere, and are particularly vulnerable to climate change due to polar amplification of global mean annual temperature increases. Many studies on the dynamics of Arctic carbon stores focus on the 10-25 mm/yr increase in annual thaw depth on floodplains [Romanovsky et al., 2017]. However, river migration through permafrost deposits can source carbon from many meters below the active layer via the erosion of frozen streambanks. We hypothesized that mobilization of carbon due to bank erosion may be comparable to that released by ecological activity in the active layer of the river's floodplain, but that a significant fraction of the bank carbon is then re-buried in downstream point bars. To test this hypothesis, we conducted a field expedition to the Koyukuk River--a large meandering tributary of the Yukon River in Alaska--during June and July 2018. We present a map correlating multiple generations of point bar deposits across the floodplain of the Koyukuk with total organic carbon (TOC) content, bulk density, and permafrost occurrence. We also measured channel migration rates using remote sensing imagery to develop mass-balance scaling relationships and compared estimates of the carbon flux from top-down melting of the river floodplain versus fluxes from bank erosion. The results indicate that permafrost occurs only on older, relict point bar and floodplain deposits, which contain thick horizons of peat moss. More recent point bar and active floodplain deposits have little to no persistent ice or peat moss. Therefore, as the Koyukuk River migrates and reworks its floodplain, older carbon-rich deposits are replaced by younger, permafrost-free deposits, representing an important but under-constrained process in Arctic carbon dynamics.
2019069955 Hilton, Robert G. (Durham University, United Kingdom); Tipper, Edward; Galy, Valier V.; Garnett, Mark H.; Dellinger, Mathieu; Schwab, Melissa; Tank, Suzanne; Bryant, Charlotte L.; Ascough, Philippa and Eglinton, Timothy I. Old dissolved inorganic carbon in the Mackenzie River basin; a smoking gun for the degradation of aged organic matter? [abstr.]: in Goldschmidt 2018, V.M. Goldschmidt Conference - Program and Abstracts, 28, 2018. Meeting: Goldschmidt 2018, August 12-17, 2018, Boston, MA.
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