Permafrost Monthly Alerts (PMAs)

USPA LogoThe USPA is pleased to announce the availability of an updated searchable database on permafrost-related publications. The American Geosciences Institute (AGI), with support from the National Science Foundation (NSF), has migrated the previous Cold Regions Bibliography to a new platform. Included are the USPA supported PMAs dating back to 2011. The Bibliography is searchable at


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Entries in each category are listed in chronological order starting with the most recent citation. 

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2021060254 Yin Han (Harbin Normal University, College of Geographical Science, Harbin, China); Li Miao; Man Haoran; Dong Xingfeng; Lu Boquan and Zang Shuying. Retrieval and analysis of land surface temperature in permafrost regions in northeast China based on AMSR2 data: Earth Science Informatics, 14(3), p. 1245-1260, illus. incl. 4 tables, geol. sketch map, 55 ref., September 2021.

The land surface temperature (LST) in permafrost regions in the Northeast permafrost on March 22 (spring), June 24 (summer), September 21 (autumn), and December 24 (winter) in 2019 were retrieved based on the AMSR2 brightness temperature data. An in-depth analysis of the temperature retrieval accuracy between different types of frozen ground, vegetation cover, and during the four seasons of the day or night was conducted. The results show that: (1) The retrieval accuracy of the four seasons lowers in the seasonal order of summer > autumn > spring > winter, and the accuracy of data at the night was better than that of the day; (2) The retrieval accuracy of different vegetation cover types lowers in the order of grassland>agricultural land>forest land, and; (3) The retrieval accuracy of different frozen ground types lowers in the order of the zone of seasonal frost>zone of isolated patches of thawing permafrost>zone of island permafrost zone>continuous permafrost zone.

DOI: 10.1007/s12145-021-00666-7

2021060453 Wei Da (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Qi Yahui; Ma Yaoming; Wang Xufeng; Ma Weiqiang; Gao Tanguang; Huang Lin; Zhao Hui; Zhang Jianxin and Wang Xiaodan. Plant uptake of CO2 outpaces losses from permafrost and plant respiration on the Tibetan Plateau: Proceedings of the National Academy of Sciences of the United States of America, 118(33), Article e2015283118, illus. incl. sketch map, 63 ref., August 17, 2021.

DOI: 10.1073/pnas.2015283118

2021059206 Michaelides, Roger J. (Colorado School of Mines, Department of Geophysics, Golden, CO); Chen, Richard H.; Zhao, Yuhuan; Schaefer, Kevin; Parsekian, Andrew D.; Sullivan, Taylor; Moghaddam, Mahta; Zebker, Howard A.; Liu Lin; Xu Xingyu and Chen, Jingyi. Permafrost dynamics observatory; Part I, Postprocessing and calibration methods of UAVSAR L-band InSAR data for seasonal subsidence estimation: Earth and Space Science, 8(7), Article e2020EA001630, illus. incl. 3 tables, 81 ref., July 2021.

Interferometric synthetic aperture radar (InSAR) has been used to quantify a range of surface and near surface physical properties in permafrost landscapes. Most previous InSAR studies have utilized spaceborne InSAR platforms, but InSAR datasets over permafrost landscapes collected from airborne platforms have been steadily growing in recent years. Most existing algorithms dedicated toward retrieval of permafrost physical properties were originally developed for spaceborne InSAR platforms. In this study, which is the first in a two part series, we introduce a series of calibration techniques developed to apply a novel joint retrieval algorithm for permafrost active layer thickness retrieval to an airborne InSAR dataset acquired in 2017 by NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar over Alaska and Western Canada. We demonstrate how InSAR measurement uncertainties are mitigated by these calibration methods and quantify remaining measurement uncertainties with a novel method of modeling interferometric phase uncertainty using a Gaussian mixture model. Finally, we discuss the impact of native SAR resolution on InSAR measurements, the limitation of using few interferograms per retrieval, and the implications of our findings for cross-comparison of airborne and spaceborne InSAR datasets acquired over Arctic regions underlain by permafrost. Abstract Copyright (2021). The Authors. Earth and Space Science published by Wiley Periodicals LLC on behalf of American Geophysical Union.

DOI: 10.1029/2020EA001630

2021053167 Mithan, H. T. (National Taiwan University, Department of Geosciences, Taipei, Taiwan); Hales, T. C. and Cleall, P. J. Topographic and ground-ice controls on shallow landsliding in thawing Arctic permafrost: Geophysical Research Letters, 48(13), Article e2020GL092264, illus. incl. sketch map, 52 ref., July 16, 2021.

An increase in Arctic shallow landsliding is a potential consequence of climate warming. Warmer summer-air temperatures and larger rainfall events drive heat into the active layer, melting ice and decreasing soil shear stress. Topography has the potential to exacerbate landsliding by controlling the distribution of ground ice and the movement of water in the subsurface. We demonstrate that shallow Arctic landslides initiate in zero-order drainage basins consistent with models of shallow landsliding in non-permafrost environments. However, the low average slopes and low concavity of Arctic hillslopes cannot create pore-water pressures high enough to generate landsliding. Instead, two-dimensional slope stability modeling suggests that the vertical distribution of ground-ice distributions controls landslide susceptibility. High ground-ice concentrations close to the potential failure plane act as a stronger control than high average ice volumes or rapid thawing. Our results demonstrate that landslide susceptibility is strongly affected by topographic controls on ground ice and hydrology. Abstract Copyright (2021), American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020GL092264

2021053060 Puspoki, Zoltan (Mining and Geological Survey of Hungary, Budapest, Hungary); Gibbard, Philip Leonard; Nador, Annamaria; Thamo-Bozso, Edit; Sumegi, Pal; Fogarassy-Pummer, Timea; Mcintosh, Richard William; Lantos, Miklos; Toth-Makk, Agnes; Stercel, Ferenc; Krassay, Zita; Kovacs, Peter; Szocs, Teodora and Fancsik, Tamas. Fluvial magnetic susceptibility as a proxy for long term variations of mountain permafrost development in the Alp-Carpathian region: Boreas, 50(3), p. 806-825, illus. incl. 1 table, geol. sketch map, 75 ref., July 2021.

Low field magnetic susceptibility (MS) records of 13 reference boreholes representing the whole Quaternary fluvial succession of the Great Hungarian Plain were correlated to develop regional stratigraphy. Data from 12 of the boreholes were published between 2016 and 2020, the Tiszainoka borehole is newly reported in this paper. Eleven magnetic susceptibility cycles, capped by the most emergent master MS peaks (MP) and bordered by susceptibility termination surfaces, have been correlated. Supported by the already evaluated palaeomagnetic reversals and instability events, MPs have been correlated to the cold stages of the Marine Isotope Stage (MIS) records. MPs represent MIS 104, 100, 98, 82, 60, 52, 34(-36) and 26 of increased heavy oxygen isotope value, constituting the significant early Pleistocene glaciations, and MIS 18, 16, 12, 8, 6 and 2 mostly representing the substantial Middle and Upper Pleistocene European glaciation events. The interpretation of early postglacial fluvial MS maxima, which emphasizes the escape of weathering-sensitive magnetic minerals from the catchment area triggered by the thawing of mountain permafrost, is confirmed by the correlation of MPs to the changes of the global ice volume. As a result, fluvial MS records can be considered as a proxy for mountain permafrost development in the catchment areas. Regional correlations confirmed that the Koros and Jaszsag Basins and the Mako Trough are sites of almost continuous fluvial records of the past 2600 ka. Thus, the Pannonian Quaternary fluvial succession is sufficiently complete to provide a satisfactory record of mountain permafrost development of the Alp-Carpathian region, the latter being a globally relevant European representative of mid-latitude mountain regions. The similarity of the Pannonian fluvial MS succession as a permafrost proxy to the marine ice-rafted detritus (IRD) and Chinese loess/paleosol MS records promises the possibility of comparative investigations of globally relevant proxy records and mid-latitude mountain permafrost development. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1111/bor.12520

2021060575 Burn, Christopher R. (Carleton University, Department of Geography and Environmental Studies, Ottawa, ON, Canada); Lewkowicz, Antoni G. and Wilson, M. Alice. Long-term field measurements of climate-induced thaw subsidence above ice wedges on hillslopes, western Arctic Canadain Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 261-276, illus. incl. 4 tables, June 2021. Based on Publisher-supplied data.

Near-surface wedges of massive ice commonly outline polygons in tundra lowlands, but such polygons have been difficult to identify on hillslopes because soil movement flattens the ridges and infills the troughs that form beside and above the ice wedges. Over the past three decades, the active layer has thickened near the western Arctic coast of Canada and consequent thawing of ice wedges has been detected by remote sensing for flat terrain but not, generally, on hillslopes. Annual field surveys (1996-2018) at the Illisarvik field site of thaw depth and ground surface elevation show the mean subsidence rate above hillslope ice wedges has been up to 32 mm a-1 since thaw depth reached the ice-wedge tops in 2007. Annual mean ground temperatures at the site are about -3.0°C beneath late-winter snow depths characteristic of the ice-wedge troughs but about -5.3°C under conditions of the intervening polygons. The rate of thaw subsidence is high for natural, subaerial disturbances because meltwater from the ice wedges runs off downslope. The rate is constant, because the thickness of seasonally thawed ground above the ice wedges and the ice content of the ground remain the same while the troughs develop. Observations of changes in surface elevation in northern Banks Island between the late 1970s and 2019 show troughs on hillslopes where none was previously visible. Development of these troughs creates regional thermokarst landscapes, distinct from the widely recognized results of thawing relict glacier ice, that are now widespread over Canada's western Arctic coastlands. Recognition of ice-wedge occurrence and accelerated thaw subsidence on hillslopes is important in the design of infrastructure proposed for construction in rolling permafrost terrain. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2113

2021060574 Fisher, David A. (University of Ottawa, Department of Earth Sciences, Ottawa, ON, Canada); Lacelle, Denis; Pollard, Wayne and Faucher, Benoit. A model for stable isotopes of residual liquid water and ground ice in permafrost soils using arbitrary water chemistries and soil-specific empirical residual water functionsin Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 248-260, illus., June 2021. Based on Publisher-supplied data.

We present the basic theory of stable isotopes (d(18O) and d(D)) of freezing water solutions in the environment set within a water isotope-augmented version of FREZCHEM(V15). We validate this model with a couple of examples. The isotope-capable FREZCHEM is simplified to run much faster using set-piece initial chemistries to calculate the freezing temperature of the remaining water. The fast version is embedded in a semi-empirical model for residual liquid water in sub-zero soils. A uniform specific soil column is driven with a defined seasonal temperature wave. The co-isotopes of the residual water and ice are calculated as a function of time and depth. The model is applied to clayey soils of the sort sampled in detail in a 10 (10 to 20 m) core suite from the Mackenzie Delta, Canada. The stable isotopes are compared to the model ones and the match is quite good except in the uppermost 2.5 m, where an upturn in the model d(18O) curve is smaller. If the upper 2.5 m of icy soil is populated with "modern" water, and below by late glacial meltwater the size of the upturn in d(18O) starting at 2.5 m is reproduced by the model. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2079

2021060571 Guglielmin, Mauro (Insubria University, Department of Theoretical and Applied Sciences, Varese, Italy); Murton, Julian and Lewkowicz, Antoni G., editors. Hugh French memorial for permafrost and periglacial processes: Permafrost and Periglacial Processes, 32(2), p. 179-317, illus., June 2021. Individual papers are cited separately.

2021060577 Guglielmin, Mauro (Insubria University, Department of Theoretical and Applied Sciences, Varese, Italy); Ponti, Stefano; Forte, Emanuele and Cannone, Nicoletta. Recent thermokarst evolution in the Italian Central Alpsin Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 299-317, illus. incl. 7 tables, June 2021. Based on Publisher-supplied data.

Thermokarst depressions are widespread phenomena due to permafrost degradation in the Arctic, whereas only few are known from mountain permafrost of the mid-latitudes. In the Italian Central Alps, close to the Stelvio Pass (2,763 m above sea level), a ski run was built in 1987. Since 1981, statistically significant air warming has been recorded, especially during summer (+0.65°C per decade). Permafrost temperature recorded at the nearby Share Stelvio Borehole between 1990 and 2011 exhibited a rapid increase (>0.8°C per decade) and an active-layer thickening (7 cm/year). Between the years 1999 and 2003, some thermokarst depressions started to develop, initially in the lower part of the ski run and then extending to higher elevations. The depressions increased in number, size, and depth with time. Since ski-run construction, the area remained free of vegetation until early 2000, when vegetation colonization started, showing a coupling with the onset of thermokarst development and summer warming. Vegetation changes accelerated with the ingress of pioneer and early-successional as well as of late-successional species. Moreover, the ingress of shrub species (Salix spp.) typical of lower elevation belts (subalpine and even montane) was dated to 2004. All the observed features show a rapid and coupled response of the abiotic and biotic components of this ecosystem to climate warming. Our data also confirm the similarity of the observed responses and dynamics of the alpine tundra with the Arctic tundra with regard to both permafrost and vegetation. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2099

2021060573 He Ruixia (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Jin Huijun; French, Hugh M.; Vandenberghe, Jef; Li Xiaoying; Li Fang; Jiang Guanli; Zhang Ze; Chen Xuemei; Serban, Raul D.; Wang Shaoling and Guo Dongxin. Cryogenic wedges and cryoturbations on the Ordos Plateau in north China since 50 ka BP and their paleoenvironmental implicationsin Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 231-247, illus. incl. 3 tables, June 2021. Based on Publisher-supplied data.

During the last 50 ka, cryogenic wedges on the Ordos Plateau formed during three major periods: (i) early local Last Glaciation, ca. 50 ka BP; (iii) local Last Permafrost Maximum (local LPM), 25-19 ka BP; and (v) post-local LPM, 16-9 ka BP. Cryoturbations mainly formed in the following periods: (ii) pre-local LPM, 45-30 ka BP and (iv) ~20 ka BP. The coldest periods with well-developed permafrost (i and iii) were most conducive for forming cryogenic wedges. The following periods of warming climate and degrading permafrost favored the formation of cryoturbations. During the local LPM, sand wedges and polygons were well developed and widely distributed on the Ordos Plateau when mean annual air temperatures (MAATs) were approximately 12°C lower than that at present. At ~30 ka BP, MAAT was 6-7°C lower than that at present. Paleoclimate conditions on the Ordos Plateau were reconstructed since 50 ka BP as follows: cold (ca. 50 ka BP)®cool (45-30 ka BP)®very cold (25-19 ka BP)®cool (19-9 ka BP)®intermittent warming until the present day. The amount of precipitation fluctuated, but with a general trend of drying since 50 ka BP. Under the next generally warming climate (after 9 ka BP), permafrost gradually degraded and eventually disappeared from the Ordos Plateau. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2084

2021060572 Murton, Julian B. (University of Sussex, Department of Geography, Brighton, United Kingdom). What and where are periglacial landscapes?in Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 186-212, illus. incl. block diag., sect., geol. sketch maps, 186 ref., June 2021. Based on Publisher-supplied data.

Uncertainties about landscape evolution under cold, nonglacial conditions raise a question fundamental to periglacial geomorphology: what and where are periglacial landscapes? To answer this, with an emphasis on lowland periglacial areas, the present study distinguishes between characteristic and polygenetic periglacial landscapes, and considers how complete is the footprint of periglaciation? Using a conceptual framework of landscape sensitivity and change, the study applies four geological criteria (periglacial persistence, extraglacial regions, ice-rich substrates, and aggradation of sediment and permafrost) through the last 3.5 million years of the late Cenozoic to identify permafrost regions in the Northern Hemisphere. In limited areas of unglaciated permafrost regions are characteristic periglacial landscapes whose morphology has been adjusted essentially to present (i.e., Holocene interglacial) process conditions, namely thermokarst landscapes, and mixed periglacial-alluvial and periglacial-deltaic landscapes. More widespread in past and present permafrost regions are polygenetic periglacial landscapes, which inherit ancient landsurfaces on which periglacial landforms are superimposed to varying degrees, presently or previously. Such landscapes comprise relict accumulation plains and aprons, frost-susceptible and nonfrost-susceptible terrains, cryopediments, and glacial-periglacial landscapes. Periglaciation can produce topographic fingerprints at mesospatial scales (103-105 m): (1) relict accumulation plains and aprons form where long-term sedimentation buried landsurfaces; and (2) plateaux with convexo-concave hillslopes and inset with valleys, formed by bedrock brecciation, mass wasting, and stream incision in frost-susceptible terrain. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2102

2021060576 Shur, Yuri (University of Alaska Fairbanks, Institute of Northern Engineering, Fairbanks, AK); Jones, Benjamin M.; Kanevskiy, Mikhail; Jorgenson, Torre; Jones, Melissa K. Ward; Fortier, Daniel; Stephani, Eva and Vasiliev, Alexander. Fluvio-thermal erosion and thermal denudation in the yedoma region of northern Alaska; revisiting the Itkillik River exposurein Hugh French memorial for permafrost and periglacial processes (Guglielmin, Mauro, editor; et al.), Permafrost and Periglacial Processes, 32(2), p. 277-298, illus. incl. 3 tables, June 2021. Based on Publisher-supplied data.

Riverbank erosion in yedoma regions strongly affects landscape evolution, biogeochemical cycling, sediment transport, and organic and nutrient fluxes to the Arctic Ocean. Since 2006, we have studied the 35-m-high Itkillik River yedoma bluff in northern Alaska, whose retreat rate during 1995-2010 was up to 19 m/yr, which is among the highest rates worldwide. This study extends our previous observations of bluff evolution and shows that average bluff-top retreat rates decreased from 8.7-10.0 m/yr during 2011-2014 to 4.5-5.8 m/yr during 2015-2019, and bluff-base retreat rates for the same time period decreased from 4.7-7.5 m/yr to 1.3-1.7 m/yr, correspondingly. Bluff evolution initially involves rapid fluvio-thermal erosion at the base and block collapse, following by slowdown in river erosion and continuing thermal denudation of the retreating headwall with formation of baydzherakhs. Eventually, input of sediment and water from the headwall diminishes, vegetation develops, and slope gradually stabilizes. The step change in the fluvial-geomorphic system has resulted in a 60% decline in the volumetric mobilization of sediment and organic carbon between 2011 and 2019. Our findings stress the importance of sustained observations at key permafrost region study sites to elucidate critical information related to past and potential landscape evolution in the Arctic. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2105

2021053068 Garnello, A. (Northern Arizona University, Center for Ecosystem Science for Society, Flagstaff, AZ); Marchenko, S.; Nicolsky, D.; Romanovsky, V.; Ledman, J.; Celis, G.; Schädel, C.; Luo, Y. and Schuur, E. A. G. Projecting permafrost thaw of sub-arctic tundra with a thermodynamic model calibrated to site measurements: Journal of Geophysical Research: Biogeosciences, 126(6), Article e2020JG006218, illus. incl. 2 tables, 109 ref., June 2021.

Northern circumpolar permafrost thaw affects global carbon cycling, as large amounts of stored soil carbon becomes accessible to microbial breakdown under a warming climate. The magnitude of carbon release is linked to the extent of permafrost thaw, which is locally variable and controlled by soil thermodynamics. Soil thermodynamic properties, such as thermal diffusivity, govern the reactivity of the soil-atmosphere thermal gradient, and are controlled by soil composition and drainage. In order to project permafrost thaw for an Alaskan tundra experimental site, we used seven years of site data to calibrate a soil thermodynamic model using a data assimilation technique. The model reproduced seasonal and interannual temperature dynamics for shallow (5-40 cm) and deep soil layers (2-4 m), and simulations of seasonal thaw depth closely matched observed data. The model was then used to project permafrost thaw at the site to the year 2100 using climate forcing data for three future climate scenarios (RCP 4.5, 6.0, and 8.5). Minimal permafrost thawing occurred until mean annual air temperatures rose above the freezing point, after which we measured over a 1 m increase in thaw depth for every 1 °C rise in mean annual air temperature. Under no projected warming scenario was permafrost remaining in the upper 3 m of soil by 2100. We demonstrated an effective data assimilation method that optimizes parameterization of a soil thermodynamic model. The sensitivity of local permafrost to climate warming illustrates the vulnerability of sub-Arctic tundra ecosystems to significant and rapid soil thawing. Abstract Copyright (2021), American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG006218

2021053069 Mauritz, Marguerite (University of Texas at El Paso, El Paso, TX); Pegoraro, Elaine; Ogle, Kiona; Ebert, Christopher and Schuur, Edward A. G. Investigating thaw and plant productivity constraints on old soil carbon respiration from permafrost: Journal of Geophysical Research: Biogeosciences, 126(6), Article e2020JG006000, illus. incl. 2 tables, 105 ref., June 2021.

Isotopic radiocarbon (D14C) signatures of ecosystem respiration (Reco) can identify old soil carbon (C) loss and serve as an early indicator of permafrost destabilization in a warming climate. Warming also stimulates plant productivity causing plant respiration to dominate Reco D14C signatures and potentially obscuring old soil C loss. Here, we investigate how a wide spatio-temporal gradient of permafrost thaw and plant productivity affects Reco D14C patterns and isotopic partitioning. Spatial gradients came from a warming experiment with doubling thaw depth and variable biomass, and a vegetation removal manipulation to eliminate plant contributions. We sampled in August and September to capture transitions from high to low plant productivity, decreased surface soil temperature, and relatively small seasonal thaw extensions. We found that surface processes dominate spatial variation in old soil C loss and a process-based partitioning approach was crucial for constraining old soil C loss. Resampling the same plots in different times of the year revealed that old soil C losses tripled with cooling surface temperature, and the largest old soil C losses were detected when the organic-to-mineral soil horizons thawed (~50-60 cm). We suggest that the measured increase in old soil respiration over the season and when the organic-to-mineral horizon thawed, may be explained by mobilization of nitrogen that stimulates microbial decomposition at depth. Our results suggest that soil C in the organic to mineral horizon may be an important source of soil C loss as the entire Arctic region warms and could lead to nonlinearities in projected permafrost climate feedbacks. Abstract Copyright (2021), American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG006000

2021053066 Schuur, Edward A. G. (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ); Bracho, Rosvel; Celis, Gerardo; Belshe, E. Fay; Ebert, Chris; Ledman, Justin; Mauritz, Marguerite; Pegoraro, Elaine F.; Plaza, César; Rodenhizer, Heidi; Romanovsky, Vladimir; Schädel, Christina; Schirokauer, David; Taylor, Meghan; Vogel, Jason G. and Webb, Elizabeth E. Tundra underlain by thawing permafrost persistently emits carbon to the atmosphere over 15 years of measurements: Journal of Geophysical Research: Biogeosciences, 126(6), Article e2020JG006044, illus. incl. 1 table, 122 ref., June 2021.

Warming of the Arctic can stimulate microbial decomposition and release of permafrost soil carbon (C) as greenhouse gases, and thus has the potential to influence climate change. At the same time, plant growth can be stimulated and offset C release. This study presents a 15-year time series comprising chamber and eddy covariance measurements of net ecosystem C exchange in a tundra ecosystem in Alaska where permafrost has been degrading due to regional warming. The site was a carbon dioxide source to the atmosphere with a cumulative total loss of 781.6 g C m-2 over the study period. Both gross primary productivity (GPP) and ecosystem respiration (Reco) were already likely higher than historical levels such that increases in Reco losses overwhelmed GPP gains in most years. This shift to a net C source to the atmosphere likely started in the early 1990s when permafrost was observed to warm and thaw at the site. Shifts in the plant community occur more slowly and are likely to constrain future GPP increases as compared to more rapid shifts in the microbial community that contribute to increased Reco. Observed rates suggest that cumulative net soil C loss of 4.18-10.00 kg C m-2-8%-20% of the current active layer soil C pool-could occur from 2020 to the end of the century. This amount of permafrost C loss to the atmosphere represents a significant accelerating feedback to climate change if it were to occur at a similar magnitude across the permafrost region. Abstract Copyright (2021), American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG006044

2021053089 Zhang, Xiaowen (University of Florida, Department of Geological Sciences, Gainesville, FL); Bianchi, Thomas S.; Hanna, Andrea J. M.; Shields, Michael R.; Izon, Gareth; Hutchings, Jack A.; Ping, Chien-Lu; Kanevskiy, Mikhail; Haghipour, Negar and Eglinton, Timothy I. Recent warming fuels increased organic carbon export from Arctic permafrost: AGU Advances, 2(2), Article e2021AV000396, illus. incl. sketch maps, 70 ref., June 2021.

Climate-driven thawing of Arctic permafrost renders its vast carbon reserves susceptible to microbial degradation, serving as a potentially potent positive feedback hidden within the climate system. While seemingly intuitive, the relationship between thermally driven permafrost losses and organic carbon (OC) export remains largely unexplored in natural settings. Filling this knowledge gap, we present down-core bulk and compound-specific radiocarbon records of permafrost change from a sediment core taken within the Alaskan Colville River delta spanning the last c. 2,700 years. Fingerprinted by significantly older radiocarbon ages of bulk OC and long-chain fatty acids, these data expose a thermally driven increase in permafrost OC export and/or deepening of mobilizable permafrost layers over the last c. 160 years after the Little Ice Age. Comparison of OC content and radiocarbon data between recent and Roman warming episodes likely implies that the rate of warming, alongside the prevailing boundary conditions, may dictate the ultimate fate of the Arctic's permafrost inventory. Our findings highlight the importance of leveraging geological records as archives of Arctic permafrost mobilization dynamics with temperature change. Abstract Copyright (2021), The Authors.

DOI: 10.1029/2021AV000396

2021058773 Bailleul, Alida M. (Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Key Laboratory of Vertebrate Evolution and Human Origins, Beijing, China). Fossilized cell nuclei are not that rare; review of the histological evidence in the Phanerozoic: Earth-Science Reviews, 216, Article 103599, illus. incl. 1 table, 110 ref., May 2021.

The preservation of cell nuclei in deep time is an area of research that is largely unexplored, likely because of the assumption that fine intracellular organelles are too fragile to enter the fossil record. However, the literature is full of histological reports of Phanerozoic fossils presenting exquisite subcellular details, such as nuclei, nucleoli and even chromosomes seen frozen in multiple stages of cell division and cell death. Starting in the Present and going back in time all the way to the Paleozoic, all histological examinations that recognize cell nuclei in crown multicellular eukaryotes are reviewed here. In the Quaternary, cell nuclei were reported in many mammal mummies found in arctic permafrosts; in the Neogene and Paleogene most reports come from plants and insects preserved in Baltic amber; in the Mesozoic, reports mostly come from dinosaur and plant material. In the Paleozoic, nuclei are reported only in a few Carboniferous plants. The oldest non-controversial nuclei (the 609 million year-old phosphatized Weng'an embryoids) predate the Paleozoic but will also be introduced here. Potential modes of nuclear preservation are also discussed, and it can be concluded that the most important factor is the instantaneous inhibition of autolysis after death. The importance of studying fossil nuclei should not be underestimated, as their morphology hold genetic information and can give insights on the evolution of genome sizes, stases, and karyotypes. Nuclei can also inform on the evolution of cell populations, cell death within the vertebrate tree, and on the preservation of ancient DNA in deep time.

DOI: 10.1016/j.earscirev.2021.103599

2021055628 Ma Wensi (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Cryospheric Science, Lanzhou, China); Wu Tonghua; Wu Xiaodong; Yue Guangyang; Li Ren; Li Xiangfei; Zhu Xiaofan; Hu Guojie; Qiao Yongping; Hao Junming and Ni Jie. Warming could shift steppes to carbon sinks and meadows to carbon sources in permafrost regions; evidence from the improved IBIS model: Catena (Giessen), 200, Article no. 105168, illus. incl. 2 tables, sketch map, 60 ref., May 2021.

Permafrost carbon could produce a positive climate feedback. Until now, the ecosystem carbon budgets in the permafrost regions remain uncertain. Moreover, the frequently used models have some limitations especially regarding to the freeze-thaw process. Herein, we improved the IBIS model by incorporating an unfrozen water scheme and by specifying the parameters to estimate the present and future carbon budget of different land cover types (desert steppe, steppe, meadow, and wet meadow) in the permafrost regions. Incorporating an unfrozen water scheme reduced the mean errors in the soil temperature and soil water content by 25.2%, and the specifying leaf area parameters reduced the errors in the net primary productivity (NPP) by 79.9%. Further, the simulation results showed that steppes are carbon sources (39.16 gC/m2/a) and the meadows are carbon sinks (-63.42 gC/m2/a). Under the climate warming scenarios of RCP 2.6, RCP 6.0, and RCP 8.5, the desert steppe and alpine steppe would assimilated more carbon, while the meadow and wet meadow were projected to shift from carbon sinks to carbon sources in 2071-2100, implying that the land cover type plays an important role in simulating the source/sink effects of permafrost ecosystem carbon in the IBIS model. The results highlight the importance of unfrozen water to the soil hydrothermal regime and specific leaf area for the growth of alpine vegetation, and present new insights on the difference of the responses of various permafrost ecosystems to climate warming.

DOI: 10.1016/j.catena.2021.105168

2021055637 Okupny, Daniel (University of Szczecin, Institute of Marine and Environmental Sciences, Szczecin, Poland) and Pawlowski, Dominik. Elemental composition of biogenic sediments reveals palaeoclimatic changes during the late Weichselian in a Central European river valley; a statistical approach: Catena (Giessen), 200, Article no. 105188, illus. incl. 1 table, geol. sketch maps, 83 ref., May 2021.

Five sections of sediment from mire infillings located in different part of the catchment small river valley in central Europe were studied by lithological and geochemical analysis in order to examine the response of aquatic ecosystems to the environment changes during Late Weischselian (LW). Differentiation of geochemical composition and grain-size properties in biogenic deposits is being considered as a result of change hydroclimatic conditions and geology structure in individual parts of the catchment. The principal component analysis (PCA) and clustered by hierarchical method (HCA) were chosen to create the lithogeochemical facies and their chronostratigraphy variability. Biogenic sediments of the studied river mires, regardless of the location in a given reach of the valley, are represents mainly by mineral or organic-mineral lithogeochemial facies with increased of lithophilic elements (Na, K and Mg). Similar chemical composition of gyttja and peat sediments in almost all periods of LW, indicate the strongly mechanical denudation processes in the Grabia River valley. The major process, conditioning the development of the mires (in it type and rate sedimentation), was the variable terrigenous material input which are related to its variable dynamic of floods. The higher than expected chemical denudation probably a result of specific groundwater flow direction and dissolving vari-grained sands and silts, which build plains in the central part of the study catchment. The number and thickness of individual lithogeochemical facies are caused by differences in the potential volume of the hydrologically active zone and geological conditions of the emerge or disappear permafrost.

DOI: 10.1016/j.catena.2021.105188

2021052921 Sun Yuqin (Peking University, College of Engineering, Beijing, China); Clauson, Kale; Zhou Min; Sun Ziyong; Zheng Chunmiao and Zheng Yan. Hillslopes in headwaters of Qinghai-Tibetan Plateau as hotspots for subsurface dissolved organic carbon processing during permafrost thaw: Journal of Geophysical Research: Biogeosciences, 126(5), Article e2020JG006222, illus. incl. 4 tables, sect., 86 ref., May 2021.

Climate warming has accelerated thawing of northern permafrost, resulting in changes to the supply of dissolved organic carbon (DOC) to inland waters with uncertain fate. Extensive surface water and groundwater interactions occur in alpine permafrost watersheds and likely influence DOC processing differently than systems with limited interactions. Here, we quantify and characterize DOC in waters collected from eight types of water sampled across a small (25 km2) alpine (elevation 2,960-4,820 m a.s.l) watershed in the Qinghai-Tibetan Plateau (QTP) containing variably degraded permafrost. Three types of water (thermokarst ponds, red mud gully, and seepage-I) contained high DOC concentrations (5.2-22.6 mg L-1, n = 38), with carbon contributions predominantly from frozen soil meltwater. Spatial patterns of DOC in stream (0.3-4.8 mg L-1, n = 41), and subsurface waters (0.4-3.8 mg L-1, n = 34), all contained frozen soil meltwater carbon as constrained by d18O and electrical conductivity, reflecting surface-groundwater exchanges in the upper-, middle-, and lower stretches of the watershed. Further, patterns of increasing DOC loss in subsurface waters with decreased proportions of protein-like organic matter and specific UV absorbance at 254 nm, suggest subsurface microbial processing. Using previously established biodegradation DOC kinetics (0.06 day-1) from the QTP, the groundwater transit time is estimated to be between 6 and 20 days based on DOC loss changes of 32% and 74% for July and September, respectively. Mass balance of DOC inputs and export fluxes demonstrate nearly half of all DOC was lost in this small watershed, indicating hillslopes are hotspots for DOC processing, with subsurface environments playing a key role. Abstract Copyright (2021), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG006222

2021052916 Treat, Claire C. (Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Potsdam, Germany); Jones, Miriam C.; Alder, Jay; Sannel, A. Britta K.; Camill, Philip and Frolking, Steve. Predicted vulnerability of carbon in permafrost peatlands with future climate change and permafrost thaw in Western Canada: Journal of Geophysical Research: Biogeosciences, 126(5), Article e2020JG005872, illus. incl. 3 tables, 61 ref., May 2021.

Climate warming in high-latitude regions is thawing carbon-rich permafrost soils, which can release carbon to the atmosphere and enhance climate warming. Using a coupled model of long-term peatland dynamics (Holocene Peat Model, HPM-Arctic), we quantify the potential loss of carbon with future climate warming for six sites with differing climates and permafrost histories in Northwestern Canada. We compared the net carbon balance at 2100 CE resulting from new productivity and the decomposition of active layer and newly thawed permafrost peats under RCP8.5 as a high-end constraint. Modeled net carbon losses ranged from -3.0 kg C m-2 (net loss) to +0.1 kg C m-2 (net gain) between 2015 and 2100. Losses of newly thawed permafrost peat comprised 0.2-25% (median: 1.6%) of "old" C loss, which were related to the residence time of peat in the active layer before being incorporated into the permafrost, peat temperature, and presence of permafrost. The largest C loss was from the permafrost-free site, not from permafrost sites. C losses were greatest from depths of 0.2-1.0 m. New C added to the profile through net primary productivity between 2015 and 2100 offset ~40% to >100% of old C losses across the sites. Differences between modeled active layer deepening and flooding following permafrost thaw resulted in very small differences in net C loss by 2100, illustrating the important role of present-day conditions and permafrost aggradation history in controlling net C loss. Abstract Copyright (2021), . The Authors.

DOI: 10.1029/2020JG005872

2021057398 Brighenti, Stefano (Free University of Bolzano/Bozen, Faculty of Science and Technology, Bolzano, Italy); Engel, Michael; Tolotti, Monica; Bruno, Maria Cristina; Wharton, Geraldene; Comiti, Francesco; Tirler, Werner; Cerasino, Leonardo and Bertoldi, Walter. Contrasting physical and chemical conditions of two rock glacier springs: Hydrological Processes, 35(4), Paper no. e14159, illus. incl. 3 tables, 60 ref., April 2021.

Rock glaciers are increasingly influencing the hydrology and water chemistry of Alpine catchments. During three consecutive summers (2017-2019), we monitored by recording probes and fortnightly/monthly field campaigns the physical and chemical conditions of two rock glacier springs (ZRG, SRG) in the Zay and Solda/Sulden catchments (Eastern Italian Alps). The springs have contrasting hydrological conditions with ZRG emerging with evident ponding (pond-like), and SRG being a typical high-elevation seep (stream-like). Water temperature was constantly low (mean 1.2°C, standard deviation 0.1°C) at both springs. Concentrations of major ions (dominated by SO42-, HCO3-, Ca2+ and Mg2+) and trace elements (As, Sr, Ba, U, Rb) increased, and water became more enriched in heavy stable isotopes (d18O, d2H) towards autumn. This solute and isotopic enrichment had an asymptotic trend at SRG, and a unimodal pattern at ZRG, where peaks occurred 60-80 days after the snowmelt end. Wavelet analysis of electrical conductivity (EC) and water temperature records revealed daily cycles only at SRG, and significant weekly/biweekly fluctuations at both springs attributable to oscillations of meteorological conditions. Several rainfall events triggered a transient (0.5-2 h) EC drop (of 5-240 mS cm-1) and water temperature rise (of 0.2-1.4°C) at SRG (dilution and warming), whereas only intense rainfall events occasionally increased EC (by 15-85 mS cm-1) at ZRG (solute enrichment and thermal buffering), with a long-lasting effect (6-48 h). Building on previous research, we suggest that rock glacier springs with differing flow conditions, that is, stream-like and pond-like, have contrasting fluctuations of water parameters at different timescales. Thus, for pond-like springs, peaks of EC/solute concentrations might indicate a seasonal window of major permafrost thaw. Our quantitative description of the hydrochemical seasonality in rock glacier outflows and the physical and chemical response to precipitation events provides relevant information for water management in mountain areas under climate change. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.14159

2021059782 Gao Zeyong (Chinese Academy of Science, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Niu Fujun; Wang Yibo; Lin Zhanju and Wang Wei. Suprapermafrost groundwater flow and exchange around a thermokarst lake on the Qinghai-Tibet Plateau, China: Journal of Hydrology, 593, Paper no. 125882, illus. incl. 2 tables, sketch map, 56 ref., February 2021.

The dynamics of suprapermafrost groundwater regulate hydrological processes, including the fate and transport of carbon and nutrients, suitability of aquatic habitats, and evolution of permafrost in Arctic, boreal, and high-altitude regions. Nevertheless, relatively few studies have focused on these dynamics on the Qinghai-Tibet Plateau (QTP). In this study, soil hydraulic conductivities, saturated thicknesses, and related hydrological processes were observed in situ around a typical thermokarst lake during the warm season. The results showed that the water table in the active layer fluctuated markedly from June to October and at depths of up to 1.0 m. The discharge of suprapermafrost groundwater was often <0.1 m2 d-1, which was attributed to the thin aquifer and low permeability of the active layer. Groundwater fluxes were controlled by the freeze-thaw cycle and local factors, and were altered by rainfall events and evapotranspiration. The contributions of suprapermafrost groundwater to the thermokarst lake water were often <1.4 mm d-1, and were greater in the late warm season. Moreover, surface runoff in initial warm season was the dominant water resource in some open parts of the lake, and the frequent exchange between surface runoff and lake water accelerated the degradation of the permafrost beneath the lake. These findings provide insights into the role of suprapermafrost groundwater in regional hydrological cycles and the evolution of thermokarst lakes on the Qinghai-Tibet Plateau.

DOI: 10.1016/j.jhydrol.2020.125882

2021055562 Liu Wenhui (Qinghai University, Department of Geological Engineering, Xining, China); Xie Changwei; Zhao Lin; Li Ren; Liu Guangyue; Wang Wu; Liu Hairui; Wu Tonghua; Yang Guiqian; Zhang Yuxin and Zhao Shichu. Rapid expansion of lakes in the endorheic basin on the Qinghai-Tibet Plateau since 2000 and its potential drivers: Catena (Giessen), 197, Article no. 104492, illus. incl. 4 tables, geol. sketch maps, 46 ref., February 2021.

The QTP (Qinghai-Tibet Plateau) holds the greatest concentration of high-elevation inland lakes in the world, and most of these lakes are located in the QTP endorheic basin. Accelerated lake expansion in the endorheic basin since 2000 has been confirmed by many studies, but there is disagreement as to which components of the water balance explain most of the lake expansion. In this paper, based on Landsat images, meteorological data, glacier data and permafrost monitoring data, we analyzed the spatial-temporal changes in lake area and further explored the driving factors behind rapid lake expansion in different zones in the endorheic basin. The results suggested that the spatial pattern of trends in lake area in the endorheic basin from 2000 to 2017 showed a southwest-northeast transition from contracting to slightly expanding to rapidly expanding. More importantly, the dramatic lake expansion observed in most regions was statistically significant (0.01 ~ 26.29 km2/yr). Although retreating glaciers may have contributed to lake growth, this can not fully explain the recent lake expansion. We find that increasing precipitation was the primary driver behind lake expansion, and that permafrost degradation accelerated lake expansion. Lakes on the northern slope of the Gangdise Mountains, fed by the most rapidly retreating glaciers, were relatively stable or even contracted. In contrast, most of the non-glacier-fed lakes in the Hoh Xil region and the central endorheic basin nevertheless experienced significant expansion and slight expansion, respectively, which were mainly attributed to the greatest increase in AP (annual precipitation). Remarkable lake expansion was found in the continuous permafrost zone. The increasing ALT (active layer thickness) and soil temperature of permafrost resulted in an increase in meltwater from ground ice, the partial release of soil moisture and an amount of unfrozen water content, which has contributed to supply lakes and accelerated lake expansion.

DOI: 10.1016/j.catena.2020.104942

2021052610 Harms, Tamara K. (University of Alaska Fairbanks, Institute of Arctic Biology and Department of Biology and Wildlife, Fairbanks, AK); Rocher-Ros, Gerard and Godsey, Sarah E. Emission of greenhouse gases from water tracks draining Arctic hillslopes: Journal of Geophysical Research: Biogeosciences, 125(12), Article e2020JG005889, illus. incl. 2 tables, 87 ref., December 2020. Part of a special section entitled The Arctic; an AGU joint special collection.

Experimental and ambient warming of Arctic tundra results in emissions of greenhouse gases to the atmosphere, contributing to a positive feedback to climate warming. Estimates of gas emissions from lakes and terrestrial tundra confirm the significance of aquatic fluxes in greenhouse gas budgets, whereas few estimates describe emissions from fluvial networks. We measured dissolved gas concentrations and estimated emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) from water tracks, vegetated depressions that hydrologically connect hillslope soils to lakes and streams. Concentrations of trace gases generally increased as ground thaw deepened through the growing season, indicating active production of greenhouse gases in thawed soils. Wet antecedent conditions were correlated with a decline in CO2 and CH4 concentrations. Dissolved N2O in excess of atmospheric equilibrium occurred in drier water tracks, but on average water tracks took up N2O from the atmosphere at low rates. Estimated CO2 emission rates for water tracks were among the highest observed for Arctic aquatic ecosystems, whereas CH4 emissions were of similar magnitude to streams. Despite occupying less than 1% of total catchment area, surface waters within water tracks were an estimated source of up to 53-85% of total CH4 emissions from their catchments and offset the terrestrial C sink by 5-9% during the growing season. Water tracks are abundant features of tundra landscapes that contain warmer soils and incur deeper thaw than adjacent terrestrial ecosystems and as such might contribute to ongoing and accelerating release of greenhouse gases from permafrost soils to the atmosphere. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG005889

2021052596 Jorgenson, M. Torre (Alaska Ecoscience, Fairbanks, AK); Douglas, Thomas A.; Liljedahl, Anna K.; Roth, Joanna E.; Cater, Tim C.; Davis, Wendy A.; Frost, Gerald V.; Miller, Patricia F. and Racine, Charles H. The roles of climate extremes, ecological succession, and hydrology in repeated permafrost aggradation and degradation in fens on the Tanana Flats, Alaska: Journal of Geophysical Research: Biogeosciences, 125(12), Article e2020JG005824, illus. incl. 1 table, 90 ref., December 2020.

The Tanana Flats in central Alaska are a hot spot for thermokarst that is rapidly transforming the landscape. Time series analysis of high-resolution imagery showed that permafrost degradation increased the area of three large fens by 26% from 1949 to 2018, but surprisingly permafrost also aggraded in small areas. Permafrost soils in adjacent birch forests frequently had fen peat near the surface indicating recent permafrost degradation and aggradation. We attribute groundwater as the primary driver of recent permafrost degradation, while climate extremes (especially cold, less snowy winters) caused recent permafrost aggradation, but only after ecological succession provided conditions favorable for permafrost formation. Near-surface groundwater temperatures during early winters (2-6°C during 2011-2014) contributed to a near steady rate of lateral permafrost degradation (0.36 m/yr) over three periods. Fairbanks climate records (1904-2019) showed large ranges in mean winter temperatures (12°C) and snow depths (69 cm) between cold, less snowy winters and warm, snowy winters. During ecological succession from the collapsing margins to the fen centers over a »250-yr period, vegetation transitioned from aquatic forbs to shrubs and mosses, water depths decreased, and the soil carbon stock of new peat increased. These interactions among permafrost, groundwater, climate warming, and succession complicate our ability to project future ecological transitions and soil carbon changes across this dynamic boreal lowland landscape. The more frequent warm, snowy winters since 2014 and model projections for warmer winters, however, indicate that the region has crossed a tipping point where permafrost will no longer form and permafrost loss is irreversible. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG005824

2021052608 Thienpont, Joshua R. (University of Ottawa, Department of Biology, Ottawa, ON, Canada); Eickmeyer, David C.; Kimpe, Linda E. and Blais, Jules M. Thermokarst disturbance drives concentration and composition of metals and polycyclic aromatic compounds in lakes of the western Canadian Arctic: Journal of Geophysical Research: Biogeosciences, 125(12), Article e2020JG005834, illus., 48 ref., December 2020.

When assessing the environmental impact of petroleum hydrocarbon exploitation, it can be challenging to differentiate anthropogenic from natural hydrocarbon sources. For example, areas underlain by permafrost may be affected by erosion of hydrocarbon-rich deposits from thermokarst activity, complicating environmental assessments of human impacts from petroleum extraction. Here we examined polycyclic aromatic compounds (PACs) and metals in sediment cores from lakes affected to varying degrees by thawing permafrost. We used a paired-lake design on lakes with pronounced shoreline retrogressive thaw slumps and compared them to nearby lakes in undisturbed (no retrogressive thaw slump) systems in the Mackenzie Delta uplands (Northwest Territories, Canada). Total organic carbon (TOC)-normalized concentrations of parent and alkylated PACs were higher in surface sediments of slump-affected lakes. Slump-affected lakes were also enriched in metals related to local shale-based, Quaternary deposits (e.g., Ca, Sr, and Mn) when compared to reference lakes where surficial materials were not exposed by thermokarst activity. Diagnostic ratios of specific PACs suggested that slump-affected lakes also had a greater influence from petroleum-based compounds, likely sourced from the local geology. Higher PAC concentrations and petrogenic composition were best explained as a combination of low TOC availability and increased inputs of previously bound hydrocarbons from the catchment due to permafrost erosion. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG005834

2021056771 Yang Wenjing (Lanzhou University, College of Earth and Environmental Sciences, Lanzhou, China); Wang Yibo; Liu Xin; Zhao Haipeng; Wang Genxu and Shao Rui. Estimating the evaporation in the Fenghuo Mountains permafrost region of the Tibetan Plateau: Catena (Giessen), 194, Article no. 104754, illus. incl. 1 table, geol. sketch map, 55 ref., November 2020.

Accurate simulation of the daily actual evaporation (E) is important for understanding and predicting the hydrological climate and terrestrial water-carbon cycle. However, the inclement environment and sparse observation network in the high-altitude areas of the Tibetan Plateau hinder the reliable estimation of actual evaporation. The Complementary Relationship (CR) of evaporation, which is a simple method for estimating the actual evaporation implemented with only routine meteorological data, can be used to study the complex feedback between the atmosphere and the surface. In this study, the eddy covariance and meteorological data were used to test the existence of the CR in the Fenghuo Mountains in the permafrost regions of the Tibetan Plateau. We further compared the application of the generalized nonlinear CR (B2015) and the latest calibration-free CR (S2017) in estimating the actual daily evaporation. The results show that a nonlinear CR of evaporation exists in the Tibetan Plateau. The calibration-free nonlinear principle implemented improvements in the boundary condition shows a more robustness advantage than the generalized method. In addition, we also found that, except rainfall, the freezing-thawing process of active layer is a main reason of seasonal variation characteristics in energy fluxes. These findings broaden our understanding of the applicability of the CR theory and provide a simple and promising method for simulating evaporation on the Tibetan Plateau with the minimum data sets.

DOI: 10.1016/j.catena.2020.104754

2021052533 Tananaev, Nikita (Russian Academy of Sciences, Melnikov Permafrost Institute, Yakutsk, Russian Federation); Teisserenc, Roman and Debolskiy, Matvey. Permafrost hydrology research domain; process-based adjustment: Hydrology, 7(1), Paper no. 6, illus. incl. 1 table, 110 ref., March 2020.

Permafrost hydrology is an emerging discipline, attracting increasing attention as the Arctic region is undergoing rapid change. However, the research domain of this discipline had never been explicitly formulated. Both "permafrost" and "hydrology" yield differing meanings across languages and scientific domains; hence, "permafrost hydrology" serves as an example of cognitive linguistic relativity. From this point of view, the English and Russian usages of this term are explained. The differing views of permafrost as either an ecosystem class or a geographical region, and hydrology as a discipline concerned with either landscapes or generic water bodies, maintain a language-specific touch of the research in this field. Responding to a current lack of a unified approach, we propose a universal process-based definition of permafrost hydrology, based on a specific process assemblage, specific to permafrost regions and including: (1) Unconfined groundwater surface dynamics related to the active layer development; (2) water migration in the soil matrix, driven by phase transitions in the freezing active layer; and (3) transient water storage in both surface and subsurface compartments, redistributing runoff on various time scales. This definition fills the gap in existing scientific vocabulary. Other definitions from the field are revisited and discussed. The future of permafrost hydrology research is discussed, where the most important results would emerge at the interface between permafrost hydrology, periglacial geomorphology, and geocryology.

DOI: 10.3390/hydrology7010006

2021058997 Gibson, J. J. (InnoTech Alberta, Victoria, BC, Canada); Yi, Y. and Birks, S. J. Watershed, climate, and stable isotope data (oxygen-18 and deuterium) for 50 boreal lakes in the oil sands region, northeastern Alberta, Canada, 2002-2017: Data in Brief, 29(105308), illus. incl. 16 tables, 29 ref., February 24, 2020.

Watershed data, climate and stable data collected over a 16-year period from a network of 50 lakes in northeastern Alberta, are provided to allow for broader incorporation into regional assessments of environmental impacts, particularly hydrologic and geochemical processes under changing climate and land use development. Oxygen-18 and deuterium analyses of water samples are provided from late summer surveys of 50 lakes with varying land cover and permafrost conditions. Six sub-groups of lakes are represented, including Stony Mountains, West Fort McMurray, Northeast Fort McMurray, Birch Mountains, Caribou Mountains and Shield. This dataset includes 1582 isotopic analyses made on 791 water samples and 3164 isotope mass balance model outputs, as well as 800 lake/watershed parameters, 5600 climate parameters, and 800 modelled values for isotopic composition of precipitation used in the computations. Model data are provided to facilitate evaluation of transferability of the model for other applications, and to permit more sophisticated spatial analysis and intercomparison with geochemical and biological datasets. Details and further discussion on the isotope mass balance approach are provided in "Regional trends in water balance and runoff to fifty boreal lakes: a 16-year isotope mass balance assessment including evaluation of hydrologic drivers". Overall, the data are expected to be useful, in comparison with local and regional datasets, for water resource management and planning, including design of monitoring networks and environmental impact assessments for oil sands projects.

DOI: 10.1016/j.dib.2020.105308

2021054393 Magnin, Florence (Université Grenoble Alpes, Chambery, France); Haeberli, W.; Linsbauer, A.; Deline, P. and Ravanel, L. Estimating glacier-bed overdeepenings as possible sites of future lakes in the de-glaciating Mont Blanc Massif (Western European Alps): Geomorphology, 350, Article 106913, illus. incl. 5 tables, geol. sketch maps, 99 ref., February 2020. Based on Publisher-supplied data.

De-glaciating high mountain areas result in new landscapes of bedrock and debris where permafrost can degrade, persist or even newly form in cases, and of new lakes in glacier bed overdeepenings (GBOs) becoming ice-free. These landscapes with new lakes in close neighborhood to over-steepened and perennially frozen slopes are prone to chain reaction processes (e.g. rock-ice avalanches into lakes triggering impact waves, dam breach or overtopping, and debris flows) with potentially far-reaching run-out distances causing valley floors devastation. The frequency, magnitude and zonation of hazards are shifting, requiring integrative approaches combining comprehensive information about landscape evolution and related processes to support stakeholders in their adaptation strategies. In this study, we intend to setup an essential baseline for such an integrative approach in the Mont Blanc massif (MBM), which is a typical high-mountain range affected by de-glaciation processes. We first (i) predict and (ii) detect potential GBOs by combining the GlabTop model with a visual analysis based on morphological indications of glacier flow through over-deepened bed parts. We then (iii) determine the level of confidence concerning the resulting information, and (iv) estimate the approximate time range under which potential lakes could form. The location of the predicted GBOs and the shape of glacier beds are evaluated against currently forming water bodies at retreating glacier snouts, and seismic and ice penetrating radar measurements on the Argentière glacier. This comparison shows that the location of predicted GBOs is quite robust whereas their morphometric characteristics (depth, volume) are highly uncertain and tend to be underestimated. In total, 48/80 of the predicted or detected GBOs have a high level of confidence. In addition to five recently formed water bodies at glacier snouts, one of the high confidence GBOs (Talèfre glacier) which is also the most voluminous one could form imminently (during coming years), if not partially or totally drained through deeply incised gorges at the rock threshold. Twelve other lakes could form within the first half of the century under a constant or accelerated scenario of continued glacier retreat. Some of them are located below high and permanently frozen rock walls prone to destabilization and high-energy mass movements, hinting at possible hot spots in terms of hazards in the coming decades, where more detailed analysis would be required.

DOI: 10.1016/j.geomorph.2019.106913

2021054391 Vandenberghe, Jef (Vrije Universiteit, Department of Earth Sciences, Amsterdam, Netherlands); French, Hugh; Jin Huijun; Wang Xianyan; Yi Shuangwen and He Ruixia. The impact of latitude and altitude on the extent of permafrost during the Last Permafrost Maximum (LPM) in north China: Geomorphology, 350, Article 106909, February 2020. Based on Publisher-supplied data.

This paper examines the relationship between the extent of permafrost during the Last Permafrost Maximum (LPM, largely between 22 and 17 ka BP) and the altitudinal and latitudinal temperature gradients that controlled its extent. The region chosen, namely, the Qinghai-Tibet Plateau and the transition to the northern adjacent plains in the North China Plain, is of relatively limited extent in order to avoid regional effects. This area extends over 15 degrees of latitude while altitudes vary from 1000 to 1500 m above sealevel (asl) in the northern plains to more than 4000 m asl in the central-to-south part of the Qinghai-Tibet Plateau. The respective lowest southernmost permafrost occurrences at a northern and a southern position are used for reconstruction of the latitudinal and altitudinal gradients. As a first approximation, we conclude that the elevation compensation during the LPM for a 1° latitude change was between 309 m and 385 m. This is considerably higher than the value calculated for existing permafrost in the region that uses thermal data at a depth of zero amplitude change (139-198 m altitudinal compensation for 1° latitude).

DOI: 10.1016/j.geomorph.2019.106909

2021053239 Xiao Xiong (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing, China); Zhang Fan; Li Xiaoyan; Wang Guanxing; Zeng Chen and Shi Xiaonan. Hydrological functioning of thawing soil water in a permafrost-influenced alpine meadow hillslope: Vadose Zone Journal, 19, Article e20022, illus. incl. 1 table, sketch map, 71 ref., 2020.

The complex variation of the hydrological functioning of soil water has been widely studied using measurements of the stable isotopic composition of either the bulk soil water (BSW) collected by the cryogenic vacuum extraction method or the mobile soil water (MSW) collected by the zero-tension soil lysimeter method. We collected samples of precipitation, BSW, MSW, and hillslope runoff in an alpine meadow hillslope influenced by permafrost to investigate the hydrological functioning of thawing soil water. The results showed that the d2H values in BSW were generally more negative than those of the MSW, which may be a result of the depleted spring snowmelt that formed the tightly bound soil water. The relatively stable characteristics of d2H in the MSW were related to the dynamic mixing of newly infiltrated precipitation with slightly enriched mobile water held by the low soil matrix potential. The d2H values in the BSW showed higher temporal variations than the values in the MSW, which were mainly related to the mixing of depleted tightly bound soil water and enriched MSW in varying fractions. The MSW better represented the lateral subsurface flow (SSF, which further generated streamflow) than the BSW samples considering the relatively close stable isotopic values between the lateral SSF and the MSW in the same soil layer. The results of this study show the influences of the varying water level maintained by the underlying permafrost on the water and isotopic dynamics of both the soil water pools and streamflow. Abstract Copyright (2020), The Authors. Vadose Zone Journal published by Wiley Periodicals, Inc. on behalf of Soil Science Society of America.

DOI: 10.1002/vzj2.20022

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2021057684 Saylor, Emery (Shippensburg University of Pennsylvania, Department of Geography and Earth Science, Shippensburg, PA); Glodek, Steven; Joyce, Robert T.; Hegedus, Emily and Cornell, Sean R. Sedimentary analysis of a periglacial solifluction feature formed in south-central, Pennsylvania during and subsequent to the last glacial maximum (LGM) [abstr.]: in Geological Society of America, Northeastern Section, 56th annual meeting, Abstracts with Programs - Geological Society of America, 53(1), Abstract no. 16-1, March 2021. Meeting: Geological Society of America, Northeastern Section, 56th annual meeting, March 14-15, 2021, World Wide Web.

During the LGM, the Laurentide ice sheet covered NE & NW Pennsylvania. LiDAR investigations of site PA-SHPO 36AD0569, located on South Mountain in south central PA has led to identification of solifluction benches and a lobate mass movement feature. Geologic evidence (landforms, sediments, soils, etc.) demonstrates PA's Valley and Ridge experienced periglacial conditions. Since LGM, climate warming resulted in changes in surface/subsurface processes. Dominated by seasonal temperature variations, periglacial environments experience freeze-thaw cycles. These contribute to bedrock weathering, movement of surficial sediments as well as ground and surface-water flows downslope. Over hundreds of years, these contribute to distinct landforms such as solifluction benches (slope-perpendicular) and lobes (elongate slope-parallel). Lobes appear as portions of the larger benches that have surged downslope due to their inability to dewater the active layer above the immobile permafrost layer. The resulting slope failure can be a rapidly moving liquidized flow or an area of slow but fairly-cohesive creep that moves at a rate of cms/year. This study uses ground-penetrating radar and sediment analysis to identify the origin of the lobate feature found among the three LiDAR-observed solifluction benches. Five 1-m square pits were dug to refusal, and sediments were collected in 10-cm intervals. Wet and dry sediment analyses were completed to quantify grain size trends. Native American rhyolite quarrying allows us to differentiate pre-and post- anthropomorphic disturbance assemblages within the soils on and adjacent to the lobate feature. Just off the feature (LP3), 1-m of debitage-rich soil shows evidence of reverse grading, illustrating infiltration of fines to the base of the profile. In contrast, a pit dug at the base of the lobe (LP2) illustrates evidence of normal grading below 50-cm in the sterile pre-disturbance zone, whereas the soil above displays a pattern like LP3. Wet sieve analysis of an enigmatic 7+ m soil profile at the head of the lobe (UP1) is normally graded. GPR analysis (reported elsewhere) reveals complex subsurface structures. This study is significant for identifying relict periglacial features 10's to 100's of miles south of the ice-front on the basis of sediment analysis.

DOI: 10.1130/abs/2021NE-361895

2021057736 Swezey, Christopher S. (U. S. Geological Survey, Reston, VA); Brent, Emily; Colip, Grant and Mahan, Shannon. Luminescence dating of sand in Butler Cave (Burnsville Cove, Bath and Highland Counties, Virginia) reveals a sedimentary record from the last glaciation [abstr.]: in Geological Society of America, Northeastern Section, 56th annual meeting, Abstracts with Programs - Geological Society of America, 53(1), Abstract no. 20-4, March 2021. Meeting: Geological Society of America, Northeastern Section, 56th annual meeting, March 14-15, 2021, World Wide Web.

In 2020 a sand sample from Butler Cave yielded an optically stimulated luminescence (OSL) age of 34,090±3,210 calendar years (U.S. Geological Survey OSL laboratory sample BC-1). Butler Cave is located in Burnsville Cove on the east flank of Jack Mountain (a NNE-trending anticline) in Bath and Highland Counties, Virginia. Water flows down the mountain over Silurian sandstone and shale until it encounters the Silurian Tonoloway Limestone, where water enters the cave via sinkholes (many of which are clogged with sediment). The sinkholes connect to joint-controlled cave passages that descend to the east and intersect the NNE-trending cave trunk passage, which follows the axis of Sinking Creek syncline. The OSL sample was taken from part of the cave trunk passage known as Sand Canyon, which is ~250 meters (m) long, 6-8 m high, and 7-30 m wide. Under modern conditions, Sand Canyon is dry except during exceptional floods when water flows NNE through Sand Canyon to join a perennial stream named Sneaky Creek. The modern setting of Sand Canyon is an erosional landscape where very little sediment accumulates, but relict 2-3 m high terraces of sand and gravel are preserved along the passage sides. One terrace on the outside (east side) of a bend in the northern (downstream) part of Sand Canyon (where a higher-level passage leads off to the east to the Crystal Gallery) consists of a ~2 m thick unit of poorly sorted sand and gravel (mostly cobbles and pebbles), overlain by a ~0.5 m thick unit of medium sand with parallel laminations. The OSL sample was taken from this ~0.5 m thick sand. The OSL age demonstrates that Quaternary sediments from the time of the last glaciation are preserved in caves of Burnsville Cove and can be dated by OSL methods. This site was ~300 kilometers south of the glacial front in Pennsylvania, and the coarse gravel and OSL age suggest that the terrace in Butler Cave is the deposit of a fluvial flood-pulse initiated after spring thaw breakup of ice (common in permafrost regions). The modern erosional landscape of Sand Canyon suggests that as the climate became warmer and more humid following the last glaciation, sediment influx into the cave decreased as vegetation above ground became more dense, and water (with less sediment in transport) began to excavate and remove sediment that had entered the cave during the time of the last glaciation.

DOI: 10.1130/abs/2021NE-361385

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2021054190 Overbeck, Jacquelyn R. (Alaska Division of Geological and Geophysical Surveys, Fairbanks, AK); Buzard, Richard M.; Turner, Mark M.; Miller, Katie Y. and Glenn, Roberta J. T. Shoreline change at Alaska coastal communities: Report of Investigations - Alaska. Division of Geological & Geophysical Surveys, Rep. No. 2020-10, 35 p. 46 sheets, illus. incl. 3 tables, sketch maps; color geomorphologic maps, 94 ref., 2020. Includes appendices.

Many of Alaska's coastal communities are vulnerable to erosion, flooding, and permafrost degradation. However, few vulnerability assessment tools are available to the public that are complete or that utilize transparent, consistent, and quantitative methods at a scale needed for local planning. This report summarizes statewide analyses of long-term shoreline change at 48 Alaska communities. Shoreline datasets were compiled from previously published U.S. Geological Survey assessments for northern Alaska, as well as created from historical and recent aerial images by the Alaska Division of Geological & Geophysical Surveys for western Alaska. Shorelines were analyzed to calculate rates of shoreline change every 82 feet (25 meters) along coastlines and tidally influenced river banks. In northern and western Alaska, 57 percent (27 of 48 total) of communities had erosion rates greater than 3.3 feet per year (1 meter per year) over the past 60 years. Maps of shoreline change and erosion rates are included here in a small map format for use by local community entities for planning and communication with state and federal agencies. Shoreline change rates alone do not describe community vulnerability, which may also depend on the location of infrastructure and the capacity of a community to respond to erosion, as well as other factors. Shoreline change rates were determined from historical data. Future rates of shoreline change may be influenced by coastal management and changes to environmental conditions that may result from climate change.

DOI: 10.14509/30552

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