May 2021 Monthly Permafrost Alert (PMA) Program

The U.S. Permafrost Association is pleased to announce the availability of an updated searchable database on permafrost-related publications. The American Geosciences Institute, with support from the National Science Foundation, has "migrated" the previous Cold Regions Bibliography to a new platform. Included are the US Permafrost Association supported Monthly Permafrost Alerts dating back to 2011. The Bibliography is searchable at : www.coldregions.org.

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

The individual Monthly Permafrost Alerts are found on the US Permafrost Association website : http://www.uspermafrost.org/monthly-alerts.shtml.

2021 Permafrost Alert Sponsors

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SERIAL REFERENCES

2021026032 Nelson, Frederick E. (Michigan State University, Department of Geography, Environment, and Spatial Sciences, East Lansing, MI) and French, Hugh M. Stephen Taber and the development of North American cryostratigraphy and periglacial geomorphology: Permafrost and Periglacial Processes, 32(2), p.213-230, illus. incl. sect., strat. col., geol. sketch maps, 126 ref., March 15, 2021.

Stephen Taber's early work on ice segregation and frost heaving was far ahead of its time. His laboratory experiments regarding ice segregation led to our current understanding of frost heave by civil and geotechnical engineers building roads and other structures in cold regions. It also laid the foundation for later process-oriented field studies of cold-climate geomorphic processes. Taber's 1943 regional monograph on the origin and history of perennially frozen ground in Alaska, published by the Geological Society of America, was the earliest example of regional cryostratigraphy, and pioneered the regional permafrost and Quaternary studies undertaken later by Katasonov, Popov, Mackay, Péwé, Hopkins, and others. An important dimension of Taber's Alaska work was his application of knowledge gained through laboratory experimentation to the interpretation of ground-ice exposures in the field. While S. W. Muller is widely regarded as the father of permafrost studies in North America, Taber is properly viewed as the "progenitor" of cryostratigraphic studies, although he is not yet widely regarded as such. This study uses archival resources to provide historical context regarding the development of Taber's monograph, to investigate details about the review and publication process it underwent, and to explore the question of why it remains undervalued.

DOI: 10.1002/ppp.2096

2021038563 Chen, Liangzhi (University of Helsinki, Department of Geosciences and Geography, Helsinki, Finland); Aalto, Juha and Luoto, Miska. Significant shallow-depth soil warming over Russia during the past 40 years: Global and Planetary Change, 197, Article 103394, illus. incl. 1 table, 85 ref., February 2021.

Knowledge of the spatiotemporal dynamics of the soil temperature in cold environment is key to understanding the effects of climate change on land-atmosphere feedback and ecosystem functions. Here, we quantify the recent thermal status and trends in shallow ground using the most up-to-date data set of over 457 sites in Russia. The data set consists of in situ soil temperatures at multiple depths (0.8, 1.6, and 3.2 m) collected from 1975 to 2016. For the region as a whole, significant soil warming occurred over the period. The mean annual soil temperature at depths of 0.8, 1.6, and 3.2 m increased at the same level, at ca 0.30-0.31°C/decade, whereas the increase in maximum soil temperature ranged from 0.40°C/decade at 0.8 m to 0.31°C/decade at 3.2 m. Unlike the maximum soil temperature, the increases in minimum soil temperature did not vary (ca 0.25°C/decade) with depth. Due to the overall greater increase in maximum soil temperature than minimum soil temperature, the intra-annual variability of soil temperature increased over the decades. Moreover, the soil temperature increased faster in the continuous permafrost area than in the discontinuous permafrost and seasonal frost areas at shallow depths (0.8 and 1.6 m depth), and increased slower at the deeper level (3.2 m). The warming rate of the maximum soil temperature at the shallower depths was less than that at the deeper level over the discontinuous permafrost area but greater over the seasonal frost area. However, the opposite was found regarding the increase in minimum soil temperature. Correlative analyses suggest that the trends in mean and extreme soil temperatures positively relate to the trends in snow cover thickness and duration, which results in the muted response of intra-annual variability of the soil temperature as snow cover changes. This study provides a comprehensive view of the decadal evolutions of the shallow soil temperatures over Russia, revealing that the temporal trends in annual mean and extreme soil temperatures vary with depth and permafrost distribution.

DOI: 10.1016/j.gloplacha.2020.103394

2021036777 Costard, F. (CNRS/Université Paris-Saclay, Géoscience Paris Sud (GEOPS), Orsay, France); Dupeyrat, L.; Séjourné, A.; Bouchard, F.; Fedorov, A. and Saint-Bézar, B. Retrogressive thaw slumps on ice-rich permafrost under degradation; results from a large-scale laboratory simulation: Geophysical Research Letters, 48(1), Article e2020GL091070, illus., 36 ref., January 16, 2021.

In the ice-rich permafrost of the Arctic regions, thermokarst erosion on slopes induces the formation of large-scale retrogressive thaw slumps (RTS). They have significant geomorphological, hydrological, and biogeochemical impacts on the landscape. Further research is thus needed to better understand the respective effect of ice content and permafrost heterogeneities on the dynamics of these erosional features. Here, we present results of a full-scale physical modeling of RTS development in a cold room. The experimental setup was designed to simulate and compare two ground-ice settings (ice wedges, icy layers) with the thawing of ice-poor permafrost (i.e., reference model). Our results show that the melting of the icy layers induces a loss of decohesion of the overlapping frozen soil. The heterogeneous frozen soil with ice wedges needs a longer time until degradation, but undergoes a stronger and faster decohesion of its structure during the thawing phase. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020GL091070

2021036371 Liu Guimin (Lan Jiaotong University, School of Environmental and Municipal Engineering, Lanzhou, China); Wu Tonghua; Hu Guojie; Wu Xiaodong and Li Wangping. Permafrost existence is closely associated with soil organic matter preservation; evidence from relationships among environmental factors and soil carbon in a permafrost boundary area: Catena (Giessen), 196, Article no. 104894, illus. incl. 1 table, 52 ref., January 2021.

Permafrost regions store a large amount of soil organic carbon (SOC). Although permafrost degradation with climate warming can stimulate soil organic matter (SOM) decomposition, it remains unknown that whether the permafrost existence benefits SOM preservation. Here, a boundary area of permafrost and non-permafrost zone was selected to test the hypothesis that SOM underlain by permafrost has been better preserved than the area without permafrost under similar climatic conditions. The interactions among topography, vegetation cover, permafrost, soil variables and SOC distribution were examined. The results showed the sites beneath wet meadow land covers, which are usually underlain by permafrost, have higher SOC stocks than those of alpine meadows without permafrost. Based on mixed effects models, both soil water content and bulk density explained higher SOC content variances in the sites without permafrost than the sites underlain by permafrost. The north-facing non-permafrost sites have significantly higher SOC contents than those in south-facing non-permafrost sites. Vegetation cover, aspect, and permafrost have mixing effects on SOC contents both in permafrost and non-permafrost sites. Soil particle size and the rock fragment content are good predictors for prediction of SOC contents, while the best predictor was depending on the presence of permafrost. These results suggested that under similar climatic conditions, permafrost existence favors the preservation of SOM, this should be taken into consideration in the future carbon emission from permafrost regions since permafrost degradation can lag behind climate warming in many areas.

DOI: 10.1016/j.catena.2020.104894

2021036347 Yuan Ziqiang (Lanzhou University, School of Life Sciences, Lanzhou, China) and Jiang Xiaojin. Vegetation and soil covariation, not grazing exclusion, control soil organic carbon and nitrogen in density fractions of alpine meadows in a Tibetan permafrost region: Catena (Giessen), 196, Article no. 104832, illus. incl. 5 tables, sketch map, 87 ref., January 2021.

The accrual of soil organic carbon (SOC) and nitrogen (N) in grassland is an important management option to improve the ecosystem functions of grassland. However, how abiotic (such as grazing exclusion (GE)) and biotic factors influence SOC and N and their different fractions in Tibetan alpine meadows remains unclear. In this study, we evaluated the relative importance of abiotic and biotic factors that drive SOC and N contents in soil density fractions by performing redundancy analysis based on three long-term (10 years) fenced alpine meadows maintained in the permafrost region of the Tibetan Plateau in China. Biotic factors comprise plant aboveground biomass, cover and diversity, whereas abiotic factors include soil properties (i.e. soil moisture, pH, clay, silt, sand, total phosphorus, available phosphorus, microbial biomass carbon and N, available N, C:N ratio and C:P ratio) and GE. Site rather than GE has significant effects on the SOC and N contents. GE caused no increase in the SOC and N contents in the whole soil and fractions. Redundancy analysis showed that 96.7% of the variations in SOC and N fractions can be explained by the selected explanatory variables. Aboveground biomass, cover, soil moisture and clay contents were key factors that affected the SOC and N fractions. The SOC and N fractions were mainly explained by the interaction between vegetation and soil, followed by soil, vegetation and GE. The study highlighted the importance of considering the covariation of vegetation and soil for evaluating the SOC and N dynamics in alpine meadows. The effect of GE (such as 10 years) on the SOC and N contents in alpine meadows can be weak in the permafrost region of the Tibetan Plateau.

DOI: 10.1016/j.catena.2020.104832

2021036378 Zhang Shuhong (Shangqiu Normal University, College of Biology and Food, Shangqiu, China); Yang Guangli; Hou Shugui; Zhang Tingjun; Li Zhiguo and Du Wentao. Analysis of heavy metal-related indices in the Eboling permafrost on the Tibetan Plateau: Catena (Giessen), 196, Article no. 104907, illus. incl. 1 table, sketch map, 72 ref., January 2021.

The relationship between heavy metals and the expression of heavy metal resistance genes (HMRGs) in the active layer (AL) and the permafrost layer (PL) are not well understood, despite being closely linked to the impact of human activity on heavy metal levels and bacterial response to heavy metal stress. Herein, we conducted a metagenomics sequencing analysis to understand how bacteria adapt to such heavy metal stress. We detected higher levels of heavy metals in the AL relative to the PL. Consistent with this, analyses of AL samples revealed the presence of more genes associated with DNA damage repair, DNA recombination, and heavy metal resistance relative to PL samples. Heavy metal-resistant bacterial phyla including Actinobacteria, Acidobacteria, Bacteroidetes, and Cyanobacteria were more abundant in the AL than the PL. At the genera level, we found that bacteria responsible for nitrification, sulfur reduction, and methane oxidation and reduction were less prevalent in the AL relative to the PL. In summary, bacteria in the AL have evolved such that they are able to resist prolonged heavy metal pollution.

DOI: 10.1016/j.catena.2020.104907

2021034739 Arzhannikova, Anastasia (Russian Academy of Sciences, Siberian Branch, Institute of the Earth's Crust, Irkutsk, Russian Federation); Ritz, Jean-François; Larroque, Christophe; Antoine, Pierre; Arzhannikov, Sergey; Chebotarev, Aleksei; Stéphan, Jean-François; Massault, M. Marc and Michelot, Jean-Luc. Cryoturbation versus tectonic deformation along the southern edge of the Tunka Basin (Baikal rift system), Siberia; new insights from an integrated morphotectonic and stratigraphic study: Journal of Asian Earth Sciences, 204, Article 104569, illus. incl. 1 table, sects., sketch maps, 69 ref., December 2020.

The Tunka Basin is a broad, emerging basin situated between the Baikal Lake to the east and the the Hovsgol Lake to the west. The basin is bounded to the north and to the south by the Tunka and the Khamar-Daban mountain ranges, respectively. The Tunka normal fault, located at the southern foothills of the Tunka Mountain Range, is the main structure that controlled the development of the Tunka Basin during the Neogene. Paleoearthquake-surface ruptures attest of its present activity; and show that its western and eastern terminations are undergoing a tectonic inversion characterized by left-lateral-reverse deformations. The southern edge of the Tunka Basin is classically interpreted as being tectonically controlled. In this paper, we present the results of a geomorphological and stratigraphic analysis within its southwestern and southeastern parts suggesting that there is no active fault affecting the foothills of the Khamar-Daban Mountain Range. The different features observed in the Quaternary deposits are interpreted to be the result of periglacial processes induced by alternating episodes of permafrost aggradation and degradation during the Holocene. Our study concludes that the Khamar-Daban Range and the Tunka Basin are uplifting together, and that the Tunka and Mondy Faults are the two main triggers of regional earthquakes.

DOI: 10.1016/j.jseaes.2020.104569

2021033325 Gabov, Dmitriy (Russian Academy of Sciences, Ural Branch, Institute of Biology, Syktyvkar, Russian Federation); Yakovleva, Evgenia and Vasilevich, Roman. Vertical distribution of PAHs during the evolution of permafrost peatlands of the European Arctic zone: Applied Geochemistry, 123, Article 104790, illus. incl. 4 tables, sketch map, 76 ref., December 2020.

A range of polycyclic aromatic hydrocarbons has been identified, and regularities of their vertical distribution in the peatland of hummock-hollow complexes in the southern tundra--forest tundra and northern tundra--southern tundra ecotones of the European Arctic zone have been determined. Benzo[ghi]perylene, naphthalene, pyrene, fluorene, phenanthrene, benzo[b]fluoranthene and benzo[a]pyrene are displayed most in the peatlands under study. Regarding the peatland profile the vertical polyarene distribution is similar--in 150-175 cm permafrost layers (site 1) and 50(70)-210(250) cm layers (site 2), and on the border between the active layer and permafrost 35-50(60) cm (site 1) and 30(42)-50 cm (site 2) a significant increase of HCO-accumulated PAHs weight fraction is observed. PAHs content maximums in tundra peatland horizons are associated both with 4-, 5- and 6-nuclear structures at both sites under the analysis, and with a larger amount of 2- and 3-nuclear polyarenes in the peatlands on the northern tundra-southern tundra ecotone. Aeration-exposed seasonally thawing peatland layers are subject to continuous formation of primarily light 2- and 3-nuclear PAHs of natural origin resulting from microbiological decomposition of plant residues, which are subsequently involved in equilibrium cycles of chemical and biochemical transformation, with their total capacity remaining almost unchanged and constituting ~200-500 ng/g. Owing to low productivity of plant communities and absence of tree vegetation in the seasonally thawed layer, accumulation of the sum of 4-, 5- and 6-nuclear PAHs weakens significantly. One can detect dependencies between individual PAHs and the botanic composition of peat through higher weight fraction of 4-, 5- and 6-nuclear polyarenes being lignin transformation products generated more as the share of tree vegetation grows. The PAHs composition is a paleoclimatic marker reflecting adequately both changing paleovegetation stages and the degree of peat decomposition.

DOI: 10.1016/j.apgeochem.2020.104790

2021038833 Gao Zeyong (Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Niu Fujun and Lin Zhanju. Effects of permafrost degradation on thermokarst lake hydrochemistry in the Qinghai-Tibet Plateau, China: Hydrological Processes, 34(26), p. 5659-5673, illus. incl. 2 tables, geol. sketch maps, 72 ref., December 30, 2020.

Thermokarst lakes play a key role in the hydrological and biogeochemical cycles of permafrost regions. Current knowledge regarding the changes caused by permafrost degradation to the hydrochemistry of lakes in the Qinghai-Tibet Plateau (QTP) is limited. To address this gap, a systematic investigation of thermokarst lake water, suprapermafrost water, ground ice, and precipitation was conducted in the hinterland of the QTP. The thermokarst lake water in the QTP was identified to be of the Na-HCO3-Cl type. The mean concentrations of HCO3- and Na+ were 281.8 mg L-1 (146.0-546.2 mg L-1) and 73.3 mg L-1 (9.2-345.8 mg L-1), respectively. The concentrations of Li+, NH4+, K+, F-, NO2-, and NO3- were relatively low. Freeze-out fractionation concentrated the dissolved solids within the lake water during winter, which was deeply deepened on lake depth and lake ice thickness. Owing to solute enrichment, the ground ice was characterized by high salinity. Conversely, repeated replenishment via precipitation led to lower solute concentrations in the ground ice near the permafrost table compared to that within the permafrost. Although lower solute concentration existed in precipitation, the soil leaching and saline ground ice melting processes enhanced the solute load in suprapermafrost water, which is considered an important water and solute resource in thermokarst lakes. The influencing mechanism of permafrost degradation on thermokarst lake hydrochemistry is presumably linked to: (1) the liberation of soluble materials sequestered in ground ice; (2) the increase of solutes in suprapermafrost water and soil pore water; and (3) the changes in lake morphometry. These results have major implications on the understanding of the effects of ground ice melting on ecosystem functions, biogeochemical processes, and energy balance in a rapidly changing climate. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.13987

2021034717 Harding, P. (University College London, Department of Geography, Environmental Change Research Centre, London, United Kingdom); Bezrukova, E. V.; Kostrova, S. S.; Lacey, J. H.; Leng, M. J.; Meyer, H.; Pavlova, L. A.; Shchetnikov, A.; Shtenberg, M. V.; Tarasov, P. E. and Mackay, A. W. Hydrological (in)stability in southern Siberia during the Younger Dryas and early Holocene: Global and Planetary Change, 195, Article 103333, illus. incl. 1 table, 141 ref., December 2020.

Southern Siberia is currently undergoing rapid warming, inducing changes in vegetation, loss of permafrost, and impacts on the hydrodynamics of lakes and rivers. Lake sediments are key archives of environmental change and contain a record of ecosystem variability, as well as providing proxy indicators of wider environmental and climatic change. Investigating how hydrological systems have responded to past shifts in climate can provide essential context for better understanding future ecosystem changes in Siberia. Oxygen isotope ratios within lacustrine records provide fundamental information on past variability in hydrological systems. Here we present a new oxygen isotope record from diatom silica ([]18Odiatom) at Lake Baunt (55°11'15"N, 113°01,45"E), in the southern part of eastern Siberia, and consider how the site has responded to climate changes between the Younger Dryas and Early to Mid Holocene (ca. 12.4 to 6.2 ka cal BP). Excursions in []18Odiatom are influenced by air temperature and the seasonality, quantity, and source of atmospheric precipitation. These variables are a function of the strength of the Siberian High, which controls temperature, the proportion and quantity of winter versus summer precipitation, and the relative dominance of Atlantic versus Pacific air masses. A regional comparison with other Siberian []18Odiatom records, from lakes Baikal and Kotokel, suggests that []18Odiatom variations in southern Siberia reflect increased continentality during the Younger Dryas, delayed Early Holocene warming in the region, and substantial climate instability between ~10.5 to ~8.2 ka cal BP. Unstable conditions during the Early Holocene thermal optimum most likely reflect localised changes from glacial melting. Taking the profiles from three very different lakes together, highlight the influence of site specific factors on the individual records, and how one site is not indicative of the region as a whole. Overall, the study documents how sensitive this important region is to both internal and external forcing.

DOI: 10.1016/j.gloplacha.2020.103333

2021038811 Devoie, Elise G. (University of Waterloo, Department of Civil and Environmental Engineering, Waterloo, ON, Canada); Connon, Ryan F.; Craig, James R. and Quinton, William L. Subsurface flow measurements using passive flux meters in variably-saturated cold-regions landscapes: Hydrological Processes, 34(23), p. 4541-4546, illus., 31 ref., November 15, 2020.

To date, passive flux meters have predominantly been applied in temperate environments for tracking the movement of contaminants in groundwater. This study applies these instruments to reduce uncertainty in (typically instantaneous) flux measurements made in a low-gradient, wetland dominated, discontinuous permafrost environment. This method supports improved estimation of unsaturated and over-winter subsurface flows which are very difficult to quantify using hydraulic gradient-based approaches. Improved subsurface flow estimates can play a key role in understanding the water budget of this landscape. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.13900

2021038850 Turner, Jesse C. (University of Washington, Department of Civil and Environmental Engineering, Seattle, WA); Moorberg, Colby J.; Wong, Andrea; Shea, Kathleen; Waldrop, Mark P.; Turetsky, Merritt R. and Neumann, Rebecca B. Getting to the root of plant-mediated methane emissions and oxidation in a thermokarst bog: Journal of Geophysical Research: Biogeosciences, 125(11), Article e2019JG005825, illus. incl. 2 tables, 76 ref., November 2020.

Vascular plants are important in the wetland methane cycle, but their effect on production, oxidation, and transport has high uncertainty, limiting our ability to predict emissions. In a permafrost-thaw bog in Interior Alaska, we used plant manipulation treatments, field-deployed planar optical oxygen sensors, direct measurements of methane oxidation, and microbial DNA analyses to disentangle mechanisms by which vascular vegetation affect methane emissions. Vegetation operated on top of baseline methane emissions, which varied with proximity to the thawing permafrost margin. Emissions from vegetated plots increased over the season, resulting in cumulative seasonal methane emissions that were 4.1-5.2 g m-2 season-1 greater than unvegetated plots. Mass balance calculations signify these greater emissions were due to increased methane production (3.0-3.5 g m-2 season-1) and decreased methane oxidation (1.1-1.6 g m-2 season-1). Minimal oxidation occurred along the plant-transport pathway, and oxidation was suppressed outside the plant pathway. Our data indicate suppression of methane oxidation was stimulated by root exudates fueling competition among microbes for electron acceptors. This contention is supported by the fact that methane oxidation and relative abundance of methanotrophs decreased over the season in the presence of vegetation, but methane oxidation remained steady in unvegetated treatments; oxygen was not detected around plant roots but was detected around silicone tubes mimicking aerenchyma; and oxygen injection experiments suggested that oxygen consumption was faster in the presence of vascular vegetation. Root exudates are known to fuel methane production, and our work provides evidence they also decrease methane oxidation. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020JG005825

2021038857 Zhuang, Qianlai (Purdue University, Department of Earth, Atmospheric, and Planetary Sciences, West Lafayette, IN); Wang, Sirui; Zhao, Bailu; Aires, Filipe; Prigent, Catherine; Yu, Zicheng; Keller, Jason K. and Bridgham, Scott. Modeling Holocene peatland carbon accumulation in North America: Journal of Geophysical Research: Biogeosciences, 125(11), Article e2019JG005230, illus. incl. 4 tables, 102 ref., November 2020.

Peatlands are a large carbon reservoir. Yet the quantification of their carbon stock still has a large uncertainty due to lacking observational data and well-tested peatland biogeochemistry models. Here, a process-based peatland model was calibrated using long-term peat carbon accumulation data at multiple sites in North America. The model was then applied to quantify the peat carbon accumulation rates and stocks within North America over the last 12,000 years. We estimated that 85-174 Pg carbon was accumulated in North American peatlands over the study period including 0.37-0.76 Pg carbon in subtropical peatlands. During the period from 10,000 to 8,000 years ago, the warmer and wetter conditions might have played an important role in stimulating peat carbon accumulation by enhancing plant photosynthesis. Enhanced peat decomposition due to warming slowed the carbon accumulation through the rest of the Holocene. While recent modeling studies indicate that the northern peatlands will continue to act as a carbon sink in this century, our studies suggest that future enhanced peat decomposition accompanied by peatland areal changes induced by permafrost degradation and other disturbances shall confound the sink and source analysis. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2019JG005230

2021033791 Angelopoulos, Michael (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Overduin, Pier Paul; Westermann, Sebastian; Tronicke, Jens; Strauss, Jens; Schirrmeister, Lutz; Biskaborn, Boris K.; Liebner, Susanne; Maksimov, Georgii; Grigoriev, Mikhail N. and Grosse, Guido. Thermokarst lake to lagoon transitions in eastern Siberia; do submerged taliks refreeze?: Journal of Geophysical Research: Earth Surface, 125(10), Article e2019JF005424, illus. incl. block diags., sects., 2 tables, sketch maps, 95 ref., October 2020.

As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons, and, eventually, integrates them into subsea permafrost. Lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions. In this research, borehole data, electrical resistivity surveying, and modeling of heat and salt diffusion were carried out at Polar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated water body connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover. The boreholes in the center of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik, a thin ice-bearing permafrost layer, and unfrozen ground. The bathymetry showed that most of the lagoon had bedfast ice in spring. In bedfast ice areas, the electrical resistivity profiles suggested that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modeling showed that thermokarst lake taliks can refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0°C. This occurs, because the top-down chemical degradation of newly formed ice-bearing permafrost is slower than the refreezing of the talik. Hence, lagoons may precondition taliks with a layer of ice-bearing permafrost before encroachment by the sea, and this frozen layer may act as a cap on gas migration out of the underlying talik. Abstract Copyright (2020), The Authors.

DOI: 10.1029/2019JF005424

2021033799 Scherler, D. (German Research Centre for Geosciences, Potsdam, Germany) and Egholm, D. L. Production and transport of supraglacial debris; insights from cosmogenic 10Be and numerical modeling, Chhota Shigri Glacier, Indian Himalaya: Journal of Geophysical Research: Earth Surface, 125(10), Article e2020JF005586, illus. incl. sketch maps, 1 table, sects., 81 ref., October 2020.

Many mountain glaciers carry some amount of rocky debris on them, which modifies surface ablation rates. The debris is typically derived from erosion of the surrounding topography and its supraglacial extent is predominantly controlled by the relative accumulation rates of debris versus snow. Because Global Warming results in shrinking glaciers as well as thawing permafrost worldwide, changes in both rates will most likely affect the evolution of supraglacial debris cover and thus the response of glaciers to climate change. Here we report 10Be concentrations measured in five amalgamated debris samples collected from the main medial moraine of the Chhota Shigri Glacier, India. Results suggest headwall erosion rates that are ~0.5-1 mm year-1, and apparently increasing (10Be concentrations are decreasing) toward the present. We employed a numerical ice flow model that we combined with a new Lagrangian particle tracing routine to explore the impact of spatial and temporal variability in erosion rates and source areas on 10Be concentrations in the medial moraine. Our modeling results show that neither changes in source areas, related to the transient response of the glacier to ongoing climate change, nor four different scenarios of spatial and temporal variability in erosion rates could explain the observed trend in 10Be concentrations. Although not accounted for in our modeling explicitly, we suggest that the observed trend could be due to transiently enhanced erosion of recently deglaciated areas, or to greater spatial variability in erosion rates than explored in our models.

DOI: 10.1029/2020JF005586

2021038183 Gao Zeyong (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Lin Zhanju; Niu Fujun and Luo Jing. Soil water dynamics in the active layers under different land-cover types in the permafrost regions of the Qinghai-Tibet Plateau, China: Geoderma, 364, Article no. 114176, illus. incl. 5 tables, sketch map, 66 ref., April 1, 2020.

The mechanisms of hydrological processes, biochemical cycles, and permafrost revolution, and the potential impacts of climate change on these, are still poorly quantified in alpine regions, partly due to a lack of understanding of soil water dynamics in the permafrost active layer. In this study, soil water in the active layer was monitored in-situ at nine sites, including wet meadow (WM), alpine meadow (AM), alpine steppe (AS), transitional area-steppe (TA-S), transitional area-meadow (TA-M), bare land (BL), extremely degraded wet meadow (EDWM), alpine steppe on south-facing slope (ASSF), and alpine meadow on north-facing slope (AMNF) regions. These sites are located in the hinterland of the Qinghai-Tibet Plateau (QTP). Ground-ice distributions and isotope variations under different alpine ecosystems were also examined. The results demonstrate that soil water content was low at 0.5-m depth and high at the surface and at 1.0-m depth in the soil profiles from the TA-S, BL, EDWM, ASSF, and AMNF sites. However, denser vegetation coverage masked the effects of the freeze-thaw processes, which leading soil water content increased gradually with soil depth. Moreover, rainfall infiltration for recharging soil water in the lower layers was hampered due to the buffering action of mattic epipedons and the existence of clayed layers. Additionally, preferential flow often occurred in the degraded alpine meadows, which supplied deeper soil water. The Pearson correlation coefficients between soil water in the deeper layers and ground-ice were above 0.67 (significance <0.05), suggesting that deep soil water had a stronger effect on the formation of ground-ice near the permafrost table than soil water at the surface and middle root layers. Furthermore, results from the analysis of isotopic tracers suggest that precipitation directly recharged more ground-ice near permafrost table at the EDWM, ASSF, and AWNF sites, but less so at the WM, AM, AS, and BL sites, due to greater evapotranspiration and land cover. These results provide insights into the effect future climate warming can have on ecological succession and regional hydrological processes.

DOI: 10.1016/j.geoderma.2020.114176

2021032782 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; Zeng Chen; Shi Xiaonan; Wu Huawu; Jagirani, Muhammad Dodo and Che Tao. Using stable isotopes to identify major flow pathways in a permafrost influenced alpine meadow hillslope during summer rainfall period: Hydrological Processes, 34(5), p. 1104-1116, illus. incl. 2 tables, sketch map, 45 ref., February 28, 2020.

Global warming has leaded to permafrost degradation, with potential impacts on the runoff generation processes of permafrost influenced alpine meadow hillslope. Stable isotopes have the potential to trace the complex runoff generation processes. In this study, precipitation, hillslope surface and subsurface runoff, stream water, and mobile soil water (MSW) at different hillslope positions and depths were collected during the summer rainfall period to analyse the major flow pathway based on stable isotopic signatures. The results indicated that (a) compared with precipitation, the d2H values of MSW showed little temporal variation but strong heterogeneity with enriched isotopic ratios at lower hillslope positions and in deeper soil layers. (b) The d2H values of middle-slope surface runoff and shallow subsurface flow were similar to those of precipitation and MSW of the same soil layer, respectively. (c) Middle-slope shallow subsurface flow was the major flow pathway of the permafrost influenced alpine meadow hillslope, which turned into surface runoff at the riparian zone before contributing to the streamflow. (d) The slight variation of d2H values in stream water was shown to be related to mixing processes of new water (precipitation, 2%) and old water (middle-slope shallow subsurface flow, 98%) in the highly transmissive shallow thawed soil layers. It was inferred that supra-permafrost water levels would be lowered to a less conductive, deeper soil layer under further warming and thawing permafrost, which would result in a declined streamflow and delayed runoff peak. This study explained the "rapid mobilization of old water" paradox in permafrost influenced alpine meadow hillslope and improved our understanding of permafrost hillslope hydrology in alpine regions. Abstract Copyright (2020), John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.13650

2021034838 Vaks, Anton (Geological Survey of Israel, Jerusalem, Israel); Mason, A. J.; Breitenbach, S. F. M.; Kononov, A. M.; Osinzev, A. V.; Rosensaft, M.; Borshevsky, A.; Gutareva, O. S. and Henderson, G. M. Paleoclimate evidence of vulnerable permafrost during times of low sea ice: Nature (London), 577(7789), p. 221-225, illus. incl. sketch maps, 43 ref., January 9, 2020.

DOI: 10.1038/s41586-019-1880-1

2021032694 Brighenti, Stefano (University of Trento, Department of Civil, Environmental and Mechanical Engineering, Trento, Italy); Tolotti, Monica; Bruno, Maria Cristina; Engel, Michael; Wharton, Geraldene; Cerasino, Leonardo; Mair, Volkmar and Bertoldi, Walter. After the peak water; the increasing influence of rock glaciers on alpine river systems: Hydrological Processes, 33(21), p. 2804-2823, illus. incl. 5 tables, sketch map, 81 ref., October 15, 2019.

Human-accelerated climate change is quickly leading to glacier-free mountains, with consequences for the ecology and hydrology of alpine river systems. Water origin (i.e., glacier, snowmelt, precipitation, and groundwater) is a key control on multiple facets of alpine stream ecosystems, because it drives the physico-chemical template of the habitat in which ecological communities reside and interact and ecosystem processes occur. Accordingly, distinct alpine stream types and associated communities have been identified. However, unlike streams fed by glaciers (i.e., kryal), groundwater (i.e., krenal), and snowmelt/precipitation (i.e., rhithral), those fed by rock glaciers are still poorly documented. We characterized the physical and chemical features of these streams and investigated the influence of rock glaciers on the habitat template of alpine river networks. We analysed two subcatchments in a deglaciating area of the Central European Alps, where rock glacier-fed, groundwater-fed, and glacier-fed streams are all present. We monitored the spatial, seasonal, and diel variability of physical conditions (i.e., water temperature, turbidity, channel stability, and discharge) and chemical variables (electrical conductivity, major ions, and trace element concentrations) during the snowmelt, glacier ablation, and flow recession periods of two consecutive years. We observed distinct physical and chemical conditions and seasonal responses for the different stream types. Rock glacial streams were characterized by very low and constant water temperatures, stable channels, clear waters, and high concentrations of ions and trace elements that increased as summer progressed. Furthermore, one rock glacier strongly influenced the habitat template of downstream waters due to high solute export, especially in late summer under increased permafrost thaw. Given their unique set of environmental conditions, we suggest that streams fed by thawing rock glaciers are distinct river habitats that differ from those normally classified for alpine streams. Rock glaciers may become increasingly important in shaping the hydroecology of alpine river systems under continued deglaciation. Abstract Copyright (2019), John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.13533

2021034407 Tinivella, Umberta (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Geophysical Department, Trieste, Italy); Giustiniani, Michela and Marín-Moreno, Héctor. A quick-look method for initial evaluation of gas hydrate stability below subaqueous permafrost: Geosciences (Basel), 9(8), Article 329, illus. incl. 2 tables, 60 ref., August 2019.

Many studies demonstrated the coexistence of subaqueous permafrost and gas hydrate. Subaqueous permafrost could be a factor affecting the formation/dissociation of gas hydrate. Here, we propose a simple empirical approach that allows estimating the steady-state conditions for gas hydrate stability in the presence of subaqueous permafrost. This approach was derived for pressure, temperature, and salinity conditions typical of subaqueous permafrost in marine (brine) and lacustrine (freshwater) environments.

DOI: 10.3390/geosciences9080329

2021034403 Tumel, Nellie (Lomonosov Moscow State University, Faculty of Geography, Moscow, Russian Federation) and Zotova, Larisa. Diagnostics and mapping of geoecological situations in the permafrost zone of Russia: Geosciences (Basel), 9(8), Article 353, illus. incl. 4 tables, geol. sketch maps, 111 ref., August 2019. Part of a special issue titled Permafrost landscapes; classification and mapping, edited by Fedorov, A.

The diagnosis of the geoecological state of natural landscapes during the economic development of the permafrost zone should be established by assessing destructive cryogenic processes. Furthermore, the geoecological state should be considered in terms of landscape resistance to an increase in cryogenic processes. In this paper, we examine and determine lithocryogenic stability parameters, including permafrost distribution over an area, annual mean temperature, ice content (humidity), and the protective properties of the vegetation. Activation of cryogenic processes in Western Siberia was estimated in terms of the area, development rate and attenuation, natural landscape damage, and hazards to engineering and mining facility operations. The evaluation procedure and the improvement in expert numerical scores are shown. A number of approved methods are proposed for creating assessment maps at various scales using landscape indication methods, decoded satellite images, expert assessments, statistical calculations, and analysis of spatial geographical information systems. Methodical techniques for digital geocryological mapping on the basis of the landscape are presented at scales from 1:3,000,000 to 1:20,000,000. All the maps were created by the authors and can be used for a wide range of applications, including design, survey organizations, and education.

DOI: 10.3390/geosciences9080353

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CONFERENCE REFERENCES

2021036575 Macias-Fauria, Marc (University of Oxford, School of Geography and the Environment, Oxford, United Kingdom). Can the present inform our past inference on Beringian ecosystems? [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 121-2, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

A thick layer of fine-grained, ice-rich, aeolian-deposited sediment accumulated in Beringian environments in the late Pleistocene. The terrestrial Arctic permafrost holds an estimated »1500 Pg C (»40% of total terrestrial soil carbon), being particularly concentrated in the 1.2 million km2 of deep soils of the Yedoma regions of Siberia and Alaska (210-460 Pg C) and in Arctic river deltas (91 ± 39 Pg C) (Schuur et al. 2015 Nature 520). The vulnerability of such large quantities of permafrost-stored carbon with rising temperatures and permafrost thaw represents an important climate feedback identified in the high latitudes. Landcover has long been found to affect the energy and carbon budgets of these regions, greatly influencing the pace and direction of such feedback. Central to these mechanisms is the Pleistocene mammoth steppe, which has been proposed to interact with the Earth System differently to the current wet tundra/forest-tundra. Key differences involve higher albedo of grassland-dominated ecosystems - linked to both vegetation reflectance and modified snow cover; reduced surface insulation due to winter snow trampling by large animals; drier soils due to increased evapotranspiration; higher nutrient cycling and productivity through the herbivory-and-egestion pathway; and increased soil C accumulation due to deeper, diffused roots. Independently of how the demise of the Pleistocene megafauna occurred, a key question in Beringian landscapes is whether and to what extent biome-scale vegetation changes were (and might be) controlled bottom-up (climate ® vegetation cover ® fauna) or top-down (fauna ® vegetation cover climate). The latter opens the possibility for large-scale megafaunal interventions that mitigate climate change by favouring mammoth steppe-like vegetation cover. Whereas much information on which of the two possible mechanisms dominates comes from the palaeo-record, here I will discuss what evidence exists at present - the observational period - from systems where large differences in extant megaherbivore densities are found through experimental, socio-ecological, and/or opportunistic setups in northern Eurasia, including Beringian sites such as Pleistocene Park in Chersky, Sakha. The overall feasibility of such interventions, in case they prove to work, will be assessed.

DOI: 10.1130/abs/2020AM-359846

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