Permafrost Monthly Alerts (PMAs)

2020045405 Vulis, Lawrence (University of California Irvine, Department of Civil and Environmental Engineering, Irvine, CA); Tejedor, Alejandro; Schwenk, Jon; Piliouras, Anastasia; Rowland, Joel and Foufoula-Georgiou, Efi. Channel network control on seasonal lake area dynamics in Arctic deltas: Geophysical Research Letters, 47(7), Paper no. e2019GL086710, illus. incl. sketch map, 44 ref., April 16, 2020.

The abundant lakes dotting arctic deltas are hotspots of methane emissions and biogeochemical activity, but seasonal variability in lake extents introduces uncertainty in estimates of lacustrine carbon emissions, typically performed at annual or longer time scales. To characterize variability in lake extents, we analyzed summertime lake area loss (i.e., shrinkage) on two deltas over the past 20 years, using Landsat-derived water masks. We find that monthly shrinkage rates have a pronounced structured variability around the channel network with the shrinkage rate systematically decreasing farther away from the channels. This pattern of shrinkage is predominantly attributed to a deeper active layer enhancing near-surface connectivity and storage and greater vegetation density closer to the channels leading to increased evapotranspiration rates. This shrinkage signal, easily extracted from remote sensing observations, may offer the means to constrain estimates of lacustrine methane emissions and to develop process-based estimates of depth to permafrost on arctic deltas. Abstract Copyright (2020), The Authors.

DOI: 10.1029/2019GL086710

2020043698 Abolt, Charles J. (Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM); Young, Michael H.; Atchley, Adam L.; Harp, Dylan R. and Coon, Ethan T. Feedbacks between surface deformation and permafrost degradation in ice wedge polygons, Arctic Coastal Plain, Alaska: Journal of Geophysical Research: Earth Surface, 125(3), p. 1-17, illus. incl. block diags., 67 ref., March 2020.

In the past three decades, an abrupt, pan-Arctic acceleration of ice wedge melting has transformed tundra landscapes, spurring the formation of hummock-like features known as high-centered polygons (HCPs). This rapid geomorphic transition profoundly alters regional hydrology and influences surface emissions of CO₂ and CH₄. In Arctic Alaska, most recent instances of ice wedge degradation have arrested within 15-20 years of inception, stabilizing HCP microtopography. However, feedbacks between ground surface deformation and permafrost stability are incompletely understood, limiting our capacity to predict trajectories of landscape evolution in a still warmer future. Here, we use field data from a site near Prudhoe Bay, Alaska, to develop a modeling-based framework for assessing the strength of positive (i.e., exacerbating) feedbacks on ice wedge degradation, focusing on the importance of heterogeneity in surface drainage and microtopographic conditions. Our simulations suggest that, when troughs are narrow, positive feedbacks on ice wedge melting (associated with thermokarst pool formation) are relatively weak. Positive feedbacks are markedly stronger beneath wide troughs, such as those that form above older, larger ice wedges. Seasonal thaw abruptly accelerates once a talik begins to form beneath wide and deep thermokarst pools. Once a talik initiates, winter severity and snowpack thickness increase in importance as predictors of thaw intensity in summer. Our results indicate that meter-scale heterogeneity in polygonal microtopography potentially exerts strong, nonlinear controls on thermokarst trajectories. These findings are useful for predicting future thermokarst dynamics and for interpreting the results from coarser-resolution land surface models operating at greater spatial and temporal scales. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

DOI: 10.1029/2019JF005349

2020043703 Terry, Neil (U. S. Geological Survey, Earth System Processes Division, Storrs, CT); Grunewald, Elliot; Briggs, Martin; Gooseff, Michael; Huryn, Alexander D.; Kass, M. Andy; Tape, Ken D.; Hendrickson, Patrick and Lane, John W., Jr. Seasonal subsurface thaw dynamics of an aufeis feature inferred from geophysical methods: Journal of Geophysical Research: Earth Surface, 125(3), p. 1-18, illus. incl. sects., sketch map, 74 ref., March 2020.

Aufeis are sheets of ice unique to cold regions that originate from repeated flooding and freezing events during the winter. They have hydrological importance associated with summer flows and winter insulation, but little is known about the seasonal dynamics of the unfrozen sediment layer beneath them. This layer may support perennial groundwater flow in regions with otherwise continuous permafrost. For this study, ground penetrating radar (GPR) were collected in September 2016 (maximum thaw) and April 2017 (maximum frozen) at the Kuparuk aufeis field on the North Slope of Alaska. Supporting surface nuclear magnetic resonance data were collected during the maximum frozen campaign. These point-in-time geophysical data sets were augmented by continuous subsurface temperature data and periodic Structure-from-Motion digital elevation models collected seasonally. GPR and difference digital elevation model data showed up to 6 m of ice over the sediment surface. Below the ice, GPR and nuclear magnetic resonance identified regions of permafrost and regions of seasonally frozen sediment (i.e., the active layer) underlain by a substantial lateral talik that reached >13-m thickness. The seasonally frozen cobble layer above the talik was typically 3- to 5-m thick, with freezing apparently enabled by relatively high thermal diffusivity of the overlying ice and rock cobbles. The large talik suggests that year-round groundwater flow and coupled heat transport occurs beneath much of the feature. Highly permeable alluvial material and discrete zones of apparent groundwater upwelling indicated by geophysical and ground temperature data allows direct connection between the aufeis and the talik below. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

DOI: 10.1029/2019JF005345

2020043697 Ward Jones, Melissa K. (McGill University, Department of Geography, Montreal, QC, Canada); Pollard, Wayne H. and Amyot, Frances. Impacts of degrading ice-wedges on ground temperatures in a high arctic polar desert system: Journal of Geophysical Research: Earth Surface, 125(3), p. 1-17, illus. incl. 1 table, sketch maps, 67 ref., March 2020.

Ice-wedge ice is the most widespread type of massive ice found in the continuous permafrost zone. Polygonal networks of ice-wedges drive environmental changes and feedback that will likely be exacerbated with future climate change. Recent decadal-scale observations have shown that ice-wedges are degrading rapidly within the entire Circum-Arctic Region but observations of feedback associated with ground temperature regimes are still lacking in many areas. We present over a year's worth of field observations from an area with cold (-16.5°C), thick (>500 m) continuous permafrost and a mean annual air temperature of -19.7°C in the Canadian high Arctic. Topographic surveys, thaw depths, vegetation cover, soil moisture, and annual shallow (12 cm) ground temperature measurements were collected for seven ice-wedge troughs and two polygon centers in a high-centered polygon system. We show that geomorphic changes caused by ice-wedge degradation generate new responses in soil moisture, vegetation cover, and snow distribution that create a mosaic of ground temperatures that range by 5.1°C for mean annual, 2.5°C in summer, and 15.2°C in winter between polygon-centers and ice-wedge troughs. Our results show that snow redistribution due to wind induces the cooling of polygon centers, thus promoting new thermal contraction cracking and ice-wedge formation. We provide an example based on high-resolution remote sensing data on how these ice-wedge trough densities vary spatially in our study area. Capturing these fine scale geomorphic differences and resulting ground temperatures will be critical to accurately assess future changes of these common Arctic landscapes. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2019JF005173

2020043023 Evans, Sarah G. (Appalachian State University, Department of Geological and Environmental Sciences, Boone, NC); Godsey, Sarah E.; Rushlow, Caitlin R. and Voss, Clifford. Water tracks enhance water flow above permafrost in upland arctic Alaska hillslopes: Journal of Geophysical Research: Earth Surface, 125(2), p. 1-18, illus. incl. block diag., sketch map, 93 ref., February 2020.

Upland permafrost regions occupy approximately one third of the Arctic landscape. In upland regions, hydrologic fluxes are influenced by water tracks, curvilinear features on hillslopes that preferentially fill with and route water in response to snowmelt and rainfall when the soil above continuous permafrost thaws in the summer. As continued warming of the Arctic may alter hydrologic cycling leading to increased frequency of extreme hydrologic events like drought and flooding as well as modification of biogeochemical cycling, it is imperative to untangle the interplay between precipitation, runoff, and subsurface flow as water is routed from upland Arctic regions to the Arctic Ocean. This study quantifies how ground surface temperatures affect groundwater discharge from hillslopes with water tracks in the upland Arctic by employing a three-dimensional, physically based subsurface flow model with variable saturation and freeze and thaw capabilities that is calibrated to field measurements from the Upper Kuparuk River watershed on the North Slope of Alaska, USA. Model analysis indicates that higher ground surface temperatures along water track hillslopes promote increases in groundwater discharge where water tracks act as conduits for large-recharge events and continue to discharge groundwater into the autumn after the adjacent hillslope has frozen. Simulating the conditions that distinguish water tracks from their hillslope watersheds changes subsurface water storage and ground thermal responses but does not alter the total magnitude of groundwater discharge outside of parameter uncertainty. These findings suggest that water tracks play a complex and critical role in hydrologic cycles of the upland Arctic. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2019JF005256

2020039070 Hirst, Catherine (Swedish Museum of Natural History, Department of Geosciences, Stockholm, Sweden); Andersson, Per S.; Kooijman, Ellen; Schmitt, Melanie; Kutscher, Liselott; Maximov, Trofim; Mörth, Carl-Magnus and Porcelli, Don. Iron isotopes reveal the sources of Fe-bearing particles and colloids in the Lena River basin: Geochimica et Cosmochimica Acta, 269, p. 678-692, illus. incl. 1 table, sketch maps, 82 ref., January 15, 2020.

Large Arctic rivers are important suppliers of iron to the Arctic Ocean. However, the sources of Fe-bearing particles in permafrost-dominated systems and the mechanisms driving this supply of Fe are poorly resolved. Here, Fe isotope ratios were used to determine the sources of Fe-bearing particles and colloids in the Lena River and tributaries.In samples collected after the spring floods, Fe-bearing particles (>0.22 mm) carried ~70% of the Fe and have isotope ratios that are lower than, or similar to that of the continental crust. These particles are composed of a leachable Fe fraction of largely ferrihydrite, with isotope values of -1.40 ppm to -0.12 ppm, and a fraction of clays and Fe oxides with continental crust values. Co-existing Fe-bearing colloids (<0.22 mm), composed mainly of ferrihydrite, have higher isotope values, of -0.22 ppm to +1.83 ppm. A model is proposed in which soil mineral weathering generates aqueous Fe with lower d⁵⁶Fe values. During transport, a small fraction of the dissolved Fe is precipitated as colloidal ferrihydrite with higher d⁵⁶Fe values. Most of the Fe is precipitated onto mineral grains in oxic riparian zones, with the d⁵⁶Fe values largely generated during weathering. Groundwater discharge and riparian erosion supply the colloids and coated particles to the rivers. The differences between d⁵⁶Fe values in leachates and detrital grains in Fe-bearing particles agree with values determined in mineral dissolution experiments and in Fe accumulation horizons in soils. The difference in d⁵⁶Fe values between leachates and colloids reflects isotope fractionation during incremental Fe(III)_aq precipitation and Fe-OC complexation during transport towards the riparian zone. Overall, the Fe isotope values of riverine particles and colloids reflect processes that occur during mineral dissolution, transport, and secondary mineral formation in permafrost soils.

DOI: 10.1016/j.gca.2019.11.004

2020039057 Krickov, Ivan V. (Tomsk State University, BIO-GEO-CLIM Laboratory, Tomsk, Russian Federation); Lim, Artem G.; Manasypov, Rinat M.; Loiko, Sergey V.; Vorobyev, Sergey N.; Shevchenko, Vladimir P.; Dara, Olga M.; Gordeev, Vyacheslav V. and Pokrovsky, Oleg S. Major and trace elements in suspended matter of western Siberian rivers; first assessment across permafrost zones and landscape parameters of watersheds: Geochimica et Cosmochimica Acta, 269, p. 429-450, illus. incl. 2 tables, sketch maps, 84 ref., January 15, 2020.

In contrast to good understanding of chemical composition of the river suspended matter (RSM) of large rivers, small rivers remain strongly understudied, despite the fact that they can provide valuable information on mechanisms of RSM generation and transport depending on key environmental parameters of the watershed. This is especially true for permafrost-affected boreal and subarctic territories, subjected to strong modification due to permafrost thaw and landscape changes under climate warming. We selected Earth's largest frozen peatland zone, the western Siberia Lowland (WSL) in order to test an impact of climate warming, permafrost thaw and landscape zone changes on riverine transport of particulate material from mainland to the Arctic Ocean. We sampled 33 small and medium size WSL rivers during spring flood, summer baseflow and autumn flood over a 1700 km gradient of climate and permafrost. Major and trace elements in particulate (>0.45 mm) and dissolved (<0.45 mm) fraction were analyzed. We hypothesize that future increase in active layer thickness and the change of dominant landscape from bogs and lakes to forest can be predicted via analyzing the actual pattern of RSM chemical composition across various permafrost zones and landscape parameters of WSL river watershed. We observed a minimum concentration of Li, Mg, Na, K, Rb, V, Cr, Zn, Cu, Co, Ni, Al, Ga, Y, REEs, Nb, W, Ti, Zr, Hf, Th and U in RSM collected from isolated and sporadic permafrost zones. Considering all seasons together, the presence of forest in the permafrost-bearing zone increased particulate concentrations of all alkalis and alkaline-earth elements, B, As, Nb, Mn, Co, Al, Ga, REEs, Ti, Zr, Hf, Th. This is consistent with element mobilization from mineral horizons that become available for interacting with soil fluids under forested regions. Lakes retained particulate alkaline-earths, Fe, Mn, Co, trivalent and tetravalent hydrolysates (TE³⁺, TE⁴⁺). The concentration of lithogenic low-soluble elements (TE³⁺, TE⁴⁺) in the RSM strongly increased with the river size (watershed area). Compared to the world RSM average, the WSL rivers exhibited lower concentrations of all elements except Mn and P and a low share of suspended elements relative to total (suspended+dissolved) forms of trace metals and of low-mobility (lithogenic) elements. Likely reasons for these features are: (i) low runoff and low RSM concentration as there is no rock and mineral substrate exposed to physical weathering in WSL peatland; (ii) organic, rather than mineral, nature of surrounding "solid" substrates and as a result, organic rather than silicate nature of RSM, and (iii) high DOC and Fe concentration leading to high concentrations of typically low-solubilty elements in the dissolved (<0.45 mm) fraction due to colloids. From a climate warming perspective, the increase in active layer thickness and involvement of mineral horizons into soil fluid migration in discontinuous to continuous permafrost zone will likely increase the share of particulate fraction in total element transport for many soluble (labile) elements and also lithogenic elements in WSL rivers. At the same time, permafrost boundary shift northward may decrease particulate concentrations of most major and TE in rivers of discontinuous permafrost zone. The lake drainage and forest colonization of tundra and bogs in the permafrost-affected part of WSL may increase the concentration of alkali and alkaline-earth elements, divalent metals and trivalent and tetravalent hydrolysates. As a result, export of particulate metal micronutrients and toxicants from the WSL territory to the Arctic Ocean may increase.

DOI: 10.1016/j.gca.2019.11.005

2020045802 Sowers, Tyler D. (University of Delaware, Delaware Environmental Institute, Newark, DE); Wani, Rucha P.; Coward, Elizabeth K.; Fischel, Matthew H. H.; Betts, Aaron R.; Douglas, Thomas A.; Duckworth, Owen W. and Sparks, Donald L. Spatially resolved organomineral interactions across a permafrost chronosequence: Environmental Science & Technology, 54(5), p. 2951-2960, illus. incl. tables, 2020.

Permafrost contains a large (1700 Pg C) terrestrial pool of organic matter (OM) that is susceptible to degradation as global temperatures increase. Of particular importance is syngenetic Yedoma permafrost containing high OM content. Reactive iron phases promote stabilizing interactions between OM and soil minerals and this stabilization may be of increasing importance in permafrost as the thawed surface region ("active layer") deepens. However, there is limited understanding of Fe and other soil mineral phase associations with OM carbon (C) moieties in permafrost soils. To elucidate the elemental associations involved in organomineral complexation within permafrost systems, soil cores spanning a Pleistocene permafrost chronosequence (19,000, 27,000, and 36,000 years old) were collected from an underground tunnel near Fairbanks, Alaska. Subsamples were analyzed via scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectroscopy at the nano- to microscale. Amino acid-rich moieties decreased in abundance across the chronosequence. Strong correlations between C and Fe with discrete Fe(III) or Fe(II) regions selectively associated with specific OM moieties were observed. Additionally, Ca coassociated with C through potential cation bridging mechanisms. Results indicate Fe(III), Fe(II), and mixed valence phases associated with OM throughout diverse permafrost environments, suggesting that organomineral complexation is crucial to predict C stability as permafrost systems warm.

DOI: 10.1021/acs.est.9b06558

2020040970 Li Xilai (Qinghai University, Laboratory of Plateau Ecoogy and Agriculture, Xining, China); Gao, Jay; Zhang Jing; Wang Rui; Jin Liqun and Zhou Huakun. Adaptive strategies to overcome challenges in vegetation restoration to coalmine wasteland in a frigid alpine setting: Catena (Giessen), 182, Article 104142, illus. incl. 1 table, sketch maps, 45 ref., November 2019.

Existing methods of restoring vegetation to abandoned coalmine wasteland are inapplicable to the harsh Qinghai-Tibet Plateau because it faces several unique challenges, including a perennially low temperature, strong winds and solar radiation, the presence of permafrost, and the lack of suitable topsoil, all of which are absent from low-altitude regions. It remains unknown which restoration measures could be successful in this particular environmental setting. In this case study we demonstrated that these challenges can be overcome via four proposed measures, each targeting a unique challenge. Namely, the surface morphology of the mining waste must be reshaped into a pyramid-resembling terrace comprising flat strips interspersed with slopes <25° to prevent permafrost-thawing triggered debris slippage. Instead of expensive topsoil replacement, locally sourced and quickly weathered mixture of permafrost and coal gangue can be used to reconstruct the topsoil after its fertility has been enriched with fertilizers. A mixture of grass seeds suitable for the frigid environment must be sowed at a higher dosage (e.g., 300 kg·ha^-1) than the usual 20-30 kg·ha^-1. Covering the sowed fields using a mesh made from fibers considerably boosted seed germination and grass growth. Field experiments demonstrate that a combined use of the adapted measures enables vegetation to be established. Both plant height and aboveground biomass reach the peak value of 40.6 cm and 71.0 g·m^-2, respectively, after three years of restoration, but decreases by year five. Plant cover and the quantity of new seeds increase with time, peaking at 57.3% and 682.9 seeds·m^-2 at the end of year five, respectively. These vegetation properties are consistently better on sunny slopes than on shady ones. Thus, surface covering and the dosage of seeds sowed on these slopes need to be increased accordingly. It is concluded that the adapted measures are suitable for the study area and other plateau areas sharing similar environmental settings.

DOI: 10.1016/j.catena.2019.104142

2020044753 Campos, Néstor (Complutense University, Department of Geography, Madrid, Spain); Tanarro, Luis M.; Palacios, David and Zamorano, José J. Slow dynamics in debris-covered and rock glaciers in Hofsdalur, Trollaskagi Peninsula (northern Iceland): Geomorphology, 342, p. 61-77, sketch maps, sects., 6 tables, geol. sketch map, 67 ref., October 2019.

The results of previous work on the dynamics of the debris-covered and rock glaciers in Trollaskagi are contradictory. To improve our knowledge of these dynamics and determine the origin and evolution of these landforms, we analyzed two case studies located in the Hofsdalur Valley: the Hofsjokull debris-covered glacier and the Jullogil rock glacier, using digital photogrammetry combined with GIS techniques. Our most accurate results were obtained for the period 1980-1994 as follows: for the Hofsjokull debris-covered glacier a mean block displacement velocity of 0.22 m yr^-1, a block elevation difference of -0.36 m and a horizontal displacement of linear ridges of 0.21 m yr^-1; for the Jullogil rock glacier a mean block displacement velocity of 0.15 m yr^-1, a block elevation difference of -0.63 m and a horizontal displacement of linear ridges of 0.16 m yr^-1. The limits of these glaciers remained stable for »70 years, from 1946 to 2017. All our data support the fact that these landforms are stable, and having lost their ice accumulation sources, their dynamics are fundamentally related to subsidence processes. Therefore, they are relict landforms whose origin seems to be related to paraglacial processes after rapid deglaciation of the valleys, and their stagnated ice is preserved, as it is above the permafrost level.

DOI: 10.1016/j.geomorph.2019.06.005

2020045038 Zheng, Lei (University of Colorado at Boulder, Community Surface Dynamics Modeling System, Boulder, CO); Overeem, Irina; Wang, Kang and Clow, Gary D. Changing Arctic river dynamics cause localized permafrost thaw: Journal of Geophysical Research: Earth Surface, 124(9), p. 2324-2344, illus. incl. 3 tables, geol. sketch maps, 83 ref., September 2019.

Permafrost in the Arctic regions is degrading in response to decades of amplified warming. Advanced degradation of ice-rich permafrost could significantly alter the water balance by increasing runoff and flooding. How do the hydrological changes in river systems, in turn, affect the permafrost thermal state, specifically in floodplains? First, we develop a first-order heat budget approach to simulate evolving river-water temperature. The river-water thermal model includes heat exchanges at both the air-water and water-subsurface interfaces and can accurately estimate water temperature. Then, river-water temperature is employed as an upper boundary condition for the control volume permafrost model, which models the thermal state of shallow permafrost. The combined model is validated and applied in the Kuparuk River floodplain, Alaska. Results indicate that permafrost warms rapidly during inundation and that channelbelt active layer thickness can deepen by more than 1 m. We find that earlier arrival of the spring freshet and associated earlier inundation onset, as well as increase in river discharge, can significantly increase subsurface permafrost temperature and lead to a deepening of the active layer. In recent years Kuparuk River streamflow has arrived earlier, and mean annual river discharge has increased by 35% since the 1970s. New permanent water and seasonal water appeared throughout the river network of the Kuparuk River since the 1980s according to satellite observations. These hydrological changes likely have contributed to the expansion of riverbed thaw bulbs and the degradation of floodplain permafrost. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2019JF005060

2020041040 Arndt, Kyle A. (San Diego State University, Global Change Research Group, San Diego, CA); Oechel, Walter C.; Goodrich, Jordan P.; Bailey, Barbara A.; Kalhori, Aram; Hashemi, Josh; Sweeney, Colm and Zona, Donatella. Sensitivity of methane emissions to later soil freezing in arctic tundra ecosystems: Journal of Geophysical Research: Biogeosciences, 124(8), p. 2595-2609, illus. incl. 4 tables, 90 ref., August 2019.

The atmospheric methane (CH₄) concentration, a potent greenhouse gas, is on the rise once again, making it critical to understand the controls on CH₄ emissions. In Arctic tundra ecosystems, a substantial part of the CH₄ budget originates from the cold season, particularly during the "zero curtain" (ZC), when soil remains unfrozen around 0 °C. Due to the sparse data available at this time, the controls on cold season CH₄ emissions are poorly understood. This study investigates the relationship between the fall ZC and CH₄ emissions using long-term soil temperature measurements and CH₄ fluxes from four eddy covariance (EC) towers in northern Alaska. To identify the large-scale implication of the EC results, we investigated the temporal change of terrestrial CH₄ enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiagvik, AK, from 2001 to 2017 and their association with the ZC. We found that the ZC is extending later into winter (2.6 ± 0.5 days/year from 2001 to 2017) and that terrestrial fall CH₄ enhancements are correlated with later soil freezing (0.79 ± 0.18-ppb CH₄ day^-1 unfrozen soil). ZC conditions were associated with consistently higher CH₄ fluxes than after soil freezing across all EC towers during the measuring period (2013-2017). Unfrozen soil persisted after air temperature was well below 0 °C suggesting that air temperature has poor predictive power on CH₄ fluxes relative to soil temperature. These results imply that later soil freezing can increase CH₄ loss and that soil temperature should be used to model CH₄ emissions during the fall. Abstract Copyright (2019), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2019JG005242

2020041037 Zherebker, A. (Skolkovo Institute of Science and Technology, Skolkovo, Russian Federation); Podgorski, D. C.; Kholodov, V. A.; Orlov, A. A.; Yaroslavtseva, N. V.; Kharybin, O.; Kholodov, A.; Spector, V.; Spencer, R. G. M.; Nikolaev, E. and Perminova, I. V. The molecular composition of humic substances isolated from yedoma permafrost and alas cores in the eastern Siberian Arctic as measured by ultrahigh resolution mass spectrometry: Journal of Geophysical Research: Biogeosciences, 124(8), p. 2432-2445, illus. incl. 2 tables, 48 ref., August 2019.

Ongoing climate change is making the large pool of organic matter (OM) stored in Arctic permafrost vulnerable to mobilization; thus, garnering a deeper understanding of molecular transformations within the abundant pool of soil OM, specifically humic substances, is crucial. Here we present the first high-resolution mass-spectrometry examination of molecular compositions of humic acid (HA) and fulvic acid (FA) isolated from organic-rich deep yedoma (Pleistocene age ice-rich permafrost) and alas (thermokarst deposit formed during permafrost thaw) cores. The FA fractions were dominated by oxygen-rich unsaturated compounds, whereas the HA fractions were mostly composed of relatively reduced saturated and aromatic moieties. A substantial increase in contribution of both CHO-only and N-containing aliphatic compounds was observed in the HA fractions of the yedoma OM with depth, whereas the alas HA fractions were depleted in aliphatics but enriched with condensed and hydrolyzable tannins. The observed differences in compositional space of the immobile OM stored in the deep yedoma versus alas deposits were consistent with evolution of OM during thermokarst lake genesis, implying intense microbial degradation of N-rich OM released from the yedoma deposits and accumulation of highly degraded, plant-derived OM. The patterns of molecular transformations of OM were apparent in compositional space of the least degraded HA fractions as compared to much more oxidized FA fractions. This shows great promise of molecular exploration of the alkali-extracted OM, comprising up to 50% of the total organic carbon in deep permafrost both for paleoreconstructions and predictions of climate feedback to released OM due to permafrost thaw. Abstract Copyright (2019), . American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2018JG004743

2020038639 Karasiewicz, Tomasz M. (Nicolaus Copernicus University in Torun, Department of Geomorphology and Quaternary Paleogeography, Turun, Poland). The kettle-hole mire as archives of postglacial changes in biogenic sedimentation (Tuchola Forest, north-central Poland): Catena (Giessen), 176, p. 26-44, illus. incl. 6 tables, sketch map, 110 ref., May 2019.

Kettle holes are a circular-shape product of ice decay, and thus are strongly linked with young glacial landscapes. Once glaciation terminates, these holes transform either into wetland and lakes or occasionally into kettle-hole mires. Since an entire sediment sequence preserve in the kettle-holes, these provide an excellent settings to exploit any sensitive paleoenvironmental changes. Here, the kettle-hole mire located onto the Brda River outwash plain (Tuchola Forest) is explored towards a better understanding of local and global environmental trends in the Late Glacial-present day time frame. To fulfill this, multi-proxy study as geochemical, palynological and macrofossils analyses along with the radiocarbon dating are used. Therefore, this study allows to distinguish five phases of steep environmental gradients in the investigated mire, as follows: (1) paludification after glaciation, when dead-ice melted and long-term permafrost was degraded, (2) lake started to disappear in the Late Glacial, followed by a rich vegetation in the first part of the Holocene, (3) vegetation encroachment onto the lake in the first part of the Holocene, which consequently turned into an peat bog, (4) the late Holocene peat bog with a limited human influence, and finally (5) the peat bog with a major human impact along with acidification as related to sandy underlying sediments, leaching of calcium carbonate, recharge from precipitation and pine monoculture. As additionally apparent from this small ecosystem, both local (character of substrate sediments, morphology of the area, rate of permafrost melting, climate conditions and human activity) and regional (climate changes and human activity) are detectable. Nevertheless, the record of these changes is sometimes unclear.

DOI: 10.1016/j.catena.2019.01.003

2020042525 Kitover, Danielle C. (Vrije Universiteit Amsterdam, Department of Earth Sciences, Amsterdam, Netherlands); Renssen, Hans; van Balen, Ronald; Vandenberghe, Jef and Roche, Didier M. Coupling of VAMPERS within iLOVECLIM; experiments during the LGM and last deglaciation: JQS. Journal of Quaternary Science, 34(3), p. 215-227, illus. incl. 1 table, 72 ref., April 2019.

The VAMPERS (Vrije Universiteit Amsterdam Permafrost Snow Model) has been coupled within iLOVECLIM, an earth system model. This advancement allows the thermal coupling between permafrost and climate to be examined from a millennial timescale using equilibrium experiments during the Last Glacial Maximum (21 ka) and transient experiments for the subsequent deglaciation period (21-11 ka). It appears that the role of permafrost during both stable and transitional (glacial-interglacial) climate periods is seasonal, resulting in cooler summers and warmer winters by approximately ±2 °C maximum. This conclusion reinforces the importance of including the active layer within climate models. In addition, the coupling of VAMPERS also yields a simulation of transient permafrost conditions, not only for estimating areal changes in extent but also total permafrost gain/loss. Abstract Copyright (2019), John Wiley & Sons, Ltd.

DOI: 10.1002/jqs.3094

2020044072 Kaverin, D. A. (Rossiyskaya Akademiya Nauk, Ural'skoye Otdeleniye, Komi Nauchnyy Tsentr, Institut Biologii, Syktyvkar, Russian Federation); Lapina, L. E.; Pastukhov, A. V. and Novakovskiy, N. B. Vliyaniye transformatsii rastitel'nogo i pochvennogo pokrova na temperature pochv pri ekspluatatsii zimney dorogi v Bol'shezemel'skoy tundre [Transformation of vegetation, soils and change of their temperature caused by road use in the Bolshezemelskaya Tundra]: Kriosfera Zemli = Earth Cryosphere, 23(1), p. 17-27 (English sum.), illus. incl. 5 tables, sketch map, 16 ref., February 2019.

The impact of transformation in vegetation and soil cover on the soil temperature regime under winter road operation in Bolshezemelskaya tundra has been studied. Winter, summer and mean annual temperature parameters of tundra peat and mineral soils were obtained at the road section in the North Khosedau oil field. The main differences in the temperature regime of upper soil horizons (0-40 cm) at anthropogenically disturbed (tracks of the winter road) and undisturbed sites in different tundra ecosystems affected by continuous permafrost have been revealed.

2020044074 Lebedeva, L. S. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Merzlotovedeniya, Yakutsk, Russian Federation); Bazhin, K. I.; Khristoforov, I. I.; Abramov, A. A.; Pavlova, N. A.; Yefremov, V. S.; Ogonerov, V. V.; Tarbeyeva, A. M.; Fedorov, M. P.; Nesterova, N. V. and Makar'yeva, O. M. Nadmerzlotnyye subaeral'nyye taliki v basseyne reki Shestakovka (tsentral'naya Yakutiya) [Open taliks in the permafrost of the Shestakovka River basin, central Yakutia]: Kriosfera Zemli = Earth Cryosphere, 23(1), p. 40-50 (English sum.), illus. incl. sects., sketch map, 23 ref., February 2019.

This study presents the results of drilling, geophysical survey and ground temperature monitoring in the area of suprapermafrost subaerial water-bearing talik that is associated with sandy deposits in the sparsly vegetated gentle slope of the Levaya Shestakovka River terrace covered by pine forest. The talik is 180-200 m wide and more than 500 m long, has a complicated contour and consists of several water-conducting channels. The configuration of unfrozen zones assessed with a ground penetrating radar and electrical resistivity tomography is similar, thus confirming the efficiency of the applied geophysical methods. The mean value of ground temperature and its amplitude for one year at the talik area is much higher than outside of the talik. The depth of the zero annual amplitude does not exceed 6 m to the constant yearly temperature of the water-saturated deposits equal to 0°C.

2020044075 Sheykman, V. S. (Tyumenskiy Gosudarstvennyy Universitet, Tyumen, Russian Federation); Sedov, S. N.; Rusakov, A. V. and Mel'nikov, V. P. Kriotrasologicheskaya indikatsiya paleopochv [Permafrost and cryological indicators of paleosols]: Kriosfera Zemli = Earth Cryosphere, 23(1), p. 51-62 (English sum.), illus. incl. sketch map, 41 ref., February 2019.

Freezing of rocks and formation of permafrost affect soils and produce specific signatures in their solid matrix. The macro- and micromorphological signatures of frost effects remain preserved in buried soils and can serve as explicit or implicit traces of past cryogenic environments. They are, respectively, cryoturbation, aggregation and size sorting of soil particles, gleying and peat formation in well drained soils on impermeable permafrost. Such signatures are used, in terms of the cryotraceological approach, to reconstruct glacial environments during MIS-3 and MIS-2 events of the marine oxygen isotope stratigraphy in different regions.

2020044055 Gorbunov, A. P. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Merzlotovedeniya, Kazakhstanskaya Vysokogornaya Geokriologicheskaya Laboratoriya, Almaty, Kazakhstan); Zheleznyak, M. N. and Severskiy, E. V. Otsenka ob"yemov podzemnykh l'dov v gornoy sisteme Tyan'-Shanya [Assessment of ground ice volume in the Tien Shan Mountains]: Kriosfera Zemli = Earth Cryosphere, 22(6), p. 35-44 (English sum.), illus. incl. 4 tables, sketch map, 20 ref., December 2018.

This paper presents estimates of evident ground ice contained in the permafrost of the Tien Shan Mountains based on the available geocryological maps of various scales. The maps represent patterns of permafrost distribution reflected in the regional structures depending on geocryological zonality. Using the data on the areal extent, thickness and ice content of permafrost, the volumes of permafrost and ground ice have been determined. It has been revealed that the largest volumes of ground ice occur in active rock glaciers and recent moraines. The volume of glaciers relative to that of ground ice has been ascertained to decrease significantly due to the glacial degradation.

2020044053 Koronatova, N. G. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Pochvovedeniya i Agrokhimii, Novosibirsk, Russian Federation); Mironycheva-Tokareva, N. P. and Solomin, Ya. R. Temperaturnyy rezhim torfyanoy zalezhi bugrov i topey ploskobugristykh bolotnykh kompleksov Zapadnoy Sibiri [Thermal regime of peat deposits in palsas of plateau bogs of West Siberia]: Kriosfera Zemli = Earth Cryosphere, 22(6), p. 16-25 (English sum.), illus. incl. 2 tables, 29 ref., December 2018.

This study has been focused on the thermal regime of peat soils (fibrist histosols) of palsa bogs and peat plateau in northern West Siberia. Autonomous loggers recorded the temperature for 343 days every hour to a depth up to 60 cm in palsas and 120 cm in hollows (pools, lawns) in four mire ecosystems: the forest tundra hollow and palsa, and the northern taiga hollow and palsa. The data on the mean daily temperature, the mean annual temperature, the extremes, the annual amplitude, the active layer dynamics, the sums of positive and negative temperatures at different depths have been adduced. The established differences in the thermal regimes of soils were due to the differences in the ecosystems of mires, rather than in the bioclimatic zones they belong to. The high-latitude mires have the largest impact on the annual amplitude and temperature parameters obtained for the cold period.

2020044054 Pavlova, N. A. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Merzlotovedeniya, Yakutsk, Russian Federation) and Danzanova, M. V. Mezhgodovaya izmenchivost' khimicheskogo sostava tekhnogennykh kriopegov na territorii goroda Yakutska [Annual variations of cryopeg chemistry in Yakutsk City and impact of human activity]: Kriosfera Zemli = Earth Cryosphere, 22(6), p. 26-34 (English sum.), illus. incl. table, sect., 27 ref., December 2018.

Long-term and seasonal variations in major- and trace-element compositions of groundwaters in anthropogenic cryopegs stripped by boreholes in unconsolidated alluvial sediments have been monitored for thirty years at a site within Yakutsk City. Suprapermafrost cryopegs became less saline for the past five to seven years as a result of climate change in many previous years. The obtained data on chemistry and flow dynamics of groundwaters indicate enhanced hydraulic connectivity of cryopegs in the active layer. The ongoing ground temperature warming will lead to a general decrease in the contents of highly soluble salts in suprapermafrost cryopegs and to an increase in trace element abundances in pore waters.

2020038243 Ubugunov, L. L. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Geografii, Irkutsk, Russian Federation); Ubugunov, V. I.; Belozertseva, I. A.; Gyninova, A. B.; Sorokovoy, L. A. and Ubugunov, V. L. Pochvy basseyna oz. Baykal; itogi issledovaniya za 1980-2017 gody [Soils of the Lake Baikal basin; results of studies in 1980-2017]: Geografiya i Prirodnyye Resursy, 2018(4), p. 76-87 (English sum.), table, sketch maps, 39 ref., December 2018.

Long-term soil research efforts (1980-2017) in the Baikal drainage basin revealed a widespread occurrence of thin layers of skeletal soils in the tundra zone: peat-lithozems, lithozems coarse humus and humic and dark-humus, and petrozems. A variety of full-height soils is represented by podburs, peat-podburs, podburs gleyic, podzols and gleysols. It is determined that the soil cover of the mountain-taiga zone is nonuniform because of the manifestation of the vertical zonation, slope aspects and permafrost of different types. The main background of the Khangai soils consists of cryosols and podburs; Khentii--sod-podburs and dark-humus soils; near Lake Kuvsgul--cryzols, podburs and sod-podburs; the Baikal region--podburs, podzols, peat-podburs and sod-podzols, and on the windward slopes of the mountain ridges facing Baikal--podburs and coarse humus burozems. The occurrence and development of burozen soils in the Baikal regions is confirmed. In the forest-steppe zone of Hangai and Khentii, the soil diversity is presented by cryosols, sod-podburs, dark- and gray-humus soils and in the forest-steppe contact zone--chernozems and castanozems. It is established that in the Selengga Middle Mountains, the basis for soil cover is provided by sod-podburs, and the accompanying soils are gray metamorphic, light-humic and cryoarid soils. The authors identified a new type of soils, cespitose-gray soils. Psummozems and light-humic soils occur on sands. Chernozems prevail in the steppe zone, and castanozems, cryoarid and, light-humic soils are dominant in the arid steppe zone. It is established that the soils of the Baikal region differ from the soils located at the same latitude of the European territory of Russia. It is found that the mountain zonality has a determining influence on the formation and spatial distribution of soils.

2020044050 Kaverin, D. A. (Rossiyskaya Akademiya Nauk, Ural'skoye Otdeleniye, Komi Nauchnyy Tsentr, Institut Biologii, Syktyvkar, Russian Federation) and Pastukhov, A. V. Temperaturnoye sostoyaniye pochvogruntov bugristo-mochazhinnykh bolot v zone redkoostrovnogo rasprostraneniya mnogoletnemerzlykh porod (Yevropeyskiy severo-vostok Rossii) [Temperatures of soils in plateau bogs within discontinuous permafrost zone in the northeastern European part of Russia]: Kriosfera Zemli = Earth Cryosphere, 22(5), p. 47-56 (English sum.), illus. incl. 4 tables, sketch map, 27 ref., October 2018.

The temperature regime of soils and underlying sediments in peat plateaus located in the northeastern margin of the Russian Plain (65-66 °N) in the area of sporadic permafrost distribution has been characterized for the period of 2013-2016. Winter, summer and mean and annual temperature regimes are found to differentiate significantly between soils in permafrost peat mounds and thawed fens. The warming and cooling coefficients have been evaluated in order to assess the seasonal variations of temperature in peat plateau soils. A comparative analysis of the calculated warming/cooling climatic coefficients and indices revealed the warming effect of the contemporary climatic variations on peat soils within the sporadic permafrost area in the northeast of European Russia.

2020044047 Korniyenko, S. G. (Rossiyskaya Akademiya Nauk, Institut Problem Nefti i Gaza, Moscow, Russian Federation). Fizicheskoye modelirovaniye kontrastov temperatury na poverkhnoti obraztsov tundrovogo napochvennogo pokrova [Physical modeling of tundra topsoil temperature contrasts]: Kriosfera Zemli = Earth Cryosphere, 22(5), p. 20-29 (English sum.), illus. incl. 2 tables, 21 ref., October 2018.

The results of modeling temperature contrasts on the surface of single-layer and multi-layer columns containing samples of ground, substrate and tundra soil cover using an open-type simulation setup are provided, in which the temperature differences of varying permafrost conditions are simulated. Quantitative indicators of the extent of attenuation of temperature variations in the ground by lichen cover of different thickness are evaluated. Maximum (daytime) and minimum (night) values of the temperature on the surface of the samples do not differ significantly from the average values, indicating the possibility of investigating the nature of temperature anomalies on the surface of the tundra soil cover related to permafrost heterogeneity by simultaneous measurements of the soil surface temperature at any time of the day. The possibility of using the setup to characterize the thermophysical properties of soil samples and of the soil cover, as well as to study and simulate phase transitions of water is demonstrated.

2020044046 Vasil'chuk, Yu. K. (Moskovskiy Gosudarstvennyy Universitet, Moscow, Russian Federation) and Vasil'chuk, A. K. Zimniye paleotemperatury vozdukha v nizov'yakh Kolymy 30-12 tysyach let nazad po rezul'tatam izucheniya izotopnogo sostava Yedomy Plakhinskogo yara [Winter air temperatures 12-30 thousand years ago in the lower Kolyma River basin; study of stable isotopes in yedoma, Plakhinskiy Yar]: Kriosfera Zemli = Earth Cryosphere, 22(5), p. 3-19 (English sum.), illus. incl. 9 tables, sketch maps, 25 ref., October 2018.

A continuous 15-18 m long sequence of permafrost with ice wedges at the Plakhinskiy Yar site (Karetovo yedoma, left side of the Stadukhin channel, lower Kolyma River) has been studied in terms of structure, stable isotopes, radiocarbon ages, major ion chemistry, and spore-pollen spectra. The obtained data allow quantitative estimates of late Pleistocene permafrost and climate conditions in the area between 30 and 12 ka BP. The study confirms the previous inference that local winters at 30-28 ka BP were much colder than at present.

2020044049 Vasil'yev, A. A. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Kriosfery Zemli, Tyumen, Russian Federation); Oblogov, G. E.; Streletskaya, I. D. and Shirokov, R. S. Novoobrazovaniye mnogoletnemerzlykh porod na nizkikh laydakh Karskogo morya [Formation of new permafrost in tidal flats of the Kara Sea]: Kriosfera Zemli = Earth Cryosphere, 22(5), p. 39-46 (English sum.), illus. incl. sect., sketch map, 10 ref., October 2018.

Low accumulative laidas (tidal flats) are the areas of permafrost aggradation. Long-term observations of the thermal regime of upper permafrost have been carried out at the two sites--Marre-Sale (western coast of the Yamal Peninsula), and Sopochnaya Karga (western coast of the Taymyr Peninsula). The mean annual ground temperature is -3.5:-4.5°C at Marre-Sale, and -4.8:-7.7°C at Sopochnaya Karga. Heat flow from the atmosphere to the upper permafrost can reach 3.4 W/m². A high correlation between the heat flows and the average annual air temperature anomalies has been established.

2020044051 Yakovlev, D. V. (Moskovskiy Gosudarstvennyy Universitet, Moscow, Russian Federation); Yakovlev, A. G. and Valyasina, O. A. Izucheniye kriolitozony severnogo obramleniya Sibirskoy platformy po dannym regional'nykh elektrorazvedochnykh rabot [Analysis of the permafrost in the northern Siberian Platform based on data from regional electrical surveys]: Kriosfera Zemli = Earth Cryosphere, 22(5), p. 77-95 (English sum.), illus. incl. sects., sketch map, 25 ref., October 2018.

This article presents results of permafrost study within northern margins of the Siberian Platform obtained during regional geoelectric surveys by magnetotelluric and transient electromagnetic methods. The surveys aimed to identify areas promising for oil and gas within the entire sedimentary cover. From 2005 to 2016, more than 30,000 soundings were performed with a total survey line length of more than 20,000 km. A large amount of factual data acquired in the Yenisei-Khatanga and the Anabar-Lena regional troughs allowed mapping the depth of the permafrost base and provided insights about other structural features of the permafrost interval, along with the information on permafrost distribution beneath the Khatanga Bay. High-resistivity anomalies over hydrocarbon reservoirs capped by the permafrost strata associated with accumulations of gas-hydrates were identified.

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2020045801 van Huissteden, J. (Vrije Universiteit, Amsterdam, Netherlands). Thawing permafrost; permafrost carbon in a warming Arctic: Springer, Cham, Switzerland, illus., 2020. ISBN: 978-3-030-31378-4.

DOI: 10.1007/978-3-030-31379-1

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2020045696 Paull, Charles K. (Monterey Bay Aquarium Research Institute, Moss Landing, CA). Submarine permafrost dynamics along the Arctic Shelf edge [abstr.]: in Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, Abstracts with Programs - Geological Society of America, 52(2), Abstract no. 36-1, March 2020. Meeting: Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, March 20-22, 2020, Reston, VA.

Exploration in the Canadian Beaufort Sea, offshore of the Tuktoyaktuk Peninsula, has revealed a remarkable a zone of rugose morphology at the shelf edge and upper slope. This morphology is especially common in 100 to 200 m water depths where seafloor features include topographic mounds, pockmarks, slope parallel ridges, and slide scars. This area occurs at the seaward edge of a sub-sea ~600 m thick relict permafrost zone and geothermal modelling suggests that the lower 100 m of the permafrost zone has decomposed during the Holocene. Sediment cores show escaping brackish waters with pore water chloride content indicating widespread down core freshening, especially near the shelf edge on the upper slope. Bottom waters corresponding with this band have a mean annual temperature of less than -1.4°C, cold enough to freeze escaping brackish pore waters. Positive relief mound features are up to 10 m high circular to oval shaped and ~50 m in diameter, occurring at a density of ~6 per km2. Pore and lense ice has been observed in sediment cores and we interpret these features as offshore pingos. Intermixed are circular topographic depressions up to 20 m deep. Detailed investigations utilizing a mapping Autonomous Underwater Vehicle (AUV) to provide 1-m grid bathymetric and Chirp profiles, and Remotely Operated Vehicle observations, were made to provide insights as to the origin and age of these features. AUV surveys of one 8 km2 area first conducted in 2013 were repeated in 2017. Repeat mapping shows significant changes within this 4-year period. Multiple circular or elongated depressions have developed which are up to 10 m deep and 100 m long. A corresponding volume of newly accreted material around the depressions equal to the missing volume was not detected. No evidence for high methane concentrations were found within this survey area as pore waters sulfate gradients indicate the sulfate-methane transition zone is >8 m below seafloor in most sediment cores and no chemosynthetic seep fauna or authigenic carbonates were seen. We attribute the concentrated band of features to be related to the on-going degradation of relict permafrost, the expulsion of brackish waters, and formation of ground ice within the near seafloor sediments. These observations have significant geohazard implications, which may be characteristic of Arctic settings.

2020045506 Ruck, John (Franklin and Marshall College, Department of Earth and Environment, Lancaster, PA); Hertzler, Nicholas; Merritts, Dorothy; Walter, Robert C.; Marshall, Jill A.; Corbett, Lee B.; Caffee, Marc W. and Bierman, Paul R. Field and cosmogenic nuclide studies of possible last glacial maximum gelifluction benches in northeastern Pennsylvania [abstr.]: in Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, Abstracts with Programs - Geological Society of America, 52(2), Abstract no. 7-11, March 2020. Meeting: Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, March 20-22, 2020, Reston, VA.

Relict lobes, benches of poorly sorted colluvium, and barren boulder fields are abundant throughout the unglaciated part of the mid-Atlantic region; the timing and processes associated with their formation are uncertain. A new ~2-km road with exposures up to 10-m high reveals the transformation and down-slope transport of fractured sandstone bedrock to colluvium over an elevation range of 180 m. Using LiDAR, we mapped over 20 lobes and benches 3-10 m high and 50-150 m wide on Chestnut Ridge south of the last glacial maximum (LGM) and north of the penultimate ice margin. For cosmogenic analysis, we posit that colluvial sediment was transported downslope by gelifluction during active layer thaw. Relict thermal contraction polygons provide evidence for continuous permafrost during LGM. Strata within multiple benches constrain mechanisms of colluvium formation and deposition. Outcrops of fractured bedrock, possibly from high frost-cracking intensities during times of continuous permafrost, consist largely of loose, angular boulders (clast-supported) with overall fabric similar to original bedding. Within sediment lobes and benches, all exposures show slope-parallel m-scale beds of matrix-supported bouldery sediment. In situ cosmogenic 10Be concentrations in sand and clasts from one bench constrain near surface residence time of the material. Below 4 m, 10Be concentrations for clasts and matrix are similar (35,000 to 50,000 atoms/g) and 3 to 9X lower than samples above. Shallower than 4 m, in two colluvial beds, nuclide concentrations are similar for clasts and matrix (130,000 to 300,000 atoms/g). Field observations and preliminary analysis of nuclide concentrations are consistent with near-surface exposure during only the last glacial cycle and the relatively rapid erosion and deposition of colluvium via gelifluction during cold-climate conditions. Little reworking of this sediment has occurred since deposition, with exception of some near-surface winnowing of fines. Openwork boulder fields at the surface belie the underlying matrix-supported sediment and its gelifluction origin.

2020045672 Wadhams, Jane A. (Florida State University, National High Magnetic Field Laboratory, Tallahassee, FL); Newby, Sean M.; Them, Theodore R., II and Owens, Jeremy D. Thallium isotopes track changing oceanic oxygen across the Paleocene-Eocene Thermal Maximum [abstr.]: in Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, Abstracts with Programs - Geological Society of America, 52(2), Abstract no. 32-8, March 2020. Meeting: Geological Society of America, Southeastern Section, 69th annual meeting; Geological Society of America, Northeastern Section, 55th annual meeting, March 20-22, 2020, Reston, VA.

The geologically instantaneous release of massive quantities of isotopically light carbon during the most recent abrupt climate perturbation, the Paleocene-Eocene Thermal Maximum (PETM; ~55.9 Ma), makes it the best analog to better understand future climate scenarios. A ~3 ppm negative carbon isotope excursion defines the PETM but the exact cause(s) and associated magnitudes are debated. However, this excursion undoubtedly records a major perturbation to the global carbon cycle through the release of isotopically light carbon to the ocean-atmosphere system. In addition to warming, other environmental perturbations during this event include ocean acidification, permafrost loss, and a small increase in global euxinia (anoxic and sulfidic water column). However, there is limited evidence for widespread deoxygenation or organic carbon burial, which contrasts the PETM with similar climatic perturbations in the Mesozoic termed oceanic anoxic events. This research aims to better constrain the global spatiotemporal redox structure across the PETM global oceans using both novel and traditional geochemical tools. We analyzed samples from the Arctic (IODP Expedition 302, Site M0004-A) and the North American Atlantic Coastal Plain (Cambridge-Dorchester Airport) using traditional and novel geochemical proxies including trace metal concentrations, iron speciation, and thallium isotopes to constrain the local and global redox conditions pre-, syn-, and post-PETM. Thallium isotopes--a new global proxy that responds to the global burial of manganese oxides for short-term events and thus tracks the earliest marine oxygen perturbation--record conflicting trends in the two sections. During the Paleocene, however, the Arctic was a restricted basin and the observed shift from reducing to oxic conditions over the peak of the excursion suggests that the basin became progressively more well-connected to the open ocean during the event. The Atlantic Coastal Plain likely records a global signal that documents a steep decline in marine oxygen at the onset of the PETM followed by a return to pre-event values at the recovery stage. Further research will aim to understand the Arctic's changing marine and lacustrine system and additional sections are required to corroborate the Atlantic Coastal Plain's global signature.

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