February 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.

2021021726 Beerten, Koen (Belgian Nuclear Research Center, Engineered and Geosystems Analysis, Mol, Belgium); Meylemans, Erwin; Kasse, Cornelis; Mestdagh, Thomas; Van Rooij, David and Bastiaens, Jan. Networks of unusually large fossil periglacial polygons, Campine area, northern Belgium: Geomorphology, 377, Article no. 107582, illus. incl. 4 tables, March 15, 2021. Based on Publisher-supplied data.

A series of polygon networks has been discovered on the most recent LiDAR (Light Detection and Ranging) DEM (Digital Elevation Model) of Flanders (Belgium) available in a resolution of 1 m². They are located in the sandy Campine area (northern Belgium) and resemble thermal contraction crack polygon networks from present-day permafrost regions. Different network types were observed, ranging from orthogonal to hexagonal and various combinations of these. The inter-polygon troughs are typically several decimeters deep and up to several meters wide. The average polygon size is ca. 3000 m², which is equivalent to a diameter of ca. 60 m if the polygon shape is approximated with a perfect circle, or a side of ca. 55 m length if it were to be approximated by a perfect square. The average size is (much) larger than any of the studied present-day analogues, and also larger than fossil networks in the western part of Flanders, Poland and France. In contrast to the Campine polygons presented here, the fossil analogues in these countries were detected using satellite imagery and orthophotos, which may partially explain the observed size differences. The morphometric analysis of the Campine networks shows relationships between polygon type and local geomorphological position as orthogonal networks seem to have a preference to develop near shallow valley slopes. In addition, GPR (Ground Penetrating Radar) radargrams were acquired across polygon boundaries to investigate subsoil disturbances related to the former position of ice wedges or sand wedges. However, the evidence is not unequivocal due to the low dielectric contrast between the host and wedge material. It is not clear yet whether smaller 2nd and 3rd order cracks did develop but without leaving a topographical imprint. The observed polygon networks in the Campine area are interpreted as first-order networks that developed during a time span of several thousands of years, up to 10 kyr at most, in a former Late Weichselian permafrost climate.

DOI: 10.1016/j.geomorph.2020.107582

2021023059 Engel, Zbynek (Charles University, Department of Physical Geography and Geoecology, Prague, Czech Republic); Krizek, Marek; Braucher, Régis; Uxa, Tomas and Krause, David. ¹⁰Be exposure age for sorted polygons in the Sudetes Mountains: Permafrost and Periglacial Processes, 32(1), p. 154-168, illus. incl. 3 tables, sketch map, 117 ref., March 2021.

Patterned-ground landforms represent the most common phenomenon of periglacial environment, and their large sorted forms belong to the few morphological indicators of past permafrost distribution. The relic forms of patterned ground are widespread on high-elevated surfaces in the central European uplands, providing the evidence of regional periglacial conditions in the last glacial period. However, the timing of these landforms, as well as their potential for paleoclimate reconstructions, has remained unexplored. In this paper, we present ¹⁰Be exposure ages from the large sorted polygons sampled at four sites in the Sudetes Mountains, the highest part of the central European uplands. These results indicate that these landforms started to form at the end of Marine Isotope Stage 3, and the main phase of their formation occurred between 30 and 20 ka. This research confirms the hypothesis of sorted patterned-ground formation within the last (Weichselian) glacial stage (110.6-11.7 ka) and suggests that earlier-sorted features are not preserved in the Sudetes. The recognized period of enhanced periglacial activity coincides with a prominent cold interval identified earlier in both regional and northern-hemispheric proxy records. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2091

2021023050 Garibaldi, Madeleine C. (University of Lethbridge, Department of Geography and Environment, Bonnaventure Lab for Permafrost Science, Lethbridge, AB, Canada); Bonnaventure, Philip P. and Lamoureux, Scott F. Utilizing the TTOP model to understand spatial permafrost temperature variability in a high Arctic landscape, Cape Bounty, Nunavut, Canada: Permafrost and Periglacial Processes, 32(1), p. 19-34, illus. incl. 3 tables, geol. sketch maps, 67 ref., March 2021.

Ground surface and permafrost temperatures in the High Arctic are often considered homogeneous especially when viewed at the scale of climate and environmental models. However, this is generally incorrect due to highly variable, topographically redistributed snow cover, which generates a substantial degree of ground thermal heterogeneity. The objective of this study is to describe and spatially model the variability in the ground thermal regime within the Cape Bounty Arctic Watershed Observatory (CBAWO), Nunavut, Canada, using the TTOP model, for current conditions in addition to a series of future climate change scenarios. While observed air temperature was mostly uniform, annual mean ground surface and permafrost temperatures across the paired watersheds were estimated to range between -3.8 to -13.8°C and -3.9 to -14°C, respectively, similar to the -5 to -15°C magnitude and range identified from boreholes across the High Arctic. The spatial models showed higher ground surface temperatures in topographic hollows (slope bases and stream channels), and lower temperatures in areas of topographic prominence (hilltops and plateaus) following the spatial pattern of snow accumulation and redistribution. Under projected climate change, the models predicted areas with the coldest permafrost to have the largest magnitude of warming (about 9°C), while areas of warm permafrost became closer to 0°C (warming 4-7°C). This thermal heterogeneity may have implications for ground instability such as permafrost-related mass movements, hydrological connectivity, biogeochemical cycling, and microbial activity, which influence water quality and contaminant mobility. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2086

2021023053 Morgenstern, Anne (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Department of Permafrost Research, Potsdam, Germany); Overduin, Pier Paul; Günther, Frank; Stettner, Samuel; Ramage, Justine; Schirrmeister, Lutz; Grigoriev, Mikhail N. and Grosse, Guido. Thermo-erosional valleys in Siberian ice-rich permafrost: Permafrost and Periglacial Processes, 32(1), p. 59-75, illus. incl. 3 tables, sketch map, 96 ref., March 2021.

Thermal erosion is a major mechanism of permafrost degradation, resulting in characteristic landforms. We inventory thermo-erosional valleys in ice-rich coastal lowlands adjacent to the Siberian Laptev Sea based on remote sensing, Geographic Information System (GIS), and field investigations for a first regional assessment of their spatial distribution and characteristics. Three study areas with similar geological (Yedoma Ice Complex) but diverse geomorphological conditions vary in valley areal extent, incision depth, and branching geometry. The most extensive valley networks are incised deeply (up to 35 m) into the broad inclined lowland around Mamontov Klyk. The flat, low-lying plain forming the Buor Khaya Peninsula is more degraded by thermokarst and characterized by long valleys of lower depth with short tributaries. Small, isolated Yedoma Ice Complex remnants in the Lena River Delta predominantly exhibit shorter but deep valleys. Based on these hydrographical network and topography assessments, we discuss geomorphological and hydrological connections to erosion processes. Relative catchment size along with regional slope interact with other Holocene relief-forming processes such as thermokarst and neotectonics. Our findings suggest that thermo-erosional valleys are prominent, hitherto overlooked permafrost degradation landforms that add to impacts on biogeochemical cycling, sediment transport, and hydrology in the degrading Siberian Yedoma Ice Complex. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2087

2021023049 Paul, Jason R. (Wilfrid Laurier University, Department of Biology, Waterloo, ON, Canada); Kokelj, Steven V. and Baltzer, Jennifer L. Spatial and stratigraphic variation of near-surface ground ice in discontinuous permafrost of the taiga shield: Permafrost and Periglacial Processes, 32(1), p. 3-18, illus. incl. 5 tables, sketch map, 76 ref., March 2021.

The acceleration of permafrost thaw due to warming, wetting, and disturbance is altering circumpolar landscapes. The effect of thaw is largely determined by ground ice content in near-surface permafrost, making the characterization and prediction of ground ice content critical. Here we evaluate the spatial and stratigraphic variation of near-surface ground ice characteristics in the dominant forest types in the North Slave region near Yellowknife, Northwest Territories, Canada. Physical variation in the permafrost was assessed through cryostructure, soil properties, and volumetric ice content, and relationships between these parameters were determined. Near-surface ground ice characteristics were contrasted between forest types. In black spruce forests the top of the permafrost was ice-rich and characterized by lenticular and ataxitic cryostructures, indicating the presence of an intermediate layer. Most white spruce/birch forests showed similar patterns; however, an increase in the active layer thickness and permafrost thaw at some sites have eradicated the transition zone, and the large ice lenses encountered at depth reflect segregated ground ice developed during initial downward aggradation of permafrost. Our findings indicate that white spruce/birch terrain will be less sensitive than black spruce forests to near-surface permafrost thaw. However, if permafrost thaws completely, white spruce/birch terrain will probably be transformed into wetland-thaw lake complexes due to high ground ice content at depth. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2085

2021023052 Strand, Sarah M. (University Centre in Svalbard, Arctic Geology Department, Longyearbyen, Norway); Christiansen, Hanne H.; Johansson, Margareta; Akerman, Jonas and Humlum, Ole. Active layer thickening and controls on interannual variability in the Nordic Arctic compared to the circum-Arctic: Permafrost and Periglacial Processes, 32(1), p. 47-58, illus. incl. sketch map, 63 ref., March 2021.

Active layer probing in northern Sweden, northeast Greenland, and central Svalbard indicates active layer thickening has occurred at Circumpolar Active Layer Monitoring (CALM) sites with long-term, continuous observations, since the sites were established at these locations in 1978, 1996, and 2000, respectively. The study areas exhibit a reverse latitudinal gradient in average active layer thickness (ALT), which is explained by site geomorphology and climate. Specifically, Svalbard has a more maritime climate and thus the thickest active layer of the study areas (average ALT=99 cm, 2000-2018). The active layer is thinnest at the northern Sweden sites because it is primarily confined to superficial peat. Interannual variability in ALT is not synchronous across this Nordic Arctic region, but study sites in the same area respond similarly to local meteorology. ALT correlates positively with thawing degree days in Sweden and Greenland, as has been observed in other Arctic regions. However, ALT in Svalbard correlates with freezing degree days, where the maritime Arctic climate results in relatively high and variable winter air temperatures. The difference in annual ALT at adjacent sites is attributed to differences in snow cover and geomorphology. From 2000 to 2018, the average rate of active layer thickening at the Nordic Arctic CALM probing sites was 0.5 cm/yr. The average rate was 1 cm/yr for Nordic Arctic CALM database sites with significant trends, which includes a borehole in addition to probing sites. This range is in line with the circum-Arctic average of 0.8 cm/yr from 2000 to 2018. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2088

2021023060 Vandenberghe, Jef (Vrije Universiteit, Department of Earth Sciences, Amsterdam, Netherlands); Kuipers, Gerrit; Beunk, Frank F.; Yi, Keewook and van der Wateren, Frederik M. Evidence of permafrost in the Paleoproterozoic (c. 1.9 Ga) of central Sweden: Permafrost and Periglacial Processes, 32(1), p. 169-177, illus. incl. geol. sketch map, 60 ref., March 2021.

This paper reports on an ice-wedge pseudomorph that formed and is preserved in metavolcanic host material that was later transformed to metamorphic solid bedrock. It has been dated to 1,895±5 Ma by U-Pb geochronology of zircon in the bedrock, an Early Proterozoic age. Detailed observation of the deformation structures of the wedge points to an ice-wedge pseudomorph based on typical downbending around the wedge and vertical lamination in the inner part of the wedge due to slumping into the wedge after the ice melted, along with a few remains of lateral pressure structures (such as folds and upturned strata) in the adjacent host sediment. The interpretation of the wedge structure as an ice-wedge pseudomorph confirms previous work on this topic. This ice-wedge pseudomorph demonstrates for the first time the existence of permafrost at c. 1.9 Ga. It indicates that permafrost and associated conditions were present in lowlands at low latitude at discrete time intervals early in Earth's history. Although some caution should be applied, mean annual air temperature appears to have been slightly below the freezing point at that time. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2094

2021023038 Arzhanov, Maxim M. (Russian Academy of Sciences, A. M. Obukhov Institute of Atmospheric Physics, Moscow, Russian Federation); Malakhova, Valentina V. and Mokhov, Igor I. Modeling thermal regime and evolution of the methane hydrate stability zone of the Yamal Peninsula permafrost: Permafrost and Periglacial Processes, 31(4), p. 487-496, illus. incl. 1 table, sketch map, 80 ref., December 2020.

In recent years, new geophysical phenomena have been observed in the high-latitude regions of continental permafrost. Since 2014 new craters 10-20 m in diameter have been found within the Yamal Peninsula and neighboring regions. They are associated with the emissions of gases, which could have been formed during dissociation of relict gas hydrate deposits due to increases in soil temperature. This paper presents the results of numerical modeling of the thermal regime of permafrost in the north of Western Siberia with the assessment of methane hydrate stability zone under climate changes over the past 130,000 years. According to the results obtained, the upper boundary of the methane hydrate stability zone in Yamal could have reached the surface within the periods of glacial maxima (about 90,000 and 60,000 years ago). We show that at present in Yamal permafrost above the modern boundary of the stability zone, relic methane hydrates are likely to exist at depths of up to 100-150 m, they could have "survives" warming during the Holocene optimum about 6,000 years ago and remain in permafrost rocks under negative temperatures even under transgression and increased geothermal flux conditions. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2074

2021023039 Bandara, Sasiri (University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada); Froese, Duane G.; Porter, Trevor J. and Calmels, Fabrice. Holocene pore-ice d¹⁸O and d²H records from drained thermokarst lake basins in the Old Crow Flats, Yukon, Canada: Permafrost and Periglacial Processes, 31(4), p. 497-508, illus. incl. 1 table, sketch map, 62 ref., December 2020.

Thermokarst lakes form following the thaw of ice-rich permafrost and drain after a few decades to millennia. Drained thermokarst lake basins (DTLBs) become epicenters for peat accumulation and re-aggradation of ice-rich permafrost. This re-aggradation of permafrost may be interrupted by subsequent thermokarst lake formation with sufficient disturbance. Thermokarst lakes and DTLBs are abundant near Old Crow, Yukon, Canada, but little is known about their evolution through the Holocene. In this study, we investigate the hydrology and drainage histories of seven DTLBs from the Old Crow Flats on the basis of cryostratigraphy, radiocarbon dating, and pore-ice d¹⁸O and d²H records. Cryostratigraphic evidence implies only one of the seven studied DTLBs underwent multiple thermokarst cycles. Radiocarbon age-depth models demonstrate a slowdown in the rate of post-drainage peat accumulation with time. Pore-ice isotope analyses reveal a spectrum of possible post-drainage isotopic histories resulting from spatial variability in permafrost, vegetation, and hydrology. Unlike lacustrine silt, post-drainage peat contains relatively constant pore-ice isotope trends. In light of our findings, we propose that syngenetic peat permafrost in DTLBs preserve a warm-season sampling of local meteoric waters. These pore-ice d¹⁸O and d²H records may aid millennial-scale paleoclimate investigations, as we demonstrate through our reconstruction of Holocene climate change in northern Yukon. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2073

2021023078 Czerniawska, Jolanta and Chlachula, Jiri. Climate-change induced permafrost degradation in Yakutia, East Siberia: Arctic, 74(1), p. 405-550, December 2020.

DOI: 10.14430/arctic71674

2021023041 Hallang, Helen (Swansea University, Department of Geography, Swansea, United Kingdom); Hiemstra, John F.; Los, Sietse O.; Matthews, John A. and Froyd, Cynthia A. Carbon dioxide emissions from periglacial patterned ground under changing permafrost conditions and shrub encroachment in an alpine landscape, Jotunheimen, Norway: Permafrost and Periglacial Processes, 31(4), p. 524-537, illus. incl. 4 plates, geol. sketch map, 97 ref., December 2020.

Whether Arctic and alpine ecosystems will act as a future net sink or source of carbon remains uncertain. The present study investigates ways in which ecosystem (soil and vegetation) and geomorphological (cryogenic disturbance) factors may control or affect the future release of carbon in an alpine permafrost landscape. Rates of ecosystem respiration (R_e) were examined using a portable gas analyzer across an altitudinal transect ranging from mid- to high-alpine vegetation zones underlain by discontinuous to continuous permafrost on Galdhopiggen (Norway). Measurements were made of R_e during the peak growing season on active and relict sorted circles exhibiting varying levels of frost disturbance and shrub encroachment. R_e was found to be controlled more strongly by soil microclimate and plant growth forms than by geomorphic indicators of cryoturbation in thawing permafrost or by atmospheric conditions. The results indicate that increasing shrub cover leads to elevated R_e, while an increase in surface disturbance has the potential to lower R_e. We conclude that vegetation is likely to colonize frost-disturbed surfaces at progressively higher altitudes as freeze-thaw processes slow down or cease, and this will result in increased R_e. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2078

2021023043 Hu Jianan (Nanjing Normal University, Laboratory of Virtual Geographic Environment, Nanjing, China); Zhao Shuping; Nan Zhuotong; Wu Xiaobo; Sun Xuehui and Cheng Guodong. An effective approach for mapping permafrost in a large area using subregion maps and satellite data: Permafrost and Periglacial Processes, 31(4), p. 548-560, illus. incl. 4 tables, 47 ref., December 2020.

Permafrost distribution maps are of importance for environmental assessment, climate system modeling, and practical engineering applications. The scarcity of forcing data and parameters often limits the uses of permafrost models over large areas. However, detailed data are often available in a few subregions through field investigations. In this study, we propose a novel approach for mapping permafrost distribution in a large and data-scarce area using an empirical model with subregion permafrost maps and satellite data as inputs. The surface frost number model (FROSTNUM) was re-inferred to include an extra soil parameter to represent the thermal and moisture conditions in soils. The optimal soil parameters were determined from the subregion maps of permafrost distribution through spatial clustering, parameter optimization, and the decision tree method. FROSTNUM was fed with satellite-derived ground surface freezing and thawing indices to map the permafrost distribution over the study area. The proposed approach was evaluated in the Gaize area on the Qinghai-Tibet Plateau, where intensive field studies have been done. The simulated permafrost distribution is consistent with a map of permafrost distribution made from borehole observations and field surveys in Gaize. Due to excellent accuracy, the approach is effective and can be used in large areas with limited data. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2068

2021023048 Merlone, Andrea (Istituto Nazionale di Ricerca Metrologica, Turin, Italy); Sanna, Francesca; Coppa, Graziano; Massano, Laura and Musacchio, Chiara. Transportable system for on-site calibration of permafrost temperature sensors: Permafrost and Periglacial Processes, 31(4), p. 610-620, illus. incl. 3 tables, 25 ref., December 2020.

Evaluating the degradation of permafrost is a major challenge in understanding global warming and its impact on the cryosphere. The Global Cryosphere Watch is promoting actions towards data quality and traceability, to achieve comparability of observations from different permafrost stations. In response to this, a transportable system for on-site calibrations of permafrost temperature sensors was studied, developed and tested in the field, within the project MeteoMet. The system, here described, allows users to establish metrological traceability to permafrost temperature profiles, by performing the calibration on-site, even in remote or high-elevation areas, in realistic conditions. A field campaign at 3,000 m elevation to test the system's performance and practical use is also reported. Overall calibration uncertainty in the field accounted for <0.05°C, with contribution from reference sensors within 2 mK over the whole range; besides reducing uncertainties in each measuring point of a chain, the procedure also allows users to establish comparability among all the sensors within 0.03°C. The self-heating effect of each sensor was also evaluated as 0.007°C, and was thus considered a negligible component. The evolution of permafrost thawing can be more robustly evaluated, through documented data traceability together with improved comparability in space and time. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2063

2021023045 Nieuwendam, Alexandre (Universidade de Lisboa, Centre of Geographical Studies, Lisbon, Portugal); Vieira, Goncalo; Schaefer, Carlos; Woronko, Barbara and Johansson, Margareta. Reconstructing cold climate paleoenvironments from micromorphological analysis of relict slope deposits (Serra da Estrela, central Portugal): Permafrost and Periglacial Processes, 31(4), p. 567-586, illus. incl. 4 tables, sketch map, 77 ref., December 2020.

The paper focuses on analysis of macro- and micromorphological characteristics of relict slope deposits in Serra da Estrela (Portugal) to understand the significance of different slope processes and paleoenvironmental settings. Micromorphology is a useful sedimentology technique allowing significant advances compared to macroscopic techniques. Results show that different processes are involved in the development of the slope deposits, reflecting different environmental conditions. The main processes responsible for the emplacement of the relict slope deposits are solifluction, debris-flow and runoff, but postdepositional changes are also present. Solifluction was identified in slope deposits between 650 and 1500 m a.s.l. The common microfeatures identified are circular arrangement of grains with a core grain, rounded vesicles, vertical grains, matrix deformations and fine-grained deposits. Slope deposits above 1300 m a.s.l have a platy microstructure and coincide with the altitudinal range of the relict rock glaciers, indicating the elevation limit of permafrost. Below this altitude platy microstructures are less frequent. Slope deposits in north-facing slopes were affected by frost-induced processes in a seasonal frost regime, followed by a postdeposition illuvial phase. Debris-flow and runoff were identified in slope deposits between 680 and 1260 m a.s.l. The common microfeatures are oblique grains, grain dumps, and coarse and fine grain lineations, and banded microstructures were identified in runoff processes. Debris-flow deposits have a circular arrangement of grains without a core grain, identified in sediments in paraglacial and periglacial environments. The slope deposits show evidence of past periods of enhanced periglacial activity since the last glaciation until the Younger Dryas. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2054

2021023040 Nwaishi, Felix C. (University of Waterloo, Department of Geography & Environmental Management, Waterloo, ON, Canada); Morison, Matthew Q.; Van Huizen, Brandon; Khomik, Myroslava; Petrone, Richard M. and Macrae, Merrin L. Growing season CO₂ exchange and evapotranspiration dynamics among thawing and intact permafrost landforms in the western Hudson Bay Lowlands: Permafrost and Periglacial Processes, 31(4), p. 509-523, illus. incl. 1 table, geol. sketch map, 72 ref., December 2020.

Warming conditions across Canada's subarctic and arctic regions are causing permafrost landforms to thaw, resulting in rapid land cover change, including conversion of peat plateaus to wetland and thermokarst. These changes have important implications for northern ecosystems, including shifting controls on carbon uptake and release functions, as well as altering evapotranspiration (ET) rates, which form feedbacks with climatic change. Four landforms (peat plateau, sedge lawn, channel fen, and a thermokarst shoreline collapse scar) in the Hudson Bay Lowlands, northern Manitoba, were instrumented for weekly chamber measurements of carbon dioxide (CO₂) and water vapor flux over a summer season (May to September 2014). Relative to other landforms, thermokarst CO₂ exchange was characterized by high respiration rates early in the season, which decreased and were offset later in the season by CO₂ uptake driven by sedge productivity. For all landforms, ET peaked post-snowmelt during rapid active layer thaw, and decreased throughout the growing season, controlled primarily by atmospheric vapor deficits. This work shows distinct differences in CO₂ exchange and ET between intact and thawing permafrost features. While representative of small-scale processes in a single study region over one growing season, the results presented in this study have important implications for our understanding of ecohydrological and biogeochemical functioning of subarctic landscapes under future climates. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2067

2021023037 Paquette, Michel (Queen's University, Department of Geography and Planning, Kingston, ON, Canada); Fortier, Daniel; Lafrenière, Melissa and Vincent, Warwick F. Periglacial slopewash dominated by solute transfers and subsurface erosion on a high Arctic slope: Permafrost and Periglacial Processes, 31(4), p. 472-486, illus. incl. 2 tables, 74 ref., December 2020.

Arctic slope hydrology studies suggest that water follows preferential subsurface flow paths known as water tracks. While subsurface flow is usually expected to transport only dissolved solids, periglacial studies have indicated some evidence of lessivage associated with flow through sorted patterned ground. We investigated the transport of dissolved and suspended sediments in water tracks on a polar desert slope, and linked this transport to slope and flow path geomorphology. Solute transfer was dominated by carbonate weathering products, and concentrations of other ions increased disproportionately when the active layer thawed. Suspended sediment transport occurred in water tracks, but fluxes were supply-limited, indicating competent subsurface mechanical erosion. Solute mass fluxes were 5-10 times greater than sediment fluxes. In this dry landscape dominated by snowmelt, surface seepage leads to sediment deposition, while subsurface flow promotes lessivage. A conceptual model of nivation slopes is presented, taking into consideration the influence of flow path morphology and adaptation of the hydrological system to localized water sources from wind-drifted snowbanks. Climate-driven permafrost degradation and the increased frequency of rainfall events may result in new sediment sources and changes in flow pathways, modifying the physico-chemical properties and ecology of downstream receiving waters. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2066

2021023036 Sjoberg, Ylva (University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark); Siewert, Matthias B.; Rudy, Ashley C. A.; Paquette, Michel; Bouchard, Frédéric; Malenfant-Lepage, Julie and Fritz, Michael. Hot trends and impact in permafrost science: Permafrost and Periglacial Processes, 31(4), p. 461-471, illus. incl. 1 table, 56 ref., December 2020.

An increased interest in Arctic environments, mainly due to climate change, has changed the conditions for permafrost research in recent years. This change has been accompanied by a global increase in scientific publications, as well as a trend towards open access publications. We have analyzed abstracts, titles and keywords for publications on permafrost from 1998 to 2017 to identify developments (topics, impact and collaboration) in the field of permafrost research in light of these changes. Furthermore, to understand how scientists build on and are inspired by each other's work, we have (a) developed citation networks from scientific publications on permafrost and (b) conducted an online survey on inspiration in permafrost science. Our results show an almost 400% increase in publications containing the word permafrost in the title, keywords or abstract over the study period, and a strong increase in climate-change-related research in terms of publications and citations. Survey respondents (n=122) find inspiration not only in scientific journal publications, but to a large extent in books and public outreach materials. We argue that this increase in global-scope issues (i.e., climate change) complementing core permafrost research has provided new incentives for international collaborations and wider communication efforts. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2047

2021023047 Yoshikawa, Kenji (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Ubeda, Jose; Masías, Pablo; Pari, Walter; Apaza, Fredy; Vasquez, Pool; Ccallata, Beto; Concha, Ronald; Luna, Gonzalo; Iparraguirre, Joshua; Ramos, Isabel; de la Cruz, Gustavo; Cruz, Rolando; Pellitero, Ramón and Bonshoms, Martí Current thermal state of permafrost in the southern Peruvian Andes and potential impact from El Nino-Southern Oscillation (ENSO): Permafrost and Periglacial Processes, 31(4), p. 598-609, illus. incl. 2 tables, sketch map, 47 ref., December 2020.

Tropical high-mountain permafrost has a unique thermal regime due to its exposure to strong solar radiation and to rough surface snow morphology, which reduce ground heat transfer from the surface. Latent heat transfer and higher albedo that occur during the snow-covered season contribute to positive feedback that supports the presence of permafrost. This preliminary study reports on the thermal state characteristics of tropical mountain permafrost in Peru. This work also evaluates the potential combined impact of the El Nino-Southern Oscillation (ENSO) in the mountain permafrost of the Coropuna and Chachani volcanic complexes, both located at the western edge of the southern Peruvian Altiplano. Temperature monitoring boreholes were established at 5,217 m at Coropuna and 5,331 m at Chachani, and electrical resistivity was surveyed in both sites. This 7-year discontinuous record of permafrost temperature data encompasses historically extreme El Nino/La Nina events. Our results show that the current lower-altitude permafrost boundary (~5,100 m a.s.l.) is critically influenced by the balance of wet and dry seasons: permafrost tends to deplete during drought years. Typical permafrost thickness was 10-20 m and contained ice-rich pore spaces. The presence of permafrost and its thermal resistance depends on ice content and on higher albedo, usually due to: (a) hydrothermal alteration, which transforms the volcanic rocks into surfaces with ideal albedo for permafrost resilience; and (b) sublimation of the snow cover, forming ice-pinnacles named penitentes. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2064

2021023042 Yuan Ziqiang (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Laboratory of Frozen Soil Engineering, Lanzhou, China); Jin Huijun; Wang Qingfeng; Wu Qingbai; Li Guoyu; Jin Xiaoying and Ma Qiang. Profile distributions of soil organic carbon fractions in a permafrost region of the Qinghai-Tibet Plateau: Permafrost and Periglacial Processes, 31(4), p. 538-547, illus. incl. 2 tables, sketch map, 65 ref., December 2020.

Adequate characterization of soil organic carbon (SOC) fractions is essential to elucidate carbon dynamics in permafrost-affected ecosystems. SOC and its fractions were investigated across alpine ecosystems, including alpine swamp meadows (ASM), alpine meadows (AM) and alpine steppes (AS), in permafrost regions on the Qinghai-Tibet Plateau (QTP), southwest China. The density separation method was used to separate the SOC into light- and heavy-fraction organic carbon (LFOC and HFOC, respectively). Permafrost soils in the ASM had higher SOC, LFOC, and HFOC contents than in the AM. LFOC and HFOC contents were significantly correlated, but both were more closely related to SOC than to each other. On the ecological gradient from ASM to AS, the thickness of surficial organic horizons decreased while the thickness of mineral materials increased. SOC in the organic horizon and permafrost had high mineralization probability. At soil depths of 0-200 cm in ASM, AM, and AS, the SOC stocks were 123, 71, and 25 kg m^-2; LFOC stocks were 70, 49, and 12 kg m^-2; and HFOC stocks were 58, 37, and 15 kg m^-2, respectively. These results show that SOC fractions vary with vegetation type and active layer thickness, thus making SOC sensitive to changes in environmental conditions. Therefore, the decomposition of SOC in permafrost-affected soils of the QTP could be accelerated over a degrading permafrost and under a warming climate. Abstract Copyright (2021), John Wiley & Sons, Ltd.

DOI: 10.1002/ppp.2055

2021017928 Devoie, Élise G. (University of Waterloo, Department of Civil and Environmental Engineering, Waterloo, ON, Canada) and Craig, James R. A semianalytical interface model of soil freeze/thaw and permafrost evolution: Water Resources Research, 56(8), Article e2020WR027638, illus. incl. 3 tables, 71 ref., August 2020.

A physically based one-dimensional sharp-interface model of active layer evolution and permafrost thaw is presented. This computationally efficient, semianalytical, nonequilibrium solution to soil freeze-thaw problems in partially saturated media is proposed as a component of hydrological models to describe seasonal ground ice, active layer evolution, and changes in permafrost temperature and extent. The model is developed and validated against the analytical Stefan solution and a finite volume coupled heat and mass transfer model of freeze-thaw in unsaturated porous media. Unlike analytic models, the interface model provides a nonequilibrium solution to the heat equation while permitting a wide range of temporally variable boundary conditions and supporting the simulation of multiple interfaces between frozen and unfrozen soils. The model is implemented for use in discontinuous permafrost peatlands where soil properties are highly dependent on soil ice content and infiltration capacity is high. It is demonstrated that the model is suitable for the representation of variably saturated active layer and permafrost evolution in cases both with and without a talik. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.

DOI: 10.1029/2020WR027638

2021018109 Guillemot, Antoine (Université Grenoble Alpes, Université Savoie Mont Blanc, Institut de Recherche pour le Développement, Grenoble, France); Helmstetter, Agnès; Larose, Éric; Baillet, Laurent; Garambois, Stéphane; Mayoraz, Raphaël and Delaloye, Reynald. Seismic monitoring in the Gugla rock glacier (Switzerland); ambient noise correlation, microseismicity and modelling: Geophysical Journal International, 221(3), p. 1719-1735, illus., 60 ref., June 2020.

A network of seismometers has been installed on the Gugla rock glacier since October 2015 to estimate seismic velocity changes and detect microseismicity. These two processes are related to mechanical and structural variations occurring within the rock glacier. Seismic monitoring thus allows a better understanding of the dynamics of rock glaciers throughout the year. We observed seasonal variations in seismic wave velocity and microseismic activity over the 3 yr of the study. In the first part of our analysis, we used ambient noise correlations to compute daily changes of surface wave velocity. In winter, seismic wave velocities were higher, probably due to refreezing of the permafrost active layer and cooling of the uppermost permafrost layers, leading to increased overall rigidity of the medium. This assumption was verified using a seismic model of wave propagation that estimates the depth of P- and S-wave velocity changes from 0 down to 10 m. During melting periods, both a sudden velocity decrease and a decorrelation of the seismic responses were observed. These effects can probably be explained by the increased water content of the active layer. In the second part of our study, we focused on detecting microseismic signals generated in and around the rock glacier. This seismic activity (microquakes and rockfalls) also exhibits seasonal variations, with a maximum in spring and summer, which correlates principally with an exacerbated post-winter erosional phase of the front and a faster rock glacier displacement rate. In addition, we observed short bursts of microseismicity, both during snowfall and during rapid melting periods, probably due to pore pressure increase.

DOI: 10.1093/gji/ggaa097

2021020893 Payandi-Rolland, Dahedrey (Université de Toulouse, Géosciences Environnement Toulouse, Toulouse, France); Shirokova, Liudmila S.; Nakhle, Paty; Tesfa, Marawit; Abdou, Ahmed; Causserand, Carole; Lartiges, Bruno; Rols, Jean-Luc; Guérin, Frédéric; Bénézeth, Pascale and Pokrovsky, Oleg S. Aerobic release and biodegradation of dissolved organic matter from frozen peat; effects of temperature and heterotrophic bacteria: Chemical Geology, 536, Article 119448, illus. incl. 2 tables, 107 ref., March 20, 2020.

Understanding the conditions of dissolved organic matter (DOM) release from thawing peat in the Arctic regions and identifying the pathways of processing DOM by soil and aquatic heterotrophic bacteria are critical in the context of rapid climate change. Until now, experimental approaches did not allow quantitative predictions of temperature and biota effects on carbon release from peat in permafrost-affected aquatic environments. In this study, we incubated frozen peat and its aqueous leachate at various temperatures (4, 25 or 45°C), with and without culturable heterotrophic bacteria Iodobacter sp., extracted from thermokarst lakes, to quantify the release and the removal rate of organic carbon (OC) with time. The metabolic diversity of the native microbial community associated with the substrates involved in OC processing was also characterized. Transmission electron microscopy revealed that, after degradation, the associated bacteria are mostly located in the inner parts of plant cells, and that the degradation of organic matter around bacteria is more pronounced at 4 and 25°C compared to 45°C. The metabolic diversity of heterotrophic bacteria was equally high at 4 and 25°C, but lower at 45°C. Regardless of the microbial consortium (native community alone or with added culturable heterotrophs), both the OC release from peat and the OC removal from peat leachate by bacteria were similar at 4 and 25°C. Very low apparent activation energies of DOM biodegradation between 4 and 25°C (-4.23±12.3 kJ mol^-1) suggest that the short-period of surface water warming in summer would have an insignificant effect on DOM microbial processing. Such duration (1-3 weeks) is comparable with the water residence time in peat depressions and permafrost subsidences, where peat degradation and DOM microbial processing occur. This questions the current paradigm of a drastic effect of temperature rise on organic carbon release from frozen peatlands, and should be considered for modelling short-term climate impacts in these regions.

DOI: 10.1016/j.chemgeo.2019.119448

2021021155 Jan, Ahmad (Oak Ridge National Laboratory, Climate Change Science Institute and Environmental Sciences Division, Oak Ridge, TN); Coon, Ethan T. and Painter, Scott L. Evaluating integrated surface/subsurface permafrost thermal hydrology models in ATS (v0.88) against observations from a polygonal tundra site: Geoscientific Model Development (GMD), 13(5), p. 2259-2276, illus. incl. 2 tables, 99 ref., 2020.

Numerical simulations are essential tools for understanding the complex hydrologic response of Arctic regions to a warming climate. However, strong coupling among thermal and hydrological processes on the surface and in the subsurface and the significant role that subtle variations in surface topography have in regulating flow direction and surface storage lead to significant uncertainties. Careful model evaluation against field observations is thus important to build confidence. We evaluate the integrated surface/subsurface permafrost thermal hydrology models in the Advanced Terrestrial Simulator (ATS) against field observations from polygonal tundra at the Barrow Environmental Observatory. ATS couples a multiphase, 3D representation of subsurface thermal hydrology with representations of overland nonisothermal flows, snow processes, and surface energy balance. We simulated thermal hydrology of a 3D ice-wedge polygon with geometry that is abstracted but broadly consistent with the surface microtopography at our study site. The simulations were forced by meteorological data and observed water table elevations in ice-wedge polygon troughs. With limited calibration of parameters appearing in the soil evaporation model, the 3-year simulations agreed reasonably well with snow depth, summer water table elevations in the polygon center, and high-frequency soil temperature measurements at several depths in the trough, rim, and center of the polygon. Upscaled evaporation is in good agreement with flux tower observations. The simulations were found to be sensitive to parameters in the bare soil evaporation model, snowpack, and the lateral saturated hydraulic conductivity. Timing of fall freeze-up was found to be sensitive to initial snow density, illustrating the importance of including snow aging effects. The study provides new support for an emerging class of integrated surface/subsurface permafrost simulators.

DOI: 10.5194/gmd-13-2259-2020

2021019253 Wagner, F. M. (University of Bonn, Geophysics Section, Institute of Geosciences, Bonn, Germany); Mollaret, C.; Günther, T.; Kemna, A. and Hauck, C. Quantitative imaging of water, ice and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data: Geophysical Journal International, 219(3), p. 1866-1875, illus. incl. 2 tables, sects., 42 ref., December 2019.

Quantitative estimation of pore fractions filled with liquid water, ice and air is crucial for a process-based understanding of permafrost and its hazard potential upon climate-induced degradation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. We present a method to jointly estimate the volumetric fractions of liquid water, ice, air and the rock matrix from seismic refraction and electrical resistivity data. Existing approaches rely on conventional inversions of both data sets and a suitable a priori estimate of the porosity distribution to transform velocity and resistivity models into estimates for the four-phase system, often leading to non-physical results. Based on two synthetic experiments and a field data set from an Alpine permafrost site (Schilthorn, Bernese Alps and Switzerland), it is demonstrated that the developed petrophysical joint inversion provides physically plausible solutions, even in the absence of prior porosity estimates. An assessment of the model covariance matrix for the coupled inverse problem reveals remaining petrophysical ambiguities, in particular between ice and rock matrix. Incorporation of petrophysical a priori information is demonstrated by penalizing ice occurrence within the first two meters of the subsurface where the measured borehole temperatures are positive. Joint inversion of the field data set reveals a shallow air-rich layer with high porosity on top of a lower-porosity subsurface with laterally varying ice and liquid water contents. Non-physical values (e.g. negative saturations) do not occur and estimated ice saturations of 0-50 per cent as well as liquid water saturations of 15-75 per cent are in agreement with the relatively warm borehole temperatures between -0.5 and 3°C. The presented method helps to improve quantification of water, ice and air from geophysical observations.

DOI: 10.1093/gji/ggz402

2021019206 Hibert, C. (University of Strasbourg, Ecole et Observatoire des Sciences de la Terre, Strasbourg, France); Michéa, D.; Provost, F.; Malet, J. P. and Geertsema, M. Exploration of continuous seismic recordings with a machine learning approach to document 20 yr of landslide activity in Alaska: Geophysical Journal International, 219(2), p. 1138-1147, illus. incl. 1 table, sketch maps, 49 ref., November 2019.

Quantifying landslide activity in remote regions is difficult because of the numerous complications that prevent direct landslide observations. However, building exhaustive landslide catalogues is critical to document and assess the impacts of climate change on landslide activity such as increasing precipitation, glacial retreat and permafrost thawing, which are thought to be strong drivers of the destabilization of large parts of the high-latitude/altitude regions of the Earth. In this study, we take advantage of the capability offered by seismological observations to continuously and remotely record landslide occurrences at regional scales. We developed a new automated machine learning processing chain, based on the Random Forest classifier, able to automatically detect and identify landslide seismic signals in continuous seismic records. We processed two decades of continuous seismological observations acquired by the Alaskan seismic networks. This allowed detection of 5087 potential landslides over a period of 22 yr (1995-2017). We observe an increase in the number of landslides for the period and discuss the possible causes.

DOI: 10.1093/gji/ggz354

2021018705 Kashirtsev, V. A. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Neftegazovoy Geologii i Geofiziki, Novosibirsk, Russian Federation); Parfenova, T. M.; Moiseyev, S. A.; Chernykh, A. V.; Noviov, D. A.; Burshteyn, L. M.; Dolzhenko, K. V.; Rogov, V. I.; Mel'nik, D. S.; Zuyeva, I. N. and Chalaya, O. N. Pryamyye priznaki neftegazonosnosti i neftematerinskiye otlozheniya Sukhanskogo osadochnogo basseyna Sibirskoy platformy [The Sukhana sedimentary basin, Siberian Platform; source rock characterization and direct evidence of oil and gas presence]: Geologiya i Geofizika, 60(10), p. 1472-1487 (English sum.), illus. incl. strat. cols., geol. sketch map, 54 ref., October 2019.

The platform cover of the Sukhana sedimentary basin (Siberian Platform) is composed of Riphean, Vendian, and Cambrian clastic (terrigenous) and carbonate deposits reaching 5.5-6 km in thickness in the central part of the basin. The hydrogeological specifics of the basin is largely governed by its location within the northern geocryological zone (Olenek cryoartesan basin) and is expressed as a continuous distribution of permafrost aggraded into the permafrost zone of unique thickness. Direct indicators of ore and gas presence are the East Anabar, Central Olenek, and Siligir-Markha Fields of natural bitumen and oil shows in kimberlite pipes of the Daldyn-Alakit region (Udachnaya pipe). The bituminous-carbonate sediments of the Khatyspyt Formation (Vendian, Ediacaran) and the highly carbonaceous carbonate-siliceous-shaly sediments of the Kuonamka Formation (Lower-Middle Cambrian) are the Sukhana source rock complexes. As for the regional assessment of the petroleum potential of the entire basin, its axial part (Sukhana Depression) complicated by local uplifts is of the greatest interest. Both the Khatyspyt and Kuonamka Formations are widespread there, with the thermal maturity of their organic matter corresponding to the oil window. In addition, the regional reservoirs at the Vendian-Cambrian boundary have good petrophysical properties on both the western and the eastern flanks of the basin.

2021022501 Wetterich, Sebastian (Alfred Wegener Institute Holmholtz Center for Polar and Marine Research, Research Unit Potsdam, Potsdam, Germany); Rudaya, Natalia; Kuznetsov, Vladislav; Maksimov, Fedor; Opel, Thomas; Meyer, Hanno; Günther, Frank; Bobrov, Anatoly; Raschke, Elena; Zimmermann, Heike H.; Strauss, Jens; Starikova, Anna; Fuchs, Margret and Schirrmeister, Lutz. Ice Complex formation on Bol'shoy Lyakhovsky Island (New Siberian Archipelago, east Siberian Arctic) since about 200 ka: Quaternary Research, 92(2), p. 530-548, illus. incl. 1 table, sketch maps, 80 ref., September 2019.

Late Quaternary landscapes of unglaciated Beringia were largely shaped by ice-wedge polygon tundra. Ice Complex (IC) strata preserve such ancient polygon formations. Here we report on the Yukagir IC from Bol'shoy Lyakhovsky Island in northeastern Siberia and suggest that new radioisotope disequilibria (²³⁰Th/U) dates of the Yukagir IC peat confirm its formation during the Marine Oxygen Isotope Stage (MIS) 7a-c interglacial period. The preservation of the ice-rich Yukagir IC proves its resilience to last interglacial and late glacial-Holocene warming. This study compares the Yukagir IC to IC strata of MIS 5, MIS 3, and MIS 2 ages exposed on Bol'shoy Lyakhovsky Island. Besides high intrasedimental ice content and syngenetic ice wedges intersecting silts, sandy silts, the Yukagir IC is characterized by high organic matter (OM) accumulation and low OM decomposition of a distinctive Drepanocladus moss-peat. The Yukagir IC pollen data reveal grass-shrub-moss tundra indicating rather wet summer conditions similar to modern ones. The stable isotope composition of Yukagir IC wedge ice is similar to those of the MIS 5 and MIS 3 ICs pointing to similar atmospheric moisture generation and transport patterns in winter. IC data from glacial and interglacial periods provide insights into permafrost and climate dynamics since about 200 ka.

DOI: 10.1017/qua.2019.6

2021017679 Vandenberghe, Jef (Vrije Universiteit Amsterdam, Institute of Earth Sciences, Amsterdam, Netherlands); French, Hugh M.; Jin Huijun; Wang Xianyan; Yi Shuangwen and He Ruixia. The extent of permafrost during the last permafrost maximum (LPM) on the Ordos Plateau, north China: Quaternary Science Reviews, 214, p. 87-97, illus. incl. 1 table, sketch map, 36 ref., June 15, 2019.

This paper presents new field observations that assist in further defining the extent of Last Permafrost Maximum (LPM) permafrost and frozen ground in north China. In that respect, this region is specific by its arid environment and continental position. Bedrock exposures and sand and gravel pits were examined along a south-north transect from southern Ordos as far as the vicinity of Dongsheng District, Ordos City on the Ordos Plateau (North China). Attention focussed upon the recognition of sand-wedge remains and possible cryoturbations. Two types of wedge structures were recognized: type A wedges extend to depths in excess of 3.0 m and are thought to have formed under conditions of continuous permafrost. Type B wedges are restricted to the upper 1.5 m and are thought to reflect discontinuous permafrost and/or deep seasonal frost. OSL dating of wedge infills indicates that type A wedges formed between 23-19 ka and younger type B wedges formed until the early Holocene. It is now possible to delineate a more exact position of the boundary between continuous permafrost and discontinuous permafrost and/or deep seasonal frost on the Ordos Plateau during the LPM. This boundaries occur between Dongsheng and Jinbian at 37°-39°N.

DOI: 10.1016/j.quascirev.2019.04.019

2021022480 Grinter, Mike (University of Ottawa, Department of Earth and Environmental Sciences, Ottawa, ON, Canada); Lacelle, Denis; Baranova, Natalia; Murseli, Sarah and Clark, Ian D. Late Pleistocene and Holocene ice-wedge activity on the Blackstone Plateau, central Yukon, Canada: Quaternary Research, 91(1), p. 179-193, illus. incl. 2 tables, sketch maps, 90 ref., January 2019.

Ice-wedge activity can be used to reconstruct past environmental conditions. We investigated the moisture source and timing of ice-wedge formation on the Blackstone Plateau. A section of permafrost exposed ice wedges that developed at two distinct depths: the first set formed syngenetically and penetrated alluvial silts from the top of permafrost; the second set, truncated by an erosional or thaw contact, was found solely in icy muddy gravels (>3.1 m depth). The d¹⁸O and D-excess records of the ice wedges suggest that they formed from freezing of snow meltwater whose isotopic composition evolved during meltout. The ¹⁴C_DOC results suggest that climate was favorable to ice-wedge growth between 32,000-30,000 and 14,000-12,500 cal yr BP, but there was likely a hiatus during the last glacial maximum due to climate being too dry. During the early to mid-Holocene, ice wedges were inactive as a result of warmer and wetter climate. Ice wedge re-initiated around 6360 cal yr BP, with a peak in activity between 3980 and 920 cal yr BP, a period characterized by cool and moist climate. Overall, timing of ice-wedge activity was broadly consistent with the climate and vegetation evolution in the western Arctic.

DOI: 10.1017/qua.2018.65

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2021019417 Lindsey, Nathaniel J. Fiber-optic seismology in theory and practice: 201 p., illus. incl. 1 table, 246 ref., Doctoral, 2019, University of California at Berkeley, Berkeley, CA.

Distributed Acoustic Sensing (DAS) is an emerging tool in array seismology, which uses high frequency interferometry of pulsed laser backscattering inside optical fiber to analyze the axial strain induced on the fiber cable commonly buried in horizontal trenches and vertical wells at the surface of the Earth. This technology was developed over the last decade for hydrocarbon and carbon sequestration reservoir imaging and monitoring, but the focus in this thesis is to explore its application to problems in earth science, broadly defined. Combining DAS with telecommunications optical fiber networks offers meter-scale, long-term observations of ground motion over watershed apertures in sectors of the planet where traditional geophysics has been hindered by cost and field logistics, such as offshore and in urban areas. The thesis is organized as follows. I introduce the motivation for using fiber-optic seismology in Chapter 1. In Chapter 2, I define principles of the methodology and describe how the instrument works. In Chapter 3, I use continuous DAS recordings of ambient vehicular seismic noise generated on a local road to study degrading permafrost over a two-month period of artificial warming. In Chapter 4, I focus on earthquake ground motions recorded on horizontal DAS arrays. Unlike classic inertial seismometers, there is presently a limited amount of information about DAS instrument response, thus in Chapter 5 the aim is to use natural signals to quantify the broadband frequency range of DAS instruments and deduce the related amplitude and phase response functions. Lastly, in Chapter 6, I use fiber-optics on the seafloor of Monterey Bay, CA inside of an unused science cable to investigate the production of near-coast primary and secondary microseisms, identify unmapped seafloor faults, and observe quasi-geodetic hydrodynamic phenomena in the milli-Hertz frequency range. In Chapter 7, I summarize findings and speculate about future directions in this field.

URL: https://escholarship.org/uc/item/1fs925tc

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2021019705 Anderson, Lesleigh (U. S. Geological Survey, Denver, CO); Finney, Bruce P.; Edwards, Mary; King, Amanda L.; Wooller, Matthew J.; Finkenbinder, Matthew S. and Abbott, Mark B. Conceptualizing the shifting roles of precipitation and evaporation in Beringia across the Pleistocene-Holocene transition using a water isotope approach [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 166-4, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

The fundamental importance of moisture on Beringian landscapes is established, and yet threshold ecosystem responses to changes in precipitation (P) and evaporation (E) remain unexplored. A prominent example is a rise in P - E (moisture balance) from the full glacial into the Bolling Allerod, when lake levels rose, and shrub birch expanded regionally. However, it remains unknown how these prominent hydrologic and ecologic changes were driven by changes in P and E, respectively. Similar questions exist for the Younger Dryas and early Holocene. A better understanding of precipitation amount and seasonality, and subsequent factors contributing to water cycling such as evapotranspiration and evaporation (as influenced by temperature, humidity, radiation, wind) and infiltration/flow/permafrost are needed to understand impacts of climate change on arctic regions. Water isotope ratios are widely used to study the hydrologic cycle: oxygen and hydrogen isotope values from lake, river, frozen ground, and meteoric water contain information about many variables of importance to precipitation and evaporation fluxes. Guided in addition by proxy data, including vegetation change and lake-levels, and by isotope-enabled climate models, we present a conceptual framework to extract complex P and E information across the deglacial transition in eastern Beringia. The approach provides specific hypotheses to be tested by paleoclimatic reconstructions based on lake water isotope ratios using lake sediments.

DOI: 10.1130/abs/2020AM-358372

2021021453 Evans, Sarah (Appalachian State University, Department of Geological and Environmental Sciences, Boone, NC); Yokeley, Brandon; Stephens, Connor and Brewer, Benjamin. What causes increases in baseflow across northern Eurasian catchments underlain by permafrost? [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-9, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Warming in the Arctic is occurring at twice the rate of the global average, resulting in permafrost thaw and a restructuring of the Arctic hydrologic cycle as indicated by increased stream discharge during low-flow periods. In these cold regions, permafrost thaw is postulated to increase low-flow discharge, or baseflow, through either: (a) localized increases in groundwater storage and discharge to streams due to increased aquifer transmissivity from thickening of the freeze-thaw layer above permafrost known as the active layer, or (b) long-term increases in regional groundwater circulation via enhancement of groundwater-surface water interactions due to extensive permafrost loss over decades. While increasing baseflow has been observed throughout northern Eurasia, the precise mechanistic causes remain elusive. Here, we differentiate between where these two subsurface physical mechanisms of baseflow increase are occurring by performing a baseflow recession analysis using daily streamflow records from 1913-2003 for 139 stations in northern Eurasia underlain by varying permafrost areal extents. Results indicate that from 1913 to 2003, the majority of catchments underlain by continuous permafrost have an increasing trend in their recession flow intercepts, a proxy for increasing active layer thickness. Alternatively, the majority of catchments underlain by permafrost types that are less spatially extensive (e.g., discontinuous, sporadic, isolated, or no permafrost) have decreasing trends in their recession flow intercepts, indicating that a potential increase in active layer thickness is not the driving factor of baseflow variations in these catchments. This may indicate that in catchments underlain by continuous permafrost, active layer thickening correlates with increases in baseflow whereas, in other catchments with less extensive permafrost, increases in baseflow may be caused by wholesale permafrost loss and vertical talik expansion that enhances regional groundwater circulation. The results of this work may inform our understanding of the subsurface mechanisms responsible for the changing Arctic hydrologic cycle.

DOI: 10.1130/abs/2020AM-352989

2021021450 Fortier, Philippe (Université Laval, Département de Géologie et de Génie Géologique, Quebec City, QC, Canada); Lemieux, Jean-Michel; Young, Nathan L.; Walvoord, Michelle A.; Voss, Clifford I. and Fortier, Richard. Evolution of the cryohydrogeology dynamics at a degrading permafrost mound near Umiujaq (Nunavik, Canada) [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-6, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Numerical modeling studies of permafrost degradation generally conceptualize heat transfer as occurring exclusively by conduction. However, recent work has shown that advective heat transport by flowing groundwater can effectively control permafrost dynamics. Thus, in order to understand the impact of groundwater flow on permafrost degradation, the contribution of heat advection on thawing rates must be determined. This study characterizes the thermal and hydrogeological regimes of a permafrost mound located in the discontinuous permafrost zone near Umiujaq, Nunavik, Canada, in order to create a conceptual cryohydrogeological model. Previous work at the study site documented the spatial extent of the permafrost and deployed an extensive network of monitoring instrumentation. This instrumentation includes thermistor cables, groundwater monitoring wells, temperature and water content sensors in the active layer, heat flux plates, and a snow cover monitoring system. Data indicate that ice-rich permafrost is restricted to a 15-m-thick unit of marine silt, which is overlain by a 4-m-thick layer of sand. The active layer encompasses the full extent of the surficial sand layer, as well as the top 2 m of the silt unit. Depending on climatic and surficial conditions, the furthest extent of the freezing front in a given year may not reach the permafrost table, resulting in the formation of a sporadic talik between the active layer and the permafrost table. Data further indicate that the surficial sand layer acts as an unconfined aquifer, and that infiltrating precipitation flows downward to the permafrost table before flowing radially towards the sides of the mound. A downward hydraulic gradient was observed across the low hydraulic conductivity silt unit. A conceptual cryohydrogeological model was created to provide insight into the physical processes that govern local permafrost dynamics and degradation at the site, and to guide future field campaigns and modeling projects.

DOI: 10.1130/abs/2020AM-357506

2021021452 Lamontagne-Hallé, Pierrick (McGill University, Department of Earth and Planetary Sciences, Montreal, QC, Canada); Chen, Lin; Kurylyk, Barret and McKenzie, Jeffrey. Adapting groundwater model boundary conditions for cold regions [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-8, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Numerical groundwater models have been used for many decades to understand subsurface hydrology and to simulate future and current groundwater dynamics. However, most of these models are not adapted to cold regions. In these environments, the storage and movement of groundwater is affected by permafrost that confines groundwater flow to unfrozen zones of the ground. Permafrost thaw can greatly increase subsurface hydraulic conductivity and hydrological connectivity between aquifers and surface water bodies. New groundwater modelling tools that simulate groundwater flow and energy transport, including freezing and thawing processes, have recently been developed to better understand the impacts of climate change and permafrost thaw on northern hydrology. To date, these models have only been used by a few research groups and have not been widely used for managing cold regions groundwater resources. Compared to groundwater models that only simulate groundwater flow, these cold regions models are difficult to calibrate and replicate field data. One of the biggest challenges is to design land-surface boundary conditions. Processes such as snow insulation, snowmelt, and seasonal freezing and limited applicable field data make the accurate representation of this boundary challenging. Herein, we apply different sets of thermal and hydraulic surface boundary conditions adapted for cold regions to assess their impact on model outcomes, such as active layer thickness, permafrost thawing rate, and spatial and seasonal patterns groundwater discharge rate to the land surface. We test and compare the sensitivity of model outcomes to these boundary conditions in different settings. From these analyses, we evaluate the boundary conditions that exert the largest influence on model outcomes and provide recommendations for which boundary conditions to use depending on the setting. This study provides guidelines to develop effective conceptual and numerical groundwater models in cold regions.

DOI: 10.1130/abs/2020AM-358139

2021021455 Lanagan, Kelleen (University of Colorado at Boulder, Department of Geological Sciences, Boulder, CO) and Ge, Shemin. Impact of road construction on permafrost and groundwater hydrology in the Gates of the Arctic National Park, Alaska [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-11, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

The Alaska Industrial Development and Export Authority was approved to build a new road from the Dalton Highway to the Ambler Mining District in central Alaska. The road alignment will be approximately 340 km long and built on sensitive permafrost environments just south of the Brooks Range. Road materials have different thermal and hydrogeologic properties than the organic material and silty soil that currently comprise much of the land surface and shallow subsurface. This study attempts to address questions of how this new road may affect permafrost thaw, active layer thickness, and groundwater flow in areas along the road alignment. The Nutuvukti Lake watershed in Gates of the Arctic National Park was identified as the study area. Data from 25 soil cores were taken from the road corridor in summer 2014 with depths ranging between approximately 1.0 to 4.6 meters. A hobo logger in the study area provides hourly temperature data at the surface and 1.5 meters depth from August 2014 to July 2016. Daily mean surface temperature ranged between -15.4°C and 22.3°C. Various surface conditions and soil hydrothermal properties are considered in preliminary modeling of the thermal and hydrological processes of the study site. A sinusoidal daily mean temperature variation was applied at the land surface, and thermal properties of the soil layers are based on soil core data and previous literature. Results are compared using hydrologic and thermal properties before and after a simulated road placed on top of the existing ground. Preliminary estimates suggest that the active layer may change by tens of centimeters under the new road. As active layer thickness directly impacts shallow subsurface hydrology, model results help to assess how hydrology may be altered by the new road.

DOI: 10.1130/abs/2020AM-359727

2021021449 Lemieux, Jean-Michel (Université Laval, Département de Géologie et de Génie Géologique, Quebec City, QC, Canada); Fortier, Richard; Molson, John and Therrien, René Hydrogeology of a small watershed located in the discontinuous permafrost zone of northern Canada [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-5, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Groundwater was recently recognized as an important component of the water cycle in cold environments. In a warming climate, groundwater base flow has an important control on river discharge. Groundwater can also have an important control on permafrost dynamics due to advective heat transport. Thawing permafrost due to climate warming is also expected to allow the development of active groundwater flow systems and to increase groundwater availability as a source of drinking water for northern communities. In this context, groundwater distribution and flow dynamics were studied in a small watershed located in the discontinuous permafrost zone at Umiujaq in Nunavik (Quebec), Canada, to assess the seasonal variations and perform a quantitative analysis of the water cycle in a subarctic watershed. Due to the complexity of the subsurface geology within the watershed, an integrated investigation was instrumental to provide a detailed understanding of the hydrogeological context as a basis for the water balance. The investigation revealed a complex stratified groundwater flow system with two aquifers separated by a thick layer of deep marine sediments (silt) in which discontinuous permafrost is found. A thin water table aquifer perched over the silt unit is found in the upper part of the valley, while a confined aquifer below the silt unit is found in the lower part of the valley, with upward flow toward a small stream. While permafrost has limited impact on groundwater availability in this watershed, it exerts an important control on groundwater flow dynamics since it limits surface and groundwater interaction through the silt unit. Projected permafrost degradation will likely increase stream baseflow, especially in winter, as it will be easier for groundwater from the lower aquifer to flow upward across the silt unit.

DOI: 10.1130/abs/2020AM-351385

2021021442 Levy, Joseph (Colgate University, Department of Geology, Hamilton, NY). Water track hydropattern in the McMurdo dry valleys, Antarctica; contrasting views from space and from the subsurface [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 19-10, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Recent observations of accelerating erosion and ground ice thaw in Antarctica's coastal Dry Valleys (MDV) suggest that shrinking permafrost extents, thickening active layers, and widespread thermokarst subsidence resulting from enhanced heat transport through recently-wetted cold desert soils may be early indicators of imminent, continental-scale change in the topography, mineralogy, and the thermal state of the Antarctic terrestrial cryosphere. Water tracks are the basic unit of the subsurface hydrological system that feeds polar and permafrost wetlands. Water tracks are narrow bands of high soil moisture that route water downslope through soils, in the absence of overland flow. In water tracks, moisture moves as shallow groundwater, flowing through the active layer (the seasonally-thawed portion of soil column) along linear depressions in the ice table (the top of the permafrost that remains ice-cemented during summer). Because they are soil landforms, water tracks are notoriously difficult to measure because they cannot be easily gaged like a stream. Efforts to determine the duration, extent, and saturation of water tracks in the MDV (the hydropattern) require measurements at a range of scales: from satellite observations of regional water track wetting and soil darkening, to the plot-scale, where subsurface temperature and soil moisture conditions can be met. Here, we show that water track soil moisture conditions, and by extension, the magnitude of soil biogeochemical cycling that can occur, show mis-matches, depending on the scale and mode of observation. Water track thawing and soil moisture development typically begins early in the austral summer during November, when soil temperatures are still at or below 0°. In contrast, soil darkening from wetness exceeding a few weight percent water does not typically begin until December or later, as observed through satellite observations. This mismatch suggests that soil biogeochemical processing in water track moisture anomalies may be occurring "cryptically" in the shallow subsurface, long before seasonal thawing is apparent to remote surface observations.

DOI: 10.1130/abs/2020AM-358320

2021021447 Mohammed, Aaron A. (Dalhousie University, Department of Civil and Resource Engineering, Halifax, NS, Canada); Young, Nathan L.; Cey, Edwin E.; Hayashi, Masaki; Lemieux, Jean-Michel and Kurylyk, Barret. Modeling groundwater recharge in a changing cryosphere [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-3, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Groundwater recharge mechanisms in seasonally frozen and permafrost landscapes are governed by interactions between snow and ground freeze-thaw processes that determine the timing, magnitude, and spatial distribution of recharge. Snowmelt-driven infiltration and recharge are complicated by coupled water and heat transport phenomena such as porewater freeze-thaw, cryo-suction, preferential flow, and the influence of surface water and energy balance processes during snowmelt. Simulation of these complex processes remains a major challenge, but as numerical models and computational capability continue to improve, physically-based descriptions and meaningful representations of these interacting processes have begun to be incorporated into various modeling frameworks. This presentation discusses different approaches for simulating groundwater recharge in landscapes subject to snow and freeze-thaw processes. Modeling approaches vary from soil-water balance models, to single and dual-permeability Richards equation descriptions, to more complex fully-integrated surface water-groundwater models. Specific field and modeling examples from the seasonally frozen Canadian Prairies and the discontinuous permafrost zone in northern Canada are presented to demonstrate the importance of representing these processes when simulating recharge in cold regions, including the effects of vadose zone processes such as preferential flow, and surface processes such as changing vegetation and snowmelt dynamics. Results highlight that representing the interaction of these complex but important processes in modeling efforts can greatly improve our understanding of, and ability to simulate the effects of, snow and freeze-thaw on groundwater recharge in cold regions under changing climate, vegetation cover, and land use conditions.

DOI: 10.1130/abs/2020AM-352316

2021021451 Molson, John (Université Laval, Centre d'Etudes Nordiques, Quebec City, QC, Canada); Perreault, Julie; Liu, Weibo and Fortier, Richard. Numerical modelling of permafrost-impacted hydrogeological flow systems under climate change [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-7, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Permafrost thaw due to climate warming is having significant effects on hydrologic and hydrogeological systems in the north. Changes to ground surface conditions, and increased permeability and recharge due to melting of ground ice, for example, are creating new dynamic flow systems with implications for new water supplies. In addition, positive feedback from increased water infiltration and groundwater flow can accelerate permafrost degradation. Numerical modelling can provide important new insights into these coupled processes and can be used to predict future behavior. The numerical model HEATFLOW is here applied to simulate two well-characterized field sites in Nunavik (Quebec), Canada: one near Umiujaq in the discontinuous permafrost zone where changes in groundwater flow, surface vegetation and development of thermokarst lakes are accelerating permafrost thaw, and the other in Salluit where a river-talik (an unfrozen zone below a river) within a continuous permafrost zone has been simulated in three-dimensions. The simulations include groundwater flow coupled to advective-conductive heat transport with temperature-dependent hydraulic conductivity and thermal properties, as well as freeze-thaw and latent heat. Model spin-up periods on the order of a couple of decades are used to initialize the simulation scenarios with realistic flow velocities and temperatures. The simulated flow systems and temperature fields help to highlight the complex and dynamic interactions within these field-scale cryo-hydrogeological systems under changing surface boundary conditions. In all cases, advective heat transport by flowing groundwater plays an important role in affecting permafrost dynamics.

DOI: 10.1130/abs/2020AM-357387

2021021436 Staniszewska, Kasia (University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada); Cooke, Colin A.; Reyes, Alberto and Zazula, Grant D. Thaw features in continuous permafrost contribute minor amounts of mercury to downstream environments in the Old Crow River, Yukon [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 19-4, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Anthropogenic climate warming is leading to the acceleration of permafrost degradation and potential release of legacy contaminants, such as mercury, to aquatic systems. Point thaw features such as thermokarst lakes and retrogressive thaw slumps are potential hot spots of legacy mercury flux to downstream systems. We studied the temporal evolution of mercury and other trace element concentrations and fluxes in the Old Crow River, a pristine watershed underlain by continuous permafrost in the western Canadian Arctic. We sampled river water chemistry up- and downstream of four retrogressive thaw slumps and along eight tributaries with variable thermokarst lake connectivity during peak ground thaw, in addition to ~weekly sampling at the river mouth across the open water season. Mercury and methylmercury concentrations did not vary significantly between samples up- and downstream of the thaw slumps, nor between physiographically varied tributaries. At the river mouth, contaminant concentrations peaked during the spring freshet and were low throughout the summer to early-autumn ground thaw season. Mercury concentrations were low (<8 ng/L), and were controlled by suspended sediment with low bioavailability to aquatic organisms; dissolved mercury and methylmercury concentrations were very low. Annual flux and yield were modeled using simple linear regression with daily discharge (r >0.8). The annual mercury yield (0.8 g/km2/yr), and methylmercury yield (0.01 g/km2/yr) were low and comparable to non-permafrost-influenced wetland and forested rivers. Our results suggest that contaminant flux in this permafrost-dominated Arctic watershed is less controlled by direct release of legacy contaminants from thawing ground. Rather, the magnitude of spring freshet and-to a lesser extent-high-precipitation events in the summer control high-discharge conditions that, in turn, promote erosion of permafrost bank material and thawed slump debris in valley bottom settings.

DOI: 10.1130/abs/2020AM-359836

2021021420 Tomkins, Matt D. (University of Manchester, Department of Geography, Manchester, United Kingdom); Dortch, Jason M.; Hughes, Philip D.; Huck, Jonny and Allard, James L. Paraglacial drivers of late Pleistocene rockfall in the high mountains of the Pyrenees [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 17-14, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

While rockfalls and bedrock landslides may contribute significantly to mountain denudation, the geophysical processes which control their timing and their relative and overall importance in the evolution of mountainous topography are poorly understood. However, robust chronologies can provide valuable information on their magnitude, age and recurrence: information which can inform our understanding of the mechanisms and drivers of bedrock failure. In this study, we estimated the timing of Late Quaternary rockfall events from granitic bedrock cliffs in the Esera catchment, southern Pyrenees, based on Schmidt hammer exposure dating. This calibrated-relative age technique is based on a robust calibration dataset comprising 54 ¹⁰Be dated surfaces and enables exposure ages to be estimated based on rock surface weathering. As this approach is cost- and time-effective, it can be applied widely to undated rockfall deposits and can complement targeted cosmogenic nuclide sampling in poorly dated regions. Samples were obtained from a range of sub-catchments in the Maladeta (3,312 m) and Posets (3,371 m) massifs, and from sites with varying deglacial ages, ranging from the Last Glacial Maximum to the early Holocene. Based on a large dataset of sampled rockfall boulders (n=945), we utilised a Monte Carlo style approach to isolate component normal distributions (Gaussians) to investigate the frequency and drivers of rockfall over the last ~25 ka. These data indicate that while most bedrock cliffs are still geomorphologically active, as evidenced by the distribution of "fresh" failure scars and the deposition of unweathered rockfall boulders on weathered rockfall deposits, many deposits appear primarily paraglacial in origin. However, paraglacial intensification of rockfall activity was focused in the first few thousand years following deglaciation, with subsequent and current activity likely driven by permafrost degradation, seismicity and thermal stressing.

DOI: 10.1130/abs/2020AM-356369

2021022859 Williamson, Marie-Claude (Geological Survey of Canada, Ottawa, ON, Canada). Reactive gossans in permafrost; case studies from the Canadian Arctic Islands [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 32-6, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Gossans are surficial deposits that form through the chemical and physical weathering of the host bedrock. Gossans may produce secondary minerals that reflect the composition of their primary mineral sources, including buried ore deposits. The mineralogy of gossans (e.g. silica, jarosite and goethite) results from the oxidation of sulphides by acidic and oxidizing fluids. Research carried out by the Geological Survey of Canada (GSC) over the past decade has led to new insights on the mapping, morphology, stratigraphy, mineralogy and geochemistry of gossans that form in a permafrost environment. Gossans located on Victoria Island and Axel Heiberg Island were the focus of GSC field and laboratory studies carried out from 2011 to 2015. Study protocols included (1) the identification of gossans using satellite imagery; (2) field mapping, sampling and in situ spectral analyses; (3) mineralogical and geochemical studies; and (4) comparative studies of bedrock and stream sediments located in proximity to gossans. The distinctive colours of the oxide cap allow for the identification of gossans using multispectral and hyperspectral optical remotely sensed imagery especially in the visible-near-infrared (VNIR) portion of the electromagnetic spectrum. The small size of most gossans (a few tens of meters to less than 1 to 2 km in length) requires access to high spatial resolution images such as those provided by the WorldView multispectral sensor. Field observations and sampling of gossans at seven localities suggest that their morphology is complex. For example, the observed stratigraphy does not always match the classic gossan profile of sulphide-depleted and silica-enriched cap underlain by Fe-oxides and other secondary minerals. Gossans were grouped into three categories based on stratigraphy, presence or absence of evaporitic rocks and reactivity with permafrost. In all cases, cryogenic and oxidation processes were clearly ongoing and sulphide oxidation led to acidic conditions and the formation of relatively uniform mineralogical and textural characteristics. We propose that the pumping action of fluids in a permafrost environment, similar to a solifluction process, acts as a concentration mechanism over time and contributes to the transport of materials down slope.

DOI: 10.1130/abs/2020AM-357919

2021019706 Woudstra, Shaun H. (University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada); Jensen, Britta; Thomas, Elizabeth K. and Froese, Duane G. Middle Pleistocene loess and tephra deposits in the Fairbanks region [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 166-5, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

Reports of middle Pleistocene (»780-125 ka) loess deposits and their associated paleoecological and permafrost records are limited and fragmentary in and around Fairbanks, Alaska. The most complete middle Pleistocene deposits to date have been reported from sites along the Yukon River in Alaska-Chester Bluff and the Palisades-with some limited exposure at Gold Hill near Fairbanks. Here we report initial findings from a new site near Ester, Alaska, that indicate the presence of extensive middle Pleistocene loess deposition. The site, informally known as Largent Mine, comprises a series of placer mining cuts that expose a complex of interbedded loess, paleosols and volcanic ash (tephra), often heavily cryoturbated. Tephras collected at the site include classic late-middle Pleistocene markers such as Boneyard, Old Crow, Halfway House, VT, and DAB tephras. This suggests the preservation of a relatively complete late MIS 6 to MIS 5 record. New correlations to previously unpublished data from Birch Creek, Alaska, and several other published localities throughout Beringia, as distant as the Klondike, Yukon, indicate the presence of older middle Pleistocene loess as well. This includes the first discovery of the 80-pup tephra outside of the Klondike. Previously thought to be closer in age to Old Crow, tephra associations between Largent Mine and Birch Creek show that this tephra is older than »200 ka, potentially quite a bit older. Below 80-pup, at the loess-gravel boundary, are organic deposits with large wood fragments and the Alyeska Pipeline tephra (APt). This tephra is an important regional marker that does not have an independent age determination but is found below the Chester Bluff tephra (CBt; »360 ka) and is likely younger than »500 ka. Overall, the cross-correlations to other localities, combined with the tephra within the site, suggest that Largent Mine contains an important middle Pleistocene record. This site provides a unique snapshot into the middle Pleistocene around Fairbanks, and helps build and clarify the tephrostratigraphic framework for Beringia.

DOI: 10.1130/abs/2020AM-358992

2021021448 Young, Nathan L. (Université Laval, Département de Géologie et de Génie Géologique, Quebec City, QC, Canada); Lemieux, Jean-Michel; Delottier, Hugo; Mohammed, Aaron A.; Fortier, Richard and Fortier, Philippe. Development of a chronosequence-based conceptual model for anticipating the impact of landscape evolution on groundwater recharge in degrading permafrost environments [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-4, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

The impacts of permafrost degradation have been studied in the discontinuous permafrost zone at Umiujaq, in northern Quebec, Canada, for over 30 years, but the effects of changing land cover on groundwater recharge is not well understood. This study attempts to gain insight into how changing landcover alters the timing and volume of recharge, in addition to investigating the time scale over which these changes occur. To accomplish these goals, the water table fluctuation (WTF) method was used to compute groundwater recharge using four years of water level data and soil moisture readings from five field sites characteristic of different stages of permafrost degradation and vegetation invasion. Results indicate that as vegetation grows taller, groundwater recharge increases, likely due to increased snow thickness. Results were then combined with a preexisting conceptual model that describes the evolution from tundra to shrubland and forests to create a new model for describing how groundwater recharge is affected by landscape evolution. Finally, results estimated using the WTF method were compared to recharge values computed using a suite of 1-D heat and water flow models in order to determine whether differences in recharge timing and volume are caused by process-based changes occurring in both the saturated and unsaturated zones.

DOI: 10.1130/abs/2020AM-354357

2021021446 Zhang Fan (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China). Study on runoff generation processes based on water stable isotopes in permafrost-influenced alpine meadow area of the Tibetan Plateau [abstr.]: in Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Abstracts with Programs - Geological Society of America, 52(6), Abstract no. 20-2, October 2020. Meeting: Geological Society of America, 2020 annual meeting; GSA 2020 connects online, Oct. 26-30, 2020, World Wide Web.

The Tibetan Plateau (TP) is the headwater area of more than ten large Asiatic rivers and the permafrost degradation under global warming may change the hydrological regime of the headwater catchments. In this study, hydrometric observations and water stable isotopic method were applied to investigate the runoff generation processes in alpine meadow area, northeast TP. The following results were obtained: 1) The observed average stable isotope values of various water types was roughly in the order of snowfall » snowmelt < bulk soil water (BSW) < rainfall » stream water » mobile soil water (MSW) » lateral subsurface flow. The depleted spring snowmelt and enriched summer rainfall formed tightly bound soil water and MSW, respectively. The dynamic mixing between tightly bound soil water and MSW resulted in BSW with more depleted and variable stable isotopic feature than MSW. 2) Along with the thawing of the frozen soil, surface runoff and shallow subsurface flow (SSF) at 30-60 cm was the major flow pathway in the permafrost influenced alpine meadow hillslope during spring snowmelt and summer rainfall period, respectively. 3) The shallow SSF showed sharp increases after the soil water contents of thawed layers exceeded certain threshold values, and the frozen soil is important to promote the hillslope runoff generation by maintaining supra-permafrost water level to the highly transmissive shallow soil layer. 4) Comparison between two neighouring catchments under similar precipitation conditions indicated that streamflow of the lower catchment with less permafrost proportion and earlier thawing time has larger SSF and higher based flow component, indicating the potential changes of hydrological regimes subject to future warming.

DOI: 10.1130/abs/2020AM-354057

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