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2020028965 Ota, Mitsuaki (University of Saskatchewan, Department of Soil Science, Saskatoon, SK, Canada); Mamet, Steven D.; Muller, Amanda L.; Lamb, Eric G.; Dhillon, Gurbir; Peak, Derek and Siciliano, Steven D. Could cryoturbic diapirs be key for understanding ecological feedbacks to climate change in High Arctic polar deserts?: Journal of Geophysical Research: Biogeosciences, 125(3), e2019JG005263, illus. incl. 2 tables, sketch map, 54 ref., March 2020.
High Arctic polar deserts cover 26% of the Arctic. Increasing temperatures are predicted to significantly alter polar desert freeze-thaw and biogeochemical cycles, with important implications for greenhouse gas emissions. However, the mechanisms underlying these changing cycles are still highly uncertain. Cryoturbic, carbon-rich Bhy horizons (diapirs) in frost boils are key nutrient sources for Salix arctica. We hypothesized that diapirism leads to organic carbon characteristics that alter microbial pathways, which then control root foraging and greenhouse gas production. During July and August 2013, we characterized soil properties and examined gross nitrogen transformation rates in frost boils both with and without diapirs in two High Arctic polar deserts (dolomite and granite) near Alexandra Fjord (78°51'N 75°54'W), Ellesmere Island, Nunavut, Canada. Diapiric frost boils had 18% higher soil organic carbon in the dolomitic and 9% higher in the granitic deserts, and 29% higher total dissolved nitrogen in the dolomitic desert. However, diapirs decreased gross nitrogen mineralization rates by 30% in the dolomitic and by 48% in the granitic deserts. Attenuated total reflectance Fourier transformed mid-infrared spectroscopy revealed greater concentrations of polysaccharides and recalcitrant carbon in diapiric versus nondiapiric frost boils. These increased polysaccharide concentrations likely facilitate diapirism as soil viscosity increases with polysaccharides. Lower microbial activity or ectomycorrhizae that are known to colonize S. arctica may accumulate total dissolved nitrogen in diapirs. Our results suggest geomorphologic-plant-microbe interactions may underlie important patterns of geochemical cycling in arctic systems. Thus, polar desert frost boils should represent a key focus of future investigations of climate change in arctic systems. Abstract Copyright (2020), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2019JG005263
2020028962 Bai Ruiqiang (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Lai Yuanming; You Zhemin and Ren Jingge. Simulation of heat-water-mechanics process in a freezing soil under stepwise freezing: Permafrost and Periglacial Processes, 31(1), p. 200-212, illus. incl. 3 tables, 44 ref., January 2020.
Frost heave is a process coupling heat transfer, water migration, water-ice phase change and deformation. Frost heave forms various landforms, such as frost mounds, ice pitons, sorted polygons and stone circles, and potentially induces a variety of engineering failures, such as building inclination, differential engineering foundation and pavement cracking. To understand the mechanism of frost heave under complex freezing paths, we provide a numerical heat-water-mechanics model that incorporates shrinkage in an unfrozen zone and uses a water content criterion to judge the formation of the ice lens. The model is then used to simulate the moisture, temperature, deformation and ice lens of a freezing soil during stepwise freezing. The simulated results for temperature, displacement and the ice lens are in good agreement with measured data, indicating that the model can be used to describe the heat-water-mechanics process in freezing soils under a complex freezing path. The freezing path determines the soil's water content profile in a manner like that in a stepwise freezing process, where each step produces a water-content peak at the frozen fringe of the step. The model must consider shrinkage of the unfrozen area, or the amount of frost heave would be overestimated and the predicted ice lens would unrealistically be found in the frozen zone. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2028
2020028951 Baral, Prashant (NIIT University, Computer Science and Engineering, Neemrana, India); Haq, Mohd Anul and Yaragal, Shivaprakash. Assessment of rock glaciers and permafrost distribution in Uttarakhand, India: Permafrost and Periglacial Processes, 31(1), p. 31-56, illus. incl. 7 tables, 33 ref., January 2020.
We have compiled an inventory of 1004 rock glaciers for Uttarakhand State, India, using high-resolution satellite data freely available on Google Earth. The inventory is used to analyze the origin, spatial distribution, geometry and dynamics of rock glaciers using a combination of optical remote sensing techniques with a geographic information system (GIS). Results show that development of rock glaciers in this region depends strongly on high elevation (> 4000 m a.s.l.) and slope aspect. Rock glaciers are more dominant towards the southern quadrant (S, SE, SW) than the northern quadrant (N, NE, NW). A large number (n = 608) of small (<0.5 km2) rock glaciers originating from glacial moraine indicates glacial retreat in this region as one of the major causes for the formation of such a large number of rock glaciers. Median elevation of intact rock glaciers indicates that climatic conditions above 4600 m a.s.l. are suitable for the existence of permafrost in this region and that the lower limit of discontinuous permafrost gradually increases from west to east. Despite mean annual air temperatures below 0°C, increasing mean temperatures during warmest quarter of the year could be a strong controlling factor for permafrost thawing in the region. Logistic regression modeling using WorldClim version 2 climate data sets and Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data show that these models can produce fairly reliable estimates of permafrost probability in the studied area. MODIS LST climate data sets can be crucial for mapping and monitoring permafrost in the region. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2008
2020028957 Boisson, Antoine (Université Laval, Centre d'études nordiques, Quebec City, QC, Canada); Allard, Michel and Sarrazin, Denis. Permafrost aggradation along the emerging eastern coast of Hudson Bay, Nunavik (northern Québec, Canada): Permafrost and Periglacial Processes, 31(1), p. 128-140, illus. incl. 1 table, 40 ref., January 2020.
Emerging polar coasts have different geothermal regimes than those in submergence. While the scientific community is mainly concerned with rapidly eroding permafrost coastlines in sedimentary formations where relative sea level is rising, much less research has been dedicated to permafrost dynamics in emergent coastal regions where post-glacial uplift is ongoing. The eastern Hudson Bay coast of Nunavik (northern Québec, Canada) is undergoing glacio-isostatic uplift at a current emergence rate of about 13 mm/yr, outpacing the current global sea-level rise (»3 mm/yr) and progressively exposing new land to climate conditions favorable for permafrost formation. To observe incipient permafrost in the shore zone over time, in 2005 we strategically installed a thermistor cable down to a depth of 23 m at a high-tide level site. We detected the formation and the continuing deepening of permafrost near the surface. Freezing of the ground was also favored by a succession of several cold years in Nunavik since 2010. The near 0°C temperature profile at greater depths also reveals the cooling influence of deep Hudson Bay waters on the shore zone ground temperature regime and the probable presence of subsea permafrost offshore of the measurement site. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2033
2020028955 Eichel, Jana (Karlsruhe Institute of Technology, Institute of Geography and Geoecology, Karlsruhe, Germany); Draebing, Daniel; Kattenborn, Teja; Senn, Johannes Antenor; Klingbeil, Lasse; Wieland, Markus and Heinz, Erik. Unmanned aerial vehicle-based mapping of turf-banked solifluction lobe movement and its relation to material, geomorphometric, thermal and vegetation properties: Permafrost and Periglacial Processes, 31(1), p. 97-109, illus. incl. 1 table, 40 ref., January 2020.
Solifluction is one of the most widespread periglacial processes with low annual movement rates in the range of -millimeters to centimeters. Traditional methods to assess solifluction movement usually have low spatial resolution, which hampers our understanding of spatial movement patterns and the factors controlling them. In this study, we (a) test the applicability of unmanned aerial vehicle (UAV)-based structure-from-motion photogrammetry in comparison to a traditional total station survey to map surface movement of a turf-banked solifluction lobe (TBL) in the Turtmann Valley (Switzerland). We then (b) relate the detected movement patterns to potential geomorphometric, material, thermal and vegetation controls, which we assessed using geomorphic and vegetation mapping, electrical resistivity surveys and temperature loggers. Our results show that (a) UAV-based mapping can detect solifluction movement with high spatial resolution (one point per m2, total > 900 points) and rates and patterns consistent with a total station survey, but requires careful measurement set-up and analysis; and (b) movement rates differ between lobe tread, riser and a ridge feature. Differences can be explained by heterogeneous material, geomorphometric, thermal and vegetation properties of the TBL, which promote different solifluction processes. Our study demonstrates the applicability of UAV-based mapping in solifluction research and improves our understanding of solifluction processes and landform development. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2036
2020028961 Fisher, David A. (University of Ottawa, Department of Earth Sciences, Ottawa, ON, Canada); Lacelle, Denis and Pollard, Wayne. A model of unfrozen water content and its transport in icy permafrost soils; effects on ground ice content and permafrost stability: Permafrost and Periglacial Processes, 31(1), p. 184-199, illus. incl. 3 tables, 26 ref., January 2020.
Knowledge of the amount of unfrozen water and its migration in permafrost soils is important for understanding physico-chemical and biological processes. Here, we developed sub-routines in FREZCHEM and embedded them in the WATEREGO2 soil environmental model to: (a) estimate unfrozen water content under changing soil temperatures and water-ice phase changes; and (b) determine the effects of Van der Waals (VdW) and rheological forces driven by seasonal temperature variations on the transport of residual water and the long-term evolution of ground ice content over depths of 30 m. Together, the seasonal thermal regime and associated VdW and rheological forces on the transport of residual water lead to the evolution of distinct zones of ice-enrichment: near the surface of permafrost, at 3-5 m, 11-13 m and 17-19 m depth. The depths of ice enrichment are a function of soil thermal diffusivity, and the time needed to evolve the ground ice content is dependent on soil type, soil water chemistry and permafrost temperature. The model can explain observed variations with depth in ground ice content of icy permafrost soils and indicate that these conditions evolve over time. The findings can be used to assess the stability of permafrost to climate change under different temperature scenarios. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2031
2020028953 Gagnon, Samuel (Université Laval, Centre d'études nordiques, Quebec City, QC, Canada) and Allard, Michel. Changes in ice-wedge activity over 25 years of climate change near Salluit, Nunavik (northern Québec, Canada): Permafrost and Periglacial Processes, 31(1), p. 69-84, illus. incl. 4 tables, 44 ref., January 2020.
To assess the direct impact of climate change on ice-wedge (IW) degradation, 16 sites in the Narsajuaq river valley (Nunavik, Canada) that were extensively studied between 1989 and 1991 were revisited in 2016, 2017 and 2018. In total, 109 pits were dug to record soil characteristics and IW shapes and depths. Changes in surface conditions were also noted using side-by-side comparisons of recent (2017) and older (1989-1991) land and aerial photographs. During the past 25 years, the active layer reached depths that were 1.2-3.4 times deeper than in 1991, which led to the widespread degradation of IWs in the valley. Whereas 94% of the IWs unearthed in 1991 showed multiple recent growth structures, only 13% of the 55 IWs unearthed in 2017 still had some upgrowth stages left. IW tops are now consistently deeper than the main stages of the IWs measured in 1991. In August 2017, however, about half of the IWs had ice veins connecting them to the base of the active layer, an indication that the recent cooling spell (2010 to present) in the region was enough to reactivate frost cracking and IW growth. This paper highlights how sensitive the Arctic soil system can be to short-term climate variations. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2030
2020028954 Holloway, Jean E. (University of Ottawa, Department of Geography, Environment and Geomatics, Ottawa, ON, Canada) and Lewkowicz, Antoni G. Half a century of discontinuous permafrost persistence and degradation in Western Canada: Permafrost and Periglacial Processes, 31(1), p. 85-96, illus. incl. 3 tables, 33 ref., January 2020.
Long-term field studies of permafrost change are needed to validate predictive models but few are possible because of a paucity of direct observations prior to the late 1970s. To help fill this knowledge gap, we resurveyed a transect of 68 sites, originally investigated in 1962, to evaluate change in the isolated patches and sporadic discontinuous permafrost zones between Keg River, Alberta (57.8°N) and Hay River, Northwest Territories (60.8°N). The goal was to establish the degree of permafrost degradation due to approximately 2°C of regional climate warming over the intervening 55 years, compounded at some sites by forest fire. By 2017-2018, permafrost had degraded at 36% of the 44 sites which exhibited it in 1962, but had persisted at a minimum of 50% with a further 14% potentially retaining permafrost. This is much less degradation than reported for a 1988-1989 survey of the same transect. Permafrost was maintained under thicker organic layers (86% > 40 cm) and at the majority of sites with fine-grained substrates, while degradation occurred preferentially at sites with coarse soils and thinner organic layers. Forest fire did not enhance the degree of permafrost loss, but greater frost table depths were observed at some burned locations. This study demonstrates that while the trajectory of change is towards permafrost loss, thin permafrost in the discontinuous zone can be persistent, even when disturbed. It also underlines the importance of considering the range of landscape types when projecting the rate of future permafrost thaw. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2017
2020028958 Hrbacek, Filip (Masaryk University, Department of Geography, Brno, Czech Republic) and Uxa, Tomas. The evolution of a near-surface ground thermal regime and modeled active-layer thickness on James Ross Island, eastern Antarctic Peninsula, in 2006-2016: Permafrost and Periglacial Processes, 31(1), p. 141-155, illus. incl. 5 tables, 43 ref., January 2020.
Thermal regime and thickness of the active layer respond rapidly to climate variations, and thus they are important measures of cryosphere changes in polar environments. We monitored air temperature and ground temperature at a depth of 5 cm and modeled active-layer thickness using the Stefan and Kudryavtsev models at the Abernethy Flats site, James Ross Island, Eastern Antarctic Peninsula, in the period March 2006 to February 2016. The decadal average of air and ground temperature was -7.3 and -6.1°C, respectively, and the average modeled active-layer thickness reached 60 cm. Mean annual air temperature increased by 0.10°C y-1 over the study period, while mean annual ground temperature showed the opposite tendency of -0.05°C y-1. The cooling took place mainly in summer and caused thawing season shortening and active-layer thinning of 1.6 cm y-1. However, these trends need to be taken carefully because all were non-significant at p < 0.05. The Stefan and Kudryavtsev models reproduced the active-layer thickness with mean absolute errors of 2.6 cm (5.0%) and 3.4 cm (5.9%), respectively, which is better than in most previous studies, making them promising tools for active-layer modeling over Antarctica. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2018
2020028956 Jones, Benjamin M. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Arp, Christopher D.; Grosse, Guido; Nitze, Ingmar; Lara, Mark J.; Whitman, Matthew S.; Farquharson, Louise M.; Kanevskiy, Mikhail; Parsekian, Andrew D.; Breen, Amy L.; Ohara, Nori; Rangel, Rodrigo Correa and Hinkel, Kenneth M. Identifying historical and future potential lake drainage events on the western Arctic Coastal Plain of Alaska: Permafrost and Periglacial Processes, 31(1), p. 110-127, illus. incl. 4 tables, 32 ref., January 2020.
Arctic lakes located in permafrost regions are susceptible to catastrophic drainage. In this study, we reconstructed historical lake drainage events on the western Arctic Coastal Plain of Alaska between 1955 and 2017 using USGS topographic maps, historical aerial photography (1955), and Landsat Imagery (ca. 1975, ca. 2000, and annually since 2000). We identified 98 lakes larger than 10 ha that partially (>25% of area) or completely drained during the 62-year period. Decadal-scale lake drainage rates progressively declined from 2.0 lakes/yr (1955-1975), to 1.6 lakes/yr (1975-2000), and to 1.2 lakes/yr (2000-2017) in the »30,000-km2 study area. Detailed Landsat trend analysis between 2000 and 2017 identified two years, 2004 and 2006, with a cluster (five or more) of lake drainages probably associated with bank overtopping or headward erosion. To identify future potential lake drainages, we combined the historical lake drainage observations with a geospatial dataset describing lake elevation, hydrologic connectivity, and adjacent lake margin topographic gradients developed with a 5-m-resolution digital surface model. We identified »1900 lakes likely to be prone to drainage in the future. Of the 20 lakes that drained in the most recent study period, 85% were identified in this future lake drainage potential dataset. Our assessment of historical lake drainage magnitude, mechanisms and pathways, and identification of potential future lake drainages provides insights into how arctic lowland landscapes may change and evolve in the coming decades to centuries. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2038
2020028950 Marcer, Marco (Université Grenoble Alpes, Institut d'Urbanisme et Gèographie Alpine, Grenoble, France); Ringso Nielsen, Steffen; Ribeyre, Charles; Kummert, Mario; Duvillard, Pierre-Allain; Schoeneich, Philippe; Bodin, Xavier and Genuite, Kim. Investigating the slope failures at the Lou rock glacier front, French Alps: Permafrost and Periglacial Processes, 31(1), p. 15-30, illus. incl. 1 table, 33 ref., January 2020.
On August 14th 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three-week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast-moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2035
2020028963 Ming Feng (Chinese Academy of Sciences, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Li Dongqing and Liu Yuhang. A predictive model of unfrozen water content including the influence of pressure: Permafrost and Periglacial Processes, 31(1), p. 213-222, illus., 40 ref., January 2020.
Unfrozen water content has strong control on the permeability, strength and thermal properties of frozen soil. Several techniques have been used to measure unfrozen water content in frozen soil and many models have been developed for its prediction. However, there has been little investigation on the quantitative analysis of the relationship between pressure and unfrozen water content. With the development of artificial ground freezing techniques and deep mining, knowledge of unfrozen water content in frozen soil under high pressure is critical to the stability of the frozen structures. Here, a new predictive model is presented based on the relationship between chemical potential and unfrozen water content and a previous empirical formula. The simulation results are in good agreement with those from laboratory tests. Both the theoretical analysis and the test results indicated that: (a) the pressure applied to frozen soil reduces the freezing point of bulk water and delays the phase change, and (b) unfrozen water content increases with increasing pressure, and at higher pressures the change is greater. The results improve our understanding of the physical and mechanical properties of freezing soil under pressure for artificial ground freezing applications and deep mining engineering. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2037
2020028964 Pastor, Ada (Aarhus University, Department of Bioscience, Aarhus, Denmark); Poblador, Sílvia; Skovsholt, Louis J. and Riis, Tenna. Microbial carbon and nitrogen processes in High-Arctic riparian soils: Permafrost and Periglacial Processes, 31(1), p. 223-236, illus. incl. 4 tables, 32 ref., January 2020.
The aim of this work was to assess the biogeochemical role of riparian soils in the High Arctic to determine to what extent these soils may act as sources or sinks of carbon (C) and nitrogen (N). To do so, we compared two riparian areas that varied in riparian vegetation coverage and soil physical perturbation (i.e., thermo-erosion gully) in NE Greenland (74°N) during late summer. Microbial soil respiration (0.4-3.2 mmol CO2 m-2 s-1) was similar to values previously found across vegetation types in the same area and increased with higher temperatures, soil column depth and soil organic C degradation. Riparian soils had low nitrate concentrations (0.02-0.64 mg N-NO3- g-1), negligible net nitrification rates and negative net N mineralization rates (-0.58 to 0.33 mg N g-1 day-1), thus indicating efficient microbial N uptake due to low N availability. We did not find any effects of physical perturbation on soil respiration or on N processing, but the dissolved fraction of organic matter in the soil was one order of magnitude lower on the disturbed site. Overall, our results suggest that riparian soils are small N sources to high-Arctic streams and that a depleted dissolved organic C pool in disturbed soils may decrease exports to the adjacent streams under climate change projection. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2039
2020028959 Sun Zhe (Chinese Academy of Sciences, Cryosphere Research Station on the Qinghai-Tibetan Plateau, Lanzhou, China); Zhao Lin; Hu Guojie; Qiao Yongping; Du Erji; Zou Defu and Xie Changwei. Modeling permafrost changes on the Qinghai-Tibetan Plateau from 1966 to 2100; a case study from two boreholes along the Qinghai-Tibet engineering corridor: Permafrost and Periglacial Processes, 31(1), p. 156-171, illus. incl. 3 tables, January 2020.
Warming permafrost on a global scale is projected to have significant impacts on engineering, hydrology and environmental quality. Greater warming trends are predicted on the Qinghai-Tibetan Plateau (QTP), but most models for mountain permafrost have not considered the effects of water phase change and the state of deep permafrost due to a lack of detailed information. To better understand historical and future permafrost change based on in situ monitoring and field investigations, a numerical heat conduction permafrost model was introduced which differentiated the frozen and thawed state of soil, and considered unfrozen water content in frozen soil, distribution of ground ice and geothermal heat flow. Simulations were conducted at two sites with validation by long-term monitoring of ground temperature data. After forcing with reconstructed historical ground surface temperature series starting from 1966, the model predicted permafrost changes until 2100 under different RCP scenarios. The results indicate a slow thermal response of permafrost to climate warming at the two investigated sites. Even under the most radical warming scenario (RCP8.5), deepening of the permafrost table is not obvious before 2040. At both sites, the model indicates that shallow permafrost may disappear but deep permafrost may persist by 2100. Moreover, the simulation shows that the degradation modes may differ between zones of discontinuous and continuous permafrost. The main degradation mode of the site in the discontinuous zone appears to be upward thawing from the permafrost base, while that of the site in the continuous zone is downward thawing at the permafrost table with little change at the permafrost base. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2022
2020028952 Vergara dal Pont, Iván (Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Mendoza, Argentina); Moreiras, Stella Maris; Santibañez Ossa, Fernanda; Araneo, Diego and Ferrando, Francisco. Debris flows triggered from melt of seasonal snow and ice within the active layer in the semi-arid Andes: Permafrost and Periglacial Processes, 31(1), p. 57-68, illus. incl. 2 tables, 22 ref., January 2020.
Debris flows triggered from rapid melt of seasonal snow, and/or ice within the active layer have not been studied in periglacial areas of the semi-arid Andes. Therefore, through a representative watershed we investigated the thermo-radiative characteristics, possible water sources, and current and future frequency of these debris flows. Information was collected on three temporal clusters of debris flows during which no rains or major earthquakes occurred. The thermo-radiative conditions of each cluster were analyzed through nearby stations that cover the entire watershed altitudinal range. Snow cover was calculated using the closest satellite images before and after each cluster in order to evaluate the potential contribution of snowmelt for each. The frequency of melting-driven debris flows, for the remainder of the 21st century, was evaluated by calculating the trends of climatic variables that control them. The results indicate that debris flows show several patterns such as: a lag of several hours between the warmest hours of the day and their triggering, occurrence in clusters of 3-5 days during the early summer, and an accelerated increase in temperature over the days previous to the beginning of the clusters. In addition, it was inferred that the water of debris flows can come from the melt of seasonal snow as well as of shallow ice within the active layer. Lastly, due to a positive trend of maximum air temperature of the warmest trimester and high inter-annual variability of precipitation, a frequency increase is likely, followed by a possible decrease due to the negative and positive trends of precipitation and mean air temperature, respectively. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2020
2020028960 Wu Qingbai (Chinese Academy of Sciences, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Zhao Hongting; Zhang Zhongqiong; Chen Ji and Liu Yongzhi. Long-term role of cooling the underlying permafrost of the crushed rock structure embankment along the Qinghai-Xizang Railway: Permafrost and Periglacial Processes, 31(1), p. 172-183, illus. incl. 3 tables, 32 ref., January 2020.
Understanding the long-term role of cooling the underlying permafrost of the crushed rock structure embankment (CRSE) along the Qinghai-Xizang Railway (QXR) is crucial for the railway's safe operation. The thermal regime of the permafrost under the CRSE is analyzed here using monitoring data of soil temperature from 2005 to 2015. The results show that the CRSE plays an important long-term role in cooling the underlying permafrost under the present climate change conditions; however, different types of CRSEs have different cooling effects. A U-shaped crushed rock embankment and a crushed rock berm embankment with debris rock revetment can maintain the cooling of the permafrost underlying the embankment under a future climate warming of 1.0°C. Moreover, under an increase in air temperature of 0.5°C, a crushed-based rock embankment and a crushed rock revetment embankment can maintain the cooling of the underlying permafrost when its mean annual ground temperature is below -1.0°C. The long-term role of cooling the underlying permafrost of CRSEs indicates that the QXR must use reinforcing engineering techniques to ensure its safe operation and adaptation to a temperature increase of 1.5°C. Abstract Copyright (2020), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.2027
2020028948 Fan Wenhu (Nanjing Forestry University, School of Civil Engineering, Nanjing, China); Yang Ping and Yang, Zhaohui. Impact of freeze-thaw on the physical properties and compressibility of saturated clay: Cold Regions Science and Technology, 168, Paper no. 102873, illus. incl. 4 tables, December 2019.
Artificial ground freezing (AGF) has been widely applied in underground construction and ground deformation, particularly, thaw settlement, induced by AGF are of great concerns in soft soils. This paper describes an apparatus for simulating unidirectional freezing with or without water supply and presents the variations in physical characteristics including moisture content, void ratio, and dry density of saturated clay due to freeze-thaw (F-T) under different overburden pressure and water supply conditions. Further, consolidation tests were carried out to study the change in compressibility parameter along the specimen height due to F-T. It was found that the soil index properties and consolidation parameters including the pre-consolidation pressure and compression and swell indices change significantly due to F-T and the changes are not uniform in the unfrozen and frozen zones. For F-T under an overburden pressure with water supply, the pre-consolidation pressure increases in both the unfrozen and frozen zones. It was also found that the increase in the pre-consolidation pressure is almost proportional to the overburden pressure in the unfrozen zone but is largely insensitive to the overburden pressure in the frozen zone. Furthermore. This study demonstrates that F-T triggers a re-consolidation in clays that is significant for cases where large overburden pressure is present during ground freezing and further study is needed to understand the mechanisms responsible for these changes, and how sample preparation methods, freezing methods and temperatures, and soil index properties may affect soil compressibility, and how to estimate the settlement post F-T.
DOI: 10.1016/j.coldregions.2019.102873
2020028942 Ren, Junping (University of Ottawa, Department of Civil Engineering, Ottawa, ON, Canada); Vanapalli, Sai K.; Han Zhong; Omenogor, Kenneth O. and Bai, Yu. The resilient moduli of five Canadian soils under wetting and freeze-thaw conditions and their estimation by using an artificial neural network model: Cold Regions Science and Technology, 168, Paper no. 102894, illus. incl. 6 tables, December 2019.
The resilient modulus (MR) is a key parameter used in the mechanistic-empirical methods for the rational design of pavement structures. In permafrost and seasonally frozen regions, the MR of subgrade soils is significantly influenced by the variations in moisture content and temperature. The MR typically reduces due to the weathering action associated with wetting and freeze-thaw (F-T) cycles, which contributes to the reorientation of soil particles, loss in suction and cohesion, and formation of cracks in the subgrade soils. In the present study, the MR values of five Canadian soils that are widely used as pavement subgrades were determined under wetting and F-T conditions. The key findings from the extensive experimental investigation suggest: (i) the MR values of the soils at their respective optimum water contents significantly reduce up to the critical F-T cycle, which is typically the first or second F-T cycles; (ii) there is little change in the MR values from the critical to the tenth F-T cycle; (iii) the percentage of reduction in the measured MR at the optimum water content after the critical F-T cycle is strongly related to the soils plasticity index; (iv) the measured MR values are typically low for the specimens subjected to wetting, and the effect of F-T cycles on these specimens is insignificant; and (v) the effect of stress levels on the MR values is dependent on the initial water contents of the specimens and soil types. In addition, an artificial neural network (ANN) model was proposed and validated for estimating the MR of the tested soils taking account of various influencing factors. Both the experimental data and the developed ANN model provide valuable information for the rational design of pavements in Canada.
DOI: 10.1016/j.coldregions.2019.102894
2020027193 O'Connor, Michael T. (University of Texas at Austin, Department of Geological Sciences, Austin, TX); Cardenas, M. Bayani; Neilson, Bethany T.; Nicholaides, Kindra D. and Kling, George W. Active layer groundwater flow; the interrelated effects of stratigraphy, thaw, and topography: Water Resources Research, 55(8), p. 6555-6576, illus. incl. 2 tables, sketch map, 62 ref., August 2019.
The external drivers and internal controls of groundwater flow in the thawed "active layer" above permafrost are poorly constrained because they are dynamic and spatially variable. Understanding these controls is critical because groundwater can supply solutes such as dissolved organic matter to surface water bodies. We calculated steady-state three-dimensional suprapermafrost groundwater flow through the active layer using measurements of aquifer geometry, saturated thickness, and hydraulic properties collected from two major landscape types over time within a first-order Arctic watershed. The depth position and thickness of the saturated zone is the dominant control of groundwater flow variability between sites and during different times of year. The effect of water table depth on groundwater flow dwarfs the effect of thaw depth. In landscapes with low land-surface slopes (2-4%), a combination of higher water tables and thicker, permeable peat deposits cause relatively constant groundwater flows between the early and late thawed seasons. Landscapes with larger land-surface slopes (4-10%) have both deeper water tables and thinner peat deposits; here the commonly observed permeability decrease with depth is more pronounced than in flatter areas, and groundwater flows decrease significantly between early and late summer as the water table drops. Groundwater flows are also affected by microtopographic features that retain groundwater that could otherwise be released as the active layer deepens. The dominant sources of groundwater, and thus dissolved organic matter, are likely wet, flatter regions with thick organic layers. This finding informs fluid flow and solute transport dynamics for the present and future Arctic. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018WR024636
2020027148 Bayer, Tina K. (Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden); Gustafsson, Erik; Brakebusch, M. and Beer, Christian. Future carbon emission from boreal and permafrost lakes are sensitive to catchment organic carbon loads: Journal of Geophysical Research: Biogeosciences, 124(7), p. 1827-1848, illus. incl. 1 table, 115 ref., July 2019.
Carbon storage, processing, and transport in freshwater systems are important components of the global carbon cycle and sensitive to global change. However, in large-scale modeling this part of the boundless carbon cycle is often lacking or represented in a very simplified way. A new process-oriented lake biogeochemical model is used for investigating impacts of changes in atmospheric CO2 concentrations and organic carbon loading from the catchment on future greenhouse gas emissions from lakes across two boreal to subarctic regions (Northern Sweden and Alaska). Aquatic processes represented include carbon, oxygen, phytoplankton, and nutrient dynamics leading to CO2 and CH4 exchanges with the atmosphere. The model is running inside a macroscale hydrological model and may be easily implemented into a land surface scheme. Model evaluation demonstrates the validity in terms of average concentration of nutrients, algal biomass, and organic and inorganic carbon. Cumulative annual emissions of CH4 and CO2, as well as pathways of CH4 emissions, also compare well to observations. Model calculations imply that lake emissions of CH4 may increase by up to 45% under the Representative Concentration Pathway 8.5 scenario until 2100, and CO2 emissions may increase by up to 80% in Alaska. Increasing organic carbon loading to the lakes resulted in a linear response in CO2 and CH4 emissions across both regions, but increases in CO2 emissions from subarctic lakes in Sweden were lower than for southern boreal lakes, probably due to the higher importance of imported vegetation-"generated" inorganic carbon for CO2 emission from subarctic lakes. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2018JG004978
2020027157 Burke, Sophie A. (University of New Hampshire, Institute for the Study of Earth, Oceans, and Space, Durham, NH); Wik, Martin; Lang, Ashley; Contosta, Alexandra R.; Palace, Michael; Crill, Patrick M. and Varner, Ruth K. Long-term measurements of methane ebullition from thaw ponds: Journal of Geophysical Research: Biogeosciences, 124(7), p. 2208-2221, illus. incl. 3 tables, 67 ref., July 2019.
Arctic regions are experiencing rapid warming, leading to permafrost thaw and formation of numerous water bodies. Although small ponds in particular are considered hot spots for methane (CH4) release, long-term studies of CH4 efflux from these surfaces are rare. We have collected an extensive data set of CH4 ebullition (bubbling) measurements from eight small thaw ponds (<0.001 km2) with different physical and hydrological characteristics over four summer seasons, the longest set of observations from thaw ponds to date. The measured fluxes were highly variable with an average of 20.0 mg CH4.m-2.day-1 (median: 4.1 mg CH4.m-2.day-1, n=2,063) which is higher than that of most nearby lakes. The ponds were categorized into four types based on clear and significant differences in bubble flux. We found that the amount of CH4 released as bubbles from ponds was very weakly correlated with environmental variables, like air temperature and atmospheric pressure, and was potentially more related to differences in physical characteristics of the ponds. Using our measured average daily bubble flux plus the available literature, we estimate circumpolar thaw ponds <0.001 km2 in size to emit between 0.2 and 1.0 Tg of CH4 through ebullition. Our findings exemplify the importance of high-frequency measurements over long study periods in order to adequately capture the variability of these water bodies. Through the expansion of current spatial and temporal monitoring efforts, we can increase our ability to estimate CH4 emissions from permafrost pond ecosystems now and in the future. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004786
2020027153 Heslop, Joanne K. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Winkel, Matthias; Walter Anthony, K. M.; Spencer, Robert G. M.; Podgorski, D. C.; Zito, P.; Kholodov, A.; Zhang, M. and Liebner, Susanne. Increasing organic carbon biolability with depth in yedoma permafrost; ramifications for future climate change: Journal of Geophysical Research: Biogeosciences, 124(7), p. 2021-2038, illus. incl. 2 tables, 89 ref., July 2019.
Permafrost thaw subjects previously frozen organic carbon (OC) to microbial decomposition, generating the greenhouse gases (GHG) carbon dioxide (CO2) and methane (CH4) and fueling a positive climate feedback. Over one quarter of permafrost OC is stored in deep, ice-rich Pleistocene-aged yedoma permafrost deposits. We used a combination of anaerobic incubations, microbial sequencing, and ultrahigh-resolution mass spectrometry to show yedoma OC biolability increases with depth along a 12-m yedoma profile. In incubations at 3°C and 13°C, GHG production per unit OC at 12- versus 1.3-m depth was 4.6 and 20.5 times greater, respectively. Bacterial diversity decreased with depth and we detected methanogens at all our sampled depths, suggesting that in situ microbial communities are equipped to metabolize thawed OC into CH4. We concurrently observed an increase in the relative abundance of reduced, saturated OC compounds, which corresponded to high proportions of C mineralization and positively correlated with anaerobic GHG production potentials and higher proportions of OC being mineralized as CH4. Taking into account the higher global warming potential (GWP) of CH4 compared to CO2, thawed yedoma sediments in our study had 2 times higher GWP at 12- versus 9.0-m depth at 3°C and 15 times higher GWP at 13°C. Considering that yedoma is vulnerable to processes that thaw deep OC, our findings imply that it is important to account for this increasing GHG production and GWP with depth to better understand the disproportionate impact of yedoma on the magnitude of the permafrost carbon feedback. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004712
2020025624 James, Stephanie R. (University of Florida, Department of Geological Sciences, Gainesville, FL); Knox, Hunter A.; Abbott, Robert E.; Panning, Mark P. and Screaton, Elizabeth J. Insights into permafrost and seasonal active-layer dynamics from ambient seismic noise monitoring: Journal of Geophysical Research: Earth Surface, 124(7), p. 1798-1816, illus. incl. sects., sketch maps, 70 ref., July 2019.
Widespread permafrost thaw in response to changing climate conditions has the potential to dramatically impact ecosystems, infrastructure, and the global carbon budget. Ambient seismic noise techniques allow passive subsurface monitoring that could provide new insights into permafrost vulnerability and active-layer processes. Using nearly 2 years of continuous seismic data recorded near Fairbanks, Alaska, we measured relative velocity variations that showed a clear seasonal cycle reflecting active-layer freeze and thaw. Relative to January 2014, velocities increased up to 3% through late spring, decreased to -8% by late August, and then gradually returned to the initial values by the following winter. Velocities responded rapidly (over ~2 to 7 days) to discrete hydrologic events and temperature forcing and indicated that spring snowmelt and infiltration events from summer rainfall were particularly influential in propagating thaw across the site. Velocity increases during the fall zero-curtain captured the refreezing process and incremental ice formation. Looking across multiple frequency bands (3-30 Hz), negative relative velocities began at higher frequencies earlier in the summer and then shifted lower when active-layer thaw deepened, suggesting a potential relationship between frequency and thaw depth; however, this response was dependent on interstation distance. Bayesian tomography returned 2-D time-lapse images identifying zones of greatest velocity reduction concentrated in the western side of the array, providing insight into the spatial variability of thaw progression, soil moisture, and drainage. This study demonstrates the potential of passive seismic monitoring as a new tool for studying site-scale active-layer and permafrost thaw processes at high temporal and spatial resolution. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2019JF005051
2020027088 Farquharson, Louise M. (University of Alaska Fairbanks, Geophysical Institute Permafrost Laboratory, Fairbanks, AK); Romanovsky, Vladimir E.; Cable, William L.; Walker, Donald A.; Kokelj, Steven V. and Nicolsky, Dmitry. Climate change drives widespread and rapid thermokarst development in very cold permafrost in the Canadian High Arctic: Geophysical Research Letters, 46(12), p. 6681-6689, illus. incl. sketch map, 36 ref., June 28, 2019.
Climate warming in regions of ice-rich permafrost can result in widespread thermokarst development, which reconfigures the landscape and damages infrastructure. We present multisite time series observations which couple ground temperature measurements with thermokarst development in a region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously warm summers caused mean thawing indices to be 150-240% above the 1979-2000 normal resulting in up to 90 cm of subsidence over the 12-year observation period. Our data illustrate that despite low mean annual ground temperatures, very cold permafrost (<-10°C) with massive ground ice close to the surface is highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due to little thermal buffering from soil organic layers and near-surface vegetation, and the presence of near-surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090 under representative concentration pathway version 4.5. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2019GL082187
2020022052 Overduin, Paul P. (Alfred Wegener Institute, Centre for Polar and Marine Research, Potsdam, Germany); Schneider von Deimling, T.; Miesner, Frederieke; Grigoriev, Mikhail N.; Ruppel, Carolyn; Vasiliev, Alexander; Lantuit, Hugues; Juhls, Bennet and Westermann, Sebastian. Submarine permafrost map in the Arctic modeled using 1-D transient heat flux (SuPerMAP): Journal of Geophysical Research: Oceans, 124(6), p. 3490-3507, illus. incl. 2 tables, sketch map, 100 ref., June 2019.
Offshore permafrost plays a role in the global climate system, but observations of permafrost thickness, state, and composition are limited to specific regions. The current global permafrost map shows potential offshore permafrost distribution based on bathymetry and global sea level rise. As a first-order estimate, we employ a heat transfer model to calculate the subsurface temperature field. Our model uses dynamic upper boundary conditions that synthesize Earth System Model air temperature, ice mass distribution and thickness, and global sea level reconstruction and applies globally distributed geothermal heat flux as a lower boundary condition. Sea level reconstruction accounts for differences between marine and terrestrial sedimentation history. Sediment composition and pore water salinity are integrated in the model. Model runs for 450 ka for cross-shelf transects were used to initialize the model for circumarctic modeling for the past 50 ka. Preindustrial submarine permafrost (i.e., cryotic sediment), modeled at 12.5-km spatial resolution, lies beneath almost 2.5´106 km2 of the Arctic shelf. Our simple modeling approach results in estimates of distribution of cryotic sediment that are similar to the current global map and recent seismically delineated permafrost distributions for the Beaufort and Kara seas, suggesting that sea level is a first-order determinant for submarine permafrost distribution. Ice content and sediment thermal conductivity are also important for determining rates of permafrost thickness change. The model provides a consistent circumarctic approach to map submarine permafrost and to estimate the dynamics of permafrost in the past. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JC014675
2020028360 Kulikov, Anatoly (Russian Academy of Sciences, Siberian Branch, Institute of General and Experimental Biology, Ulan-Ude, Russian Federation); Badmaev, Nimazhap; Sympilova, Darima and Gyninova, Ayur. The use of the value of heat cycle to assess the energy stability of permafrost soils at the change of conditions on the surface: Geosciences (Basel), 9(3), Article 112, illus. incl. 3 tables, 17 ref., March 2019. This article belongs to the special issue Permafrost landscapes; classification and mapping.
The basis for assessing the stability of geosystems to changes in external heat cycle conditions is the calculation method. It is shown that permafrost soils are characterized by increased values of annual heat cycle QY>&eq;300 MJ/m2, i.e., half-sum of heat arrival and flow rate per year. This is due to the high heat consumption for melting soils (QPh=0.7-0.8 QY) and warming them in the negative temperature range (QF). The heat cycle in frozen soil (QF) always has more heat cycle than in the thawed soil (QH). The condition QF>QH means the dominance of processes occurring at negative temperature, and the difference QF-QH is a quantitative assessment of the energy stability of soils to changes in heat exchange conditions on the surface.
DOI: 10.3390/geosciences9030112
2020028325 Chuvilin, Evgeny (Skolkovo Institute of Science and Technology, Innovation Center Skolkovo, Moscow, Russian Federation) and Bukhanov, Boris. Thermal conductivity of frozen sediments containing self-preserved pore gas hydrates at atmospheric pressure; an experimental study: Geosciences (Basel), 9(2), Article no. 65, illus. incl. 5 tables, 57 ref., February 2019. This article belongs to the special issue Gas and gas hydrate in permafrost.
The paper presents the results of an experimental thermal conductivity study of frozen artificial and natural gas hydrate-bearing sediments at atmospheric pressure (0.1 MPa). Samples of hydrate-saturated sediments are highly stable and suitable for the determination of their physical properties, including thermal conductivity, due to the self-preservation of pore methane hydrate at negative temperatures. It is suggested to measure the thermal conductivity of frozen sediments containing self-preserved pore hydrates by a KD-2 needle probe which causes very little thermal impact on the samples. As shown by the special measurements of reference materials with known thermal conductivities, the values measured with the KD-2 probe are up to 20% underestimated and require the respective correction. Frozen hydrate-bearing sediments differ markedly in thermal conductivity from reference frozen samples of the same composition but free from pore hydrate. The difference depends on the physical properties of the sediments and on changes in their texture and structure associated with the self-preservation effect. Namely, it increases proportionally to the volumetric hydrate content, hydrate saturation, and the percentage of water converted to hydrate. Thermal conductivity is anisotropic in core samples of naturally frozen sediments that enclose visible ice-hydrate lenses and varies with the direction of measurements with respect to the lenses. Thermal conductivity measurements with the suggested method provide a reliable tool for detection of stable and relict gas hydrates in permafrost.
DOI: 10.3390/geosciences9020065
2020028315 Kraev, Gleb (Russian Academy of Sciences, Institute of Physicochemical and Biological Issues in Soil Science, Pushchino, Russian Federation); Rivkina, Elizaveta; Vishnivetskaya, Tatiana; Belonosov, Andrei; van Huissteden, Jacobus; Kholodov, Alexander; Smirnov, Alexander; Kudryavtsev, Anton; Teshebaeva, Kanayim and Zamolodchikov, Dmitrii. Methane in gas shows from boreholes in epigenetic permafrost of Siberian Arctic: Geosciences (Basel), 9(2), Article no. 67, illus. incl. 3 tables, strat. cols., 33 ref., February 2019. This article belongs to the special issue Gas and gas hydrate in permafrost.
The gas shows in the permafrost zone represent a hazard for exploration, form the surface features, and are improperly estimated in the global methane budget. They contain methane of either surficial or deep-Earth origin accumulated earlier in the form of gas or gas hydrates in lithological traps in permafrost. From these traps, it rises through conduits, which have tectonic origin or are associated with permafrost degradation. We report methane fluxes from 20-m to 30-m deep boreholes, which are the artificial conduits for gas from permafrost in Siberia. The dynamics of degassing the traps was studied using static chambers, and compared to the concentration of methane in permafrost as analyzed by the headspace method and gas chromatography. More than 53 g of CH4 could be released to the atmosphere at rates exceeding 9 g of CH4 m-2 s-1 from a trap in epigenetic permafrost disconnected from traditional geological sources over a period from a few hours to several days. The amount of methane released from a borehole exceeded the amount of the gas that was enclosed in large volumes of permafrost within a diameter up to 5 meters around the borehole. Such gas shows could be by mistake assumed as permanent gas seeps, which leads to the overestimation of the role of permafrost in global warming.
DOI: 10.3390/geosciences9020067
2020023219 Wang Yinghui (Shanghai Ocean University, Shanghai Engineering Research Center of Hadal Science and Technology, Shanghai, China); Spencer, Robert G. M.; Podgorski, David C.; Kellerman, Anne M.; Rashid, Harunur; Zito, Phoebe; Xiao Wenjie; Wei Dandan; Yang Yuanhe and Xu Yunping. Spatiotemporal transformation of dissolved organic matter along an alpine stream flow path on the Qinghai-Tibet Plateau; importance of source and permafrost degradation: Biogeosciences, 15(21), p. 6637-6648, illus. incl. 2 tables, 61 ref., November 2018.
The Qinghai-Tibet Plateau (QTP) accounts for approximately 70% of global alpine permafrost and is an area sensitive to climate change. The thawing and mobilization of ice-rich and organic-carbon-rich permafrost impact hydrologic conditions and biogeochemical processes on the QTP. Despite numerous studies of Arctic permafrost, there are no reports to date for the molecular-level in-stream processing of permafrost-derived dissolved organic matter (DOM) on the QTP. In this study, we examine temporal and spatial changes of DOM along an alpine stream (3850-3207 m above sea level) by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), accelerator mass spectrometry (AMS) and UV-visible spectroscopy. Compared to downstream sites, dissolved organic matter (DOM) at the headstream site exhibited older radiocarbon age, higher mean molecular weight, higher aromaticity and fewer highly unsaturated compounds. At the molecular level, 6409 and 1345 formulas were identified as unique to the active layer (AL) leachate and permafrost layer (PL) leachate, respectively. Comparing permafrost leachates to the downstream site, 59% of AL-specific formulas and 90% of PL-specific formulas were degraded, likely a result of rapid in-stream degradation of permafrost-derived DOM. From peak discharge in the summer to low flow in late autumn, the DOC concentration at the headstream site decreased from 13.9 to 10.2 mg L-1, while the 14C age increased from 745 to 1560 years before present (BP), reflecting an increase in the relative contribution of deep permafrost carbon due to the effect of changing hydrological conditions over the course of the summer on the DOM source (AL vs. PL). Our study thus demonstrates that hydrological conditions impact the mobilization of permafrost carbon in an alpine fluvial network, the signature of which is quickly lost through in-stream mineralization and transformation.
DOI: 10.5194/bg-15-6637-2018
2020023218 Zheng, Jianqiu (Oak Ridge National Laboratory, Biosciences Division, Oak Ridge, TN); RoyChowdhury, Taniya; Yang, Ziming; Gu, Baohua; Wullschleger, Stan D. and Graham, David E. Impacts of temperature and soil characteristics on methane production and oxidation in Arctic tundra: Biogeosciences, 15(21), p. 6621-6635, illus., 65 ref., November 2018.
Rapid warming of Arctic ecosystems accelerates microbial decomposition of soil organic matter and leads to increased production of carbon dioxide (CO2) and methane (CH4). CH4 oxidation potentially mitigates CH4 emissions from permafrost regions, but it is still highly uncertain whether soils in high-latitude ecosystems will function as a net source or sink for CH4 in response to rising temperature and associated hydrological changes. We investigated CH4 production and oxidation potential in permafrost-affected soils from degraded ice-wedge polygons on the Barrow Environmental Observatory, Utqiagvik (Barrow), Alaska, USA. Frozen soil cores from flat and high-centered polygons were sectioned into organic, transitional, and permafrost layers, and incubated at -2, +4 and +8 °C to determine potential CH4 production and oxidation rates. Significant CH4 production was only observed from the suboxic transition layer and permafrost of flat-centered polygon soil. These two soil sections also exhibited highest CH4 oxidation potentials. Organic soils from relatively dry surface layers had the lowest CH4 oxidation potential compared to saturated transition layer and permafrost, contradicting our original assumptions. Low methanogenesis rates are due to low overall microbial activities measured as total anaerobic respiration and the competing iron-reduction process. Our results suggest that CH4 oxidation could offset CH4 production and limit surface CH4 emissions, in response to elevated temperature, and thus must be considered in model predictions of net CH4 fluxes in Arctic polygonal tundra. Future changes in temperature and soil saturation conditions are likely to divert electron flow to alternative electron acceptors and significantly alter CH4 production, which should also be considered in CH4 models.
DOI: 10.5194/bg-15-6621-2018
2020023268 Ulyantsev, A. S. (Russian Academy of Sciences, P. Shirshov Institute of Oceanology, Moscow, Russian Federation); Belyaev, N. A.; Bratskaya, S. Yu. and Romankevich, E. A. The molecular composition of lignin as an indicator of subaqueous permafrost thawing: Doklady Earth Sciences, 482(2), p. 1357-1361, illus. incl. 1 table, sketch map, 15 ref., October 2018.
DOI: 10.1134/S1028334X1810029X
2020021864 Grenier, Christophe (Université Paris-Saclay, Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France); Anbergen, Hauke; Bense, Victor; Chanzy, Quentin; Coon, Ethan; Collier, Nathaniel; Costard, François; Ferry, Michel; Frampton, Andrew; Frederick, Jennifer; Gonçalvès, Julio; Holmén, Johann; Jost, Anne; Kokh, Samuel; Kurylyk, Barret; McKenzie, Jeffrey; Molson, John; Mouche, Emmanuel; Orgogozo, Laurent; Pannetier, Romain; Rivière, Agnès; Roux, Nicolas; Rühaak, Wolfram; Scheidegger, Johanna; Selroos, Jan-Olof; Therrien, René; Vidstrand, Patrik and Voss, Clifford. Groundwater flow and heat transport for systems undergoing freeze-thaw; intercomparison of numerical simulators for 2D test cases: Advances in Water Resources, 114, p. 196-218, illus. incl. 10 tables, 97 ref., April 2018.
In high-elevation, boreal and arctic regions, hydrological processes and associated water bodies can be strongly influenced by the distribution of permafrost. Recent field and modeling studies indicate that a fully-coupled multidimensional thermo-hydraulic approach is required to accurately model the evolution of these permafrost-impacted landscapes and groundwater systems. However, the relatively new and complex numerical codes being developed for coupled non-linear freeze-thaw systems require verification.This issue is addressed by means of an intercomparison of thirteen numerical codes for two-dimensional test cases with several performance metrics (PMs). These codes comprise a wide range of numerical approaches, spatial and temporal discretization strategies, and computational efficiencies. Results suggest that the codes provide robust results for the test cases considered and that minor discrepancies are explained by computational precision. However, larger discrepancies are observed for some PMs resulting from differences in the governing equations, discretization issues, or in the freezing curve used by some codes.
DOI: 10.1016/j.advwatres.2018.02.001
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The USPA is pleased to announce the availability of an updated searchable database on permafrost-related publications. The American Geosciences Institute (AGI), with support from the National Science Foundation (NSF), has migrated the previous Cold Regions Bibliography to a new platform. Included are the USPA supported PMAs dating back to 2011. The Bibliography is searchable at 
