2021017259 Cai, Lei (NORCE Norwegian Research Centre, Bergen, Norway); Lee, Hanna; Aas, Kjetil Schanke and Westermann, Sebastian. Projecting circum-Arctic excess-ground-ice melt with a sub-grid representation in the community land model: The Cryosphere (Online), 14(12), p. 4611-4626, illus. incl. 3 tables, 63 ref., December 2020.
To address the long-standing underrepresentation of the influences of highly variable ground ice content on the trajectory of permafrost conditions simulated in Earth system models under a warming climate, we implement a sub-grid representation of excess ground ice within permafrost soils using the latest version of the Community Land Model (CLM5). Based on the original CLM5 tiling hierarchy, we duplicate the natural vegetated land unit by building extra tiles for up to three cryostratigraphies with different amounts of excess ice for each grid cell. For the same total amount of excess ice, introducing sub-grid variability in excess-ice contents leads to different excess-ice melting rates at the grid level. In addition, there are impacts on permafrost thermal properties and local hydrology with sub-grid representation. We evaluate this new development with single-point simulations at the Lena River delta, Siberia, where three sub-regions with distinctively different excess-ice conditions are observed. A triple-land-unit case accounting for this spatial variability conforms well to previous model studies for the Lena River delta and displays markedly different dynamics of future excess-ice thaw compared to a single-land-unit case initialized with average excess-ice contents. For global simulations, we prescribed a tiling scheme combined with our sub-grid representation to the global permafrost region using presently available circum-Arctic ground ice data. The sub-grid-scale excess ice produces significant melting of excess ice under a warming climate and enhances the representation of sub-grid variability of surface subsidence on a global scale. Our model development makes it possible to portray more details on the permafrost degradation trajectory depending on the sub-grid soil thermal regime and excess-ice melting, which also shows a strong indication that accounting for excess ice is a prerequisite of a reasonable projection of permafrost thaw. The modeled permafrost degradation with sub-grid excess ice follows the pathway that continuous permafrost transforms into discontinuous permafrost before it disappears, including surface subsidence and talik formation, which are highly permafrost-relevant landscape changes excluded from most land models. Our development of sub-grid representation of excess ice demonstrates a way forward to improve the realism of excess-ice melt in global land models, but further developments require substantially improved global observational datasets on both the horizontal and vertical distributions of excess ground ice.
2021017260 Hornum, Mikkel Toft (University Centre in Svalbard, Department of Arctic Geology, Longyearbyen, Svalbard and Jan Mayen Islands); Hodson, Andrew Jonathan; Jessen, Soren; Bense, Victor and Senger, Kim. Numerical modelling of permafrost spring discharge and open-system pingo formation induced by basal permafrost aggradation: The Cryosphere (Online), 14(12), p. 4627-4651, illus. incl. sect., 3 tables, sketch map, 110 ref., December 2020.
In the high Arctic valley of Adventdalen, Svalbard, sub-permafrost groundwater feeds several pingo springs distributed along the valley axis. The driving mechanism for groundwater discharge and associated pingo formation is enigmatic because wet-based glaciers are not present in the adjacent highlands and the presence of continuous permafrost seems to preclude recharge of the sub-permafrost groundwater system by either a subglacial source or a precipitation surplus. Since the pingo springs enable methane that has accumulated underneath the permafrost to escape directly to the atmosphere, our limited understanding of the groundwater system brings significant uncertainty to predictions of how methane emissions will respond to changing climate. We address this problem with a new conceptual model for open-system pingo formation wherein pingo growth is sustained by sub-permafrost pressure effects, as related to the expansion of water upon freezing, during millennial-scale basal permafrost aggradation. We test the viability of this mechanism for generating groundwater flow with decoupled heat (one-dimensional transient) and groundwater (three-dimensional steady state) transport modelling experiments. Our results suggest that the conceptual model represents a feasible mechanism for the formation of open-system pingos in lower Adventdalen and elsewhere. We also explore the potential for additional pressurisation and find that methane production and methane clathrate formation and dissolution deserve particular attention on account of their likely effects upon the hydraulic pressure. Our model simulations also suggest that the generally low-permeability hydrogeological units cause groundwater residence times to exceed the duration of the Holocene. The likelihood of such pre-Holocene groundwater ages is supported by the geochemistry of the pingo springs which demonstrates an unexpected seaward freshening of groundwater potentially caused by a palaeo-subglacial meltwater "wedge" from the Weichselian. Whereas permafrost thickness (and age) progressively increases inland, accordingly, the sub-permafrost meltwater wedge thins, and less unfrozen freshwater is available for mixing. Our observations imply that millennial-scale permafrost aggradation deserves more attention as a possible driver of sustained flow of sub-permafrost groundwater and methane to the surface because, although the hydrological system in Adventdalen at first appears unusual, it is likely that similar systems have developed in other uplifted valleys throughout the Arctic.
2021017250 Nitze, Ingmar (Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany); Cooley, Sarah W.; Duguay, Claude R.; Jones, Benjamin M. and Grosse, Guido. The catastrophic thermokarst lake drainage events of 2018 in northwestern Alaska; fast-forward into the future: The Cryosphere (Online), 14(12), p. 4279-4297, illus. incl. 4 tables, sketch map, 96 ref., December 2020.
Northwestern Alaska has been highly affected by changing climatic patterns with new temperature and precipitation maxima over the recent years. In particular, the Baldwin and northern Seward peninsulas are characterized by an abundance of thermokarst lakes that are highly dynamic and prone to lake drainage like many other regions at the southern margins of continuous permafrost. We used Sentinel-1 synthetic aperture radar (SAR) and Planet CubeSat optical remote sensing data to analyze recently observed widespread lake drainage. We then used synoptic weather data, climate model outputs and lake ice growth simulations to analyze potential drivers and future pathways of lake drainage in this region. Following the warmest and wettest winter on record in 2017/2018, 192 lakes were identified as having completely or partially drained by early summer 2018, which exceeded the average drainage rate by a factor of ~10 and doubled the rates of the previous extreme lake drainage years of 2005 and 2006. The combination of abundant rain- and snowfall and extremely warm mean annual air temperatures (MAATs), close to 0°C, may have led to the destabilization of permafrost around the lake margins. Rapid snow melt and high amounts of excess meltwater further promoted rapid lateral breaching at lake shores and consequently sudden drainage of some of the largest lakes of the study region that have likely persisted for millennia. We hypothesize that permafrost destabilization and lake drainage will accelerate and become the dominant drivers of landscape change in this region. Recent MAATs are already within the range of the predictions by the University of Alaska Fairbanks' Scenarios Network for Alaska and Arctic Planning (UAF SNAP) ensemble climate predictions in scenario RCP6.0 for 2100. With MAAT in 2019 just below 0°C at the nearby Kotzebue, Alaska, climate station, permafrost aggradation in drained lake basins will become less likely after drainage, strongly decreasing the potential for freeze-locking carbon sequestered in lake sediments, signifying a prominent regime shift in ice-rich permafrost lowland regions.
2021017252 Subedi, Rupesh (Carleton University, Department of Geography and Environmental Studies, Ottawa, ON, Canada); Kokelj, Steven V. and Gruber, Stephan. Ground ice, organic carbon and soluble cations in tundra permafrost soils and sediments near a Laurentide ice divide in the Slave geological province, Northwest Territories, Canada: The Cryosphere (Online), 14(12), p. 4341-4364, illus. incl. 2 tables, sketch map, 100 ref., December 2020. Includes 4 appendices.
The central Slave Geological Province is situated 450-650 km from the presumed spreading centre of the Keewatin Dome of the Laurentide Ice Sheet, and it differs from the western Canadian Arctic, where recent thaw-induced landscape changes in Laurentide ice-marginal environments are already abundant. Although much of the terrain in the central Slave Geological Province is mapped as predominantly bedrock and ice-poor, glacial deposits of varying thickness occupy significant portions of the landscape in some areas, creating a mosaic of permafrost conditions. Limited evidence of ice-rich ground, a key determinant of thaw-induced landscape change, exists. Carbon and soluble cation contents in permafrost are largely unknown in the area. Twenty-four boreholes with depths up to 10 m were drilled in tundra north of Lac de Gras to address these regional gaps in knowledge and to better inform projections and generalizations at a coarser scale. Excess-ice contents of 20%-60%, likely remnant Laurentide basal ice, are found in upland till, suggesting that thaw subsidence of metres to more than 10 m is possible if permafrost were to thaw completely. Beneath organic terrain and in fluvially reworked sediment, aggradational ice is found. The variability in abundance of ground ice poses long-term challenges for engineering, and it makes the area susceptible to thaw-induced landscape change and mobilization of sediment, solutes and carbon several metres deep. The nature and spatial patterns of landscape changes, however, are expected to differ from ice-marginal landscapes of western Arctic Canada, for example, based on greater spatial and stratigraphic heterogeneity. Mean organic-carbon densities in the top 3 m of soil profiles near Lac de Gras are about half of those reported in circumpolar statistics; deeper deposits have densities ranging from 1.3-10.1 kg C m-3, representing a significant additional carbon pool. The concentration of total soluble cations in mineral soils is lower than at previously studied locations in the western Canadian Arctic. This study can inform permafrost investigations in other parts of the Slave Geological Province, and its data can support scenario simulations of future trajectories of permafrost thaw. Preserved Laurentide basal ice can support new ways of studying processes and phenomena at the base of an ice sheet.
2021017256 Wetterich, Sebastian (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany); Kizyakov, Alexander; Fritz, Michael; Wolter, Juliane; Mollenhauer, Gesine; Meyer, Hanno; Fuchs, Matthias; Aksenov, Aleksei; Matthes, Heidrun; Schirrmeister, Lutz and Opel, Thomas. The cryostratigraphy of the yedoma cliff of Sobo-Sise Island (Lena Delta) reveals permafrost dynamics in the central Laptev Sea coastal region during the last 52 kyr: The Cryosphere (Online), 14(12), p. 4525-4551, illus. incl. 3 tables, sketch map, 113 ref., December 2020.
The present study examines the formation history and cryolithological properties of the late-Pleistocene Yedoma Ice Complex (IC) and its Holocene cover in the eastern Lena delta on Sobo-Sise Island. The sedimentary sequence was continuously sampled at 0.5 m resolution at a vertical Yedoma cliff starting from 24.2 m above river level (a.r.l.). The sequence differentiates into three cryostratigraphic units: Unit A, dated from ca. 52 to 28 cal kyr BP; Unit B, dated from ca. 28 to 15 cal kyr BP; Unit C, dated from ca. 7 to 0 cal kyr BP. Three chronologic gaps in the record are striking. The hiatus during the interstadial marine isotope stage (MIS) 3 (36-29 cal kyr BP) as well as during stadial MIS 2 (20-17 cal kyr BP) might be related to fluvial erosion and/or changed discharge patterns of the Lena river caused by repeated outburst floods from the glacial Lake Vitim in southern Siberia along the Lena river valley towards the Arctic Ocean. The hiatus during the MIS 2-1 transition (15-7 cal kyr BP) is a commonly observed feature in permafrost chronologies due to intense thermokarst activity of the deglacial period. The chronologic gaps of the Sobo-Sise Yedoma record are similarly found at two neighbouring Yedoma IC sites on Bykovsky Peninsula and Kurungnakh-Sise Island and are most likely of regional importance. The three cryostratigraphic units of the Sobo-Sise Yedoma exhibit distinct signatures in properties of their clastic, organic, and ice components. Higher permafrost aggradation rates of 1 m kyr-1 with higher organic-matter (OM) stocks (29±15 kg C m-3, 2.2±1.0 kg N m-3; Unit A) and mainly coarse silt are found for the interstadial MIS 3 if compared to the stadial MIS 2 with 0.7 m-1 permafrost aggradation, lower OM stocks (14±8 kg C m-3, 1.4±0.4 kg N m-3; Unit B), and pronounced peaks in the coarse-silt and medium-sand fractions. Geochemical signatures of intra-sedimental ice reflect the differences in summer evaporation and moisture regime by higher ion content and less depleted ratios of stable d18O and stable dD isotopes but lower deuterium excess (d) values during interstadial MIS 3 if compared to stadial MIS 2. The d18O and dD composition of MIS 3 and MIS 2 ice wedges shows characteristic well-depleted values and low d values, while MIS 1 ice wedges have elevated mean d values between 11 ppm and 15 ppm and surprisingly low d18O and dD values. Hence, the isotopic difference between late-Pleistocene and Holocene ice wedges is more pronounced in d than in d values. The present study of the permafrost exposed at the Sobo-Sise Yedoma cliff provides a comprehensive cryostratigraphic inventory, insights into permafrost aggradation, and degradation over the last approximately 52 kyr as well as their climatic and morphodynamic controls on the regional scale of the central Laptev Sea coastal region in NE Siberia.
2021017261 Yu, Lianyu (University of Twente, Faculty of Geo-information Science and Earth Observation (ITC), Enschede, Netherlands); Fatichi, Simone; Zeng, Yijian and Su, Zhongbo. The role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze-thaw cycles: The Cryosphere (Online), 14(12), p. 4653-4673, illus. incl. 1 table, sketch map, 93 ref., December 2020. Includes appendix.
The vadose zone is a zone sensitive to environmental changes and exerts a crucial control in ecosystem functioning and even more so in cold regions considering the rapid change in seasonally frozen ground under climate warming. While the way in representing the underlying physical process of the vadose zone differs among models, the effect of such differences on ecosystem functioning and its ecohydrological response to freeze-thaw cycles are seldom reported. Here, the detailed vadose zone process model STEMMUS (Simultaneous Transfer of Energy, Mass and Momentum in Unsaturated Soil) was coupled with the ecohydrological model Tethys-Chloris (T&C) to investigate the role of influential physical processes during freeze-thaw cycles. The physical representation is increased from using T&C coupling without STEMMUS enabling the simultaneous mass and energy transfer in the soil system (liquid, vapor, ice)--and with explicit consideration of the impact of soil ice content on energy and water transfer properties--to using T&C coupling with it. We tested model performance with the aid of a comprehensive observation dataset collected at a typical meadow ecosystem on the Tibetan Plateau. Results indicated that (i) explicitly considering the frozen soil process significantly improved the soil moisture/temperature profile simulations and facilitated our understanding of the water transfer processes within the soil-plant-atmosphere continuum; (ii) the difference among various representations of vadose zone physics have an impact on the vegetation dynamics mainly at the beginning of the growing season; and (iii) models with different vadose zone physics can predict similar interannual vegetation dynamics, as well as energy, water, and carbon exchanges, at the land surface. This research highlights the important role of vadose zone physics for ecosystem functioning in cold regions and can support the development and application of future Earth system models.
2021011951 Zhu Chenyi (Peking University, College of Urban and Environmental Sciences, Beijing, China); Liu Hongyan; Wang Hongya; Feng Siwen and Han Yue. Vegetation change at the southern boreal forest margin in northeast China over the last millennium; the role of permafrost dynamics: Palaeogeography, Palaeoclimatology, Palaeoecology, 558, Article no. 109959, illus. incl. 1 table, sketch map, 55 ref., November 15, 2020.
To better understand the nature and causes of boreal forest change and, in particular, the role of permafrost dynamics, we reconstruct the recent vegetation history of the Greater Hingan Mountains of northeast China based on a lake sediment core. This core is located in an area of boreal forest underlain by permafrost, and spans a 1000-year warming-to-cooling cycle. Palynological assemblages indicate that, throughout most of its history, vegetation was characterized by changes in the relative proportions of taxa, including the cold-resistant boreal conifer species Larix and Pinus, and warmth-adapted temperate broadleaf shrub species Corylus and Rhododendron, corresponding to variations in temperature. However, after ~1950 CE, rapid warming led to the breakdown of this relationship between vegetation and climate, and the proportion of conifers increased in the short term, most likely due to permafrost thawing. This effect was most pronounced in lowland areas whose frost table depth was initially ~20 cm closer to the surface than the corresponding frost table on mountain slopes. The increase in frost table depth due to warmer temperatures provided greater root space for shallow-rooted conifers in lowlands, as well as meltwater from thawing permafrost. We speculate that the coupled system of vegetation, climate and permafrost was stable before ~1950 CE; however, most recently, there has been a transition due to warming-induced permafrost thawing. As the southern boundary of permafrost moves poleward, it is suspected that lowland rather than slope sites will witness the sharpest vegetation shifts.
2021017028 Lim, M. (Northumbria University, Engineering and Environment, Newcastle Upon Tyne, United Kingdom); Whalen, D.; Martin, J.; Mann, P. J.; Hayes, S.; Fraser, P.; Berry, H. B. and Ouellette, D. Massive ice control on permafrost coast erosion and sensitivity: Geophysical Research Letters, 47(17), Paper no. e2020GL087917, illus., 42 ref., September 16, 2020.
High overall rates of permafrost cliff retreat, coupled with spatial variability, have been accompanied by increased uncertainty over future landscape dynamics. We map long-term (>80 years) retreat of the shoreline and photogrammetrically analyze historic aerial imagery to quantify the processes at a permafrost coast site with massive ground ice. Retreat rates have been relatively constant, but topographic changes show that subsidence is a potentially critical but often ignored component of coastal sensitivity, exceeding landward recession by over three times during the last 24 years. We calibrate novel passive seismic surveys along clear and variable exposures of massive ground ice and then spatially map key subsurface layers. Combining decadal patterns of volumetric change with new ground ice variation maps enables past trends to be interpreted, future volumetric geomorphic behavior to be better constrained, and improves the assessment of permafrost coast sensitivity and the release of carbon-bearing material. Abstract Copyright (2020), The Authors.
2021017109 Zwieback, Simon (University of Guelph, Department of Geography, Guelph, ON, Canada); Boike, Julia; Marsh, P. and Berg, A. Debris cover on thaw slumps and its insulative role in a warming climate: Earth Surface Processes and Landforms, 45(11), p. 2631-2646, illus., 62 ref., September 15, 2020.
Thaw slumps in ice-rich permafrost can retreat tens of metres per summer, driven by the melt of subaerially exposed ground ice. However, some slumps retain an ice-veneering debris cover as they retreat. A quantitative understanding of the thermal regime and geomorphic evolution of debris-covered slumps in a warming climate is largely lacking. To characterize the thermal regime, we instrumented four debris-covered slumps in the Canadian Low Arctic and developed a numerical conduction-based model. The observed surface temperatures >20°C and steep thermal gradients indicate that debris insulates the ice by shifting the energy balance towards radiative and turbulent losses. After the model was calibrated and validated with field observations, it predicted sub-debris ice melt to decrease four-fold from 1.9 to 0.5 mas the thickness of the fine-grained debris quadruples from 0.1 to 0.4 m. With warming temperatures, melt is predicted to increase most rapidly, in relative terms, for thick (~0.5-1.0 m) debris covers. The morphology and evolution of the debris-covered slumps were characterized using field and remote sensing observations, which revealed differences in association with morphology and debris composition. Two low-angle slumps retreated continually despite their persistent fine-grained debris covers. The observed elevation losses decreased from ~1.0 m/yr where debris thickness ~0.2 m to 0.1 m/yr where thickness ~1.0 m. Conversely, a steep slump with a coarse-grained debris veneer underwent short-lived bursts of retreat, hinting at a complex interplay of positive and negative feedback processes. The insulative protection and behaviour of debris vary significantly with factors such as thickness, grain size and climate: debris thus exerts a fundamental, spatially variable influence on slump trajectories in a warming climate. Copyright 2020 John Wiley & Sons, Ltd.
2021015705 Ruppel, C. D. (U. S. Geological Survey, Woods Hole, MA) and Waite, W. F. Timescales and processes of methane hydrate formation and breakdown, with application to geologic systems: Journal of Geophysical Research: Solid Earth, 125(8), Article e2018JB016459, illus. incl. 4 tables, sketch maps, 250 ref., August 2020.
Gas hydrate is an ice-like form of water and low molecular weight gas stable at temperatures of roughly -10°C to 25°C and pressures of ~3 to 30 MPa in geologic systems. Natural gas hydrates sequester an estimated one sixth of Earth's methane and are found primarily in deepwater marine sediments on continental margins, but also in permafrost areas and under continental ice sheets. When gas hydrate is removed from its stability field, its breakdown has implications for the global carbon cycle, ocean chemistry, marine geohazards, and interactions between the geosphere and the ocean-atmosphere system. Gas hydrate breakdown can also be artificially driven as a component of studies assessing the resource potential of these deposits. Furthermore, geologic processes and perturbations to the ocean-atmosphere system (e.g., warming temperatures) can cause not only dissociation, but also more widespread dissolution of hydrate or even formation of new hydrate in reservoirs. Linkages between gas hydrate and disparate aspects of Earth's near-surface physical, chemical, and biological systems render an assessment of the rates and processes affecting the persistence of gas hydrate an appropriate Centennial Grand Challenge. This paper reviews the thermodynamic controls on methane hydrate stability and then describes the relative importance of kinetic, mass transfer, and heat transfer processes in the formation and breakdown (dissociation and dissolution) of gas hydrate. Results from numerical modeling, laboratory, and some field studies are used to summarize the rates of hydrate formation and breakdown, followed by an extensive treatment of hydrate dynamics in marine and cryospheric gas hydrate systems. Abstract Copyright (2020), The Authors.
2021015518 Zorigt, Munkhtsetseg (National University of Mongolia, School of Engineering and Applied Sciences, Ulaanbaatar, Mongolia); Myagmar, Khulan; Orkhonselenge, Alexander; van Beek, Eelco; Kwadijk, Jaap; Tsogtbayar, Jargaltulga; Yamkhin, Jambaljav and Dechinlkhundev, Dorjsuren. Modeling permafrost distribution over the river basins of Mongolia using remote sensing and analytical approaches: Environmental Earth Sciences, 79(12), Article 308, illus. incl. 3 tables, sketch maps, 40 ref., June 7, 2020.
The spatial distribution of permafrost and associated mean annual ground temperature (MAGT) and active layer thickness (ALT) are crucial data for hydrological studies. In this paper, we present the current state of knowledge on the spatial distribution of the permafrost properties of 29 river basins in Mongolia. The MAGT and ALT values are estimated by applying TTOP and Kudryavtsev methods. The main input of both methods is the spatially distributed surface temperature. We used the 8-day land surface temperature (LST) data from the day- and night-time Aqua and Terra images of the moderate resolution imaging spectroradiometer (MODIS). The gaps of the MODIS LST data were filled by spatial interpolation. Next, an LST model was developed based on 34 observational borehole data using a panel regression analysis (Baltagi, Econometric analysis of panel data, 3 edn, Wiley, New York, 2005). The model was applied for the whole country and covered the period from August 2012 to August 2013. The results show that the permafrost covers 26.3% of the country. The average MAGT and ALT for the permafrost region is -1.6°C and 3.1 m, respectively. The MAGT above -2°C (warm permafrost) covers approximately 67% of the total permafrost area. The permafrost area and distribution in cold and warm permafrost varies highly over the country, in particular in regions where the river network is highly developed. High surface temperatures associated with climate change would result in changes of permafrost conditions, and, thus, would impact the surface water availability in these regions. The data on permafrost conditions presented in this paper can be used for further research on changes in the hydrological conditions of Mongolia.
2021017262 Zhang Shunyao (Chengdu University of Technology, College of Earth Sciences, Chengdu, China); Zhang Fugui; Shi Zeming; Qin Aihua; Wang Huiyan; Sun Zhongjun; Yang Zhibin; Zhu Youhai; Pang Shouji and Wang Pingkang. Sources of seasonal wetland methane emissions in permafrost regions of the Qinghai-Tibet Plateau: Scientific Reports, 10(7520), 11 p., illus. incl. sketch map, 50 ref., May 5, 2020.
2021015277 Koroleva, E. S. (Russian Academy of Sciences, Earth's Cryosphere Institute, Tyumen, Russian Federation); Khairullin, R. R.; Babkina, E. A.; Slagoda, E. A.; Khomutov, A. V.; Melnikov, V. P.; Babkin, E. M. and Tikhonravova, Ya. V. Seasonal thawing local changes indicators for UAV-based cryolithozone mapping: Doklady Earth Sciences, 491(1), p. 179-182, illus. incl. sketch map, 9 ref., March 2020.
Remote sensing methods make it possible to evaluate the reaction of the cryolithozone and tundra landscapes in hard-to-reach Arctic areas based on the indicators of modern climate changes. In 2016-2019, numerous organic frost boils were discovered on the peatland surfaces of drained lakes in the southern tundra of the Pur-Taz interfluve in the northern part of West Siberia and studied. It is established that the formation of frost boils caused by organic mass injections occurs in the summertime and that they indicate local deepening of seasonal thawing. Frost boils emerging at peatlands in summertime was identified after analysis of UAV survey in 2019. Local deepening of seasonal thaw layer on polygonal peatlands is evidence of permafrost reaction to global warming.
2021016971 Burke, Eleanor J. (Met Office Hadley Centre, Exeter, United Kingdom); Zhang, Yu and Krinner, Gerhard. Evaluating permafrost physics in the Coupled Model Intercomparison Project 6 (CMIP6) models and their sensitivity to climate change: The Cryosphere (Online), 14(9), p. 3155-3174, illus. incl. 5 tables, sketch maps, 65 ref., 2020.
Permafrost is a ubiquitous phenomenon in the Arctic. Its future evolution is likely to control changes in northern high-latitude hydrology and biogeochemistry. Here we evaluate the permafrost dynamics in the global models participating in the Coupled Model Intercomparison Project (present generation--CMIP6; previous generation--CMIP5) along with the sensitivity of permafrost to climate change. Whilst the northern high-latitude air temperatures are relatively well simulated by the climate models, they do introduce a bias into any subsequent model estimate of permafrost. Therefore evaluation metrics are defined in relation to the air temperature. This paper shows that the climate, snow and permafrost physics of the CMIP6 multi-model ensemble is very similar to that of the CMIP5 multi-model ensemble. The main differences are that a small number of models have demonstrably better snow insulation in CMIP6 than in CMIP5 and a small number have a deeper soil profile. These changes lead to a small overall improvement in the representation of the permafrost extent. There is little improvement in the simulation of maximum summer thaw depth between CMIP5 and CMIP6. We suggest that more models should include a better-resolved and deeper soil profile as a first step towards addressing this. We use the annual mean thawed volume of the top 2 m of the soil defined from the model soil profiles for the permafrost region to quantify changes in permafrost dynamics. The CMIP6 models project that the annual mean frozen volume in the top 2 m of the soil could decrease by 10%-40%°C-1 of global mean surface air temperature increase.
2021013458 Jafarov, Elchin E. (Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM); Harp, Dylan R.; Coon, Ethan T.; Dafflon, Baptiste; Tran, Anh Phuong; Atchley, Adam L.; Lin, Youzuo and Wilson, Cathy J. Estimation of subsurface porosities and thermal conductivities of polygonal tundra by coupled inversion of electrical resistivity, temperature, and moisture content data: The Cryosphere (Online), 14(1), p. 77-91, illus. incl. 3 tables, 36 ref., 2020.
Studies indicate greenhouse gas emissions following permafrost thaw will amplify current rates of atmospheric warming, a process referred to as the permafrost carbon feedback. However, large uncertainties exist regarding the timing and magnitude of the permafrost carbon feedback, in part due to uncertainties associated with subsurface permafrost parameterization and structure. Development of robust parameter estimation methods for permafrost-rich soils is becoming urgent under accelerated warming of the Arctic. Improved parameterization of the subsurface properties in land system models would lead to improved predictions and a reduction of modeling uncertainty. In this work we set the groundwork for future parameter estimation (PE) studies by developing and evaluating a joint PE algorithm that estimates soil porosities and thermal conductivities from time series of soil temperature and moisture measurements and discrete in-time electrical resistivity measurements. The algorithm utilizes the Model-Independent Parameter Estimation and Uncertainty Analysis toolbox and coupled hydrological-thermal-geophysical modeling. We test the PE algorithm against synthetic data, providing a proof of concept for the approach. We use specified subsurface porosities and thermal conductivities and coupled models to set up a synthetic state, perturb the parameters, and then verify that our PE method is able to recover the parameters and synthetic state. To evaluate the accuracy and robustness of the approach we perform multiple tests for a perturbed set of initial starting parameter combinations. In addition, we varied types and quantities of data to better understand the optimal dataset needed to improve the PE method. The results of the PE tests suggest that using multiple types of data improve the overall robustness of the method. Our numerical experiments indicate that special care needs to be taken during the field experiment setup so that (1) the vertical distance between adjacent measurement sensors allows the signal variability in space to be resolved and (2) the longer time interval between resistivity snapshots allows signal variability in time to be resolved.
2021017280 Patzner, Monique S. (University of Tuebingen, Department of Geomicrobiology, Tubingen, Germany); Mueller, Carsten W.; Malusova, Miroslava; Baur, Moritz; Nikeleit, Verena; Scholten, Thomas; Hoeschen, Carmen; Byrne, James M.; Borch, Thomas; Kappler, Andreas and Bryce, Casey. Iron mineral dissolution releases iron and associated organic carbon during permafrost thaw: Nature Communications, 11(1), Paper no. 6329, illus. incl. sketch map, 86 ref., 2020.
It has been shown that reactive soil minerals, specifically iron(III) (oxyhydr)oxides, can trap organic carbon in soils overlying intact permafrost, and may limit carbon mobilization and degradation as it is observed in other environments. However, the use of iron(III)-bearing minerals as terminal electron acceptors in permafrost environments, and thus their stability and capacity to prevent carbon mobilization during permafrost thaw, is poorly understood. We have followed the dynamic interactions between iron and carbon using a space-for-time approach across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost thaw. We show through bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS) that organic carbon is bound to reactive Fe primarily in the transition between organic and mineral horizons in palsa underlain by intact permafrost (41.8±10.8 mg carbon per g soil, 9.9 to 14.8% of total soil organic carbon). During permafrost thaw, water-logging and O2 limitation lead to reducing conditions and an increase in abundance of Fe(III)-reducing bacteria which favor mineral dissolution and drive mobilization of both iron and carbon along the thaw gradient. By providing a terminal electron acceptor, this rusty carbon sink is effectively destroyed along the thaw gradient and cannot prevent carbon release with thaw.
2021016962 Wang Junfeng (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Wu Qingbai; Yuan Ziqiang and Kang, Hojeong. Soil respiration of alpine meadow is controlled by freeze-thaw processes of active layer in the permafrost region of the Qinghai-Tibet Plateau: The Cryosphere (Online), 14(9), p. 2835-2848, illus. incl. 4 tables, 74 ref., 2020.
Freezing and thawing action of the active layer plays a significant role in soil respiration (Rs) in permafrost regions. However, little is known about how the freeze-thaw processes affect the Rs dynamics in different stages of the alpine meadow underlain by permafrost in the Qinghai-Tibet Plateau (QTP). We conducted continuous in situ measurements of Rs and freeze-thaw processes of the active layer at an alpine meadow site in the Beiluhe permafrost region of the QTP and divided the freeze-thaw processes into four different stages in a complete freeze-thaw cycle, comprising the summer thawing (ST) stage, autumn freezing (AF) stage, winter cooling (WC) stage, and spring warming (SW) stage. We found that the freeze-thaw processes have various effects on the Rs dynamics in different freeze-thaw stages. The mean Rs ranged from 0.12 to 3.18 mmol m-2 s-1 across the stages, with the lowest value in WC and highest value in ST. Q10 among the different freeze-thaw stages changed greatly, with the maximum (4.91±0.35) in WC and minimum (0.33±0.21) in AF. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to total Rs of a complete freeze-thaw cycle (1692.98±51.4 g CO2 m-2) were 61.32±0.32%, 8.89±0.18%, 18.43±0.11%, and 11.29±0.11%, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as climate change and permafrost degradation continue, great changes in freeze-thaw process patterns may trigger more Rs emissions from this ecosystem because of a prolonged ST stage.
2021016489 Carey, Joanna C. (Babson College, Division of Math and Science, Wellesley, MA); Abbott, Benjamin W. and Rocha, Adrian V. Plant uptake offsets silica release from a large arctic tundra wildfire: Earth's Future, 7(9), p. 1044-1057, illus. incl. 4 tables, 93 ref., September 2019.
Rapid climate change at high latitudes is projected to increase wildfire extent in tundra ecosystems by up to fivefold by the end of the century. Tundra wildfire could alter terrestrial silica (SiO2) cycling by restructuring surface vegetation and by deepening the seasonally thawed active layer. These changes could influence the availability of silica in terrestrial permafrost ecosystems and alter lateral exports to downstream marine waters, where silica is often a limiting nutrient. In this context, we investigated the effects of the largest Arctic tundra fire in recent times on plant and peat amorphous silica content and dissolved silica concentration in streams. Ten years after the fire, vegetation in burned areas had 73% more silica in aboveground biomass compared to adjacent, unburned areas. This increase in plant silica was attributable to significantly higher plant silica concentration in bryophytes and increased prevalence of silica-rich gramminoids in burned areas. Tundra fire redistributed peat silica, with burned areas containing significantly higher amorphous silica concentrations in the O-layer, but 29% less silica in peat overall due to shallower peat depth post burn. Despite these dramatic differences in terrestrial silica dynamics, dissolved silica concentration in tributaries draining burned catchments did not differ from unburned catchments, potentially due to the increased uptake by terrestrial vegetation. Together, these results suggest that tundra wildfire enhances terrestrial availability of silica via permafrost degradation and associated weathering, but that changes in lateral silica export may depend on vegetation uptake during the first decade of postwildfire succession. Abstract Copyright (2019). The Authors.
2021017263 Song Chunlin (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Wang Genxu; Mao Tianxu; Chen Xiaopeng; Huang Kewei; Sun Xiangyang and Hu Zhaoyong. Importance of active layer freeze-thaw cycles on the riverine dissolved carbon export on the Qinghai-Tibet Plateau permafrost region: PeerJ, Article 7146, 25 p., illus. incl. 3 tables, geol. sketch map, 75 ref., June 17, 2019.
The Qinghai-Tibet Plateau (QTP) is experiencing severe permafrost degradation, which can affect the hydrological and biogeochemical processes. Yet how the permafrost change affects riverine carbon export remains uncertain. Here, we investigated the seasonal variations of dissolved inorganic and organic carbon (DIC and DOC) during flow seasons in a watershed located in the central QTP permafrost region. The results showed that riverine DIC concentrations (27.81±9.75 mg L-1) were much higher than DOC concentrations (6.57±2.24 mg L-1). DIC and DOC fluxes were 3.95 and 0.94 g c m-2 year-1, respectively. DIC concentrations increased from initial thaw (May) to freeze period (October), while DOC concentrations remained relatively steady. Daily dissolved carbon concentrations were more closely correlated with baseflow than that with total runoff. Spatially, average DIC and DOC concentrations were positively correlated with vegetation coverage but negatively correlated with bare land coverage. DIC concentrations increased with the thawed and frozen depths due to increased soil interflow, more thaw-released carbon, more groundwater contribution, and possibly more carbonate weathering by soil CO2 formed carbonic acid. The DIC and DOC fluxes increased with thawed depth and decreased with frozen layer thickness. The seasonality of riverine dissolved carbon export was highly dependent on active layer thawing and freezing processes, which highlights the importance of changing permafrost for riverine carbon export. Future warming in the QTP permafrost region may alter the quantity and mechanisms of riverine carbon export.
2021013453 Demidov, Nikita (Arctic and Antarctic Research Institute, St. Petersburg, Russian Federation); Wetterich, Sebastian; Verkulich, Sergey; Ekaykin, Aleksey; Meyer, Hanno; Anisimov, Mikhail; Schirrmeister, Lutz; Demidov, Vasily and Hodson, Andrew J. Geochemical signatures of pingo ice and its origin in Grondalen, west Spitsbergen: The Cryosphere (Online), 13(11), p. 3155-3169, illus. incl. 3 tables, 43 ref., 2019.
Pingos are common features in permafrost regions that form by subsurface massive-ice aggradation and create hill-like landforms. Pingos on Spitsbergen have been previously studied to explore their structure, formation timing and connection to springs as well as their role in postglacial landform evolution. However, detailed hydrochemical and stable-isotope studies of massive-ice samples recovered by drilling have yet to be used to study the origin and freezing conditions in pingos. Our core record of 20.7 m thick massive pingo ice from Grondalen is differentiated into four units: two characterised by decreasing d18O and dD and increasing d (units I and III) and two others showing the opposite trend (units II and IV). These delineate changes between episodes of closed-system freezing with only slight recharge inversions of the water reservoir and more complicated episodes of groundwater freezing under semi-closed conditions when the reservoir was recharged. The water source for pingo formation shows similarity to spring water data from the valley with prevalent Na+ and HCO3- ions. The sub-permafrost groundwater originates from subglacial meltwater that most probably followed the fault structures of Grondalen and Bohmdalen. The presence of permafrost below the pingo ice body suggests that the talik is frozen, and the water supply and pingo growth are terminated. The maximum thaw depth of the active layer reaching the top of the massive ice leads to its successive melt with crater development and makes the pingo extremely sensitive to further warming.
2021014675 Krzyszowska Waitkus, Anna J. (Environmental Consulting, Laramie, WY) and Waitkus, Brian. Effects of fuel spills on Arctic soil, 32 years later (Hornsund, Svalbard): Polish Polar Research, 40(4), p. 295-309, illus. incl. 1 table, sketch map, 42 ref., 2019.
The purpose of the study was to estimate in 2012 range and degree of soil contamination due to local diesel fuel leakage spills that occurred in 1980 and from any subsequent activities in the vicinity of the scientific Polish Polar Station in Hornsund, Svalbard. The area of the study covered the immediate vicinity of station buildings including areas of the 1980's fuel barrel storage depot and location of current fuel tanks. Results of the study were compared with a similar study performed in 1980. As of 2012, areas potentially contaminated covered 0.9 ha, which was a 50% decrease compared to 1980. The area contaminated with total petroleum hydrocarbons was extremely localized. Spread of petroleum hydrocarbons from 1980's source of pollution investigated 32 years later showed that petroleum derived products were environmentally mobile. Concentrations of total petroleum hydrocarbons in surface soils of the unsaturated active layer above the permafrost decreased significantly mostly due to surface runoff and dispersion through ephemeral drainages. Concentrations of total petroleum hydrocarbons increased with depth through time in sandy soils on the flat area where the largest 1980's fuel barrel depot was located.
2021013447 Léger, Emmanuel (Lawrence Berkeley National Laboratory, Berkeley, CA); Dafflon, Baptiste; Robert, Yves; Ulrich, Craig; Peterson, John E.; Biraud, Sébastien C.; Romanovsky, Vladimir E. and Hubbard, Susan S. A distributed temperature profiling method for assessing spatial variability in ground temperatures in a discontinuous permafrost region of Alaska: The Cryosphere (Online), 13(11), p. 2853-2867, illus., 71 ref., 2019.
Soil temperature has been recognized as a property that strongly influences a myriad of hydro-biogeochemical processes and reflects how various properties modulate the soil thermal flux. In spite of its importance, our ability to acquire soil temperature data with high spatial and temporal resolution and coverage is limited because of the high cost of equipment, the difficulties of deployment, and the complexities of data management. Here we propose a new strategy that we call distributed temperature profiling (DTP) for improving the characterization and monitoring near-surface thermal properties through the use of an unprecedented number of laterally and vertically distributed temperature measurements. We developed a prototype DTP system, which consists of inexpensive, low-impact, low-power, and vertically resolved temperature probes that independently and autonomously record soil temperature. The DTP system concept was tested by moving sequentially the system across the landscape to identify near-surface permafrost distribution in a discontinuous permafrost environment near Nome, Alaska, during the summertime. Results show that the DTP system enabled successful acquisition of vertically resolved profiles of summer soil temperature over the top 0.8 m at numerous locations. DTP also enabled high-resolution identification and lateral delineation of near-surface permafrost locations from surrounding zones with no permafrost or deep permafrost table locations overlain by a perennially thawed layer. The DTP strategy overcomes some of the limitations associated with - and complements the strengths of - borehole-based soil temperature sensing as well as fiber-optic distributed temperature sensing (FO-DTS) approaches. Combining DTP data with co-located topographic and vegetation maps obtained using unmanned aerial vehicle (UAV) and electrical resistivity tomography (ERT) data allowed us to identify correspondences between surface and subsurface property distribution and in particular between topography, vegetation, shallow soil properties, and near-surface permafrost. Finally, the results highlight the considerable value of the newly developed DTP strategy for investigating the significant variability in and complexity of subsurface thermal and hydrological regimes in discontinuous permafrost regions.
2021013439 Mollaret, Coline (University of Fribourg, Department of Geosciences, Fribourg, Switzerland); Hilbich, Christin; Pellet, Cécile; Flores-Orozco, Adrian; Delaloye, Reynald and Hauck, Christian. Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites: The Cryosphere (Online), 13(10), p. 2557-2578, illus. incl. 1 table, 100 ref., 2019.
Mountain permafrost is sensitive to climate change and is expected to gradually degrade in response to the ongoing atmospheric warming trend. Long-term monitoring of the permafrost thermal state is a key task, but problematic where temperatures are close to 0°C because the energy exchange is then dominantly related to latent heat effects associated with phase change (ice-water), rather than ground warming or cooling. Consequently, it is difficult to detect significant spatio-temporal variations in ground properties (e.g. ice-water ratio) that occur during the freezing-thawing process with point scale temperature monitoring alone. Hence, electrical methods have become popular in permafrost investigations as the resistivities of ice and water differ by several orders of magnitude, theoretically allowing a clear distinction between frozen and unfrozen ground. In this study we present an assessment of mountain permafrost evolution using long-term electrical resistivity tomography monitoring (ERTM) from a network of permanent sites in the central Alps. The time series consist of more than 1000 datasets from six sites, where resistivities have been measured on a regular basis for up to 20 years. We identify systematic sources of error and apply automatic filtering procedures during data processing. In order to constrain the interpretation of the results, we analyse inversion results and long-term resistivity changes in comparison with existing borehole temperature time series. Our results show that the resistivity dataset provides valuable insights at the melting point, where temperature changes stagnate due to latent heat effects. The longest time series (19 years) demonstrates a prominent permafrost degradation trend, but degradation is also detectable in shorter time series (about a decade) at most sites. In spite of the wide range of morphological, climatological, and geological differences between the sites, the observed inter-annual resistivity changes and long-term tendencies are similar for all sites of the network.
2021013428 Shatilla, Nadine J. (McMaster University, Watershed Hydrology Group, Hamilton, ON, Canada) and Carey, Sean K. Assessing inter-annual and seasonal patterns of DOC and DOM quality across a complex alpine watershed underlain by discontinuous permafrost in Yukon, Canada: Hydrology and Earth System Sciences (HESS), 23(9), p. 3571-3591, illus. incl. 2 tables, 123 ref., 2019.
High-latitude environments store approximately half of the global organic carbon pool in peatlands, organic soils and permafrost, while large Arctic rivers convey an estimated 18-50 Tg C a-1 to the Arctic Ocean. Warming trends associated with climate change affect dissolved organic carbon (DOC) export from terrestrial to riverine environments. However, there is limited consensus as to whether exports will increase or decrease due to complex interactions between climate, soils, vegetation, and associated production, mobilization and transport processes. A large body of research has focused on large river system DOC and dissolved organic matter (DOM) lability and observed trends conserved across years, whereas investigation at smaller watershed scales show that thermokarst and fire have a transient impact on hydrologically mediated solute transport. This study, located in the Wolf Creek Research Basin situated ~20 km south of Whitehorse, YT, Canada, utilizes a nested design to assess seasonal and annual patterns of DOC and DOM composition across diverse landscape types (headwater, wetland and lake) and watershed scales. Peak DOC concentration and export occurred during freshet, as is the case in most northern watersheds; however, peaks were lower than a decade ago at the headwater site Granger Creek. DOM composition was most variable during freshet with high A254 and SUVA254 and low FI and BIX. DOM composition was relatively insensitive to flow variation during summer and fall. The influence of increasing watershed scale and downstream mixing of landscape contributions was an overall dampening of DOC concentrations and optical indices with increasing groundwater contribution. Forecasted vegetation shifts, enhanced permafrost and seasonal thaw, earlier snowmelt, increased rainfall and other projected climate-driven changes will alter DOM sources and transport pathways. The results from this study support a projected shift from predominantly organic soils (high aromaticity and less fresh) to decomposing vegetation (more fresh and lower aromaticity). These changes may also facilitate flow and transport via deeper flow pathways and enhance groundwater contributions to runoff.
2021013421 Wilkerson, Jordan (Harvard University, Department of Chemistry and Chemical Biology, Cambridge, MA); Dobosy, Ronald; Sayres, David S.; Healy, Claire; Dumas, Edward; Baker, Bruce and Anderson, James G. Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method: Atmospheric Chemistry and Physics, 19(7), p. 4257-4268, illus. incl. 2 tables, 56 ref., 2019.
The microbial by-product nitrous oxide (N2O), a potent greenhouse gas and ozone depleting substance, has conventionally been assumed to have minimal emissions in permafrost regions. This assumption has been questioned by recent in situ studies which have demonstrated that some geologic features in permafrost may, in fact, have elevated emissions comparable to those of tropical soils. However, these recent studies, along with every known in situ study focused on permafrost N2O fluxes, have used chambers to examine small areas (<50 m2). In late August 2013, we used the airborne eddy-covariance technique to make in situ N2O flux measurements over the North Slope of Alaska from a low-flying aircraft spanning a much larger area: around 310 km2. We observed large variability of N2O fluxes with many areas exhibiting negligible emissions. Still, the daily mean averaged over our flight campaign was 3.8 (2.2-4.7) mg N2O m-2 d-1 with the 90% confidence interval shown in parentheses. If these measurements are representative of the whole month, then the permafrost areas we observed emitted a total of around 0.04-0.09 g m-2 for August, which is comparable to what is typically assumed to be the upper limit of yearly emissions for these regions.
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