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2020019644 Tanski, George (Vrije Universiteit Amsterdam, Faculty of Science, Earth and Climate, Amsterdam, Netherlands); Wagner, Dirk; Knoblauch, Christian; Fritz, Michael; Sachs, Torsten and Lantuit, Hugues. Rapid CO2 release from eroding permafrost in seawater: Geophysical Research Letters, 46(20), p. 11244-11252, illus. incl. 1 table, 68 ref., October 28, 2019.
Permafrost is thawing extensively due to climate warming. When permafrost thaws, previously frozen organic carbon (OC) is converted into carbon dioxide (CO2) or methane, leading to further warming. This process is included in models as gradual deepening of the seasonal non-frozen layer. Yet, models neglect abrupt OC mobilization along rapidly eroding Arctic coastlines. We mimicked erosion in an experiment by incubating permafrost with seawater for an average Arctic open-water season. We found that CO2 production from permafrost OC is as efficient in seawater as without. For each gram (dry weight) of eroding permafrost, up to 4.3±1.0 mg CO2 will be released and 6.2±1.2% of initial OC mineralized at 4°C. Our results indicate that potentially large amounts of CO2 are produced along eroding permafrost coastlines, onshore and within nearshore waters. We conclude that coastal erosion could play an important role in carbon cycling and the climate system. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2019GL084303
2020019616 Wu Mousong (Wuhan University, Laboratory of Water Resources and Hydropower Engineering Science, Wuhan, China); Huang Jiesheng; Tan Xiao and Wu Jingwei. Water, salt and heat influences on carbon and nitrogen dynamics in seasonally frozen soils in Hetao irrigation district, Inner Mongolia, China: Pedosphere, 29(5), p. 632-641, illus. incl. 4 tables, 30 ref., October 2019.
URL: https://doi.org/10.1016/S1002-0160(17)60463-6
2020019646 Zhang Guofei (Nanjing Normal University, Laboratory of Virtual Geographic Environment, Nanjing, China); Nan Zhuotong; Wu Xiaobo; Ji Hailong and Zhao Shuping. The role of winter warming in permafrost change over the Qinghai-Tibet Plateau: Geophysical Research Letters, 46(20), p. 11261-11269, illus. incl. geol. sketch maps, 30 ref., October 28, 2019.
Winter warming is fast than summer warming on the Qinghai-Tibet Plateau (QTP). However, no assessment of winter warming effects on permafrost has been attempted. Here we conducted hypothetical control experiments and used the Noah land surface model to evaluate the impacts of winter warming on the QTP permafrost. The results show that air temperature in winter (November-April) was increasing at a rate of 0.66°C/decade during 1980s-2000s, over double that in summer (May-October). The mean annual ground temperature of permafrost increased by 0.13°C/decade. The summer warming dominated the variations in thermal regime of permafrost before 2000. After that, the influence of winter warming on permafrost thermal regime has gradually grown and exceeded that of summer warming. Winter warming has amplified the thermal degradation of permafrost. Our findings reveal that alpine continuous permafrost on the northern QTP has experienced a prominent regional warming due to rapid winter warming since 2000. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2019GL084292
2020019491 Hong, Wei-Li (Geological Survey of Norway (NGU), Trondheim, Norway); Lepland, Aivo; Himmler, Tobias; Kim, Ji-Hoon; Chand, Shyam; Sahy, Diana; Solomon, Evan A.; Rae, James W. B.; Martma, Tonu; Nam, Seung-Il and Knies, Jochen. Discharge of meteoric water in the eastern Norwegian Sea since the last glacial period: Geophysical Research Letters, 46(14), p. 8194-8204, illus. incl. sects., sketch map, 93 ref., July 28, 2019.
Submarine groundwater discharge could impact the transport of critical solutes to the ocean. However, its driver(s), significance over geological time scales, and geographical coverage are poorly understood. We characterize a submarine groundwater seep from the continental slope off northern Norway where substantial amount of meteoric water was detected. We reconstruct the seepage history from textural relationships and U-Th geochronology of authigenic minerals. We demonstrate how glacial-interglacial dynamics have promoted submarine groundwater circulation more than 100 km offshore and result in high fluxes of critical solutes to the ocean. Such cryosphere-hydrosphere coupling is likely common in the circum-Arctic implying that future decay of glaciers and permafrost in a warming Arctic is expected to attenuate such a coupled process and thus decreases the export of critical solutes. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2019GL084237
2020019486 Lu, Zhengyao (Lund University, Department of Physical Geography and Ecosystem Science, Lund, Sweden); Miller, Paul A.; Zhang, Qiong; Warlind, David; Nieradzik, Lars; Sjolte, Jesper; Li, Qiang and Smith, Benjamin. Vegetation pattern and terrestrial carbon variation in past warm and cold climates: Geophysical Research Letters, 46(14), p. 8133-8143, illus. incl. geol. sketch maps, 47 ref., July 28, 2019.
Understanding the transition of biosphere-atmosphere carbon exchange between glacial and interglacial climates can constrain uncertainties in its future projections. Using an individual-based dynamic vegetation model, we simulate vegetation distribution and terrestrial carbon cycling in past cold and warm climates and elucidate the forcing effects of temperature, precipitation, atmospheric CO2 concentration (pCO2), and landmass. Results are consistent with proxy reconstructions and reveal that the vegetation extent is mainly determined by temperature anomalies, especially in a cold climate, while precipitation forcing effects on global-scale vegetation patterns are marginal. The pCO2 change controls the global carbon balance with the fertilization effect of higher pCO2 linking to higher vegetation coverage, an enhanced terrestrial carbon sink, and increased terrestrial carbon storage. Our results indicate carbon transfer from ocean and permafrost/peat to the biosphere and atmosphere and highlight the importance of forest expansion as a driver of terrestrial ecosystem carbon stock from cold to warm climates. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2019GL083729
2020019488 Mu Cuicui (Lanzhou University, College of Earth and Environmental Sciences, Key Laboratory of Western China's Environmental Systems, Lanzhou, China); Zhang Tingjun; Abbott, Benjamin W.; Wang, Kang; Ge, Shemin; Sayedi, Sayedeh Sara; Fan, Chengyan and Peng, Xiaoqing. Organic carbon pools in the subsea permafrost domain since the last glacial maximum: Geophysical Research Letters, 46(14), p. 8166-8173, illus. incl. geol. sketch map, 1 table, sketch maps, 52 ref., July 28, 2019.
Sea level rise after the Last Glacial Maximum inundated several million square kilometers of Arctic permafrost, while estimates of organic carbon (OC) quantity and vulnerability to mineralization are exceedingly uncertain. We compiled geophysical measurements from Arctic continental shelves to estimate current subsea permafrost OC stocks. We found that marine transgression since the Last Glacial Maximum inundated approximately 3.92´106 km2 of permafrost, which contained 1,460±1,010 Pg OC in the top 25 m of sediment. We estimated that current subsea permafrost underlies an area of 2.30´106 km2 and contains 860±590 Pg OC, not including methane hydrates. Most of the ~600 Pg of OC that thawed after the marine transgression is still present on the continental shelves. Although our estimates of subsea OC storage remain highly uncertain due to the sparse and uneven distribution of data, they suggest that current estimates of subsea OC substantially underestimate a major component of the global carbon cycle. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2019GL083049
2020016180 Peng Cheng (China University of Geosciences, Laboratory of Geo-detection, Beijing, China); Zou Changchun; Lu, Z. Q.; Yu, C. Q.; Liu, A. Q.; Tang, Y. Y.; Hu, X. D.; Zhang, S. X.; Wen, H. J.; Li, Y. H. and Wang, W. C. Evidence of pore- and fracture-filling gas hydrates from geophysical logs in consolidated rocks of the Muli area, Qinghai-Tibetan Plateau permafrost, China: Journal of Geophysical Research: Solid Earth, 124(7), p. 6297-6314, illus. incl. 2 tables, geol. sketch maps, 67 ref., July 2019.
Natural gas hydrates were discovered in the Muli area of the Qinghai-Tibetan Plateau permafrost, which is an area of alpine permafrost in the midlatitudes. Resistivity models were employed to understand the distribution and accumulation mechanism of gas hydrates in the Muli area, as these models are suitable for use in detecting the presence and amount of pore- and fracture-filling gas hydrates in consolidated rocks, and geophysical logs were used to constrain gas hydrate saturation. The results show that resistivity logs are sensitive to gas hydrate saturation in consolidated rocks in the Muli area. Geophysical log analysis enabled the discovery of eleven pore-filling gas hydrate reservoirs (total thickness: 21.95 m) and nine fracture-filling gas hydrate reservoirs (total thickness: 90.55 m). It is hypothesized that gas accumulation is more likely to occur in fractures within mudstones due to good permeability and sealing properties and that fracture-filling gas hydrates are more likely to occur than pore-filling gas hydrates. Poor preservation conditions may thus be the key factor in the absence of gas hydrates in the eastern part of the study area. Evidence from geophysical logs shows that the upper boundary of the gas hydrate stability zone in the Muli area is at a depth of 133.25 m and that the lower boundary is deeper than 400 m. The results of this study are useful for further gas hydrate exploration in alpine permafrost at the midlatitudes. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JB016041
2020020530 Coperey, Antoine (Université Savoie-Mont Blanc, Université Grenoble Alpes, CNRS, Grenoble, France); Revil, Andre; Abdulsamad, F.; Stutz, B.; Duvillard, Pierre-Allain and Ravanel, L. Low-frequency induced polarization of porous media undergoing freezing; preliminary observations and modeling: Journal of Geophysical Research: Solid Earth, 124(5), p. 4523-4544, illus. incl. 4 tables, 81 ref., May 2019.
We investigate the thermal dependence of the complex conductivity of nine porous materials in the temperature range +20°C to -10 or -15°C. The selected samples include three soils, two granites, three clay-sands mixes, and one graphitic tight sandstone. A total of 12 experiments is conducted with one sample tested at three different salinities. Our goal is to use this database to extend the dynamic Stern layer polarization model in freezing conditions. We observe two polarization mechanisms, one associated with the effect of the change in the liquid water content and its salinity upon the polarization of the porous material. A second mechanism, at higher frequencies (>10 Hz), is likely associated with the polarization of ice. At low frequencies and above the freezing point, the in-phase and quadrature conductivities depend on temperature in a predictable way. This dependence is due to the dependence of the mobility of the charge carriers with temperature. Below the freezing point, the in-phase and quadrature conductivity follow a brutal decay with temperature. This dependence is modeled through an exponential freezing curve function. We were also able to determine how the (apparent) formation factor and surface conductivity change with temperature and water content below the freezing point. Our model is able to replicate the data at low frequencies and predicts correctly the fact that the ratio between the normalized chargeability and the surface conductivity is independent of the water content and temperature and equals a well-defined dimensionless number R. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JB017015
2020017418 Cunliffe, Andrew M. (University of Exeter, Geography, Exeter, United Kingdom); Tanski, George; Radosavljevic, Boris; Palmer, William F.; Sachs, Torsten; Lantuit, Hugues; Kerby, Jeffrey T. and Myers-Smith, Isla H. Rapid retreat of permafrost coastline observed with aerial drone photogrammetry: The Cryosphere (Online), 13(5), p. 1513-1528, illus. incl. 2 tables, 91 ref., May 2019.
Permafrost landscapes are changing around the Arctic in response to climate warming, with coastal erosion being one of the most prominent and hazardous features. Using drone platforms, satellite images, and historic aerial photographs, we observed the rapid retreat of a permafrost coastline on Qikiqtaruk - Herschel Island, Yukon Territory, in the Canadian Beaufort Sea. This coastline is adjacent to a gravel spit accommodating several culturally significant sites and is the logistical base for the Qikiqtaruk - Herschel Island Territorial Park operations. In this study we sought to (i) assess short-term coastal erosion dynamics over fine temporal resolution, (ii) evaluate short-term shoreline change in the context of long-term observations, and (iii) demonstrate the potential of low-cost lightweight unmanned aerial vehicles ("drones") to inform coastline studies and management decisions. We resurveyed a 500 m permafrost coastal reach at high temporal frequency (seven surveys over 40 d in 2017). Intra-seasonal shoreline changes were related to meteorological and oceanographic variables to understand controls on intra-seasonal erosion patterns. To put our short-term observations into historical context, we combined our analysis of shoreline positions in 2016 and 2017 with historical observations from 1952, 1970, 2000, and 2011. In just the summer of 2017, we observed coastal retreat of 14.5 m, more than 6 times faster than the long-term average rate of 2.2±0.1 ma-1 (1952-2017). Coastline retreat rates exceeded 1.0±0.1 m d-1 over a single 4 d period. Over 40 d, we estimated removal of ca. 0.96 m3 m-1 d-1. These findings highlight the episodic nature of shoreline change and the important role of storm events, which are poorly understood along permafrost coastlines. We found drone surveys combined with image-based modelling yield fine spatial resolution and accurately geolocated observations that are highly suitable to observe intra-seasonal erosion dynamics in rapidly changing Arctic landscapes.
DOI: 10.5194/tc-13-1513-2019
2020017629 Elder, Clayton D. (University of California, Department of Earth System Science, Irvine, CA); Schweiger, Matthew; Lam, B.; Crook, E. D.; Xu, Xiaomei; Walker, J.; Walter Anthony, K. M. and Czimczik, Claudia I. Seasonal sources of whole-lake CH4 and CO2 emissions from interior Alaskan thermokarst lakes: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1209-1229, illus. incl. 4 tables, 45 ref., May 2019.
The lakes that form via ice-rich permafrost thaw emit CH4 and CO2 to the atmosphere from previously frozen ancient permafrost sources. Despite this potential to positively feedback to climate change, lake carbon emission sources are not well understood on whole-lake scales, complicating upscaling. In this study, we used observations of radiocarbon (14C) and stable carbon (13C) isotopes in the summer and winter dissolved CH4 and CO2 pools, ebullition-CH4, and multiple independent mass balance approaches to characterize whole-lake emission sources and apportion annual emission pathways. Observations focused on five lakes with variable thermokarst in interior Alaska. The 14C age of discrete ebullition-CH4 seeps ranged from 395±15 to 28,240±150 YBP across all study lakes; however, dissolved 14CH4 was younger than 4,730 YBP. In the primary study lake, Goldstream L., the integrated whole-lake 14C age of ebullition-CH4, as determined by three different approaches, ranged from 3,290 to 6,740 YBP. A new dissolved-14C-CH4-based approach to estimating ebullition 14C age and flux showed close agreement to previous ice-bubble surveys and bubble-trap flux estimates. Differences in open water versus ice-covered dissolved gas concentrations and their 14C and 13C isotopes revealed the influence of winter ice trapping and forcing ebullition-CH4 into the underlying water column, where it comprised 50% of the total dissolved CH4 pool by the end of winter. Across the study lakes, we found a relationship between the whole-lake 14C age of dissolved CH4 and CO2 and the extent of active thermokarst, representing a positive feedback system that is sensitive to climate warming. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004735
2020017630 Fuchs, Matthias (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Lenz, Josefine; Jock, Suzanne; Nitze, Ingmar; Jones, Benjamin M.; Strauss, Jens; Günther, Frank and Grosse, Guido. Organic carbon and nitrogen stocks along a thermokarst lake sequence in Arctic Alaska: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1230-1247, illus. incl. 4 tables, sketch maps, 86 ref., May 2019.
Thermokarst lake landscapes are permafrost regions, which are prone to rapid (on seasonal to decadal time scales) changes, affecting carbon and nitrogen cycles. However, there is a high degree of uncertainty related to the balance between carbon and nitrogen cycling and storage. We collected 12 permafrost soil cores from six drained thermokarst lake basins (DTLBs) along a chronosequence north of Teshekpuk Lake in northern Alaska and analyzed them for carbon and nitrogen contents. For comparison, we included three lacustrine cores from an adjacent thermokarst lake and one soil core from a non thermokarst affected remnant upland. This allowed to calculate the carbon and nitrogen stocks of the three primary landscape units (DTLB, lake, and upland), to reconstruct the landscape history, and to analyze the effect of thermokarst lake formation and drainage on carbon and nitrogen stocks. We show that carbon and nitrogen contents and the carbon-nitrogen ratio are considerably lower in sediments of extant lakes than in the DTLB or upland cores indicating degradation of carbon during thermokarst lake formation. However, we found similar amounts of total carbon and nitrogen stocks due to the higher density of lacustrine sediments caused by the lack of ground ice compared to DTLB sediments. In addition, the radiocarbon-based landscape chronology for the past 7,000 years reveals five successive lake stages of partially, spatially overlapping DTLBs in the study region, reflecting the dynamic nature of ice-rich permafrost deposits. With this study, we highlight the importance to include these dynamic landscapes in future permafrost carbon feedback models. Abstract Copyright (2019). The Authors.
DOI: 10.1029/2018JG004591
2020017633 Grant, Robert F. (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Mekonnen, Zelalem A.; Riley, William J.; Arora, Bhavna and Torn, Margaret S. Modeling climate change impacts on an Arctic polygonal tundra; 2, Changes in CO2 and CH4 exchange depend on rates of permafrost thaw as affected by changes in vegetation and drainage: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1323-1341, illus. incl. 4 tables, 57 ref., May 2019.
Model projections of future CO2 and CH4 exchange in Arctic tundra diverge widely. Here we used ecosys to examine how climate change will affect CO2 and CH4 exchange in troughs, rims, and centers of a coastal polygonal tundra landscape at Barrow, AK. The model was shown to simulate diurnal and seasonal variation in CO2 and CH4 fluxes associated with those in air and soil temperatures (Ta and Ts) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising Ta, atmospheric CO2 concentrations (Ca), and precipitation (P) increased net primary productivity (NPP) from 50-150 g C m-2 y-1, consistent with current biometric estimates, to 200-250 g C m-2 y-1. Concurrent increases in heterotrophic respiration (Rh) were slightly smaller, so that net CO2 exchange rose from values of -25 (net emission) to +50 (net uptake) g C m-2 y-1 to ones of -10 to +65 g C m-2 y-1. Increases in net CO2 uptake were largely offset by increases in CH4 emissions from 0-6 to 1-20 g C m-2 y-1, reducing gains in net ecosystem productivity. These increases in net CO2 uptake and CH4 emissions were modeled with hydrological boundary conditions that were assumed not to change with climate. Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004645
2020017632 Grant, Robert F. (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Mekonnen, Zelalem A. and Riley, William J. Modeling climate change impacts on an arctic polygonal tundra; 1, Rates of permafrost thaw depend on changes in vegetation and drainage: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1308-1322, illus. incl. 5 tables, 47 ref., May 2019.
Model projections of permafrost thaw during the next century diverge widely. Here we used ecosys to examine how climate change will affect permafrost thaw in a polygonal tundra at Barrow AK. The model was tested against diurnal and seasonal variation in energy exchange, soil heat flux, soil temperature (Ts), and active layer depth (ALD) measured during 2014 and 2015, and interannual variation in ALD measured from 1991 to 2015. During RCP 8.5 climate change from 2015 to 2085, increases in Ta and precipitation (P) to 6.2°C and 27% above current values, and in atmospheric CO2 concentrations (Ca) to 763 mmol mol-1, altered energy exchange by increasing leaf area index of dominant sedge relative to that of moss. Increased Ca and sedge leaf area index imposed greater stomatal control of transpiration and reduced soil heat fluxes, slowing soil warming, limiting increases in evapotranspiration, and thereby causing gradual soil wetting. Consequently, increases in surface Ts and ALD of 2.4-4.7°C and 21-24 cm above current values were modeled after 70 years. ALD increase was slowed if model boundary conditions were altered to improve landscape drainage. These rates were smaller than those of earlier modeling studies, some of which did not account for changes in vegetation, but are closer to those derived from current studies of warming impacts in the region. Therefore, accounting for climate change effects on vegetation density and composition, and consequent effects on surface energy budgets, will cause slower increases in Ts and ALD to be modeled during climate change simulations. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004644
2020017624 Lin Shan (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Wang Genxu; Feng Jinming; Dan Li; Sun Xiangyang; Hu Zhaoyong; Chen Xiaopeng and Xiao Xiao. A carbon flux assessment driven by environmental factors over the Tibetan Plateau and various permafrost regions: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1132-1147, illus. incl. 5 tables, 58 ref., May 2019.
In this study, the spatiotemporal changes in net primary production (NPP) and drivers, including climate change, atmospheric CO2 concentration and land use change, over the Tibetan Plateau from 1979 to 2016 were investigated using the version 4.5 of the Community Land Model. Based on high-resolution atmospheric forcing data, six numerical experiments were designed to assess the relative contribution of different environmental factors on NPP. Our simulation results suggest that NPP over the Tibetan Plateau has increased significantly at a rate of 2.25 Tg C/year2 since 1979. At the plateau scale, changes in precipitation, CO2 concentration, and land use change contributed approximately 63.3%, 16.7%, and 9.5% to the interannual variation of NPP, respectively. Temperature did not exert a significant effect on the trends of NPP, which results from the increasing temperature enhancing the autotrophic respiration (AR) more than the gross primary production. We also divided the alpine grasslands into four types, including alpine meadow of permafrost, alpine steppe of permafrost, alpine meadow of seasonal frost, and alpine steppe of seasonal frost. We found that the increasing rate of NPP in permafrost regions was significantly higher than that in seasonal frost regions. Compared with other factors, precipitation change played a dominant role in the NPP over the four different types of grasslands. Temperature-induced change on NPP and AR was larger in the alpine meadow regions compared to in the alpine steppe regions. In addition, NPP and AR showed a more remarkable response to temperature change over alpine meadow of permafrost than other regions. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004789
2020017634 Mao Chao (Chinese Academy of Sciences, Institute of Botany, Laboratory of Vegetation and Environmental Change, Beijing, China); Kou Dan; Wang Guanqin; Peng Yunfeng; Yang Guibiao; Liu Futing; Zhang Jinbo and Yang Yuanhe. Trajectory of topsoil nitrogen transformations along a thermo-erosion gully on the Tibetan Plateau: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1342-1354, illus. incl. 1 table, 72 ref., May 2019.
Permafrost thaw, especially thermokarst formation, that is, ground collapse due to thawing of ice-rich permafrost, is expected to alter soil gross nitrogen (N) transformations, which can regulate plant productivity and ecosystem carbon cycle. However, it remains unclear how thermokarst formation modifies soil N processes in permafrost ecosystems. Here 15N pool dilution techniques were used to evaluate changes in topsoil gross N transformations during various thaw stages (early, middle, and late stages) along a thermo-erosion gully on the Tibetan Plateau. Structural equation modeling was then conducted to explore the relative importance of biotic and abiotic factors in affecting soil gross N transformations. The results showed that topsoil gross N mineralization (GNM) decreased at the three stages, reflecting declined inorganic N production after permafrost collapse. In contrast, topsoil gross nitrification increased only during the early stage. Additionally, the ratio of microbial N immobilization to GNM was enhanced during the middle and late stages, indicating a stronger microbial N limitation after thermokarst formation. The structural equation modeling analysis revealed that soil moisture played an important role in modulating gross N transformations. For GNM, decreased soil moisture had inhibiting effects via regulating the microbial biomass, microbial community, and enzyme activities along the thaw sequence. For gross nitrification, declined soil moisture exerted facilitating effects directly by improving oxygen availability and indirectly by modulating the abundances of ammonia-oxidizing archaea and bacteria during the early stage. Overall, these results demonstrated that thermokarst formation altered soil N processes, potentially triggering interactions between ecosystem N and carbon cycles after permafrost thaw. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004805
2020016111 Maslakov, Alexey (Lomonosov Moscow State University, Faculty of Geography, Moscow, Russian Federation); Shabanova, Natalia; Zamolodchikov, Dmitry; Volobuev, Vasili and Kraev, Gleb. Permafrost degradation within eastern Chukotka CALM sites in the 21st century based on CMIP5 climate models: Geosciences (Basel), 9(5), Article no. 232, illus. incl. 8 tables, sketch map, 59 ref., May 2019. This article belongs to the special issue Cryosphere II.
Permafrost degradation caused by contemporary climate change significantly affects arctic regions. Active layer thickening combined with the thaw subsidence of ice-rich sediments leads to irreversible transformation of permafrost conditions and activation of exogenous processes, such as active layer detachment, thermokarst and thermal erosion. Climatic and permafrost models combined with a field monitoring dataset enable the provision of predicted estimations of the active layer and permafrost characteristics. In this paper, we present the projections of active layer thickness and thaw subsidence values for two Circumpolar Active Layer Monitoring (CALM) sites of Eastern Chukotka coastal plains. The calculated parameters were used for estimation of permafrost degradation rates in this region for the 21st century under various IPCC climate change scenarios. According to the studies, by the end of the century, the active layer will be 6-13% thicker than current values under the RCP (Representative Concentration Pathway) 2.6 climate scenario and 43-87% under RCP 8.5. This process will be accompanied by thaw subsidence with the rates of 0.4-3.7 cm·a-1. Summarized surface level lowering will have reached up to 5 times more than current active layer thickness. Total permafrost table lowering by the end of the century will be from 150 to 310 cm; however, it will not lead to non-merging permafrost formation.
DOI: 10.3390/geosciences9050232
2020017621 Zhang Xianliang (Shenyang Agricultural University, College of Forestry, Shenyang, China); Bai Xueping; Hou Meiting; Chen Zhenju and Manzanedo, Rubén D. Warmer winter ground temperatures trigger rapid growth of Dahurian larch in the permafrost forests of northeast China: Journal of Geophysical Research: Biogeosciences, 124(5), p. 1088-1097, illus. incl. 1 table, 52 ref., May 2019.
Permafrost degradation due to rapid increase in ground surface temperature (GST) in recent years may strongly affect boreal forest ecosystems. However, comparatively few studies have explored how changes in permafrost affect tree growth dynamics in boreal forest. Here, we used a tree ring network of 12 Dahurian larch (Larix gmelinii) sites across permafrost regions in northeast China. We observed an increase in L. gmelinii growth over the past decade, seemingly linked to a shift in their climatic limitations, where winter GST has become the most strongly limiting factor for L. gmelinii growth. The recent increase in growth was particularly strong in older trees (>300 years), which could be related to older trees having a more developed root system. GST was the main limiting factor for tree growth. While summer GST had a somewhat consistently positive correlation with tree growth, winter GST has shifted from a negative to a strongly positive correlation with growth in the last decade, coincidental with a sharp increase in winter GST since 2004. Winter GST is also strongly correlated with the rapidly thawing permafrost dynamics. Overall, our results suggest a link between recent changes in the permafrost and shifts in climate-growth correlations for one of the main boreal tree species. As a result, L. gmelinii has experienced an important increase in radial growth that may indicate that, unlike what has been reported for other boreal species, it may temporally benefit from warming climate in the continuous permafrost region of the Asian boreal forests. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004882
2020019438 Sun Xiyong (China Geological Survey, China Aero Geophysical Survey & Remote Sensing Center for Natural Resources, Beijing, China); Zhang Ruijiang; Huang Wei; Sun Ang; Lin Liangjun; Xu Honggen and Jiang Decai. The response between glacier evolution and eco-geological environment on the Qinghai-Tibet Plateau: China Geology, 2(1), p. 1-7, illus. incl. 1 table, geol. sketch map, 33 ref., March 2019.
Based on the remote sensing survey and monitoring results of snow lines on the Qinghai-Tibet Plateau, the authors analyzed the following eco-geological factors such as water resources, permafrost, desertification, wetlands, lake, geological disasters, sea-level rising, earthquake, etc., affected by the change of snow lines over the past 40 years, and discuss the response between glacier evolution and the eco-geological environment preliminarily.
DOI: 10.31035/cg2018078
2020015818 Badmaev, Nimazhap (Russian Academy of Sciences, Siberian Branch, Institute of General and Experimental Biology, Ulan-Ude, Russian Federation) and Bazarov, Aleksandr. Monitoring network for atmospheric and soil parameters measurements in permafrost area of Buryatia, Russian Federation: Geosciences (Basel), 9(1), Article no. 6, illus. incl. 1 table, sketch map, 19 ref., January 2019. This article belongs to the special issue Permafrost landscapes; classification and mapping.
The monitoring network for the measurement of atmospheric and soil climate parameters was created at the southern boundary of the permafrost zone within the territory of the Republic of Buryatia, Russian Federation. Based on the obtained data, the processes of soil freezing and thawing were studied. Negative temperatures in cold soils occurred within 5.5-6 months, whereas the subsoil was in a thawed state most of the year. On the contrary, permafrost-affected soils were thawed for 4.5-5 months, remaining frozen in the subsoil for most of the year. We propose referring to the observed spatial-temporal differences in the temperature dynamics as the "mirror imaging" of the distribution of heat and cold (frost) in the studied soils of the permafrost zone.
DOI: 10.3390/geosciences9010006
2020015829 Kalinicheva, Svetlana (Russian Academy of Sciences, Siberian Branch, Melnikov Permafrost Institute, Yakutsk, Russian Federation); Fedorov, Alexander N. and Zhelezniak, Mikhail N. Mapping mountain permafrost landscapes in Siberia using Landsat thermal imagery: Geosciences (Basel), 9(1), Article no. 4, illus. incl. 2 tables, sketch maps, 26 ref., January 2019. This article belongs to the special issue Permafrost landscapes; classification and mapping.
Intensive development of South Yakutia, a mountainous area in the Russian sporadic permafrost zone, must be founded on knowledge about regional permafrost conditions. New permafrost maps for mountainous areas in South Yakutia (the Elkon Mountains and the Olekma-Chara Upland) are presented that provide a more detailed and updated description of permafrost distribution in the area than those that were hitherto available. These maps are based on the previously-developed and tested method of detecting permafrost and unfrozen ground using Landsat-5/TM satellite data with relatively high resolution. The method represents a scheme for permafrost identification based on a set of landscape indicators: terrain elevation, slope angle and exposition, vegetation, snow cover, and land surface temperature (LST). A correlation analysis of satellite data to full-scale field data has been carried out for the two areas under consideration. Indicator properties of LST obtained by Landsat-5/TM Band 6 Infrared have been characterized in detail for detection and regional mapping of permafrost. The effect of landscape factors (landscape cryo-indicators) on ground temperature and condition, frozen or unfrozen reflected in LST intensity, is demonstrated.
DOI: 10.3390/geosciences9010004
2020015835 Yakushev, Vladimir S. (Gubkin Russian State University of Oil and Gas (National Research University), Department of Gas and Gas Condensate Field Development and Operation, Moscow, Russian Federation). Experimental modeling of methane hydrate formation and decomposition in wet heavy clays in Arctic regions: Geosciences (Basel), 9(1), Article no. 13, illus., 18 ref., January 2019. This article belongs to the special issue Gas and gas hydrate in permafrost.
Experimental studies on clay sample saturation by methane hydrates proved that clay particles play an important role in the hydrate accumulation and decomposition processes in sediments. Depending on water content, the same clay mineral can serve as inhibitor, neutral component and promoter of hydrate formation. Wet clay is a good mineral surface for hydrate formation, but clays represent the worst media for hydrate accumulation and existence. Nevertheless, there are many observations of hydrate presence in clay-containing sediments, especially offshore. Experimental modelling of metastable hydrate decomposition in sediment samples recovered from permafrost in "Yamal crater" in the Russian Arctic has shown that metastable hydrates located in frozen, salted clays can generate huge volumes of gas, even with a negligible (tenth and hundredth of a degree) temperature rise.
DOI: 10.3390/geosciences9010013
2020017364 Falatkova, Kristyna (Charles University, Department of Physical Geography and Geoecology, Prague, Czech Republic); Sobr, Miroslav; Neureiter, Anton; Schöner, Wolfgang; Jansky, Bohumir; Häusler, Hermann; Engel, Zbynek and Benes, Vojtech. Development of proglacial lakes and evaluation of related outburst susceptibility at the Adygine ice-debris complex, northern Tien Shan: Earth Surface Dynamics, 7(1), p. 301-320, illus. incl. 5 tables, 104 ref., 2019.
The formation and development of glacial lakes in mountainous regions is one of the consequences of glacier recession. Such lakes may drain partially or completely when the stability of their dams is disturbed or as a consequence of impacts. We present a case study from the Central Asian mountain range of Tien Shan--a north-oriented tributary of the Adygine Valley, where the retreat of a polythermal glacier surrounded by permafrost has resulted in the formation of several generations of lakes. The aim of this study was to analyse the past development of different types of glacial lakes influenced by the same glacier, to project the site's future development, and to evaluate the outburst susceptibility of individual lakes with an outlook for expected future change. We addressed the problem using a combination of methods, namely bathymetric, geodetic and geophysical on-site surveys, satellite images and digital elevation model analysis, and modelling of glacier development. Based on this case of the glacial lakes being of varied age and type, we demonstrated the significance of glacier ice in lake development. Lake 3, which is in contact with the glacier terminus, has changed rapidly over the last decade, expanding both in area and depth and increasing its volume by more than 13 times (7800 to 106 000 m3). The hydrological connections and routing of glacier meltwater have proved to be an important factor as well, since most lakes in the region are drained by subsurface channels. As the site is at the boundary between continuous and discontinuous permafrost, the subsurface water flow is strongly governed by the distribution of non-frozen zones above, within, or beneath the perennially frozen ground. In the evaluation of lake outburst susceptibility, we have highlighted the importance of field data, which can provide crucial information on lake stability. In our case, an understanding of the hydrological system at the site, and its regime, helped to categorise Lake 2 as having low outburst susceptibility, while Lake 1 and Lake 3 were labelled as lakes with medium outburst susceptibility. Further development of the site will be driven mainly by rising air temperatures and increasingly negative glacier mass balance. All three climate model scenarios predicted a significant glacier areal decrease by 2050, specifically leaving 73.2% (A1B), 62.3% (A2), and 55.6% (B1) of the extent of the glacier in 2012. The glacier retreat will be accompanied by changes in glacier runoff, with the first peak expected around 2020, and the formation of additional lakes.
DOI: 10.5194/esurf-7-301-2019
2020017347 Köhler, Andreas (University of Oslo, Department of Geosciences, Oslo, Norway) and Weidle, Christian. Potentials and pitfalls of permafrost active layer monitoring using the HVSR method; a case study in Svalbard: Earth Surface Dynamics, 7(1), p. 1-16, illus. incl. 1 table, sketch map, 55 ref., 2019.
Time-lapse monitoring of the subsurface using ambient seismic noise is a popular method in environmental seismology. We assess the reliability of the horizontal-to-vertical spectral ratio (HVSR) method for monitoring seasonal permafrost active layer variability in northwest Svalbard. We observe complex HVSR variability between 1 and 50 Hz in the record of a temporary seismic deployment covering frozen and thawed soil conditions between April and August 2016. While strong variations are due to changing noise conditions, mainly affected by wind speed and degrading coupling of instruments during melt season, a seasonal trend is observed at some stations that has most likely a subsurface structural cause. A HVSR peak emerges close to the Nyquist frequency (50 Hz) in beginning of June which is then gradually gliding down, reaching frequencies of about 15-25 Hz in the end of August. This observation is consistent with HVSR forward modeling for a set of structural models that simulate different stages of active layer thawing. Our results reveal a number of potential pitfalls when interpreting HVSRs and suggest a careful analysis of temporal variations since HVSR seasonality is not necessarily related to changes in the subsurface. In addition, we investigate if effects of changing noise sources on HVSRs can be avoided by utilizing a directional, narrowband (4.5 Hz) repeating seismic tremor which is observed at the permanent seismic broadband station in the study area. A significant change of the radial component HVSR shape during summer months is observed for all tremors. We show that a thawed active layer with very low seismic velocities would affect Rayleigh wave ellipticities in the tremor frequency band. We compile a list of recommendations for future experiments, including comments on network layouts suitable for array beamforming and waveform correlation methods that can provide essential information on noise source variability.
DOI: 10.5194/esurf-7-1-2019
2020019267 Chuvilin, Evgeny (Skolkovo Institute of Science and Technology, Moscow, Russian Federation); Bukhanov, Boris; Davletshina, Dinara; Grebenkin, Sergey and Istomin, Vladimir. Dissociation and self-preservation of gas hydrates in permafrost: Geosciences (Basel), 8(12), Article 431, illus. incl. 1 table, 62 ref., December 2018.
Gases releasing from shallow permafrost above 150 m may contain methane produced by the dissociation of pore metastable gas hydrates, which can exist in permafrost due to self-preservation. In this study, special experiments were conducted to study the self-preservation kinetics. For this, sandy samples from gas-bearing permafrost horizons in West Siberia were first saturated with methane hydrate and frozen and then exposed to gas pressure drop below the triple-phase equilibrium in the "gas-gas hydrate-ice" system. The experimental results showed that methane hydrate could survive for a long time in frozen soils at temperatures of -5 to -7 °C at below-equilibrium pressures, thus evidencing the self-preservation effect. The self-preservation of gas hydrates in permafrost depends on its temperature, salinity, ice content, and gas pressure. Prolonged preservation of metastable relict hydrates is possible in ice-rich sandy permafrost at -4 to -5 °C or colder, with a salinity of <0.1% at depths below 20-30 m.
DOI: 10.3390/geosciences8120431
2020019292 Chuvilin, Evgeny (Skolkovo Institute of Science and Technology, Innovation Center Skolkovo, Moscow, Russian Federation) and Davletshina, Dinara. Formation and accumulation of pore methane hydrates in permafrost; experimental modeling: Geosciences (Basel), 8(12), Article 467, illus. incl. 3 tables, 61 ref., December 2018.
Favorable thermobaric conditions of hydrate formation and the significant accumulation of methane, ice, and actual data on the presence of gas hydrates in permafrost suggest the possibility of their formation in the pore space of frozen soils at negative temperatures. In addition, today there are several geological models that involve the formation of gas hydrate accumulations in permafrost. To confirm the literature data, the formation of gas hydrates in permafrost saturated with methane has been studied experimentally using natural artificially frozen in the laboratory sand and silt samples, on a specially designed system at temperatures from 0 to -8 °C. The experimental results confirm that pore methane hydrates can form in gas-bearing frozen soils. The kinetics of gas hydrate accumulation in frozen soils was investigated in terms of dependence on the temperature, excess pressure, initial ice content, salinity, and type of soil. The process of hydrate formation in soil samples in time with falling temperature from +2 °C to -8 °C slows down. The fraction of pore ice converted to hydrate increased as the gas pressure exceeded the equilibrium. The optimal ice saturation values (45-65%) at which hydrate accumulation in the porous media is highest were found. The hydrate accumulation is slower in finer-grained sediments and saline soils. The several geological models are presented to substantiate the processes of natural hydrate formation in permafrost at negative temperatures.
DOI: 10.3390/geosciences8120467
2020019278 Fedorov, Alexander (Melnikov Permafrost Institute, Yakutsk, Russian Federation); Vasilyev, Nikolay; Torgovkin, Yaroslav; Shestakova, Alena; Varlamov, Stepan; Zheleznyak, Mikhail; Shepelev, Viktor; Konstantinov, Pavel; Kalinicheva, Svetlana; Basharin, Nikolay; Makarov, Viktor; Ugarov, Innokenty; Efremov, Peter; Argunov, Radomir; Egorova, Larisa; Samsonova, Vera; Shepelev, Andrey; Vasiliev, Alexander; Ivanova, Rosaliya; Galanin, Alexey; Lytkin, Vasily; Kuzmin, Georgy and Kunitsky, Viktor. Permafrost-landscape map of the Republic of Sakha (Yakutia) on a scale 1:1,500,000: Geosciences (Basel), 8(12), Article 465, illus. incl. 3 tables, 60 ref., December 2018.
The history of permafrost landscape map compilation is related to the study of ecological problems with permafrost. Permafrost-landscape studies are now widely used in geocryological mapping. Permafrost-landscape classifications and mapping are necessary for studying the trends in development of the natural environment in northern and high-altitude permafrost regions. The cryogenic factor in the permafrost zone plays a leading role in the differentiation of landscapes, so it must be considered during classification construction. In this study, a map's special content was developed using publications about Yakutian nature, archive sources from academic institutes, the interpretation of satellite images, and special field studies. Overlays of 20 types of terrain, identified by geological and geomorphological features, and 36 types of plant groupings, allowed the systematization of permafrost temperature and active layer thickness in 145 landscape units with relatively homogeneous permafrost-landscape conditions in the Sakha (Yakutia) Republic. This map serves as a basis for applied thematic maps related to the assessment and forecast of permafrost changes during climate warming and anthropogenic impacts.
DOI: 10.3390/geosciences8120465
2020019289 Streletskaya, Irina (Moscow State University, Department of Cryolitology and Glaciology, Moscow, Russian Federation); Vasiliev, Alexander; Oblogov, Gleb and Streletskiy, Dmitry. Methane content in ground ice and sediments of the Kara Sea coast: Geosciences (Basel), 8(12), Article 434, illus. incl. 3 tables, 54 ref., December 2018.
Permafrost degradation of coastal and marine sediments of the Arctic Seas can result in large amounts of methane emitted to the atmosphere. The quantitative assessment of such emissions requires data on variability of methane content in various types of permafrost strata. To evaluate the methane concentrations in sediments and ground ice of the Kara Sea coast, samples were collected at a series of coastal exposures. Methane concentrations were determined for more than 400 samples taken from frozen sediments, ground ice and active layer. In frozen sediments, methane concentrations were lowest in sands and highest in marine clays. In ground ice, the highest concentrations above 500 ppmV and higher were found in massive tabular ground ice, with much lower methane concentrations in ground ice wedges. The mean isotopic composition of methane is -68.6 ppm in permafrost and -63.6 ppm in the active layer indicative of microbial genesis. The isotopic compositions of the active layer is enriched relative to permafrost due to microbial oxidation and become more depleted with depth. Ice-rich sediments of Kara Sea coasts, especially those with massive tabular ground ice, hold large amounts of methane making them potential sources of methane emissions under projected warming temperatures and increasing rates of coastal erosion.
DOI: 10.3390/geosciences8120434
2020020486 Krickov, Ivan V. (Tomsk State University, BIO-GEO-CLIM Laboratory, Tomsk, Russian Federation); Lim, Artem G.; Manasypov, Rinat M.; Loiko, Sergey V.; Shirokova, Liudmila S.; Kirpotin, Sergey N.; Karlsson, Jan and Pokrovsky, Oleg S. Riverine particulate C and N generated at the permafrost thaw front; case study of western Siberian rivers across a 1700 km latitudinal transect: Biogeosciences, 15(22), p. 6867-6884, illus. incl. 1 table, sketch map, 102 ref., November 2018.
In contrast to numerous studies on the dynamics of dissolved (<0.45 mm) elements in permafrost-affected high-latitude rivers, very little is known of the behavior of river suspended (>0.45 mm) matter (RSM) in these regions. In order to test the effect of climate, permafrost and physio-geographical landscape parameters (bogs, forest and lake coverage of the watershed) on RSM and particulate C, N and P concentrations in river water, we sampled 33 small and medium-sized rivers (10-100 000 km2 watershed) along a 1700 km N-S transect including both permafrost-affected and permafrost-free zones of the Western Siberian Lowland (WSL). The concentrations of C and N in RSM decreased with the increase in river watershed size, illustrating (i) the importance of organic debris in small rivers which drain peatlands and (ii) the role of mineral matter from bank abrasion in larger rivers. The presence of lakes in the watershed increased C and N but decreased P concentrations in the RSM. The C:N ratio in the RSM reflected the source from the deep soil horizon rather than surface soil horizon, similar to that of other Arctic rivers. This suggests the export of peat and mineral particles through suprapermafrost flow occurring at the base of the active layer. There was a maximum of both particulate C and N concentrations and export fluxes at the beginning of permafrost appearance, in the sporadic and discontinuous zone (62-64 ° N). This presumably reflected the organic matter mobilization from newly thawed organic horizons in soils at the active latitudinal thawing front. The results suggest that a northward shift of permafrost boundaries and an increase in active layer thickness may increase particulate C and N export by WSL rivers to the Arctic Ocean by a factor of 2, while P export may remain unchanged. In contrast, within a long-term climate warming scenario, the disappearance of permafrost in the north, the drainage of lakes and transformation of bogs to forest may decrease C and N concentrations in RSM by 2 to 3 times.
DOI: 10.5194/bg-15-6867-2018
2020017283 Luo Lihui (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, State Key Laboratory of Frozen Soils Engineering, Lanzhou, China); Zhang Zhongqiong; Ma Wei; Yi Shuhua and Zhuang Yanli. PIC v1.3; comprehensive R package for computing permafrost indices with daily weather observations and atmospheric forcing over the Qinghai-Tibet Plateau: Geoscientific Model Development (GMD), 11(6), p. 2475-2491, illus. incl. 5 tables, 60 ref., June 2018.
An R package was developed for computing permafrost indices (PIC v1.3) that integrates meteorological observations, gridded meteorological datasets, soil databases, and field measurements to compute the factors or indices of permafrost and seasonal frozen soil. At present, 16 temperature- and depth-related indices are integrated into the PIC v1.3 R package to estimate the possible trends of frozen soil in the Qinghai-Tibet Plateau (QTP). These indices include the mean annual air temperature (MAAT), mean annual ground surface temperature (MAGST), mean annual ground temperature (MAGT), seasonal thawing-freezing n factor (nt/nf), thawing-freezing degree-days for air and the ground surface (DDTa/DDTs/DDFa/DDFs), temperature at the top of the permafrost (TTOP), active layer thickness (ALT), and maximum seasonal freeze depth. PIC v1.3 supports two computational modes, namely the stations and regional calculations that enable statistical analysis and intuitive visualization of the time series and spatial simulations. Datasets of 52 weather stations and a central region of the QTP were prepared and simulated to evaluate the temporal-spatial trends of permafrost with the climate. More than 10 statistical methods and a sequential Mann-Kendall trend test were adopted to evaluate these indices in stations, and spatial methods were adopted to assess the spatial trends. Multiple visual methods were used to display the temporal and spatial variability of the stations and region. Simulation results show extensive permafrost degradation in the QTP, and the temporal-spatial trends of the permafrost conditions in the QTP are close to those of previous studies. The transparency and repeatability of the PIC v1.3 package and its data can be used and extended to assess the impact of climate change on permafrost.
DOI: 10.5194/gmd-11-2475-2018
2020017275 Castro-Morales, Karel (Max Planck Institute for Biogeochemistry, Jena, Germany); Kleinen, Thomas; Kaiser, Sonja; Zaehle, Sonke; Kittler, Fanny; Kwon, Min Jung; Beer, Christian and Göckede, Mathias. Year-round simulated methane emissions from a permafrost ecosystem in northeast Siberia: Biogeosciences, 15(9), p. 2691-2722, illus. incl. 2 tables, 107 ref., May 2018.
Wetlands of northern high latitudes are ecosystems highly vulnerable to climate change. Some degradation effects include soil hydrologic changes due to permafrost thaw, formation of deeper active layers, and rising topsoil temperatures that accelerate the degradation of permafrost carbon and increase in CO2 and CH4 emissions. In this work we present 2 years of modeled year-round CH4 emissions into the atmosphere from a Northeast Siberian region in the Russian Far East. We use a revisited version of the process-based JSBACH-methane model that includes four CH4 transport pathways: plant-mediated transport, ebullition and molecular diffusion in the presence or absence of snow. The gas is emitted through wetlands represented by grid cell inundated areas simulated with a TOPMODEL approach. The magnitude of the summertime modeled CH4 emissions is comparable to ground-based CH4 fluxes measured with the eddy covariance technique and flux chambers in the same area of study, whereas wintertime modeled values are underestimated by 1 order of magnitude. In an annual balance, the most important mechanism for transport of methane into the atmosphere is through plants (61%). This is followed by ebullition (~35%), while summertime molecular diffusion is negligible (0.02%) compared to the diffusion through the snow during winter (~4%). We investigate the relationship between temporal changes in the CH4 fluxes, soil temperature, and soil moisture content. Our results highlight the heterogeneity in CH4 emissions at landscape scale and suggest that further improvements to the representation of large-scale hydrological conditions in the model will facilitate a more process-oriented land surface scheme and better simulate CH4 emissions under climate change. This is especially necessary at regional scales in Arctic ecosystems influenced by permafrost thaw.
DOI: 10.5194/bg-15-2691-2018
2020020464 Magnan, Gabriel (Université du Québec à Montréal, Geotop Research Center, Quebec, QC, Canada); van Bellen, Simon; Davies, Lauren; Froese, Duane; Garneau, Michelle; Mullan-Boudreau, Gillian; Zaccone, Claudio and Shotyk, William. Impact of the Little Ice Age cooling and 20th century climate change on peatland vegetation dynamics in central and northern Alberta using a multi-proxy approach and high-resolution peat chronologies: Quaternary Science Reviews, 185, p. 230-243, illus. incl. 1 table, sketch map, 107 ref., April 1, 2018.
Northern boreal peatlands are major terrestrial sinks of organic carbon and these ecosystems, which are highly sensitive to human activities and climate change, act as sensitive archives of past environmental change at various timescales. This study aims at understanding how the climate changes of the last 1000 years have affected peatland vegetation dynamics in the boreal region of Alberta in western Canada. Peat cores were collected from five bogs in the Fort McMurray region (56-57° N), at the southern limit of sporadic permafrost, and two in central Alberta (53° N and 55° N) outside the present-day limit of permafrost peatlands. The past changes in vegetation communities were reconstructed using detailed plant macrofossil analyses combined with high-resolution peat chronologies (14C, atmospheric bomb-pulse 14C, 210Pb and cryptotephras). Peat humification proxies (C/N, H/C, bulk density) and records of pH and ash content were also used to improve the interpretation of climate-related vegetation changes. Our study shows important changes in peatland vegetation and physical and chemical peat properties during the Little Ice Age (LIA) cooling period mainly from around 1700 CE and the subsequent climate warming of the 20th century. In some bogs, the plant macrofossils have recorded periods of permafrost aggradation during the LIA with drier surface conditions, increased peat humification and high abundance of ericaceous shrubs and black spruce (Picea mariana). The subsequent permafrost thaw was characterized by a short-term shift towards wetter conditions (Sphagnum sect. Cuspidata) and a decline in Picea mariana. Finally, a shift to a dominance of Sphagnum sect. Acutifolia (mainly Sphagnum fuscum) occurred in all the bogs during the second half of the 20th century, indicating the establishment of dry ombrotrophic conditions under the recent warmer and drier climate conditions.
DOI: 10.1016/j.quascirev.2018.01.015
2020015145 Fuchs, Matthias (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Department of Periglacial Research, Potsdam, Germany); Grosse, Guido; Strauss, Jens; Günther, Frank; Grigoriev, Mikhail; Maximov, Georgy M. and Hugelius, Gustaf. Carbon and nitrogen pools in thermokarst-affected permafrost landscapes in Arctic Siberia: Biogeosciences, 15(3), p. 953-971, illus. incl. 5 tables, sketch map, 108 ref., February 2018.
Ice-rich yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected yedoma landscapes - on Sobo-Sise Island and on Bykovsky Peninsula in the north of eastern Siberia. Soil cores up to 3 m depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from 5 m resolution, multispectral RapidEye satellite imagery. Mean landscape C and N storage in the first metre of soil for Sobo-Sise Island is estimated to be 20.2 kg C m-2 and 1.8 kg N m-2 and for Bykovsky Peninsula 25.9 kg C m-2 and 2.2 kg N m-2. Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holocene-age cover layers which can reach up to 2 m on top of intact yedoma landforms. Reconstructed sedimentation rates of 0.10-0.57 mm yr-1 suggest sustained mineral soil accumulation across all investigated landforms. Both yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). We further estimate that an active layer deepening of about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by ~5.8 Tg (13.2 kg C m-2). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates.
DOI: 10.5194/bg-15-953-2018
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