2020037944 Hu Guojie (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Cryosphere Research Station on Qinghai-Xizang Plateau, Lanzhou, China); Zhao Lin; Zhu Xiaofan; Wu Xiaodong; Wu Tonghua; Li Ren; Xie Changwei and Hao Junming. Review of algorithms and parameterizations to determine unfrozen water content in frozen soil: Geoderma, 368, Article no. 114277, illus. incl. 3 tables, sketch map, 117 ref., June 1, 2020.
Unfrozen water plays an important role in a number of processes, including water and heat transfer, frost heave, thaw settlement and simulations for the hydro-thermo-mechanical interactions in frozen soil. Past studies have demonstrated that considering the unfrozen water content in cold regions can significantly improve accuracy in coupling heat and water transfer modeling in frozen soil. However, differences between experimental data and theoretical understanding have resulted in discrepancies between parameterizations. To address this, we presented the first study to synthesize the algorithms and parameterizations used for unfrozen water content; we also discussed influential factors on unfrozen water content in frozen soil. We then provided a comprehensive discussion of the progress in algorithms and parameterizations regarding unfrozen water content and summarized them into four categories, which were calculated using soil temperature, specific surface area of soil particles, soil water curve, and different types of water. Selected unfrozen water content parameterizations were then evaluated based on those previous results as well as the data collected from our field observation station in permafrost region on the Qinghai-Tibet Plateau (QTP). These results revealed that empirical parameterizations were useful for calculating unfrozen water content. In addition, the physical parameterizations had higher accuracy for calculating unfrozen water content, but they were more complicated and difficult to use in practical applications. Unfrozen water content parameterizations were influenced by many factors, and the warming and cooling processes were especially important when calculating unfrozen water content. Finally, future research should aim to improve our theoretical understanding and to develop simple parameterizations that couple land surface processes models in cold regions. It is expected that this review will provide a sound theoretical basis for the further study of the unfrozen water content in frozen soil and its subsequent effects on hydrothermal transfer processes in cold regions.
2020037941 Pushkareva, Ekaterina (University of Rostock, Department of Applied Ecology and Phycology, Rostock, Germany); Eckhardt, Kai-Uwe; Hotter, Vivien; Frossard, Aline; Leinweber, Peter; Frey, Beat and Karsten, Ulf. Chemical composition of soil organic matter and potential enzyme activity in the topsoil along a moisture gradient in the High Arctic (Svalbard): Geoderma, 368, Article no. 114304, illus. incl. 3 tables, 49 ref., June 1, 2020.
The soil active layer in the High Arctic is a reservoir for nutrients and microbial communities, but their behavior and interactions remain unclear. Therefore, the objective of this study was to characterize soil organic matter (SOM) composition and potential enzyme activities in soil active layer of Svalbard. Samples from two different sites and two different soil layers (biocrust: 0-1 cm; mineral soil: 5-10 cm depth) were collected along a moisture gradient. The molecular SOM composition was assessed using pyrolysis-field ionization mass spectrometry (Py-FIMS), and the potential activities of seven extracellular enzymes characteristic for different soil microbial processes were measured. In general, SOM in both sites was dominated by lipids/sterols, alkylaromatics and phenols/lignin monomers. Dehydroergosterol prevailed in a majority of the samples. Biocrusts samples in both sites had higher total ion intensity and volatile matter, but lower lipid and alkylaromatics contents. The potential enzyme activities varied significantly across the sites, depths and moisture gradients and, in general, were higher in the biocrusts than in underlying soils. Besides, majority of measured enzyme activities were lower in the wetter plots. Taken together, our results expand the knowledge of SOM and enzyme activity in High Arctic topsoil, which is important for better understanding the dynamic of soil biotic and abiotic processes in polar environments, particularly in the context of climate change.
2020035825 Douglas, Peter M. J. (McGill University, Department of Earth and Planetary Sciences, Montreal, QC, Canada); Gonzalez Moguel, Regina; Walter Anthony, Katey M.; Wik, Martin; Crill, Patrick M.; Dawson, Katherine S.; Smith, Derek A.; Yanay, Ella; Lloyd, Max K.; Stolper, Daniel A.; Eiler, John M. and Sessions, Alex L. Clumped isotopes link older carbon substrates with slower rates of methanogenesis in northern lakes: Geophysical Research Letters, 47(6), Paper no. e2019GL086756, illus., 56 ref., March 28, 2020.
The release of long-stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (D18) and 14C measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that D18 values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 D18 and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from D18 values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes. Abstract Copyright (2020), American Geophysical Union. All Rights Reserved.
2020034406 Huang Kewei (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Dai Junchen; Wang Genxu; Chang Juan; Lu Yaqiong; Song Chunlin; Hu Zhaoyong; Ahmed, Naveed and Ye Renzheng. The impact of land surface temperatures on suprapermafrost groundwater on the central Qinghai-Tibet Plateau: Hydrological Processes, 34(6), p. 1475-1488, illus. incl. 2 tables, sketch maps, 53 ref., March 15, 2020.
To investigate the influences of land surface temperatures (LSTs) on suprapermafrost groundwater discharge, a river valley was selected in a typical permafrost region of Fenghuoshan (FHS) watershed on the central Qinghai-Tibet Plateau. We developed a two-dimensional model to simulate the suprapermafrost groundwater seasonal dynamics controlled by LSTs and the changing trends under a warming climate scenario (3°C/100 year). We calibrated key parameters of our model by the field observations at FHS watershed and analysed the relationship between the different LSTs and the suprapermafrost groundwater discharge dynamics in the active layer. The results show that (a) by changing the permeability of the active layer, the LSTs have a significant effect on the suprapermafrost groundwater discharge. A higher LST causes more suprapermafrost groundwater discharge, resulting in a different discharge pattern and affecting the ability to replenish the nearby river in the permafrost area. (b) Under a warming climate, the most obvious change in the suprapermafrost groundwater occurs in the freeze initiation period (from October to December), and there is a significant increase in the suprapermafrost groundwater discharge rate. This study reveals that the LST has a controlling effect on the seasonal dynamics of shallow groundwater systems in permafrost regions, indicating that the impact of local topography on the suprapermafrost groundwater should not be ignored in suprapermafrost groundwater simulations. Moreover, the warming simulation results demonstrate that the freezing season is the significant transformation period of suprapermafrost groundwater dynamics under future climate change, which can be used to better understand hydrological and ecological process changes in permafrost regions under climate warming. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2020034391 Langford, Joelle E. (University of Western Ontario, Department of Earth Sciences, London, ON, Canada); Schincariol, Robert A.; Nagare, Ranjeet M.; Quinton, William L. and Mohammed, Aaron A. Transient and transition factors in modeling permafrost thaw and groundwater flow: Ground Water, 58(2), p. 258-268, illus., 58 ref., March 2020.
Permafrost covers approximately 24% of the Northern Hemisphere, and much of it is degrading, which causes infrastructure failures and ecosystem transitions. Understanding groundwater and heat flow processes in permafrost environments is challenging due to spatially and temporarily varying hydraulic connections between water above and below the near-surface discontinuous frozen zone. To characterize the transitional period of permafrost degradation, a three-dimensional model of a permafrost plateau that includes the supra-permafrost zone and surrounding wetlands was developed. The model is based on the Scotty Creek basin in the Northwest Territories, Canada. FEFLOW groundwater flow and heat transport modeling software is used in conjunction with the piFreeze plug-in, to account for phase changes between ice and water. The Simultaneous Heat and Water (SHAW) flow model is used to calculate ground temperatures and surface water balance, which are then used as FEFLOW boundary conditions. As simulating actual permafrost evolution would require hundreds of years of climate variations over an evolving landscape, whose geomorphic features are unknown, methodologies for developing permafrost initial conditions for transient simulations were investigated. It was found that a model initialized with a transient spin-up methodology, that includes an unfrozen layer between the permafrost table and ground surface, yields better results than with steady-state permafrost initial conditions. This study also demonstrates the critical role that variations in land surface and permafrost table microtopography, along with talik development, play in permafrost degradation. Modeling permafrost dynamics will allow for the testing of remedial measures to stabilize permafrost in high value infrastructure environments. Abstract Copyright (2019), National Ground Water Association.
2020035679 Li Zongxing (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Laboratory of Ecohydrology of Inland River Basin/Gansu Qilian Mountains Eco-Environment Research Center, Lanzhou, China); Li Zongjie; Feng Qi; Zhang Baijuan; Gui Juan; Xue Jian and Gao Wende. Runoff dominated by supra-permafrost water in the source region of the Yangtze River using environmental isotopes: Journal of Hydrology, 582, Paper no. 124506, illus. incl. block diags., 6 tables, sketch map, 83 ref., March 2020.
Accelerating multiphase water transformation affects runoff processes and components greatly and have changed the spatiotemporal patterns of water resources in the Third Polar Region. The source region of the Yangtze River is one location where accelerated warming has resulted in the gradual extension of the ablation period since 1990. This has caused the acceleration of multiphase water transformation, characterized by increases in the rate of glacial retreat, maximum freezing depth, and annual actual evapotranspiration and by decreased snowfall. In response, the total runoff increased by 53% at the Tuotuohe national hydrological station (TTH) and 6% at the Zhimenda national hydrological station (ZMD) during the periods 1961-1990 and 1991-2017, respectively. Under these conditions, runoff components were being determined based on stable isotope tracing. Substantial seasonal differences in d18O (dD) among precipitation, river water, supra-permafrost water, and glaciers snow meltwater indicate that the runoff has been replenished by multiple components, and that these first infiltrate the ground, becoming part of the groundwater, and then recharge river water. Supra-permafrost water rather than precipitation now dominates river water. Based on the end-member mixing analysis model, supra-permafrost water, precipitation, and glaciers snow meltwater accounted for 51%, 26%, and 23% of river water at the TTH station from June 2016 to May 2018; the corresponding values at the ZMD station were 49%, 34%, and 17%. Additionally, there are also differences in the seasonal contributions of runoff components to river water. Seasonal variations in the freezing and thawing of the active layer directly trigger the runoff process. Future research should be focused on determining the mechanisms underlying the dynamics of precipitation-supra-permafrost water-runoff, which will aid the assessment of the impacts of an unstable Asian Water Tower on water resources.
2020034401 McMillan, Hilary (San Diego State University, Department of Geography, San Diego, CA). Linking hydrologic signatures to hydrologic processes; a review: Hydrological Processes, 34(6), p. 1393-1409, illus. incl. 1 table, 104 ref., March 15, 2020.
Hydrologic signatures are metrics that quantify aspects of streamflow response. Linking signatures to underlying processes enables multiple applications, such as selecting hydrologic model structure, analysing hydrologic change, making predictions in ungauged basins, and classifying watershed function. However, many lists of hydrologic signatures are not process-based, and knowledge about signature-process links has been scattered among studies from experimental watersheds and model selection experiments. This review brings together those studies to catalogue more than 50 signatures representing evapotranspiration, snow storage and melt, permafrost, infiltration excess, saturation excess, groundwater, baseflow, connectivity, channel processes, partitioning, and human alteration. The review shows substantial variability in the number, type, and timescale of signatures available to represent each process. Many signatures provide information about groundwater storage, partitioning, and connectivity, whereas snow processes and human alteration are underrepresented. More signatures are related to the seasonal scale than the event timescale, and land surface processes (ET, snow, and overland flow) have no signatures at the event scale. There are limitations in some signatures that test for occurrence but cannot quantify processes, or are related to multiple processes, making automated analysis more difficult. This review will be valuable as a reference for hydrologists seeking to use streamflow records to investigate a particular hydrologic process or to conduct large-sample analyses of patterns in hydrologic processes. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2020038009 Vadakkedath, Vishakh (Warsaw University of Technology, Hydro and Environmental Engineering, Warsaw, Poland); Zawadzki, Jaroslaw and Przezdziecki, Karol. Multisensory satellite observations of the expansion of the Batagaika Crater and succession of vegetation in its interior from 1991 to 2018: Environmental Earth Sciences, 79(6), Article 150, illus. incl. 6 tables, sketch maps, 24 ref., March 2020.
On-site monitoring in large areas located in inaccessible regions can be difficult and costly. Thus remote sensing is an essential tool for mapping and monitoring changes in such regions. Therefore, this paper describes long-term multisensory satellite observations of the expansion of the Batagaika crater in Northern Siberia and natural succession of vegetation in its interior from 1991 to 2018. Landsat 5 TM, Landsat 7 + ETM, Landsat 8 OLI/TIRS imageries were mainly used as a data source for analyses, although Sentinel-2A imagery and DEM image from ASTER satellite were also employed for calculating a vegetation index and expansion in the crater area. The observations were conducted in years 1991-2018 and were made in a summer season. The results reveal that the crater area increased by almost three times during these 27 years and that the fastest expansion took place between 2010 and 2014 with 22.7% increment. The analysis of elevation of the crater revealed that in 2018 its maximum depth was ca 70 m and that depth was decreasing towards its north-east tail. Additionally, the satellite imagery of land surface temperature which is a driving force of crater expansion was visualized for chosen hot days within the time frame 2010-2018. The study of temporal and spatial changes in NDVI spatial distributions inside the crater revealed also a high rate of the succession of vegetation, which may reduce melting of permafrost inside the Batagaika crater and its further expansion.
2020035693 Xu Xiangtian (Inner Mongolia University, Institute of Transportation, Hohhot, China); Bai Ruiqiang; Lai Ying; Zhang Mingyi and Ren Jingge. Work conjugate stress and strain variables for unsaturated frozen soils: Journal of Hydrology, 582, Paper no. 124537, illus., 58 ref., March 2020.
In general, most of the foundations of structures in the cold regions rest on frozen soils which are often under unsaturated state and subject to mechanical and thermal loads. The thermal loads will induce water migration and water-ice phase change, as a result, the dynamic phase transition between unfrozen water and ice occurs and degree of saturation in frozen soils is affected. These complicate the understanding of the strength and deformation characteristics of frozen soils under mechanical and thermal loads. Furthermore, it leads to a necessity to develop a coupling thermo-hydro-mechanical model for practical permafrost engineering. Up to date, there are limited studies to quantify this complicated problem by a framework with proper stress and strain variables for unsaturated frozen soils. This study derives the expression of input work rate for unsaturated frozen soils based on the multiphase porous media theory. Work conjugate stress and strain variables have been determined based on the expression of input work rate. This set of variables not only can smoothly transit from unsaturated frozen state to unsaturated unfrozen state when temperature is above freezing point, but also can smoothly transit from unsaturated state to saturate state. The proposed framework can be consistently applied to multi-phase soils with unsaturated frozen soils, unsaturated soils and saturated soils. Moreover, the application of the framework can be further extended to other porous mediums. Additionally, the selected variables in this framework are validated against published experimental results. This framework can subsequently be used to establish the coupled thermo-hydro-mechanical models for unsaturated and saturated frozen soils.
2020033980 Chiasson-Poirier, G. (Université de Montréal, Département de Géographie, Montreal, QC, Canada); Franssen, J.; Lafrenière, M. J.; Fortier, D. and Lamoureux, S. F. Seasonal evolution of active layer thaw depth and hillslope-stream connectivity in a permafrost watershed: Water Resources Research, 56(1), Article e2019WR025828, illus. incl. sketch map, 68 ref., January 2020.
To advance our understanding of permafrost hillslope drainage dynamics and its influence on streamflow hydrochemistry, we instrumented a hillslope-stream sequence located in the headwaters of the Niaqunguk River watershed, Nunavut, Canada (63°N, 68°W). We combined high spatial resolution field measurements of water and frost tables across the hillslope, with semiweekly measurements of groundwater and streamflow chemistry to track the evolution of streamflow chemistry during active layer thaw. Interestingly, localized differential thaw patterns emerged under near saturation conditions across the instrumented hillslope, the result of a low-frequency high-magnitude summer rainfall event. Hillslope structure and uneven active layer thaw created two distinct fill-and-spill domains. A subsurface domain defined by frost table microtopography and a surface domain defined by surface topography. We observed a seasonal shift in streamflow chemistry with an increased influence of water flowing through the underlying mineral soils as the active layer thawed. As thaw progressed streamflow chemistry began to match that of the riparian groundwater, which was a mixture of hillslope surface and subsurface water. Hillslope-stream surface connections were sporadic and occurred when rainfall and saturation conditions across the lower portion of the hillslope were sufficient for water to spill out of midslope surface depressions and across a saturated riparian zone and into the stream. This research shows how hillslope structure and thaw processes influence hillslope-stream connectivity in permafrost terrain. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2020034056 Conroy, Nathan Alec (Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM); Newman, Brent David; Heikoop, Jeffrey Martin; Perkins, George Bradford; Feng, Xiahong; Wilson, Cathy Jean and Wullschleger, Stan Duane. Timing and duration of hydrological transitions in Arctic polygonal ground from stable isotopes: Hydrological Processes, 34(3), p. 749-764, illus. incl. 2 tables, sketch maps, 47 ref., January 30, 2020.
Land surface models and Earth system models that include Arctic landscapes must capture the abrupt hydrological transitions that occur during the annual thaw and deepening of the active layer. In this work, stable water isotopes (d2H and d18O) are used to appraise hydrologically significant transitions during annual landscape thaw at the Barrow Environmental Observatory (Utqiagvik, Alaska). These hydrologically significant periods are then linked to annual shifts in the landscape energy balance, deduced from meteorological data and described by the microclimatic periods: Winter, Pre-Melt, Melt, Post-Melt, Summer, and Freeze-Up. The tight coupling of the microclimatic periods with the hydrological transitions supports the use of microclimatic periods as a means of linking polygonal surface water hydrology to meteorological datasets, which provides a mechanism for improving the representation of polygonal surface water hydrology in process-based models. Rayleigh process reconstruction of the isotopic changes revealed that 19% of winter precipitation was lost to sublimation prior to melting and that 23% of surface water was lost to evaporation during the first 10 days post-melt. This agrees with evaporation rates reported in a separate study using an eddy covariance flux tower located nearby. An additional 17% was lost to evaporation during the next 33 days. Stable water isotopes are also used to identify the dominant sources of surface water to various hydrogeomorphological features prevalent in polygonal terrain (a lake, a low centre polygon centre, troughs within the rims of low centre polygons, flat centre polygon troughs, a high centre polygon trough, and drainages). Hydrogeomorphologies that retained significant old water or acted as snow drifts are isotopically distinct during the Melt Period and therefore are easily distinguished. Biogeochemical changes related to the annual thaw are also reported and coupled to the hydrological transitions, which provides insight into the sources and sinks of these ions to and from the landscape. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2020034053 King, Tyler V. (Utah State University, Department of Civil and Environmental Engineering, Logan, UT); Neilson, Bethany T.; Overbeck, Levi D. and Kane, Douglas L. A distributed analysis of lateral inflows in an Alaskan Arctic watershed underlain by continuous permafrost: Hydrological Processes, 34(3), p. 633-648, illus. incl. 2 tables, sketch maps, 65 ref., January 30, 2020.
Lateral inflows control the spatial distribution of river discharge, and understanding their patterns is fundamental for accurately modelling instream flows and travel time distributions necessary for evaluating impacts of climate change on aquatic habitat suitability, river energy budgets, and fate of dissolved organic carbon. Yet, little is known about the spatial distribution of lateral inflows in Arctic rivers given the lack of gauging stations. With a network of stream gauging and meteorological stations within the Kuparuk River watershed in northern Alaska, we estimated precipitation and lateral inflows for nine subcatchments from 1 July to 4 August,2013, 2014, and 2015. Total precipitation, lateral inflows, runoff ratios (area-normalized lateral inflow divided by precipitation), percent contribution to total basin discharge, and lateral inflow per river kilometre were estimated for each watershed for relatively dry, moderate, or wet summers. The results show substantial variability between years and subcatchments. Total basin lateral inflow depths ranged 24-fold in response to a threefold change in rainfall between dry and wet years, whereas within-basin lateral inflows varied fivefold from the coastal plain to the foothills. General spatial trends in lateral inflows were consistent with previous studies and mean summer precipitation patterns. However, the spatially distributed nature of these estimates revealed that reaches in the vicinity of a spring-fed surficial ice feature do not follow general spatial trends and that the coastal plain, which is typically considered to produce minimal runoff, showed potential to contribute to total river discharge. These findings are used to provide a spatially distributed understanding of lateral inflows and identify watershed characteristics that influence hydrologic responses. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2020033970 Song Chunlin (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Wang Genxu; Mao Tianxu; Huang Kewei; Sun Xiangyang; Hu Zhaoyong; Chang Ruiying; Chen Xiaopeng and Raymond, Peter A. Spatiotemporal variability and sources of DIC in permafrost catchments of the Yangtze River source region; insights from stable carbon isotope and water chemistry: Water Resources Research, 56(1), Article e2019WR025343, illus. incl. 3 tables, sketch maps, 120 ref., January 2020.
Riverine dissolved inorganic carbon (DIC) exports play a central role in the regional and global carbon cycles. Here, we investigated the spatiotemporal variability and sources of DIC in eight catchments in the Yangtze River source region (YRSR) with variable permafrost coverage and seasonally thawed active layers. The YRSR catchments are DIC-rich (averagely 25 mg C L-1) and export 3.51 g m-2 yr-1 of DIC. The seasonal changes of temperature, active layer, flow path, and discharge can alter DIC and stable carbon isotope of DIC (d13C-DIC). The most depleted d13C-DIC values were found in the thawed period, suggesting the soil-respired CO2 during the active layer thaw period can promote bicarbonate production via H2CO3 weathering. Spatially, d13C-DIC values increased downstream, likely due to CO2 outgassing and changed permafrost coverage and runoff. We found that evaporite dissolution and silicate weathering in the seasonally thawed active layer contributed 44.2% and 30.9% of stream HCO3-, respectively, while groundwater and rainwater contributed 16.7% and 7.3% of HCO3-, respectively. Pure carbonate rock weathering played a negligible role in DIC production. These results were compatible with d13C-DIC source approximation results. Silicate weathering increased from initial thaw to thawed period, reflecting the active layer thaw and subsequent hydrology change impacts. Silicate weathering consumed 1.25 ´ 1010 mol of CO2 annually, while evaporite dissolution may produce CO2 and neutralize this CO2 sink. This study provides new understanding of the riverine DIC export processes of the YRSR. As permafrost degrades, the quantity, sources, and sinks of riverine DIC may also change spatiotemporally. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2020034023 Wohl, Ellen (Colorado State University, Department of Geosciences, Fort Collins, CO); Lininger, Katherine B.; Rathburn, Sara L. and Sutfin, Nicholas A. How geomorphic context governs the influence of wildfire on floodplain organic carbon in fire-prone environments of the Western United States: Earth Surface Processes and Landforms, 45(1), p. 38-55, illus. incl. 2 tables, 161 ref., January 2020.
We draw on published studies of floodplain organic carbon storage, wildfire-related effects on floodplains in temperate and high latitudes, and case studies to propose a conceptual model of the effects of wildfire on floodplain organic carbon storage in relation to climate and valley geometry. Soil organic carbon typically constitutes the largest carbon stock in floodplains in fire-prone regions, although downed wood can contain significant organic carbon. We focus on the influence of wildfire on soil organic carbon and downed wood as opposed to standing vegetation to emphasize the geomorphic influences resulting from wildfire on floodplain organic carbon stocks. The net effect of wildfire varies depending on site-specific characteristics including climate and valley geometry. Wildfire is likely to reduce carbon stock in steep, confined valley segments because increased water and sediment yields following fire create net floodplain erosion. The net effect of fire in partly confined valleys depends on site-specific interactions among floodplain aggradation and erosion, and, in high-latitude regions, permafrost degradation. In unconfined valleys in temperate latitudes, wildfire is likely to slightly increase floodplain organic carbon stock as a result of floodplain aggradation and wood deposition. In unconfined valleys in high latitudes underlain by permafrost, wildfire is likely in the short-term to significantly decrease floodplain organic carbon via permafrost degradation and reduce organic-layer thickness. Permafrost degradation reduces floodplain erosional resistance, leading to enhanced stream bank erosion and greater carbon fluxes into channels. The implications of warming climate and increased wildfires for floodplain organic carbon stock thus vary. Increasing wildfire extent, frequency, and severity may result in significant redistribution of organic carbon from floodplains to the atmosphere via combustion in all environments examined here, as well as redistribution from upper to lower portions of watersheds in the temperate zone and from floodplains to the oceans via riverine transport in the high-latitudes. Copyright 2019 John Wiley & Sons, Ltd.
2020038038 Nitzbon, Jan (Alfred Wegener Institute, Potsdam, Germany); Westermann, Sebastian; Langer, Moritz; Martin, Leo C. P.; Strauss, Jens; Laboor, Sebastian and Boike, Julia. Fast response of cold ice-rich permafrost in northeast Siberia to a warming climate: Nature Communications, 11(Article 2201), illus., 64 ref., 2020.
The ice- and organic-rich permafrost of the northeast Siberian Arctic lowlands (NESAL) has been projected to remain stable beyond 2100, even under pessimistic climate warming scenarios. However, the numerical models used for these projections lack processes which induce widespread landscape change termed thermokarst, precluding realistic simulation of permafrost thaw in such ice-rich terrain. Here, we consider thermokarst-inducing processes in a numerical model and show that substantial permafrost degradation, involving widespread landscape collapse, is projected for the NESAL under strong warming (RCP8.5), while thawing is moderated by stabilizing feedbacks under moderate warming (RCP4.5). We estimate that by 2100 thaw-affected carbon could be up to three-fold (twelve-fold) under RCP4.5 (RCP8.5), of what is projected if thermokarst-inducing processes are ignored. Our study provides progress towards robust assessments of the global permafrost carbon-climate feedback by Earth system models, and underlines the importance of mitigating climate change to limit its impacts on permafrost ecosystems. URL: http://creativecommons.org/licenses/by/4.0/.
2020030376 Katsuta, Nagayoshi (Gifu University, Faculty of Education, Gifu, Japan); Matsumoto, Genki I.; Hase, Yoshitaka; Tayasu, Ichiro; Haraguchi, Takashi F.; Tani, Eriko; Shichi, Koji; Murakami, Takuma; Naito, Sayuri; Nakagawa, Mayuko; Hasegawa, Hitoshi and Kawakami, Shin-ichi. Siberian permafrost thawing accelerated at the Bolling/Allerod and Preboreal warm periods during the last deglaciation: Geophysical Research Letters, 46(23), p. 13961-13971, illus. incl. geol. sketch map, 68 ref., December 16, 2019.
This study investigated a continuous sediment core, retrieved from the deepest part in Lake Hovsgol, northwestern Mongolia. Its surrounds are occupied by a continuous Siberian permafrost zone. Distinct geochemical and lithological features suggest that the watershed soil was moistened during the last deglaciation, associated with climate amelioration. Especially, the calcareous glacial clay layers (ca 13.7 and ca 11.0 cal. ka BP), with high sulfur content peaks and positive shifts of d34S values, well correlate with the timing of meltwater pulses 1A and 1B, leading to rapid warming such as Bolling/Allerod and Preboreal Holocene, respectively. This finding allows our interpretation for the calcareous glacial clay layers produced by landslide-induced debris flow, which resulted from intensive water discharge from rapid thawing of permafrost during the abrupt warming periods. Our correlation with Lake Baikal records suggests that these permafrost thawings have accelerated over the area of the Selenga drainage basin (continental interior Eurasia). Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2020032065 Wieder, William R. (National Center for Atmospheric Research, Climate and Global Dynamics Laboratory, Boulder, CO); Sulman, Benjamin N.; Hartman, Melannie D.; Koven, Charles D. and Bradford, Mark A. Arctic soil governs whether climate change drives global losses or gains in soil carbon: Geophysical Research Letters, 46(24), p. 14486-14495, illus. incl. 1 table, sketch maps, 69 ref., December 28, 2019.
Key uncertainties in terrestrial carbon cycle projections revolve around the timing, direction, and magnitude of the carbon cycle feedback to climate change. This is especially true in carbon-rich Arctic ecosystems, where permafrost soils contain roughly one third of the world's soil carbon stocks, which are likely vulnerable to loss. Using an ensemble of soil biogeochemical models that reflect recent changes in the conceptual understanding of factors responsible for soil carbon persistence, we quantify potential soil carbon responses under two representative climate change scenarios. Our results illustrate that models disagree on the sign and magnitude of global soil changes through 2100, with disagreements primarily driven by divergent responses of Arctic systems. These results largely reflect different assumptions about the nature of soil carbon persistence and vulnerabilities, underscoring the challenges associated with setting allowable greenhouse gas emission targets that will limit global warming to 1.5°C. Abstract Copyright (2019), The Authors.
2020032062 Yoneda, Jun (National Institute of Advanced Industrial Science and Technology (AIST), Department of Energy and Environment, Sapporo, Japan); Kida, Masato; Konno, Yoshihiro; Jin, Yusuke; Morita, Sumito and Tenma, Norio. In situ mechanical properties of shallow gas hydrate deposits in the deep seabed: Geophysical Research Letters, 46(24), p. 14459-14468, illus. incl. sketch map, 1 table, sect., 69 ref., December 28, 2019.
Natural gas hydrates (or methane hydrates) could become a major energy source but could also exacerbate global warming, because as the climate warms, hydrate deposits deep under the oceans or in permafrost may release methane into the atmosphere. There are many shallow deposits of gas hydrates in fine-grained muddy sediments on the seafloor. However, the mechanical properties of these sediments have not yet been investigated because of the engineering challenges in coring and testing at in situ temperatures and pressures. Here we present the first uniaxial and triaxial strength and stiffness measurements of pure massive natural gas hydrates and muddy sediments containing hydrate nodules obtained by pressure coring. As a result, we were able to observe the hydrate undergoing a catastrophic brittle failure. Its strength and deformation moduli were 3 and 300 MPa, respectively. Muddy sediments containing hydrate nodules had the same strength as that of hydrate-free sediments. Abstract Copyright (2019), The Authors.
2020030346 Batchelor, Cameron J. (University of Wisconsin-Madison, Department of Geoscience, Madison, WI); Orland, Ian J.; Marcott, Shaun A.; Slaughter, Richard; Edwards, R. Lawrence; Zhang, Pu; Li, Xianglei and Cheng, Hai. Distinct permafrost conditions across the last two glacial periods in midlatitude North America: Geophysical Research Letters, 46(22), p. 13318-13326, illus. incl. sketch maps, 59 ref., November 28, 2019.
During past glacial periods, extensive areas of North America were covered by permafrost. The timing and extent of these paleo-permafrost conditions, however, remains ambiguous. Here we present a 250,000-year record of speleothem growth from a midlatitude North American cave and report 141 U-Th ages with hiatuses in growth that reflect the development of temporally continuous permafrost. Combined with U-Th ages from other speleothem studies, we demonstrate that regional permafrost conditions occurred during both of the prior two glacial maxima but were markedly shorter in duration during the penultimate (Marine Isotope Stage 6, MIS 6) versus the last (MIS 2) glacial period. Notably, a network of sea surface temperatures indicates that mid- and low-latitude temperatures were 0.9 °C ± 0.2 °C warmer during the culmination of MIS 6 versus MIS 2. Our results illustrate the importance of developing regional paleo-permafrost records and highlight the sensitivity of permafrost conditions during glacial periods to relatively small differences in global-scale temperature. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2020035634 Devoie, Élise G. (University of Waterloo, Department of Civil and Environmental Engineering, Waterloo, ON, Canada); Craig, James R.; Connon, Ryan F. and Quinton, William L. Taliks; a tipping point in discontinuous permafrost degradation in peatlands: Water Resources Research, 55(11), p. 9838-9857, illus. incl. sketch map, 70 ref., November 2019.
Taliks (perennially thawed soil in a permafrost environment) are generally found beneath water bodies or wetlands, and their development and evolution in other environments is poorly documented. Sustained isolated taliks between seasonally frozen surface soils and permafrost have been observed at the Scotty Creek Research Station in the discontinuous permafrost region of the Northwest Territories, Canada. These taliks have been expanding both vertically and laterally over the past decade of monitoring. The main controls on expansion are thought to be (1) the availability of energy, determined by incoming radiation and advective heat flux, (2) the ability to transfer this energy to the freezing/thawing front, determined by the thermal conductivity (soil properties and moisture content), and (3) the presence and thickness of the snowpack. These controls are investigated using data collected in the field to inform a 1-D coupled thermodynamic freeze-thaw and unsaturated flow model. The model was successfully used to represent observed thaw rates in different parts of the landscape. It is found that high soil moisture, deeper snowpacks, and warmer or faster advective flow rates all contribute to accelerated talik growth and subsequent permafrost degradation. Simulations show that slight perturbations of available energy or soil properties, such as an increase in average surface temperature of 0.5°C or a 1-cm change in snow water equivalent, can lead to talik formation, highlighting the vulnerability of this landscape to changes in climate or land cover. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2020037732 Lu, R. (Lawrence Livermore National Laboratory, Livermore, CA); Stern, L. A.; Du Frane, W. L.; Pinkston, J. C.; Roberts, J. J. and Constable, S. The effect of brine on the electrical properties of methane hydrate: Journal of Geophysical Research: Solid Earth, 124(11), p. 10,877-10,892, illus. incl. 1 table, 70 ref., November 2019.
Gas hydrates possess lower electrical conductivity (inverse of resistivity) than either seawater or ice, but higher than clastic silts and sands, such that electromagnetic methods can be employed to help identify their natural formation in marine and permafrost environments. Controlled laboratory studies offer a means to isolate and quantify the effects of changing individual components within gas-hydrate-bearing systems, in turn yielding insight into the behavior of natural systems. Here we investigate the electrical properties of polycrystalline methane hydrate with >&eq;25% gas-filled porosity and in mixture with brine. Initially, pure methane hydrate was synthesized from H2O ice and CH4 gas while undergoing electrical impedance measurement, then partially dissociated to assess the effects of pure pore water accumulation on electrical conductivity. Methane hydrate+brine mixtures were then formed by either adding NaCl (0.25-2.5 wt%) to high-purity ice or by using frozen seawater as a reactant. Conductivity was obtained from impedance measurements made in situ throughout synthesis while temperature cycled between +15°C and -25°C. Several possible conduction mechanisms were subsequently determined using equivalent circuit modeling. Samples with low NaCl concentration show a doping/impurity effect and a log linear conductivity response as a function of temperature. For higher salt content samples, conductivity increases exponentially with temperature and the log linear relationship no longer holds; instead, we observe phase changes within the samples that follow NaCl-H2O-CH4 phase equilibrium predictions. Final samples were quenched in liquid nitrogen and imaged by cryogenic scanning electron microscopy (cryo-SEM) to assess grain-scale characteristics. Abstract Copyright (2019). American Geophysical Union. All Rights Reserved.
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