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The Permafrost Dynamics Observatory (PDO) combines L-band interferometric synthetic aperture radar (InSAR) and P-band polarimetric synthetic aperture radar (PolSAR) to simultaneously estimate the seasonal thaw depth and soil moisture profile of the active layer in permafrost regions. L-band InSAR can measure seasonal subsidence due to thawing of the active layer and P-band PolSAR backscatter is sensitive to subsurface soil moisture. A joint retrieval scheme is developed as both subsidence and soil moisture are essential to accurate active layer thickness (ALT) estimation. The PDO joint retrieval has been applied to airborne L- and P-band SAR data acquired over Arctic-boreal region during the 2017 Arctic-Boreal Vulnerability Experiment (ABoVE) airborne campaign. In this paper, we describe the forward models and joint inversion used in the PDO retrievals and compare the results with in-situ ALT and soil moisture data estimated from ground-penetrating radar (GPR).

Aims: For informed predictions on the sensitivity of Arctic tundra landscape to permafrost thaw, we aimed to investigate the distribution pattern of near-surface ground ice and its influencing factors in Northeast Siberia. Methods: Near-surface permafrost cores (60 cm) were sampled along small-scale topographic gradients in two drained lakebeds. We investigated which factors (vegetation, hydrological and soil) correlated strongest with ice content and explored its spatial heterogeneity at different scales (1 to 100 m). Results: The ice content was highest in the depressions of the wet lakebed and lowest at the slopes of the dry lakebed. In the wet lakebed the ice content increased with depth, while in the dry lakebed the vertical distribution depended on topographical position. Spatial variability in ice content was similar at different scales, stressing strong influence of local drivers. 0–60 cm ice content correlated strongest with soil moisture of the overlying unfrozen soil, while 0–20 cm ice content correlated strongest with vegetation characteristics. Conclusions: Our study implies that vegetation effect on microclimate is strong enough to affect near-surface ice distribution, and that ice-rich tundra may be highly sensitive to thaw once climate warming offsets the protective impact of vegetation.

The dominant mechanism of heat transfer during ground thaw is typically assumed to be vertical conduction. However, the addition of lateral subsurface water flow introduces the potential for the forced convection of energy, having an influence on ground temperatures and thaw rates. Field observations of snowmelt run-off and rates of ground thaw for two slopes within the Wolf Creek basin, Yukon, Canada, highlighted different rates of ground thaw with slope position. Ground temperatures were numerically simulated to evaluate the relative influence of conduction and convection on the thawing of these slopes; each slope comprised different soils and had a different slope aspect. Both slopes were composed of an organic layer overlying a mineral soil. Lateral water flow above the frozen layer occurred within both slopes as a result of a perched saturated zone above the organic–mineral interface. The numerical models reveal that lateral diversion within a surficial, high-hydraulic conductivity layer, such as an organic layer, can initiate convective heat transfer. However, the observed differential thaw was determined to be a result of conduction and variations in the initial ice content and snow cover rather than lateral convection of heat.

The physical and mechanical processes relating to infrastructure are strongly intertwined in subgrades of road or railway in warm permafrost regions, where the evolution of these processes may influence the functionality of infrastructure. Thus, this study analyzed the embankment thermal regime and thaw settlement behavior based on monitored data for three sections of the newly constructed Gonghe–Yushu expressway (GYE) in a warm permafrost area of Tibet. The efficiencies of crushed rock, ventilated, and insulated embankments in maintaining permafrost temperature were evaluated in relation to the permafrost table (PT) and the annual warming rate of the permafrost. The deformation characteristics of three embankments for different soil layers are summarized, along with analysis of heat balance. The results show that: (a) the permafrost thaw rate has a positive linear correlation with mean annual ground temperature; (b) the permafrost displays a warming trend regardless of whether PT increases or decreases; (c) the total deformation of a given embankment shows a tendency toward settlement; and (d) subgrade peak thaw settlement occurs later than its maximum seasonal thaw depth.

Various climatic parameters (average annual, winter, and summer air temperature, winter and summer total precipitation) and their temporal variability are analyzed to explain the activation of cryogenic processes in Central Yamal. The effect of fluctuations of these parameters on the thaw depth and ground temperature is analyzed. The regression analysis is carried out to reconstruct ground temperature during earlier periods of time in the years preceding the activation of thermal denudation and the formation of gas emission craters.

Frost heave is the prevailing damage to the embankment in cold regions. It is a challenge to ascertain frost damage behavior of the embankment due to the complication of freezing-thawing process involving water migration, heat convection process of water, ice-water phase transition, and frost heave. To investigate the freezing behavior of the embankment, a hydro-thermo-mechanical numerical model is deduced, and an embankment model test is carried out. Finally, the moisture, temperature, and deformation during the freezing-thawing process are analyzed. The results show that (1) there exist two warm frozen layers and a frozen layer at the bottom of the embankment at the time of the minimum air temperature and at the time of the maximum thaw depth, respectively. (2) Under the drive of temperature gradient, the water migrates and the redistributions occur. The soil in the freezing-thawing front is filled with unfrozen water and ice, and its water content is high, which directly lead to frost heave. (3) The horizontal deformation at the shoulder is larger than those in other zones, which easily leads to denudation damage. Meantime, the deformation difference between the shoulder and middle will lead to the longitudinal cracks and consequently embankment failures. The study will provide a theoretical basis and reference for the design, maintenance and research of embankment in cold regions.

Hydrologic flowpaths might propagate biogeochemical signals among connected ecosystems or alter and dampen signals because of reactions or retention occurring during transport. In the Arctic, experimentally warmed terrestrial tundra releases inorganic nitrogen (N), but the fate of this newly released N remains unclear. Nitrogen could be passively transported downslope in flowing water, or retained when flowpaths intercept N-limited ecosystems. We applied nutrient spiraling theory to simultaneously measure reaction and transport of ammonium (NH4+) and phosphate (PO43−), nutrients limiting primary productivity in Arctic ecosystems. Pulse fertilization experiments were focused on flowpaths known as water tracks that hydrologically connect soils to receiving streams and lakes in upland tundra of Alaska. Water tracks typically retained PO43−, but passively transported NH4+, thus potentially propagating NH4+ produced by warming tundra soils to downstream ecosystems. Nutrient uptake was uncorrelated with the relative proportion of downslope transport in transient storage zones, but greater NH4+ uptake occurred as advective hydrologic flux increased relative to dispersion. Phosphate uptake declined as thaw depth increased over the summer season likely because of declining capacity for biotic uptake or sorption in deeper soils. Phosphorus limitation in fluvial ecosystems of the Arctic might result in efficient transport of inorganic N to N-limited lentic and coastal ecosystems, where increasing subsidies furnished by N loss from warming terrestrial tundra could support enhanced primary production.

Terrestrial Arctic ecosystems play a key role in the global carbon (C) cycle, as they store a large amount of organic matter in permafrost. Among regions with continuous permafrost, Svalbard has one of the warmest permafrost and may provide a template of the environmental responses of Arctic regions to future climate change. We analyze the CO2 fluxes at a polygonal tundra site in Adventdalen (Svalbard) during one full growing season across a vegetation and environmental gradient to understand how the interaction of different abiotic (thaw depth, ground surface temperature (GST), soil moisture, photosynthetic active radiation - PAR) and biotic (leaf area index (LAI), and plant phenology) factors affect the CO2 fluxes and identify the drivers of Net Ecosystem Exchange (NEE) and Ecosystem Respiration (ER). Three distinct periods (early, peak, and late) characterized the growing season based on plant phenology and the main environmental conditions. Comparing early, peak and late season, both NEE and ER exhibited specific patterns: ER shown high values since the early season, only slightly increased at peak, and then decreased drastically in the late season, with GST being the most important driver of ER. The drivers of NEE changed during the season: thaw depth, PAR and GST during the early season, LAI at peak, and PAR during the late season. These data allow to highlight that the thawing and freezing of the upper part of the active layer during the early and late season controls ER, possibly due to the response of microbial respiration in the upper part of the soil. Especially during the late season, despite the fully developed active layer (reaching its highest thawing depth), the freezing of the uppermost 2 cm of soil induced the drastic decrease of the respiratory efflux. In addition, the seasonal C balance of our plots indicated a seasonal source at our plots, in apparent contrast with previous eddy covariance (EC) measurements from a wetter area nearby. This difference implies that drier ecosystems act as sources while wetter ecosystems are sinks, suggesting that a drying trend in polygonal tundra could switch these ecosystems from CO2 sinks to sources in a feedback to future climate change.

The response of CH4 emission from natural wetlands due to meteorological conditions is important because of its strong greenhouse effect. To understand the relationship between CH4 flux and wetting, we observed interannual variations in chamber CH4 flux, as well as the concentration, δ13C , and δD of dissolved CH4 during the summer from 2009 to 2013 at the taiga–tundra boundary in the vicinity of Chokurdakh (70 ∘ 37 ′ N, 147 ∘ 55 ′ E), located on the lowlands of the Indigirka River in northeastern Siberia. We also conducted soil incubation experiments to interpret δ13C and δD of dissolved CH4 and to investigate variations in CH4 production and oxidation processes. Methane flux showed large interannual variations in wet areas of sphagnum mosses and sedges (36–140 mg CH4 m −2 day −1 emitted). Increased CH4 emission was recorded in the summer of 2011 when a wetting event with extreme precipitation occurred. Although water level decreased from 2011 to 2013, CH4 emission remained relatively high in 2012, and increased further in 2013. Thaw depth became deeper from 2011 to 2013, which may partly explain the increase in CH4 emission. Moreover, dissolved CH4 concentration rose sharply by 1 order of magnitude from 2011 to 2012, and increased further from 2012 to 2013. Large variations in δ13C and δD of dissolved CH4 were observed in 2011, and smaller variations were seen in 2012 and 2013, suggesting both enhancement of CH4 production and less significance of CH4 oxidation relative to the larger pool of dissolved CH4 . These multi-year effects of wetting on CH4 dynamics may have been caused by continued soil reduction across multiple years following the wetting. Delayed activation of acetoclastic methanogenesis following soil reduction could also have contributed to the enhancement of CH4 production. These processes suggest that duration of water saturation in the active layer can be important for predicting CH4 emission following a wetting event in the permafrost ecosystem.

Increased road-building activity in the arctic has the potential to impact adjacent ecosystems. Roads in permafrost regions are often built atop insulative gravel pads that generate dust plumes, altering soil chemistry and ecosystem function of nearby tundra. Here, we measure edaphic and vegetation characteristics along transects of decreasing dust deposition perpendicular to the Dalton Highway in northern Alaska. We quantify the impact of dust deposition on normalized difference vegetation index (NDVI), a proxy for aboveground plant biomass. Deposition of calcium carbonate-rich dust declined from 1.625 grams m−2 day−1 immediately adjacent to the road, to negligible levels 625 meters away. Along these transects from the road, we found declines in soil moisture and temperature, thaw depth, shrub height, and foliar nitrogen content, indicating that tundra roads create corridors with edaphic conditions favorable to vascular plant growth. At sites nearest the road, dust deposited on leaf surfaces reduced measured NDVI values by 0.24 by blocking reflectance properties of the underlying leaves. Our findings on the impacts of roads and dust deposition on adjacent tundra may aid planning of future infrastructure projects. We caution that dust deposition may negatively bias NDVI-based estimates of plant biomass, especially where unpaved roads are common.

Aims: For informed predictions on the sensitivity of Arctic tundra landscape to permafrost thaw, we aimed to investigate the distribution pattern of near-surface ground ice and its influencing factors in Northeast Siberia. Methods: Near-surface permafrost cores (60 cm) were sampled along small-scale topographic gradients in two drained lakebeds. We investigated which factors (vegetation, hydrological and soil) correlated strongest with ice content and explored its spatial heterogeneity at different scales (1 to 100 m). Results: The ice content was highest in the depressions of the wet lakebed and lowest at the slopes of the dry lakebed. In the wet lakebed the ice content increased with depth, while in the dry lakebed the vertical distribution depended on topographical position. Spatial variability in ice content was similar at different scales, stressing strong influence of local drivers. 0–60 cm ice content correlated strongest with soil moisture of the overlying unfrozen soil, while 0–20 cm ice content correlated strongest with vegetation characteristics. Conclusions: Our study implies that vegetation effect on microclimate is strong enough to affect near-surface ice distribution, and that ice-rich tundra may be highly sensitive to thaw once climate warming offsets the protective impact of vegetation.

Understanding the driving forces for alpine vegetation variations at different permafrost degrading stages is important when the Tibetan Plateau is experiencing climate warming. We applied the modified Frost Number model to simulate frozen ground distributions in the Tibetan Plateau and calculated the maximum thawing depth by the Stefan approach. We classified the simulated frozen ground into three subzones: seasonal frozen ground zone, changing zone, and permafrost zone. We evaluated the effects of precipitation, air temperature, and maximum thawing depth on Normalized Difference Vegetation Index (NDVI) in the subzones across five different stages from 1982 to 2012. The results show that permafrost zone, changing zone, and seasonal frozen ground zone account for about 30.6 percent, 23.3 percent, and 46.1 percent of the study area, respectively. Over the five stages, permafrost areas decreased at fast, slow, fastest, and then slowest rate from stage1 to stage 5, and the large continuous permafrost area has been degraded into pieces. Precipitation is strongly correlated with NDVI and contributes most `to the changes of NDVI. Maximum thawing depth and particularly air temperature show a much smaller correlation and contribute less to the variation rate of NDVI. The findings will have broad applications in investigating the impact of climate and environment changes on alpine vegetation variations in the Tibetan Plateau.

Frost damage develops unevenly inside concrete, adversely affecting the structural performance of existing RC structures. A recent study reported by Hayashida et al. (2014) revealed that RC beams subjected to freeze–thaw action exhibited unexpected shear failure under different degrees of damage depth. Although extensive research has been conducted to investigate freeze–thaw damage mechanisms, most such work has been limited to examination of small-scale specimens of plain concrete or mortar. Few practice-based approaches to assess the mechanical performance of large-scale RC members have been reported. Several works bridge the gap using finite element models coupled with poro-mechanics (Gong et al. 2018) and continuum damage mechanics (Berto et al. 2015). However, these are complex and challenging to implement for the assessment of existing deteriorated structures. In this respect, a simple physical model to predict shear strength is necessary for practical use. The shear strength of an existing RC bridge pier is assessed using the upper bound theorem in these analyses. The upper bound theorem in the plastic analysis requires equality between internal and external works and explicitly accounts for different shear transfer actions. Based on freeze–thaw depth obtained from on-site inspections, the analyzed piers are divided into undamaged and damaged zones. Their internal work is minimized with respect to the angles of inclination under an assumed displacement field. The shear strength is determined accordingly. The developed analysis showed that the current shear strength was 12 % less than that in the intact condition. Furthermore, reduction in shear strength under different levels of freeze–thaw depth is discussed in terms of shear resisting components.

Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw.

The paper studies the initial boundary-edge problem for the non-stationary one-dimensional thermal conductivity equation, which models the temperature distribution in the glacier. The mathematical model has been constructed taking into account solid-liquid phase transitions. Data from meteorological stations were used to determine the model parameters, with the help of which the necessary physical and thermophysical characteristics of the calculation area were obtained. The finite volume method was used for numerical solution of the problem. The non-stationary periodic regime was investigated, temperature-depth dependences were plotted for each month and the depth of the active layer and the depth of zero annul amplitudes for two glaciers: the Vavilov Ice Cap and the Austre Gronfjordbreen were found. Glacier temperature regime forecast for the year 2100 are modelled for three global warming scenarios: a moderate RCP2.6, the RCP7 corresponding to current emissions and the RCP1.9 adopted at the Paris Agreement in 2015. The scenarios are based on the IPCC AR5 and SSP databases, and on the existing policy framework and stated policy intentions The IEA Stated Policies Scenario (STEPS). The plotted graphs clearly show that even the moderate RCP2.6 scenario (2°C warming) can lead to noticeable glacier thawing, while the RCP7 scenario would lead to unprecedented consequences. In turn, a scenario limiting climate warming to 1.5°C from pre-industrial levels (RCP1.9) would markedly slow glacial thawing. Having analysed the irreversible degradation of the ice cover at a warming of an additional 0.5°C, and considering the adverse effects of this warming on many areas, the need to contain the rate of temperature increase is clear. The simulations have clearly confirmed the impact of global warming on our planet's cryosphere., В статье исследуется начально-краевая задача для нестационарного одномерного уравнения теплопроводности, моделирующего распределение температуры в леднике. Математическая модель построена с учетом фазовых переходов твердое тело-жидкость.Для определения параметров модели использовались данные с метеорологических станций, с помощью которых были получены необходимые физические и теплофизические характеристики расчетной зоны. Для численного решения задачи был использован метод конечных объемов. Был исследован нестационарный периодический режим, построены зависимости температуры от глубины для каждого месяца и найдена глубина активного слоя, а также глубина нулевых амплитуд аннуляций для двух ледников: ледяной шапки Вавилова и Аустре-Гронфьордбрина. Прогноз температурного режима ледников на 2100 год смоделирован для трех сценариев глобального потепления: умеренный RCP2.6, RCP7, соответствующий текущим выбросам, и RCP1.9, принятый в Парижском соглашении в 2015 году. Сценарии основаны на базах данных IPCC AR5 и SSP, а также на существующей структуре политики и заявленных политических намерениях в Сценарии (STEPS), изложенном МЭА. Построенные графики ясно показывают, что даже умеренный сценарий RCP2.6 (потепление на 2°C) может привести к заметному таянию ледников, в то время как сценарий RCP7 приведет к беспрецедентным последствиям. В свою очередь, сценарий, ограничивающий потепление климата до 1,5°C по сравнению с доиндустриальным уровнем (RCP1.9), заметно замедлил бы таяние ледников. Проанализировав необратимое разрушение ледяного покрова при потеплении еще на 0,5°C, и учитывая неблагоприятные последствия этого потепления для многих районов, необходимость сдерживания темпов повышения температуры становится очевидной. Моделирование четко подтвердило влияние глобального потепления на криосферу нашей планеты., Международный научный журнал "Современные информационные технологии и ИТ-образование", Выпуск 4 2021, Pages 1007-1021

In this paper, the law of ice-rich permafrost embankment thaw consolidation is studied based on three-dimensional nonlinear large strain thaw consolidation theory. To avoid problems associated with numerical simulation efficiency and stability when a nonlinear stress-strain relationship is employed, a segment interpolation function is used to implement the nonlinear relationship between the compression modulus and the void ratio, and the corresponding simulation strategy is proposed. Through a comparison of the monitoring and calculated results, it is indicated that the calculation accuracy on ice-rich embankment thaw settlement can be notably improved after nonlinear theory is implemented with the proposed numerical simulation method. A further analysis of the calculated results indicates that the interactive effects between the thermal and mechanical fields can be more reasonably described by nonlinear theory than by linear theory. It is also determined that the postthaw pore water in the shallow embankment dissipates in the early operation period, while in the following long operation period, the development of the permafrost embankment thaw settlement is mainly due to the dissipation of newly postthaw pore water at the thaw depth or the permafrost table. This is one of the main differences in the law of permafrost embankment thaw settlement compared with that of unfrozen embankments.

Questions Is it possible to map floristic gradients in heterogeneous boreal vegetation by using remote‐sensing data? Does a continuous vegetation map enable the creation of a spatially continuous map of seasonal permafrost soil thaw depth? Location Bonanza Creek LTER, Fairbanks, Alaska, USA. Methods Vegetation records are subjected to an ordination to extract the predominant floristic gradient. The ordination scores are then extrapolated using Sentinel 2 imagery and a digital elevation model (DEM). As the relation between vegetation pattern and seasonal thaw depth was confirmed in this study, the spatial distribution of ordination scores is then used to predict seasonal thaw depth over the same area. Results The first dimension of the ordination space separates species corresponding to moist and cold soil conditions from species associated with well‐drained soils. This floristic gradient was successfully mapped within the sampled plant communities. The extrapolated thaw depths follow the typical distribution along a topographical and geomorphological gradient for this region. Besides vegetation information also DEM derivatives show high contributions to the thaw depth modeling. Conclusion We demonstrate that floristic gradient mapping in boreal vegetation is possible. The accuracy of the thaw depth prediction model is comparable to that in previous analyses but uses a more parsimonious set of predictors, underlining the efficacy of this approach.

Field collection of permafrost vegetation and seasonal thaw depth measurements are a time consuming and labor intensive procedure. To address this, in this study we assessed the capacity of airborne hyperspectral and LiDAR data for upscaling in-situ point data to map vegetation and summer thaw depth at an experimental site near Fairbanks, Alaska, USA. The site represents roughly three quarters of the most common vegetation in the boreal and taiga permafrost zones. An overall accuracy of 93% was achieved for mapping five different vegetation types, and a correlation coefficient (r) of 0.66 was produced for thaw depth modeling using a machine learning algorithm when two remote sensing data sources were combined. Object-based vegetation and thaw depth maps were produced. This study demonstrates that fine spatial resolution hyperspectral data could be valuable for permafrost characterization, while the contribution from LiDAR was marginal at the testing site.

Permafrost is a ubiquitous phenomenon in the Arctic. Its future evolution is likely to control changes in northern high-latitude hydrology and biogeochemistry. Here we evaluate the permafrost dynamics in the global models participating in the Coupled Model Intercomparison Project (present generation – CMIP6; previous generation – CMIP5) along with the sensitivity of permafrost to climate change. Whilst the northern high-latitude air temperatures are relatively well simulated by the climate models, they do introduce a bias into any subsequent model estimate of permafrost. Therefore evaluation metrics are defined in relation to the air temperature. This paper shows that the climate, snow and permafrost physics of the CMIP6 multi-model ensemble is very similar to that of the CMIP5 multi-model ensemble. The main differences are that a small number of models have demonstrably better snow insulation in CMIP6 than in CMIP5 and a small number have a deeper soil profile. These changes lead to a small overall improvement in the representation of the permafrost extent. There is little improvement in the simulation of maximum summer thaw depth between CMIP5 and CMIP6. We suggest that more models should include a better-resolved and deeper soil profile as a first step towards addressing this. We use the annual mean thawed volume of the top 2 m of the soil defined from the model soil profiles for the permafrost region to quantify changes in permafrost dynamics. The CMIP6 models project that the annual mean frozen volume in the top 2 m of the soil could decrease by 10 %–40 %∘C-1 of global mean surface air temperature increase.

Wildfires are relatively rare in subarctic tundra ecosystems, but they can strongly change ecosystem properties. Short-term fire effects on subarctic tundra vegetation are well documented, but long-term vegetation recovery has been studied less. The frequency of tundra fires will increase with climate warming. Understanding the long-term effects of fire is necessary to predict future ecosystem changes. We used a space-for-time approach to assess vegetation recovery after fire over more than four decades. We studied soil and vegetation patterns on three large fire scars (>44, 28 and 12 years old) in dry, lichen-dominated forest tundra in Western Siberia. On 60 plots, we determined soil temperature and permafrost thaw depth, sampled vegetation and measured plant functional traits. We assessed trends in Normalized Difference Vegetation Index (NDVI) to support the field-based results on vegetation recovery. Soil temperature, permafrost thaw depth and total vegetation cover had recovered to pre-fire levels after >44 years, as well as total vegetation cover. In contrast, after >44 years, functional groups had not recovered to the pre-fire state. Burnt areas had lower lichen and higher bryophyte and shrub cover. The dominating shrub species, Betula nana, exhibited a higher vitality (higher specific leaf area and plant height) on burnt compared with control plots, suggesting a fire legacy effect in shrub growth. Our results confirm patterns of shrub encroachment after fire that were detected before in other parts of the Arctic and Subarctic. In the so far poorly studied Western Siberian forest tundra we demonstrate for the first time, long-term fire-legacies on the functional composition of relatively dry shrub- and lichen-dominated vegetation.

High-latitude tundra ecosystems are increasingly affected by climate warming. As an important fraction of soil microorganisms, fungi play essential roles in carbon (C) degradation, especially the old, chemically recalcitrant C. However, it remains obscure how fungi respond to climate warming and whether fungi, in turn, affect C stability of tundra. In a two-year winter soil warming experiment of 2 °C by snow fences, we investigated responses of fungal communities to warming in the active layer of the Alaskan tundra. Although fungal community composition, revealed by 28S rRNA gene amplicon sequencing, remained unchanged (P > 0.05), fungal functional gene composition, revealed by a microarray named GeoChip, was altered (P < 0.05). Changes in functional gene composition were linked to winter soil temperature, thaw depth, soil moisture, and gross primary productivity (Canonical Correlation Analysis, P < 0.05). Specifically, relative abundances of fungal genes encoding invertase, xylose reductase, and vanillin dehydrogenase significantly increased (P < 0.05), indicating higher C degradation capacities of fungal communities under warming. Accordingly, we detected changes of fungal gene networks under warming, including higher average path distance, lower average clustering coefficient, and lower percentage of negative links, indicating that warming potentially changed fungal interactions. Together, our study revealed higher C degradation capacities of fungal communities under short-term warming and highlights the potential impacts of fungal communities on mediating tundra ecosystem respiration, and consequently future C stability of high-latitude tundra.

The spatial distribution of permafrost and associated mean annual ground temperature (MAGT) and active layer thickness (ALT) are crucial data for hydrological studies. In this paper, we present the current state of knowledge on the spatial distribution of the permafrost properties of 29 river basins in Mongolia. The MAGT and ALT values are estimated by applying TTOP and Kudryavtsev methods. The main input of both methods is the spatially distributed surface temperature. We used the 8-day land surface temperature (LST) data from the day- and night-time Aqua and Terra images of the moderate resolution imaging spectroradiometer (MODIS). The gaps of the MODIS LST data were filled by spatial interpolation. Next, an LST model was developed based on 34 observational borehole data using a panel regression analysis (Baltagi, Econometric analysis of panel data, 3 edn, Wiley, New York, 2005). The model was applied for the whole country and covered the period from August 2012 to August 2013. The results show that the permafrost covers 26.3% of the country. The average MAGT and ALT for the permafrost region is − 1.6 °C and 3.1 m, respectively. The MAGT above -2 °C (warm permafrost) covers approximately 67% of the total permafrost area. The permafrost area and distribution in cold and warm permafrost varies highly over the country, in particular in regions where the river network is highly developed. High surface temperatures associated with climate change would result in changes of permafrost conditions, and, thus, would impact the surface water availability in these regions. The data on permafrost conditions presented in this paper can be used for further research on changes in the hydrological conditions of Mongolia.

The pathways and timing of drainage from inundated ice-wedge polygon centers in a warming climate have important implications for carbon flushing, advective heat transport, and transitions from carbon dioxide to methane dominated emissions. This research helps to understand this process by providing the first in-depth analysis of drainage from a single polygon based on fundamental hydrogeological principles. We use a recently developed analytical solution to evaluate the effects of polygon aspect ratios (radius to thawed depth) and hydraulic conductivity anisotropy (horizontal to vertical hydraulic conductivity) on drainage pathways and temporal depletion of ponded water heights of inundated ice-wedge polygon centers. By varying the polygon aspect ratio, we evaluate the effect of polygon size (width), inter-annual increases in active layer thickness, and seasonal increases in thaw depth on drainage. One of the primary insights from the model is that most inundated ice-wedge polygon drainage occurs along an annular region of the polygon center near the rims. This implies that inundated polygons are most intensely flushed by drainage in an annular region along their horizontal periphery, with implications for transport of nutrients (such as dissolved organic carbon) and advection of heat towards ice wedge tops. The model indicates that polygons with large aspect ratios and high anisotropy will have the most distributed drainage. Polygons with large aspect ratio and low anisotropy will have their drainage most focused near the their periphery and will drain most slowly. Polygons with small aspect ratio and high anisotropy will drain most quickly.

This paper presents the results of 39 years of observations conducted at the Chabyda station to monitor the thermal state of permafrost landscapes under current climatic warming. The analysis of long-term records from weather stations in the region has revealed one of the highest increasing trends in mean annual air temperature in northern Russia. The partitioning of the energy balance in different landscape units within the study area has been analyzed. Quantitative relationships in the long-term variability of ground thermal parameters, such as the ground temperature at the bottom of the active layer and seasonal thaw depth, have been established. The ground temperature dynamics within the depth of zero annual amplitude indicates that both warm and cold permafrost are thermally stable. The short-term variability of the snow accumulation regime is the main factor controlling the thermal state of the ground in permafrost landscapes. The depth of seasonal thaw is characterized by low interannual variability and exhibits little response to climate warming, with no statistically significant increasing or decreasing trend. The results of the ground thermal monitoring can be extended to similar landscapes in the region, providing a reliable basis for predicting heat transfer in natural, undisturbed landscapes.

Climate-induced warming of permafrost soils is a global phenomenon, with regional and site-specific variations which are not fully understood. In this context, a 2-D automated electrical resistivity tomography (A-ERT) system was installed for the first time in Antarctica at Deception Island, associated to the existing Crater Lake site of the Circumpolar Active Layer Monitoring – South Program (CALM-S) – site. This setup aims to (i) monitor subsurface freezing and thawing processes on a daily and seasonal basis and map the spatial and temporal variability in thaw depth and to (ii) study the impact of short-lived extreme meteorological events on active layer dynamics. In addition, the feasibility of installing and running autonomous ERT monitoring stations in remote and extreme environments such as Antarctica was evaluated for the first time. Measurements were repeated at 4 h intervals during a full year, enabling the detection of seasonal trends and short-lived resistivity changes reflecting individual meteorological events. The latter is important for distinguishing between (1) long-term climatic trends and (2) the impact of anomalous seasons on the ground thermal regime. Our full-year dataset shows large and fast temporal resistivity changes during the seasonal active layer freezing and thawing and indicates that our system setup can resolve spatiotemporal thaw depth variability along the experimental transect at very high temporal resolution. The largest resistivity changes took place during the freezing season in April, when low temperatures induce an abrupt phase change in the active layer in the absence of snow cover. The seasonal thawing of the active layer is associated with a slower resistivity decrease during October due to the presence of snow cover and the corresponding zero-curtain effect. Detailed investigation of the daily resistivity variations reveals several periods with rapid and sharp resistivity changes of the near-surface layers due to the brief surficial refreezing of the active layer in summer or brief thawing of the active layer during winter as a consequence of short-lived meteorological extreme events. These results emphasize the significance of the continuous A-ERT monitoring setup which enables detecting fast changes in the active layer during short-lived extreme meteorological events. Based on this first complete year-round A-ERT monitoring dataset on Deception Island, we believe that this system shows high potential for autonomous applications in remote and harsh polar environments such as Antarctica. The monitoring system can be used with larger electrode spacing to investigate greater depths, providing adequate monitoring at sites and depths where boreholes are very costly and the ecosystem is very sensitive to invasive techniques. Further applications may be the estimation of ice and water contents through petrophysical models or the calibration and validation of heat transfer models between the active layer and permafrost.

The Mohe–Daqing oil pipeline (MDOP) of China–Russia crude oil pipeline (CRCOP) goes through a 441 km permafrost in high-latitude regions, the most critical problem of which is the thawing settlement of the oil pipe. Global warming effect, oil temperature, and construction technology causes the increase of ground temperature and accelerates the degradation of permafrost. The influence of geohazards on the existing CRCOP and its accompanying road was investigated in this study, which showed that the current engineering had been affected by freezing-thawing influence. It would be more serious for the thermal disturbance between each other. In view of this problem, the thermal stability of the oil pipe and accompanying road was simulated based on the MDOP, considering various scenarios of different oil temperatures, whether global warming is considered or not, whatever the thermal insulation layer is and regardless of the different distances from the accompanying road. The numerical results indicate that the oil temperature had considerable influence on the thawing rate of permafrost. Placing the thermal insulation material around the oil pipe can effectively mitigate or even control the degradation of permafrost. With this measurement, the thaw depth has remained stable after 5 years of construction, and had been controlled within 3.0 m when the thermal insulation thickness reached 8.0 cm. The accompanying road can also have an adverse effect on the permafrost for its thermal interaction with the oil pipe. The larger the distance, the lesser the thermal disturbance. Therefore, the thermal stability of MDOP can positively adopt a suitable oil temperature for thermal insulation thickness, along with an optimized distance away from the accompanying road as well. This study would also provide an essential theoretical and technological support for the design of oil pipeline in other permafrost regions.

Permafrost is an important component of the Arctic system and its future fate is likely to control changes in northern high latitude hydrology and biogeochemistry. Here we evaluate the permafrost dynamics in the global models participating in the Coupled Model Intercomparison Project (present generation – CMIP6; previous generation – CMIP5) along with the the sensitivity of permafrost to climate change. Whilst the northern high latitude air temperatures are relatively well simulated by the climate models, they do introduce a bias into any subsequent model estimate of permafrost. Therefore evaluation metrics are defined in relation to the air temperature. This paper shows the climate, snow and permafrost physics of the CMIP6 multi-model ensemble is very similar to that of the CMIP5 multi-model ensemble. The main difference is that a small number of models have demonstrably better snow insulation in CMIP6 than in CMIP5 which improves their representation of the permafrost extent. The simulation of maximum summer thaw depth does not improve between CMIP5 and CMIP6. We suggest that models should include a better resolved and deeper soil profile as a first step towards addressing this. We use the annual mean thawed volume of the top 2 m of the soil defined from the model soil profiles for the permafrost region to quantify changes in permafrost dynamics. The CMIP6 models suggest this is projected to increase by 20–30 %/°C of global mean temperature increase. Under climate change and in equilibrium this may result in an additional 80–120 Gt C/°C of permafrost carbon becoming vulnerable to decomposition.

Plant traits reflect growth strategies and trade-offs in response to environmental conditions. Because of climate warming, plant traits might change, altering ecosystem functions and vegetation–climate interactions. Despite important feedbacks of plant trait changes in tundra ecosystems with regional climate, with a key role for shrubs, information on responses of shrub functional traits is limited. Here, we investigate the effects of experimentally increased permafrost thaw depth and (possibly thaw-associated) soil nutrient availability on plant functional traits and strategies of Arctic shrubs in northeastern Siberia. We hypothesize that shrubs will generally shift their strategy from efficient conservation to faster acquisition of resources through adaptation of leaf and stem traits in a coordinated whole-plant fashion. To test this hypothesis, we ran a 4 year permafrost thaw and nutrient fertilization experiment with a fully factorial block design and six treatment combinations – permafrost thaw (control, unheated cable, heated cable) × fertilization (no nutrient addition, nutrient addition). We measured 10 leaf and stem traits related to growth, defence and the resource economics spectrum in four shrub species (Betula nana, Salix pulchra, Ledum palustre and Vaccinium vitis-idaea), which were sampled in the experimental plots. The plant trait data were statistically analysed using linear mixed-effect models and principal component analysis (PCA). The response to increased permafrost thaw was not significant for most shrub traits. However, all shrubs responded to the fertilization treatment, despite decreased thaw depth and soil temperature in fertilized plots. Shrubs tended to grow taller but did not increase their stem density or bark thickness. We found a similar coordinated trait response for all four species at leaf and plant level; i.e. they shifted from a conservative towards a more acquisitive resource economy strategy upon fertilization. In accordance, results point towards a lower investment into defence mechanisms, and hence increased shrub vulnerability to herbivory and climate extremes. Compared to biomass and height only, detailed data involving individual plant organ traits such as leaf area and nutrient contents or stem water content can contribute to a better mechanistic understanding of feedbacks between shrub growth strategies, permafrost thaw and carbon and energy fluxes. In combination with observational data, these experimental tundra trait data allow for a more realistic representation of tundra shrubs in dynamic vegetation models and robust prediction of ecosystem functions and related climate–vegetation–permafrost feedbacks.

Connections between vegetation and soil thermal dynamics are critical for estimating the vulnerability of permafrost to thaw with continued climate warming and vegetation changes. The interplay of complex biophysical processes results in a highly heterogeneous soil temperature distribution on small spatial scales. Moreover, the link between topsoil temperature and active layer thickness remains poorly constrained. Sixty-eight temperature loggers were installed at 1–3 cm depth to record the distribution of topsoil temperatures at the Trail Valley Creek study site in the northwestern Canadian Arctic. The measurements were distributed across six different vegetation types characteristic for this landscape. Two years of topsoil temperature data were analysed statistically to identify temporal and spatial characteristics and their relationship to vegetation, snow cover, and active layer thickness. The mean annual topsoil temperature varied between −3.7 and 0.1 ∘C within 0.5 km2. The observed variation can, to a large degree, be explained by variation in snow cover. Differences in snow depth are strongly related with vegetation type and show complex associations with late-summer thaw depth. While cold winter soil temperature is associated with deep active layers in the following summer for lichen and dwarf shrub tundra, we observed the opposite beneath tall shrubs and tussocks. In contrast to winter observations, summer topsoil temperature is similar below all vegetation types with an average summer topsoil temperature difference of less than 1 ∘C. Moreover, there is no significant relationship between summer soil temperature or cumulative positive degree days and active layer thickness. Altogether, our results demonstrate the high spatial variability of topsoil temperature and active layer thickness even within specific vegetation types. Given that vegetation type defines the direction of the relationship between topsoil temperature and active layer thickness in winter and summer, estimates of permafrost vulnerability based on remote sensing or model results will need to incorporate complex local feedback mechanisms of vegetation change and permafrost thaw.

The aim of this paper was to reveal the distribution law of permafrost thermal thawing sensibility and thaw depth caused by road construction in Qinghai-Tibet engineering corridor (QTEC). The prediction models of permafrost thermal thawing sensibility and thaw depth have been developed by incorporating the MODIS and in situ soil temperature observation data. The comprehensive earth-atmosphere-coupled numerical models of different embankment structures have been utilized to calculate the thaw depth of the underlying permafrost foundation. Finally, using the given data and above developed prediction models, the distribution maps of permafrost thermal thawing sensibility and thaw depth in QTEC are obtained by grid calculation. The results show the following: (1) Insensitive permafrost of QTEC mainly distributes in the large-scale mountain and high latitude area, and highly sensitive permafrost is located in the perennial river bed, flood plain, and terrace regions. (2) Road construction has a strong thermal disturbance to underlying permafrost, and the proportion of large thaw depth area of separate embankment is obviously smaller than that of 26 m full-width embankment. (3) Increase of subgrade interval reduces the proportion of large thaw depth areas, and the application of separate embankment structure is an effective engineering means for the Qinghai-Tibet expressway.

Thermokarst features, such as thaw ponds, are hotspots for methane emissions in warming lowland tundra. Presently we lack quantitative knowledge on the formation rates of thaw ponds and subsequent vegetation succession, necessary to determine their net contribution to greenhouse gas emissions. This study sets out to identify development trajectories and formation rates of small-scale (2), shallow arctic thaw ponds in north-eastern Siberia. We selected 40 ponds of different age classes based on a time-series of satellite images and measured vegetation composition, microtopography, water table, and thaw depth in the field and measured age of colonizing shrubs in thaw ponds using dendrochronology. We found that young ponds are characterized by dead shrubs, while older ponds show rapid terrestrialization through colonization by sedges and Sphagnum moss. While dead shrubs and open water are associated with permafrost degradation (lower surface elevation, larger thaw depth), sites with sedge and in particular Sphagnum display indications of permafrost recovery. Recruitment of Betula nana on Sphagnum carpets in ponds indicates a potential recovery toward shrub-dominated vegetation, although it remains unclear if and on what timescale this occurs. Our results suggest that thaw ponds display potentially cyclic vegetation succession associated with permafrost degradation and recovery. Pond formation and initial colonization by sedges can occur on subdecadal timescales, suggesting rapid degradation and initial recovery of permafrost. The rates of formation and recovery of small-scale, shallow thaw ponds have implications for the greening/browning dynamics and carbon balance of this ecosystem.

Fire severity is increasing across the boreal forest biome as climate warms, and initial post-fire changes in tree demographic processes could be important determinants of long-term forest structure and carbon dynamics. To examine soil burn severity impacts on tree regeneration, we conducted experimental burns in summer 2012 that created a gradient of residual post-fire soil organic layer (SOL) depth within a mature, sparse-canopy Cajander larch (Larix cajanderi Mayr.) forest in the Eastern Siberian Arctic. Each fall from 2012 to 2016, we added larch seeds to plots along the burn severity gradient. We tracked density of new larch germinants and established seedlings (alive ≥ 1 year) during subsequent growing seasons, along with changes in seedbed conditions (permafrost thaw depth, moisture, and temperature). Over the study, a cumulative total of 17 and 18 new germinants m−2 occurred in high and moderate severity treatments, respectively, while germinants were rare in unburned and low severity treatments ( 50%) germinated in summer 2017, following a mast event in fall 2016, suggesting safe sites for germination were not fully occupied in previous years despite seed additions. By 2017, established seedling density was ∼5 times higher on moderate and high severity treatments compared to other treatments. Cumulative total density of new germinants and established seedlings increased linearly with decreasing residual SOL depth, as did thaw depth, soil moisture, and soil temperature. Our findings suggest that increased soil burn severity could improve seedbed conditions and increase larch recruitment, assuming seed sources are available. If these demographic changes persist as stands mature, a climate-driven increase in soil burn severity could shift forest structure from sparse-canopy stands, which dominate this region of the Siberian Arctic, to high density stands, with potential implications for carbon, energy, and water cycling.

Arctic climate warming will be primarily during winter, resulting in increased snowfall in many regions. Previous tundra research on the impacts of deepened snow has generally been of short duration. Here, we report relatively long-term (7-9 years) effects of experimentally deepened snow on plant community structure, net ecosystem CO2 exchange (NEE), and soil biogeochemistry in Canadian Low Arctic mesic shrub tundra. The snowfence treatment enhanced snow depth from 0.3 to ~1 m, increasing winter soil temperatures by ~3°C, but with no effect on summer soil temperature, moisture, or thaw depth. Nevertheless, shoot biomass of the evergreen shrub Rhododendron subarcticum was near-doubled by the snowfences, leading to a 52% increase in aboveground vascular plant biomass. Additionally, summertime NEE rates, measured in collars containing similar plant biomass across treatments, were consistently reduced ~30% in the snowfenced plots due to decreased ecosystem respiration rather than increased gross photosynthesis. Phosphate in the organic soil layer (0-10 cm depth) and nitrate in the mineral soil layer (15-25 cm depth) were substantially reduced within the snowfences (47-70 and 43%-73% reductions, respectively, across sampling times). Finally, the snowfences tended (p = .08) to reduce mineral soil layer C% by 40%, but with considerable within- and among plot variation due to cryoturbation across the landscape. These results indicate that enhanced snow accumulation is likely to further increase dominance of R. subarcticum in its favored locations, and reduce summertime respiration and soil biogeochemical pools. Since evergreens are relatively slow growing and of low stature, their increased dominance may constrain vegetation-related feedbacks to climate change. We found no evidence that deepened snow promoted deciduous shrub growth in mesic tundra, and conclude that the relatively strong R. subarcticum response to snow accumulation may explain the extensive spatial variability in observed circumpolar patterns of evergreen and deciduous shrub growth over the past 30 years.

In this study, we monitored a thaw slump in the permafrost region of the Qinghai–Tibet Plateau in China, including its thaw settlement and solifluction creep characteristics, and analyzed the change in soil properties and hydrothermal process in the active layer. In addition, the change of the thaw slump active layer was compared with the change of the active layer in lakeshore areas, which were affected by thermokarst lakes, to study the relationship between thaw slump and thermokarst lake. Results showed that thaw slump solifluction creep displacement mainly occurred at the top 50 cm surface soil layer. Under the influence of the thaw slump, the active layer soil bulk density increases gradually along the slope; fine soil particles and soil organic carbon first deposit at the top 30–40 cm of the active layer at gentle slope area, and then are significantly leached at the slope bottom. Since the effect of thaw slump weakens the buffering effects of the active layer on heat transfer, the active layer gradually deepened along the slope and the ablation of the underlying ice–rich permafrost increased, which resulted in the increase of the thaw settlement. Concurrently, a large amount of thaw water from the thawed permafrost was released to the active layer, resulting in overland flow at the front part of the gentle slope area and ponding depression at the slope bottom. The active layer changes of the thaw slump and those of thermokarst lake shore were very similar. These results suggest that active layer soil properties were changed by thaw slump, leading to the increase in underlying permafrost ablation, causing large amounts of thaw water accumulating at poorly drained sites, to form sparse small–sized thermokarst lakes. For some large thermokarst lakes adjacent to a small thaw slump, lake coastal erosion caused the thaw slump, and further evolution of the thaw slump resulted in the changes of lakeshore active layer.

A new Circumpolar Active Layer Monitoring (CALM) site was established in 2009 at the Limnopolar Lake watershed in Byers Peninsula, Livingston Island, Antarctica, to provide a node in the western Antarctic Peninsula, one of the regions that recorded the highest air temperature increase in the planet during the last decades. The first detailed analysis of the temporal and spatial evolution of the thaw depth at the Limnopolar Lake CALM-S site is presented here, after eight years of monitoring. The average values range between 48 and 29cm, decreasing at a ratio of 16cm/decade. The annual thaw depth observations in the 100×100 m CALM grid are variable (Variability Index of 34 to 51%), although both the Variance Coefficient and the Climate Matrix Analysis Residual point to the internal consistency of the data. Those differences could be explained then by the terrain complexity and node-specific variability due to the ground properties. The interannual variability was about 60% during 2009-2012, increasing to 124% due to the presence of snow in 2013, 2015 and 2016. The snow has been proposed here as one of the most important factors controlling the spatial variability of ground thaw depth, since its values correlate with the snow thickness but also with the ground surface temperature and unconfined compression resistance, as measured in 2010. The topography explains the thaw depth spatial distribution pattern, being related to snowmelt water and its accumulation in low-elevation areas (downslope-flow). Patterned grounds and other surface features correlate well with high thaw depth patterns as well. The edaphic factor (E=0.05842m2/°C·day; R2=0.63) is in agreement with other permafrost environments, since frozen index (F>0.67) and MAAT (

Northeast China contains a large concentration of wetlands, primarily in two prominent types, freshwater marshes on the lowlands plains to the northeast and mountain permafrost peatlands in the north. Both wetlands types are threatened by disturbance, the marshes from agricultural conversion and the peatlands due to climate warming and loss of permafrost. Here we compare two seasons of ecosystem-scale CH4 fluxes measured via eddy covariance for a permafrost peatland in the Da Xing’anling Mountains and a freshwater marsh on the Sanjiang Plain. The objectives were to quantify CH4 fluxes, compare seasonal trends in the flux and determine the dominant environmental and biophysical drivers of the CH4 flux for these two distinct wetland types. CH4 fluxes at the marsh had a strong seasonal trend peaking in mid-summer, while the pattern for the peatland was muted. Maximum instantaneous fluxes were 1.34 μg CH4 m−2 s−1 and 9.5 μg CH4 m−2 s−1 at the peatland and marsh, respectively. Total seasonal CH4 emissions for the peatland, 0.38–1.27 g C-CH4 m−2, were an order of magnitude smaller than those at the marsh, 19.71–21.8 g C-CH4 m−2. Differences between years were small for both wetlands. We used path analysis to examine environmental and biophysical drivers of the flux and found that soil temperature (average soil temperature between 10 cm to 60 cm depths for the peatland and 10 cm depth for the marsh) was most strongly correlated with seasonal CH4 variability for both wetlands. Secondary influences were thaw depth for the peatland and net ecosystem CO2 exchange for the marsh. Given the temperature sensitivity of CH4 flux for both of these wetlands, future climate warming will likely increase CH4 emissions in northeast China, as well, the continued loss of permafrost in the mountain peatlands will likely further contribute to enhanced CH4 emissions.

The influence of vegetation and microtopography on fine‐scale variability of thaw depth is largely unknown but potentially important for improving modeling of ecosystem–permafrost interactions. To elucidate their influence, we measured tree density, shrub cover and cryptogam presence (lichen and bryophyte) on forested permafrost peat plateaus in the discontinuous permafrost zone in the southern Northwest Territories, Canada. Greater tree density was associated with shallower thaw depth (approximately one quarter of the variance), whereas shrub cover had a negligible influence on thaw depth. Cryptogam species influenced thaw depth, with greater thaw depth associated with Sphagnum than with Cladonia (a difference on the order of 10%). Greater thaw depth occurred beneath hummocks than beneath hollows (a difference also on the order of 10%). Together, canopy cover, cryptogam species and microforms contribute to a variation of roughly half the variance in thaw depth in the peat plateau landscape.

The freezing-thawing processes in soils are important components of terrestrial hydrology, which significantly influence energy and water exchanges between land surface and sub-surface. Long-term changes in frost and thaw depths are also an important indicator of climate change. A water-heat coupled movements model is established with frozen soil in this paper, which treats the freezing/thawing front as a moving interface governed by some Stefan problems with two free boundaries. The numerical simulation is conducted by using the modified finite difference method. The model is validated to compare its predictions with GEWEX Asian Monsoon Experiment(GAME)-Tibet observations at D66 site in Tibetan Plateau. The results show that the simulated soil temperature, soil water content and frost/thaw depth are in excellent agreement with the measured values. Finally, optimal error estimation for L^∞ norm is derived on the model problem by using coordinate transformation method. The numerical simulation system is established on the basis of rigorous mathematics and mechanics, which successfully solved the important and difficult problems of environmental science.

Thawing of frozen peat in discontinuous permafrost zones may significantly modify the environment at local (slumps and engineering damages) and global (greenhouse gases regime) scales. We studied the aquatic geochemistry of CO2, CH4, dissolved organic carbon (DOC), P, Si, and colloidal trace metal from hollows, depressions, permafrost subsidences and soil waters in the actively thawing discontinuous permafrost zone of Western Siberia Lowland (WSL). This site of abrupt permafrost collapse is dominated by minerotrophic fens located within the flat mound peat bog. The CO2, DOC, major and trace metal concentrations decreased with the increase of the surface area of the water body, along the hydrological continuum (soil water → hollows → depressions and permafrost subsidences → thaw ponds → thermokarst lakes). Aqueous concentrations of CO2, CH4, Ca, Si, P, Al, Fe, Nd, and U were a factor of 4 to 10 higher in the site of catastrophic thaw compared to the steady thawing of a palsa peat bog that was previously studied in the same region. The colloids (1 kDa–0.45 μm) formed in hot spots were strongly enriched in Fe, Al, and trivalent and tetravalent hydrolysates relative to organic carbon. Because the increase in the thickness of the thawing depth intensifies the input of inorganic components from deep mineral horizons, abrupt permafrost thaw enriches the surface waters in Al-rich colloids and low molecular weight organic complexes. As a result, the WSL's surface water colloidal composition may shift from DOM-rich and DOM-Fe-rich to DOM-Al-rich, and the release of low-soluble trivalent and tetravalent hydrolysates from the soil to the river will increase. We hypothesize that in sites of abrupt permafrost thaw, there is direct mobilization of soil waters to a hydrological network (rivers and lakes) and there is minimal transformation by autochthonous processes, which is unlike the case of steady permafrost thawing. Therefore, the change in physical factors, such as water pathways and the water residence time, within a given elementary landscape will likely control the overall impact of on-going permafrost thaw on both the surface water chemistry and dissolved greenhouse gas pattern of the territory. For this, high-resolution (

The currently observed climate warming will lead to widespread degradation of near-surface permafrost, which may release substantial amounts of inorganic nitrogen (N) into arctic ecosystems. We studied 11 soil profiles at three different sites in arctic eastern Siberia to assess the amount of inorganic N stored in arctic permafrost soils. We modelled the potential thickening of the active layer for these sites using the CryoGrid2 permafrost model and representative concentration pathways (RCPs) 4.5 (a stabilisation scenario) and 8.5 (a business as usual emission scenario, with increasing carbon emissions). The modelled increases in active-layer thickness (ALT) were used to estimate potential annual liberation of inorganic N from permafrost soils during the course of climate change. We observed significant stores of inorganic ammonium in permafrost, up to 40-fold higher than in the active layer. The modelled increase in ALT under the RCP8.5 scenario can result in substantial liberation of N, reaching values up to the order of magnitude of annual fixation of atmospheric N in arctic soils. However, the thaw-induced liberation of N represents only a small flux in comparison with the overall ecosystem N cycling.

The response of dissolved organic carbon (DOC) flux to permafrost degradation is one of the major sources of uncertainty in predicting the permafrost carbon feedback. We investigated DOC export and properties over two complete flow seasons in a catchment on the northern Qinghai-Tibetan Plateau. DOC concentration and biodegradability decreased systematically as thaw depth increased through the season, attributable to changing carbon sources and degree of microbial processing. Increasing DOC aromaticity and δ13C-DOC indicated shifts towards more recalcitrant carbon sources and greater residence time in soils prior to reaching the stream network. These strong and consistent seasonal trends suggest that gradual active layer deepening may decrease DOC export and biodegradability from permafrost catchments. Because these patterns are opposite observations from areas experiencing abrupt permafrost collapse (thermokarst), the overall impact of permafrost degradation on DOC flux and biodegradability may depend on the proportion of the landscape experiencing gradual thaw versus thermokarst.

The coal mining has brought a series of ecological problems and environmental problems in permafrost regions. Taking Muli coal-mining area as an example, this article attempts to analyse the environmental harms caused by coal mining and its protection measures in permafrost regions of Qinghai–Tibet Plateau. This article analyses the influence of open mining on the surrounding permafrost around the open pit by using the numerical simulation. The results show that (1) based on the interrelation between coal mining and permafrost environment, these main environmental harm include the permafrost change and the natural environment change in cold regions; (2) once the surface temperature rises due to open mining, the permafrost will disappear with the increase of exploitation life. If considering the solar radiation, the climate conditions and the geological condition around the pit edge, the maximum thaw depth will be more than 2 m; (3) the protection measures are proposed to avoid the disadvantage impact on the permafrost environment caused by coal mining. It will provide a scientific basis for the resource development and environment protection in cold regions.