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Permafrost plays an important role in hydrological processes of alpine regions. The frost table in the active layer on the permafrost acts as an impermeable boundary and regulates water generation from hillslopes and its routing to streams. Past studies focused on modes or critical conditions of flow generation, rather than on the capacity of the active layer on the permafrost to recharge flow. This study aimed to characterize the role of supra-permafrost groundwater in the generation of runoff on hillslopes during the active layer thawing processes. The study focused on an alpine meadow permafrost hillslope located in the northeastern Tibet Plateau during the months of July and August in both 2021 and 2022. Hydrometeorological variables, including precipitation, air temperature, soil temperature, soil moisture, thaw depths, supra-permafrost groundwater level, and runoff generation were monitored in field. Partial Least Squares Path Modeling was selected to analyze the relations between the above variables. The results showed that infiltrated rainwater tended to move into deep thawed soil, following which the frozen layer forced horizontal transport along the hillslope. This indicated that thaw depths along the soil profile regulated the dominant runoff path. The accumulated precipitation of the previous days had a significant impact on runoff generation. There was minimal lateral subsurface flow when the saturated zone was absent, whereas lateral subsurface flow increased with increasing thickness of the saturated zone. Runoff generation on the hillslope was regulated by both thaw depths and the thickness of the saturated zone along the soil profile. This study can act as a reference for runoff generation processes of permafrost hillslopes.

Svalbards permafrost is thawing as a direct consequence of climate change. In the Low Arctic, vegetation has been shown to slow down and reduce the active layer thaw, yet it is unknown whether this also applies to High Arctic regions like Svalbard where vegetation is smaller, sparser, and thus likely less able to insulate the soil. Therefore, it remains unknown which components of High Arctic vegetation impact active layer thaw and at which temporal scale this insulation could be effective. Such knowledge is necessary to predict and understand future changes in active layer in a changing Arctic. In this study we used frost tubes placed in study grids located in Svalbard with known vegetation composition, to monitor the progression of active layer thaw and analyze the relationship between vegetation composition, vegetation structure and snow conditions, and active layer thaw early in summer. We found that moss thickness, shrub and forb height, and vascular vegetation cover delayed soil thaw immediately after snow melt. These insulating effects attenuated as thaw progressed, until no effect on thaw depth was present after 8 weeks. High Arctic mosses are expected to decline due to climate change, which could lead to a loss in insulating capacity, potentially accelerating early summer active layer thaw. This may have important repercussions for a wide range of ecosystem functions such as plant phenology and decomposition processes. Plain Language Summary: Temperatures are rising in the Arctic, causing increased thaw of the layer of soil located above the permanently frozen ground. In Low Arctic regions vegetation cools the soil, which reduces the thawing. So far, we do not know whether the small plants growing in the High Arctic may be able to slow or reduce thaw. We measured soil thaw throughout the summer in High Arctic Svalbard in locations where vegetation composition is known. We also measured thickness of the moss layer, height of plants and snow depth. We found that moss thickness was the strongest factor in insulating the soil. Also the cover of plants, height of shrubs and forbs, and height of grass‐like plants slowed soil thaw in the early summer. The insulating effects became less over time and no effects were found 8 weeks after onset of thaw. As climate change is causing changes in the Arctic vegetation, mosses and small shrubs are expected to decrease. As we found these to be the most important factors in insulating the soil, a future decrease in mosses and small shrubs may cause accelerated soil thaw at the start of summer. Key Points: High Arctic vegetation slows active layer thaw in early summer after snow meltMosses show a stronger negative relation with thaw depth than vascular vegetationFactors influencing active layer thaw change over time in early summer [ABSTRACT FROM AUTHOR]

Intraspecific trait variation can influence plant performance in different environments and may thereby determine the ability of individual plants to respond to climate change. However, our understanding of its patterns and environmental drivers across different spatial scales is incomplete, especially in understudied regions like the Arctic.To fill this knowledge gap, we examined above‐ground and below‐ground traits from three shrub taxa expanding across the tundra biome and evaluated their relationships with multiple microenvironmental and macroclimatic factors. The traits reflected plant size and structure (plant height, leaf area and root to shoot ratio), leaf economics (specific leaf area, nitrogen content), and root economics and collaboration with mycorrhizal fungi (specific root length, root tissue density, nitrogen content, and ectomycorrhizal colonisation intensity). We also measured leaf and root δ15N and leaf δ13C to characterise nitrogen source and acquisition pathways and plant water stress. Traits were measured in replicated plots (N = 135) varying in soil microclimate, thaw depth and organic layer thickness established across five sites spanning a macroclimate gradient in northern Alaska. This hierarchical design allowed us to disentangle the independent and combined effects of fine‐scale and broad‐scale factors on intraspecific trait variation.We found substantial intraspecific variation at fine spatial scales for most traits and less variation along the macroclimate gradient and between shrub taxa. Consistent with these patterns, microenvironmental factors, mainly soil moisture and thaw depth, interacted with macroclimate, mainly climatic water deficit, to structure size‐structural and leaf trait variation. In contrast, most root traits responded additively to thaw depth and macroclimate.Synthesis. Our results demonstrate that above‐ground and below‐ground tundra shrub traits respond differently to microenvironmental and macroclimatic variation. These differing responses contribute to substantial trait variation at fine spatial scales and may decouple above‐ground and below‐ground trait responses to climate change. [ABSTRACT FROM AUTHOR]

In regions characterized by continuous permafrost, hydrological modeling remains a complex activity, primarily due to constraints related to the prevailing climatic conditions and the specific behavior of the active layer. High-latitude regions receive less solar radiation; thus, most creeks are active only during summertime and stay frozen in the winter. To realistically simulate watersheds underlain by continuous permafrost, the heat transfer through the soil needs to be accounted for in the modeling process. In this study, a watershed located in a continuous permafrost zone in Russia is investigated. A model is proposed to integrate this heat transfer into an existing conceptual rain-flow transformation model, Hydrologiska Byråns Vattenbalansavdelning (HBV), to calculate the seasonal thaw depth and determine the components of water balance. The proposed integration is a novelty compared to the standard model, as it enables the physical and thermal properties of the soil to be taken into account. It was found that the proposed model, HBV-Heat, performs better than the stand-alone HBV model. Specifically, the average Nash–Sutcliffe efficiency (NSE) increases by 30% for the whole calibration period. In terms of the water balance components, the results are consistent with previous studies, showing that surface runoff represents 64% of the observed precipitation. [ABSTRACT FROM AUTHOR]

Surface conditions are known to mediate the impacts of climate warming on permafrost. This calls for a better understanding of the environmental conditions that control the thermal regime and the depth of the active layer, especially within heterogeneous tundra landscapes. This study analyzed the spatial relationships between thaw depths, ground surface temperature (GST), and environmental conditions in a High Arctic tundra environment at Bylot Island, Nunavut, Canada. Measurements were distributed within the two dominant landforms, namely earth hummocks and low‐center polygons, and across a topographic gradient. Our results revealed that GST and thaw depth were highly heterogeneous, varying by up to 3.7°C and by more than 20 cm over short distances (<1 m) within periglacial landforms. This microscale variability sometimes surpassed the variability at the hillslope scale, especially in summer. Late‐winter snowpack thickness was found to be the prime control on the spatial variability in winter soil temperatures due to the highly heterogeneous snow cover induced by blowing snow, and this thermal effect carried over into summer. However, microtopography was the predominant driver of the spatial variability in summer GST, followed by altitude and moss thickness. In contrast, the spatial variability in thaw depth was influenced predominantly by variations in moss thickness. Hence, summer microclimate conditions dominated active layer development, but a thicker snowpack favored soil cooling in the following summer, due to the later disappearance of snow cover. These results enhance our understanding of High Arctic tundra environments and highlight the complexity of considering surface feedback effects in future projections of permafrost states within heterogeneous tundra landscapes. [ABSTRACT FROM AUTHOR]

A simple stochastic representation of the spatial variability in thaw depth is proposed. Thaw depth distribution measured in the two larch‐type forests in eastern Siberia, Spasskaya Pad and Elgeeii, showed different spatial, seasonal, and interannual variability, respectively. Year‐to‐year variation in active‐layer thickness was minor in Spasskaya Pad compared to Elgeeii. A gamma distribution adequately represented both sites' thaw depth spatial variability as the cumulative probability. Thus, we developed a simple model using the gamma distribution that illustrates the spatial variability in thaw depth at any thawing stage as a function of a given mean thaw depth. A hierarchy of models was introduced that sequentially considered the constant state, linearity, and nonlinearity in the dependence of the rate parameter of the gamma distribution on the mean thaw depth. Although the requirements of the model levels differed between Spasskaya Pad and Elgeeii, the proposed model successfully represented the spatial variability in thaw depth at both sites during different thaw seasons. [ABSTRACT FROM AUTHOR]

Arctic warming causes permafrost thaw and accelerates microbial decomposition of soil organic matter (SOM) to carbon dioxide (CO2) and methane (CH4). The determining factors for the ratio between CO2 and CH4 formation are still not well understood due to scarce in situ measurements, particularly in remote Arctic regions. We quantified the CO2:CH4 ratios of SOM decomposition in wet and dry tundra soils by using CO2 fluxes from clipped plots and in situ CH4 fluxes from vegetated plots. At the water‐saturated site, CO2:CH4 ratios decreased sharply from 95 at beginning of July to about 10 in August and September with a median of 12.2 (7.70–17.1; 25%–75% quartiles) over the whole vegetation period. When considering CH4 oxidation, estimated to reduce in situ CH4 fluxes by 10%–31%, even lower CO2:CH4 ratios were calculated (median 10.9–8.41). Active layer depth and soil temperature were the main factors controlling these ratios. Methane production was associated with subsoil (40 cm) temperature, while heterotrophic respiration was related to topsoil (5 cm) temperatures. As expected, CO2:CH4 ratios were substantially higher at the dry site (median 373, 292–500, 25%–75% quartiles). Both tundra types lost carbon preferentially in form of CO2, and CH4‐C represented only 0.27% of the dry tundra total carbon loss and 6.91% of the wet tundra total carbon loss. The current study demonstrates the dynamic of in situ CO2:CH4 ratios from SOM decomposition and will help improve simulations of future CO2 and CH4 fluxes from thawing tundra soils. Plain Language Summary: Global warming causes the thaw of the permanently frozen soil in Arctic regions, exposing soil organic matter (SOM) previously frozen to decomposition, increasing the emission of carbon dioxide (CO2) and methane (CH4), which are greenhouse gases. It is crucial to quantify the ratio of CO2 and CH4 produced because CH4 has a stronger global warming potential than CO2. We partitioned SOM decomposition into CO2 and CH4 formation (CO2:CH4 ratios) in wet and dry tundra soils on Samoylov Island, Northeastern Siberia, and we related these ratios to environmental variables. Deeper active layer, which is the topsoil layer that freezes and thaws annually, and higher subsoil (40 cm) temperature at the interface between the active layer and the permafrost, foster CH4 production and decrease CO2:CH4 ratios. Carbon was preferentially lost in form of CO2 by the soils, but CH4 had a larger contribution to the carbon loss in the wet tundra. Our study indicates that warming and deepening of the active layer can result in rising CH4 production. Further understanding of in situ CO2:CH4 ratios from SOM decomposition will help improve simulations on future CO2 and CH4 fluxes from thawing tundra soils. Key Points: Topsoil (5 cm) warming increases the CO2:CH4 production ratio, while warming of subsoil (40 cm) leads to lower CO2:CH4 production ratiosThe CO2:CH4 production ratio is associated with active‐layer depth (ALD) due to a direct effect of ALD on CH4 productionCarbon was preferentially lost in form of CO2 at wet and dry sites, but CH4 had a higher contribution at the wet tundra site [ABSTRACT FROM AUTHOR]

In regions characterized by continuous permafrost, hydrological modeling remains a complex activity, primarily due to constraints related to the prevailing climatic conditions and the specific behavior of the active layer. High-latitude regions receive less solar radiation; thus, most creeks are active only during summertime and stay frozen in the winter. To realistically simulate watersheds underlain by continuous permafrost, the heat transfer through the soil needs to be accounted for in the modeling process. In this study, a watershed located in a continuous permafrost zone in Russia is investigated. A model is proposed to integrate this heat transfer into an existing conceptual rain-flow transformation model, Hydrologiska Byråns Vattenbalansavdelning (HBV), to calculate the seasonal thaw depth and determine the components of water balance. The proposed integration is a novelty compared to the standard model, as it enables the physical and thermal properties of the soil to be taken into account. It was found that the proposed model, HBV-Heat, performs better than the stand-alone HBV model. Specifically, the average Nash–Sutcliffe efficiency (NSE) increases by 30% for the whole calibration period. In terms of the water balance components, the results are consistent with previous studies, showing that surface runoff represents 64% of the observed precipitation.

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.

The present paper proposes an iterative implicit numerical method for simulating the thaw depth of permafrost soil. For this purpose, the enthalpy-porosity model was used for the phase change process, and the finite difference scheme FTCS (Forward Time Centered Space) was used for discretization. An artificial mushy zone was maintained with the same thickness by keeping the regularization parameter proportional to the temperature gradient. In doing so, we made the scheme more stable and convergence occurred faster. The model accuracy was validated by comparing the numerical results with the analytical Stefan solution and with the results of a derived numerical model, based on an explicit scheme. The model performance was also tested against observation data collected on four different landscapes with different soil profiles and located on a basin underlain by continuous permafrost. It was found that the proposed model matched noticeably well the analytical solution for a volumetric liquid fraction (phi) equal to 0.5 regardless of the grid resolution. Furthermore, compared with the observation data, the model reproduced the annual maximum thaw depth with an absolute error lying between 0.7 and 7.7%. In addition, the designed algorithm allowed the model to converge after a maximum of eight iterations, reducing the computational time by around 75% compared to the explicit model. The results were so encouraging that the model can be included in a hydrological modeling of permafrost watersheds or cold regions in general. [ABSTRACT FROM AUTHOR]

The expected thaw depth of the foundation soil is one of the parameters influencing the selection of technical solutions of road design in the permafrost area. The purpose of this research is a quantitative assessment of the degree of influence of air temperature on thaw depth of the road foundation soil in the permafrost area. A standard formula to calculate thaw depth of melting bodies of flat symmetry obtained through a solution of the one phase Stefan problem at boundary conditions of the first kind was used for the analysis. An algorithm using an analytical formula to assess the influence of the main initial parameters and accuracy of their determination on the resulting value, the thaw depth of the soil, is proposed. The results of the calculations are presented in a graphical form displaying the influence of average air temperature and the accuracy of its setting on the thaw depth of the road foundation soil. It was determined that the degree of change in thaw depth is non-linear and depends on both the average air temperature and on the accuracy with which it is set. For every average air temperature value there is a specific measure of required accuracy for thermal calculations so that the error of thaw depth determination does not exceed the permitted error. A 3D chart showing the expected percentage error in thaw depth forecasting depending on the average air temperature and the accuracy of its setting for an array of initial values was created.

The present paper proposes an iterative implicit numerical method for simulating the thaw depth of permafrost soil. For this purpose, the enthalpy-porosity model was used for the phase change process, and the finite difference scheme FTCS (Forward Time Centered Space) was used for discretization. An artificial mushy zone was maintained with the same thickness by keeping the regularization parameter proportional to the temperature gradient. In doing so, we made the scheme more stable and convergence occurred faster. The model accuracy was validated by comparing the numerical results with the analytical Stefan solution and with the results of a derived numerical model, based on an explicit scheme. The model performance was also tested against observation data collected on four different landscapes with different soil profiles and located on a basin underlain by continuous permafrost. It was found that the proposed model matched noticeably well the analytical solution for a volumetric liquid fraction (phi) equal to 0.5 regardless of the grid resolution. Furthermore, compared with the observation data, the model reproduced the annual maximum thaw depth with an absolute error lying between 0.7 and 7.7%. In addition, the designed algorithm allowed the model to converge after a maximum of eight iterations, reducing the computational time by around 75% compared to the explicit model. The results were so encouraging that the model can be included in a hydrological modeling of permafrost watersheds or cold regions in general.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract 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 CO 2 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 CO 2 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 CO 2 sinks to sources in a feedback to future climate change. Highlights • We emphasize the role of the uppermost soil layer controlling CO 2 fluxes in the Arctic. • The drivers of NEE and ER change during the growing season (early, peak, late). • Thaw depth, GST, LAI and PAR in turn drive NEE; GST always drives ER. • At late season despite the maximum thawing the uppermost soil freezing controls ER. • The shift from wet to dry vegetation can switch ecosystems from CO 2 sinks to sources. [ABSTRACT FROM AUTHOR]

Active layer thickness (ALT) is a critical metric for monitoring permafrost. How soil moisture influences ALT depends on two competing hypotheses: (a) increased soil moisture increases the latent heat of fusion for thaw, resulting in shallower active layers, and (b) increased soil moisture increases soil thermal conductivity, resulting in deeper active layers. To investigate their relative influence on thaw depth, we analyzed the Field Measurements of Soil Moisture and Active Layer Thickness (SMALT) in Alaska and Canada dataset, consisting of thousands of measurements of thaw depth and soil moisture collected at dozens of sites across Alaska and Canada as part of NASA’s Arctic Boreal Vulnerability Experiment (ABoVE). As bulk volumetric water content (VWC) integrated over the entire active layer increases, ALT decreases, supporting the latent heat hypothesis. However, as VWC in the top 12 cm of soil increases, ALT increases, supporting the thermal conductivity hypothesis. Regional temperature variations determine the baseline thaw depth while precipitation may influence the sensitivity of ALT to changes in VWC. Soil latent heat dominates over thermal conductivity in determining ALT, and the effect of bulk VWC on ALT appears consistent across sites.

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 29 cm, decreasing at a ratio of 16 cm/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 = 0.05842 m 2 /°C·day; R 2 = 0.63) is in agreement with other permafrost environments, since frozen index (F > 0.67) and MAAT (<− 2 °C) denote a continuous permafrost existence in the area. All these characteristics provided the basis for further comparative analyses between others nearby CALM sites. [ABSTRACT FROM AUTHOR]

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 toward 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. [ABSTRACT FROM AUTHOR]

Permafrost landscape dynamics were investigated between 1998 and 2012 at Neleger, near Yakutsk, in central Yakutia, to determine the effects on permafrost of clear cutting of larch forest. Changes in ground temperature, soil moisture, seasonal thaw depth and surface subsidence at a control (forest) site and a site cleared of forest were associated with vegetation recovery and climate change. Before clear cutting (1998-2000), permafrost temperatures were similar to the 1998-2012 average. After cutting (2001-04), permafrost temperatures decreased in the undisturbed forest site, but increased in the cleared site. The thermal disturbance of clear cutting caused increases in thaw depth and led to 4.8 cm of ground surface subsidence. Significant warming of permafrost in 2005-08, coincident with maximum snow depth and precipitation, caused up to 14.6 cm of additional ground subsidence, which represented the maximum changes observed in the landscape. Between 2009 and 2012, permafrost began to stabilise and subsidence was restricted to 1.8 cm. The reduced thaw depth and the growth of young birch shoots during this period indicated stabilisation of permafrost conditions and the beginning of landscape restoration. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Soil is a significant source of CO 2 emission to the atmosphere, and this process is accelerating at high latitudes due to rapidly changing climates. To investigate the sensitivity of soil CO 2 emissions to high temporal frequency variations in climate, we performed continuous monitoring of soil CO 2 efflux using Forced Diffusion (FD) chambers at half-hour intervals, across three representative Alaskan soil cover types with underlying permafrost. These sites were established during the growing season of 2015, on the Seward Peninsula of western Alaska. Our chamber system is conceptually similar to a dynamic chamber, though FD is more durable and water-resistant and consumes less power, lending itself to remote deployments. We first conducted methodological tests, testing different frequencies of measurement, and did not observe a significant difference between collecting data at 30-min and 10-min measurement intervals (averaged half-hourly) ( p < 0.001). Temperature and thaw depth, meanwhile, are important parameters in influencing soil carbon emission. At the study sites, we observed cumulative soil CO 2 emissions of 62.0, 126.3, and 133.5 gC m − 2 for the growing period, in sphagnum, lichen, and tussock, respectively, corresponding to 83.8, 63.7, and 79.6% of annual carbon emissions. Growing season soil carbon emissions extrapolated over the region equated to 0.17 ± 0.06 MgC over the measurement period. This was 47% higher than previous estimates from coarse-resolution manual chamber sampling, presumably because it better captured high efflux events. This finding demonstrates how differences in measurement method and frequency can impact interpretations of seasonal and annual soil carbon budgets. We conclude that annual CO 2 efflux-measurements using FD chamber networks would be an effective means for quantifying growing and non-growing season soil carbon budgets, with optimal pairing with time-lapse imagery for tracking local and regional changes in environment and climate in a warming Arctic. [ABSTRACT FROM AUTHOR]

Tree-ring width and stable isotopic composition are widely used for the reconstruction of environmental conditions. Eco-physiological models simulating δ 13 C and δ 18 O provide tools to constrain the interpretation of measured tree-ring variations and their relationships to environmental variables. Here, we apply biochemical models of photosynthesis and a model of stomatal conductance to simulate the intra-annual dynamics of δ 13 C values in photo assimilates and tree-rings. We use these models to investigate the physiological responses of larch trees growing on permafrost to variability in precipitation and permafrost depth associated with regional temperature and precipitation changes. Tree-ring width, δ 13 C and δ 18 O in wood and cellulose were measured in larch ( Larix cajanderi Mayr.) samples from northeastern Yakutia (69°N, 148°E) for the period from 1945 to 2004 and used for comparisons with modeled δ 13 C and δ 18 O data. Mechanistic models that quantify physical and biochemical fractionation processes leading to oxygen isotope variation in organic matter are used to identify source water for trees growing on permafrost in Siberia. These models allowed us to investigate the influence of a variety of climatic factors on Siberian forest ecosystem water relations that impact isotope fractionation. Based on δ 13 C and δ 18 O in tree wood and cellulose measurements as well as outputs from different eco-physiological models, we assume that larch trees from northeastern Yakutia can have limited access to the additional thawed permafrost water during dry summer periods. [ABSTRACT FROM AUTHOR]

Road pavements in frost-susceptible regions are challenged by frost-thaw induced damages. Spring load restriction (SLR) is intended to reduce road distresses caused by heavily loaded truck traffic. Winter weight premiums (WWP) is applied during early freezing season by increasing the maximum allowable axle loads to reduce the economic difficulties that trucking industries undergo during thaw season. While there are various timelines for applying and removing SLR, this paper reviews three of the SLR prediction models along with a WWP computer simulation and verifies the calculations based on each method using two years of monitored field moisture and temperature data from the fully instrumented integrated road research facility (IRRF) test road in Edmonton, Alberta, Canada. The results revealed that two of the methods showed a significantly better performance in determining the start and end dates of SLR as opposed to the other method. Computer simulations obtained the pavement critical depth beyond which traffic loading did not affect the subgrade material in early freezing season, and collected data aided in estimating the start date of WWP application on the test road. The results were in good agreement with the recommendations suggested by authorities. [ABSTRACT FROM AUTHOR]

The China–Russia Crude Oil Pipeline (CRCOP) was built to transport Siberian crude oil across 1030 km of frozen ground. The Chinese portion of the CRCOP crosses 441 km of discontinuous permafrost zones along the eastern flanks of the Da Xing'anling (Hinggan) Mountains. Significant thaw settlement of some of the pipeline foundation soils has occurred since the pipeline began operating in January 2011. The differential thaw settlement around the pipeline at the transitions between the thaw-settling and thaw-stable zones may lead to displacement or even buckling of the pipeline. To evaluate the engineering safety and long-term stability of pipeline foundations, ground-penetrating radar (GPR) was used to detect the freeze–thaw states of pipeline foundation soils in the permafrost zones. From April 2012 to November 2013, a total of 2780 m of GPR profiles and 62 cross-sections (perpendicular to the CRCOP route) were obtained at eight GPR study sites on various terrains and vegetative coverage, with different thermal insulation configurations around the pipe, and with and without thermosyphons installed. The GPR profiles were interpreted and cross-checked with data from drilling, hand-dug pit or trench excavations, and ground temperature measurements. The results showed that the foundation soils around the pipeline were thawing, with maximum thaw depths under the pipeline of about 1.1 m to 4.5 m from the pipe bottom and increased maximum thaw depths of 0.5 m to 3.7 m during the period of this study. However, GPR profiles from the areas with dense vegetative coverage, and with pipe insulation of 80-mm-thick extruded polystyrene (XPS), and also with vertical thermosyphons installed, showed that permafrost foundation soils were thermally better protected, with only minor thaw settlement. The thermal states of pipeline foundation soils and the underlying permafrost varied markedly with different terrains. The drainage patterns and engineering activities, especially the heating from operating oil flows at an average annual oil temperature of 7.7 °C (with a range of 0.7 °C to 20.4 °C) along the pipeline route may have been responsible for the extensive and substantial thaw subsidence in the ice-rich permafrost zones. Additionally, there was positive feedback between the thaw subsidence of ground surface in the vicinity of the pipeline route and the thaw settlement of the pipeline foundation soils. The greater the earth surface subsidence, the more surface water ponding and soil disturbances, and even more progressive thawing. Therefore, some measures are recommended for stabilizing the pipeline foundation soils. The research results also indicate that the GPR method is effective, nondestructive, and convenient for evaluating the spatiotemporal extent and development processes of the freeze–thaw states of pipeline foundation soils and the underlying permafrost. [ABSTRACT FROM AUTHOR]

This study, conducted at the Emuer River in northern China during the growing season of 2014, investigated the concentrations and sources of dissolved CH 4 and CO 2 in wetland rivers in the permafrost region, as well as the total export of dissolved gaseous carbon (C) transported by streamflow. CH 4 and CO 2 concentrations in these rivers, ranging from 0.410–1.045 to 107.838–190.925 μmol L −1 , respectively, were among the highest levels of gaseous C concentrations reported from studies around the world. The concentrations of the C gases varied greatly with streamflow, but the influence of hydrological, as well as meteorological parameters, was not significant, except for the influence of the thaw depth of the soil active layer of adjacent wetlands on CH 4 concentrations. δ 18 O‰ values suggest the observed dissolved gases originated mainly from soil pore water in the active layers of the wetlands, as opposed to organic-rich sediments in river beds, which serves as a common source for riverine CH 4 and CO 2 according to many other studies. A total of 444.30 t C was exported by the 3rd order main Emuer river during the growing season, and an export coefficient of 4.65 mg C m −2 day −1 was calculated for the wetland ecosystem. The dataset in this study is significant with regard to the global carbon balance because it is representative of the extensive wetlands occurring throughout the Eurasian permafrost. [ABSTRACT FROM AUTHOR]

Ecosystem-scale methane (CH 4 ) exchange was observed in a poorly-drained black spruce forest over permafrost in interior Alaska during the snow-free seasons of 2011–2013, using the eddy covariance technique. The magnitude of average CH 4 exchange differed depending on wind direction, reflecting spatial variation in soil moisture condition around the observation tower, due to elevation change within the small catchment. In the drier upper position, the seasonal variation in CH 4 emission was explained by the variation in soil water content only. In the wetter bottom, however, in addition to soil temperature and soil water content, seasonal thaw depth of frozen soil was also an important variable explaining the seasonal variation in CH 4 exchange for this ecosystem. Total snow-free season (day of year 134–280) CH 4 exchanges were 12.0 ± 1.0, 19.6 ± 3.0, and 36.6 ± 4.4 mmol m −2 season −1 for the drier upper position, moderately wet area, and wetter bottom of the catchment, respectively. Observed total season CH 4 emission was nearly one order smaller than those reported in other northern wetlands, due probably to the relatively low ground water level and low soil temperature. The interannual variation of total snow-free season CH 4 emission in the wetter bottom of the catchment was influenced by the amount of rainfall and thaw depth. On the other hand, in the drier upper position the amount of rainfall did not strongly affect the total season CH 4 emission. Different responses of CH 4 exchange to environmental conditions, depending on the position of a small catchment, should be considered when estimating the spatial variation in CH 4 exchange accurately in ecosystems over permafrost. [ABSTRACT FROM AUTHOR]