Permafrost thaw is transforming boreal forests into mosaics of wetlands and drier uplands. Topographic controls on hydrological and ecological conditions impact methane (CH4) fluxes, contributing to uncertainty in local and regional CH4 budgets and underlying drivers. The objective of this study was to explore CH4 fluxes and their drivers in a transitioning boreal forest-fen ecosystem (Goldstream Valley, Alaska, USA). This landscape is characterized by thawing discontinuous permafrost and heterogeneous mosaics of fens, collapse-scar channels, and small mounds of permafrost soils. From a survey in July 2021, observed chamber CH4 fluxes included fen areas with intermediate to very high emissions (29.8-635.3 mg CH4 m(-2) d(-1)), clustered locations with CH4 uptake (-2.11 to -0.7 mg CH4 m(-2) d(-1)), and three anomalous emission hotspots (342.4-772.4 mg CH4 m(-2) d(-1)) that were located near samples with lower emissions. Some surface and near-surface variables partially explained the spatial variation in CH4 flux. Log-transformed CH4 flux had a positive linear relationship with soil moisture at 20 cm depth (R-2 = 0.31, p-value < 1e-5) and negative linear relationships with microtopography (R-2 = 0.13, p-value < 0.006) and slope (R-2 = 0.28, p-value < 2e-5). Methane emissions generally occurred in flat, wet, graminoid-dominated fens, whereas CH4 uptake occurred on permafrost mounds dominated by feather mosses and woody vegetation. However, the CH4 hotspots occurred on drier, slightly sloped locations with low or undetectable near-surface methanogen abundance, suggesting that CH4 was produced in deeper soils. When the hotspot samples were omitted, log-transformed CH4 flux had a positive linear relationship with near-surface methanogen abundance (R-2 = 0.29, p-value = 0.0023), and stronger linear relationships with soil moisture, slope, and soil macronutrient concentrations. Our findings suggest that some CH4 emission hotspots could arise from CH4 in deep taliks. The inference that methanogenesis occurs in deep taliks was strengthened by the identification of intrapermafrost taliks across the study area using low-frequency geophysical induction. This study assesses surface spatial heterogeneity in the context of subsurface permafrost conditions and highlights the complexity of CH4 flux patterns in transitioning forest-wetland ecosystems. To better inform regional CH4 budgets, further research is needed to understand the spatial distribution of terrestrial CH4 hotspots and to resolve their surface, near-surface, and subsurface drivers.

Permafrost thaw and thermokarst development pose urgent challenges to Arctic communities, threatening infrastructure and essential services. This study examines the reciprocal impacts of permafrost degradation and infrastructure in Point Lay (Kali), Alaska, drawing on field data from similar to 60 boreholes, measured and modeled ground temperature records, remote sensing analysis, and community interviews. Field campaigns from 2022-2024 reveal widespread thermokarst development and ground subsidence driven by the thaw of ice-rich permafrost. Borehole analysis confirms excess-ice contents averaging similar to 40%, with syngenetic ice wedges extending over 12 m deep. Measured and modeled ground temperature data indicate a warming trend, with increasing mean annual ground temperatures and active layer thickness (ALT). Since 1949, modeled ALTs have generally deepened, with a marked shift toward consistently thicker ALTs in the 21st century. Remote sensing shows ice wedge thermokarst expanded from 60% in developed areas by 2019, with thaw rates increasing tenfold between 1974 and 2019. In contrast, adjacent, undisturbed tundra exhibited more consistent thermokarst expansion (similar to 0.2% yr(-1)), underscoring the amplifying role of infrastructure, surface disturbance, and climate change. Community interviews reveal the lived consequences of permafrost degradation, including structural damage to homes, failing utilities, and growing dependence on alternative water and wastewater strategies. Engineering recommendations include deeper pile foundations, targeted ice wedge stabilization, aboveground utilities, enhanced snow management strategies, and improved drainage to mitigate ongoing infrastructure issues. As climate change accelerates permafrost thaw across the Arctic, this study highlights the need for integrated, community-driven adaptation strategies that blend geocryological research, engineering solutions, and local and Indigenous knowledge.

As a result of the research performed, the emission of CO2 from soils in the southern tundra ecosystems of the northeastern Russian Plain has been estimated using the example of the environs of Vorkuta. The soil cover of the studied area is presented by Histic Turbic Cryosol, Histic Reductaquic Glacic Cryosol, Reductaquic Glacic Cryosol, and Reductaquic Glacic Cryosol. Atypically high values of CO2 emission from soils [2.13 +/- 0.13 g C/(m2 day)] were largely due to the weather of the 2022 growing season: high air temperatures and low precipitation. About 60% of the variability in the emission value was due to the content of microbial biomass carbon and extractable soil carbon, temperature, and soil moisture. High spatial variation in the content of extractable carbon and microbial biomass carbon and parameters of hydrothermal regime of soils was found. The soils were characterized by low values of extractable organic carbon and soil microbial biomass carbon (224 +/- 18 and 873 +/- 73 mg C/kg of soil, respectively). The thickness of organic horizon of soil determines 72% of variability in the content of microbial biomass carbon and 79% of variability in the content of extractable carbon. Regular measurements of CO2 emissions from soils of tundra ecosystems in the northeast of the Russian Plain should obtain special attention, as this will improve the accuracy of assessing the global greenhouse gas flows.

Permafrost peatlands store substantial amounts of carbon, though persistence of this soil carbon is unknown in a rapidly warming Arctic. To investigate potential carbon production from soils at different stages of permafrost degradation, we incubated soils from a palsa mire in northern Fennoscandia. Three soil horizons from four thaw stages were included within the transect, beginning with intact permafrost and ending in an established post-thaw wetland. Samples were incubated anaerobically for a year at different temperatures (4 degrees C, 20 degrees C) with the aim of investigating drivers of carbon degradation rates. Additional subsamples from the intact palsa were incubated under aerobic conditions, or inoculated with thermokarst pond water to further explore thaw processes on soil. Total CO2 and CH4 produced ranged from 9,910 +/- 626 (from the surface peat of the established post-thaw wetland, at 20 degrees C) to 1,921 +/- 126 mu g C g-1 DW (from the intermediate thaw stage of the palsa permafrost, incubated at 20 degrees C). The CH4 temperature sensitivity was markedly higher in permafrost soils, with Q 10 s more than four times larger than that of the active layer (active layer average: 1.7 +/- 1.6, permafrost average: 8.4 +/- 5). Methanogenesis generally increased with thaw, but the largest increase of cumulative methane production was between the wetland thaw stages (from 633 to 2,880 mu g CH4-C g-1 DW), where graminoids colonized the post-thaw environment. This uptick in CH4 production 30+ years after post-thaw wetland establishment implies that increases in CH4 production are largely due to vegetation inputs rather than thawed permafrost carbon contributions.

Permafrost is both a product of climate change and an indicator of its progression. Rising air temperature has led to permafrost degradation, resulting in the melting of ground ice and the release of carbon to the atmosphere, creating a positive feedback loop. Extreme weather events, particularly extreme rainfall, have been increasing, yet the effects of extreme rainfall on permafrost remain unclear. Here, we use long-term observational data to investigate the effects of extreme rainfall on the hydrothermal properties of the active layer at two sites in China's upper Heihe River Basin, EBoA and PT5. Two methods are applied: hierarchical linear regression and a relative variation ratio. The results for both sites indicate that when rainfall exceeds 10 mm, soil temperatures increase. This suggests warming effects of extreme rainfall on the active layer that maybe attributable to reduced heat loss from decreased actual evapotranspiration, as well as increased thermal conductivity and heat transfer due to elevated soil moisture during extreme rainfall events. Future studies investigating the effects of extreme rainfall via irrigation experiments and physical modeling could benefit our results as a reference for the design of controlled experiments.

The distribution and variation of active layer thickness (ALT) are crucial indicators for assessing the stability and environmental conditions of permafrost regions, which significantly impact regional hydrology, ecology, climate change, engineering construction, and disaster risk assessment. Based on the measured ALT data and Stefan equation, this study investigated the spatial distribution characteristics of ALT in the Tuotuo River region and explored the factors influencing its variability. The results showed that the ALT in the Tuotuo River area ranged from 0.15 to 5.18 m, with an average value of 2.65 m. The spatial distribution showed that the ALT was thinner in the southern region, which exhibited strong spatial heterogeneity, while the northeastern region generally had thicker ALT. Additionally, mountain areas tended to have thinner ALT, whereas plains showed thicker ALT. There was a good linear correlation between the simulated and measured ALT values, and the R 2 was up to 80%. The ALT in the Tuotuo River area was mainly controlled by air temperature and surface water thermal conditions. Among all factors, soil water content was identified as the key determinant. Topographic factors influenced ALT distribution and variation mainly through their impact on soil water content.

Permafrost, a critical global cryospheric component, supports subarctic boreal forests but is frequently disturbed by wildfires, an important driver of permafrost degradation. Wildfires reduce vegetation, organic layers, and surface albedo, leading to active layer thickening and ground subsidence. Recent studies using interferometric synthetic aperture radar (InSAR) have confirmed the rapid and extensive post-fire permafrost degradation, and have largely focused on short-term impacts. However, the longer-term post-fire permafrost deformation, potentially persisting for decades, remains poorly understood due to limited data. Here, we applied InSAR in North Yukon to detect deformation signals across multiple fire scars in the past five decades. Using a chronosequence (space-for-time substitution) approach, we summarize a continuous trajectory of post-fire permafrost evolution: (a) an initial degradation stage, characterized by abrupt subsidence up to 50 mm/year and gradually slowing over the first decade, with cumulative subsidence exceeding 100 mm locally; (b) an aggradation stage from approximately 15 to 30 years after fire, marked by ground uplift reaching 25 mm/year before gradually declining, compensating for the earlier subsidence; and (c) a stabilization stage beyond three to four decades, where permafrost nearly recovers to pre-fire conditions with indistinguishable deformation between burned and unburned areas. Notably, the rarely-reported uplift phase appears closely related to vegetation regeneration and fire-greening feedback that provide thermal protection, suggesting a critical mechanism of permafrost recovery. These findings provide new insights into the resilience of boreal-permafrost systems to wildfires and also underscore the importance of long-term InSAR monitoring in understanding permafrost responses to wildfires under climate change.

Increasing Arctic warming rates drive significant environmental change, including permafrost thaw and new groundwater pathway development, thereby increasing groundwater vulnerability to contaminant transport at the thousands of unremediated sites in the circumpolar north. As a first step in assessing hydrogeological controls of Arctic contaminant transport, this study uses numerical modelling to disentangle the impacts of increasing precipitation and air temperature on groundwater flow within the active layer at a high arctic site (63 degrees 30 ' N). The study uses the numerical model SUTRA 4.0 to simulate groundwater flow and energy transport, including dynamic freeze-thaw processes, across an Arctic hillslope under current and future air temperatures due to climate warming. The model domain represents a two-dimensional hillslope terminating in a lake. Two layers implemented in the model represent unconsolidated glacial till and underlying crystalline bedrock. Four simulation cases are examined based on downscaled CMIP5 projections under the high-emissions business as usual scenario: Baseline Conditions (1981-2010), Near-Projections (2011-2040), Mid-Projections (2041-2070), and Far Projections (2071-2100). Climate projections indicate increasing mean annual air temperatures, reducing annual air temperature amplitude, and increasing precipitation. Further, model results show that groundwater flow dynamics are primarily influenced by the coupling of both increased mean annual temperatures and precipitation, with the consequent deepening and prolonged thawing of the active layer allowing for increased groundwater exfiltration to the lake. Sensitivity analysis identifies overburden permeability, overburden residual liquid freezing temperature, and model base temperature as significant parameters that affect model outcomes. Finally, a variable transmissivity assessment provides new insight into active layer groundwater flows.

Understanding the evolution of permafrost extent and active layer thickness (ALT) surrounding Antarctica is critical to global climate change and ecosystem transformations in the polar regions. However, due to the remoteness and harsh environment of Antarctica, most studies lack long-term and a regional perspective on the variations of ALT in Antarctica, resulting in hindering accurate assessment of ALT dynamics. In this study, based on MODIS land surface temperature (LST) and soil climate station data, we used the Stefan model to reconstruct ALT in the ice-free area of the McMurdo Dry Valleys (MDV) in East Antarctica from 2003 to 2022. The modeled ALT was verified against ground observations showing a good correlation (R) of 0.72 (p < 0.001), with an RMSE of 12.66 cm. The results indicate that the ALT exhibits a decreasing trend from coastal to inland, ranging from a maximum of 60 cm near the coastal area to zero in the polar plateau. Furthermore, within the inland valleys, deeper ALT values are mainly distributed in the lower elevation areas, reaching up to 60 cm at the lowest altitudes. During the period from 2003 to 2022, the interannual variability in ALT was notable, especially in coastal areas, with a maximum amplitude close to 30 cm in the years 2012 and 2016. Our study proved that the Stefan model with parameters estimated by MODIS LST and soil climate station data has good potential to reconstruct large-scale ALT in the ice-free area of Antarctica.

Climate change impacts have destabilized the permafrost in the SRYY. This study developed a MODIS land surface temperature correction equation for the SRYY, analyzed permafrost variations over 2001-2020 using the Stefan equation, the Temperature at the Top of Permafrost model (TTOP) model, and the soil thermal conductivity parameterization scheme, and applied a structural equation model to identify permafrost change drivers. Leveraging the CMIP6 data, future active layer thickness (ALT) and permafrost distribution were projected under diverse scenarios. The main conclusions are as follows: The ALT in the SRYY thickened at a rate of 1.06 cm/year, with significant changes concentrated in the Tuotuo and Damqu River basins. In the future about 2100, under SSP245, the ALT in the SRYY will increase by about 30 cm compared with the historical period, and the permafrost area will reduce by a minimum of 2 x 104 km2 and a maximum of 12.3 x 104 km2. And under the SSP585, the ALT will thicken by about 60 cm, with an average decrease in permafrost area of 16.3 x 104 km2. High-altitude permafrost exhibited stronger responses to climate change, faster warming rates mainly led to this result. Variations in moisture conditions were another important cause, in which soil water content was a key factor, and the role of precipitation deserved more consideration.