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Recent studies have observed high methane concentrations in runoff water and the ambient air at various glacier sites, including the Greenland Ice Sheet, the glacier forefield in Svalbard, and the ice cap in Iceland. This study extends these findings to smaller mountain glaciers in Alaska. Methane and carbon dioxide concentrations in the ambient air near the meltwater outlet, fluxes of these gases at the surface of runoff water and riverbank sediments, and dissolved methane content in the runoff water were measured at four glaciers. Three of the four glaciers showed conspicuous signals of methane emissions from runoff water, with the Castner Glacier terminus exhibiting a methane concentration three times higher than background levels, along with elevated dissolved methane levels in the runoff water. This study marks the detection of significant methane emissions from small mountain glacier runoff, contributing to the understanding that mountain glaciers also release methane into the atmosphere.

Vegetation composition shifts, and in particular, shrub expansion across the Arctic tundra are some of the most important and widely observed responses of high-latitude ecosystems to rapid climate warming. These changes in vegetation potentially alter ecosystem carbon balances by affecting a complex set of soil–plant–atmosphere interactions. In this review, we synthesize the literature on (a) observed shrub expansion, (b) key climatic and environmental controls and mechanisms that affect shrub expansion, (c) impacts of shrub expansion on ecosystem carbon balance, and (d) research gaps and future directions to improve process representations in land models. A broad range of evidence, including in-situ observations, warming experiments, and remotely sensed vegetation indices have shown increases in growth and abundance of woody plants, particularly tall deciduous shrubs, and advancing shrublines across the circumpolar Arctic. This recent shrub expansion is affected by several interacting factors including climate warming, accelerated nutrient cycling, changing disturbance regimes, and local variation in topography and hydrology. Under warmer conditions, tall deciduous shrubs can be more competitive than other plant functional types in tundra ecosystems because of their taller maximum canopy heights and often dense canopy structure. Competitive abilities of tall deciduous shrubs vs herbaceous plants are also controlled by variation in traits that affect carbon and nutrient investments and retention strategies in leaves, stems, and roots. Overall, shrub expansion may affect tundra carbon balances by enhancing ecosystem carbon uptake and altering ecosystem respiration, and through complex feedback mechanisms that affect snowpack dynamics, permafrost degradation, surface energy balance, and litter inputs. Observed and projected tall deciduous shrub expansion and the subsequent effects on surface energy and carbon balances may alter feedbacks to the climate system. Land models, including those integrated in Earth System Models, need to account for differences in plant traits that control competitive interactions to accurately predict decadal- to centennial-scale tundra vegetation and carbon dynamics.

Massive ground ice found in the Barrow Permafrost Tunnel at 3–7 m depths from the surface has been interpreted as an ice wedge and used to reconstruct early Holocene environmental changes. To better understand the development of this ground ice, we conducted radiocarbon dating for 34 samples of plant remains from the massive ground ice and underlying sediment layer. A significantly large gap in the measured radiocarbon ages (more than 24 ka) between massive ice and the underlying sediment layer throughout the tunnel profile suggested at least two possibilities. One is that the lower and older sediment layer had thrust upwards at the boundary between intruding ice wedge and adjacent sediment, and the growing ice had pushed the sediment sideways. Another is that erosional events had removed surface materials at about 12–36 ka BP (14–41 cal ka BP) before the overlaying sediment layer with massive ground ice developed. The overall distribution of radiocarbon ages from the massive ice supported the ice-wedge hypothesis as a formation mechanism, although our results showed several age inversions and large fluctuations. Dating of densely spaced samples revealed two ground-ice regions with similar ages around 11–11.5 and 10–10.5 ka BP divided by a relatively narrow region of transitional ages along the tunnel long-axis. This distribution may be explained by a possible misalignment between the sampling direction and the ice-wedge growth line or by intermittent ice growth with repeated cracking at more random locations than the classic ice-wedge growth model suggested.

Tundra fires are increasing in their frequencies and intensities due to global warming, which alter revegetation patterns through various pathways. To understand the effects of tundra fire and the resultant thermokarst on revegetation, vegetation and related environmental factors were compared between burned and unburned areas of Seward Peninsula, Alaska, using a total of 140 plots, 50 cm × 50 cm each. The area was burned in 2002 and surveyed in 2013. Seven vegetation types were classified by a cluster analysis and were categorized along a fire-severity gradient from none to severe fire intensity. The species richness and diversity were higher in intermediately disturbed plots. Severe fire allowed the immigration of fire-favored species (e.g., Epilobium angustifolium, Ceratodon purpureus) and decreased or did not change the species diversity, indicating that species replacement occurred within the severely burned site. Although thermokarsts (ground subsidence) broadly occurred on burned sites, due to thawing, the subsidence weakly influenced vegetation patterns. These results suggest that the fire directly altered the species composition at a landscape scale between the burned and unburned sites and it indirectly altered the plant cover and diversity through the differential modification, such as thermokarst, at a small scale within the burned site.

Permafrost is known to occur in high mountainous areas such as the Daisetsu Mountains in Japan, which are located at the southernmost limit of the permafrost distribution in the world. In this study, areas with climatic conditions suitable for sustaining permafrost in the Daisetsu Mountains are projected using bias-corrected and downscaled climate model outputs and statistical relationships between surface air temperatures and permafrost areas. Using freezing and thawing indices, the size of the area in the Daisetsu Mountains where climatic conditions were suitable for permafrost were estimated to be approximately 150 km 2 in 2010. Under the RCP8.5 scenario, this area is projected to decrease to about 30 km 2 by 2050 and it is projected to disappear by around 2070. Under the RCP2.6 scenario, the area is projected to decrease to approximately 20 km 2 by 2100. The degradation of mountain permafrost could potentially affect the stability of trekking trails due to slope displacement, and it may also have deleterious effects on current alpine ecosystems. It is therefore important to accurately monitor changes in the mountain ecosystem environment and to implement measures to adapt to an environment that is projected to change significantly in the future.

High-latitude and altitude cold regions are affected by climate warming and permafrost degradation. One of the major concerns associated with degrading permafrost is thaw subsidence (TS) due to melting of excess ground ice and associated thaw consolidation. Field observations, remote sensing, and numerical modeling are used to measure and estimate the extent and rates of TS across broad spatial and temporal scales. Our new data synthesis effort from diverse permafrost regions of North America and Eurasia, confirms widespread TS across the panarctic permafrost domain with rates of up to 2 cm yr−1 in the areas with low ice content and more than 3 cm yr−1 in regions with ice-rich permafrost. Areas with human activities or areas affected by wildfires exhibited higher subsidence rates. Our findings suggest that permafrost landscapes are undergoing geomorphic change that is impacting hydrology, ecosystems, and human infrastructure. The development of a systematic TS monitoring is urgently needed to deliver consistent and continuous exchange of data across different permafrost regions. Integration of coordinated field observations, remote sensing, and modeling of TS across a range of scales would contribute to better understanding of rapidly changing permafrost environments and resulting climate feedbacks.

During the Late Pleistocene, a severely cold and dry climate strengthened dust production across the Northern Hemisphere. Despite many studies examining aridification and dust production, there is a lack of understanding about dust transportation during global climate variability. Long-range transported (LRT) dust can be traced by comparing global geochemical signatures and constraining provenance relationships. Here we report rare earth element abundances and strontium, neodymium, and oxygen isotope compositions of inorganic substances in ice wedges from Batagay and Central Yakutia (Cyuie and Churapcha), which comprise Yedoma deposits that formed in unglaciated Beringia. Distinct geochemical properties reflect differences between local and LRT dust contributions. Particles in the Batagay ice wedges show higher similarities to Chinese aeolian deposits, while those in Central Yakutia indicate stronger local input. These provenance constraints highlight variability in atmospheric circulation transporting dust to the Arctic during the Late Pleistocene, linking climate changes to aerosol distribution. Dust preserved in Siberian ice wedges reveals shifts in wind patterns during the last glacial stage. Long-range dust transport from China to the Arctic operated under similar mechanisms as today but was blocked during the Last Glacial Maximum.

Global warming is progressing more rapidly in the Arctic compared with other regions of the world, and the increasing temperature has caused gradual permafrost thaw, resulting in significant changes in hydrological processes. However, the quantitative contributions of different water sources to Arctic watersheds under ongoing climate change remain poorly understood. Therefore, this study aims to address this gap by applying a water isotope-based mixing model to better quantify the sources and pathways of water flow in permafrost-affected catchments. In this study, isotopic and chemical data were used to determine the water sources and flowpaths of the Sagavanirktok (Sag) River on the North Slope in Alaska (USA) in the summer of 2022. Results obtained using a Bayesian mixing model indicate that meltwater from permafrost ice wedges contributes 17.7% upstream and 22.2% downstream to the Sag River. At the upstream with a frozen active layer or transient layer (including seasonal intrasediment ice), lower active layer water (mineral-rich) and upper active layer water (organic-rich) accounted for 31.5% and 18.1%, respectively. By contrast, at the downstream, the contribution of active layer water was 26.9%, which was similar to that of the other sources. The sources and flowpaths of Arctic freshwater affect changes in the geochemical characteristics of the freshwater, which is channeled to the Arctic Ocean through major Arctic rivers. This study quantitatively assesses permafrost ice wedge melt in an Arctic basin and provides insights to facilitate investigations of hydrological processes and geochemical changes associated with climate change in Arctic water systems.

Eroding permafrost coasts are likely indicators and integrators of changes in the Arctic System as they are susceptible to the combined effects of declining sea ice extent, increases in open water duration, more frequent and impactful storms, sea-level rise, and warming permafrost. However, few observation sites in the Arctic have yet to link decadal-scale erosion rates with changing environmental conditions due to temporal data gaps. This study increases the temporal fidelity of coastal permafrost bluff observations using near-annual high spatial resolution (<1 m) satellite imagery acquired between 2008-2017 for a 9 km segment of coastline at Drew Point, Beaufort Sea coast, Alaska. Our results show that mean annual erosion for the 2007-2016 decade was 17.2 m yr−1, which is 2.5 times faster than historic rates, indicating that bluff erosion at this site is likely responding to changes in the Arctic System. In spite of a sustained increase in decadal-scale mean annual erosion rates, mean open water season erosion varied from 6.7 m yr−1 in 2010 to more than 22.0 m yr−1 in 2007, 2012, and 2016. This variability provided a range of coastal responses through which we explored the different roles of potential environmental drivers. The lack of significant correlations between mean open water season erosion and the environmental variables compiled in this study indicates that we may not be adequately capturing the environmental forcing factors, that the system is conditioned by long-term transient effects or extreme weather events rather than annual variability, or that other not yet considered factors may be responsible for the increased erosion occurring at Drew Point. Our results highlight an increase in erosion at Drew Point in the 21st century as well as the complexities associated with unraveling the factors responsible for changing coastal permafrost bluffs in the Arctic.

Permafrost is a large reservoir of soil organic carbon, accounting for about half of all the terrestrial storage, almost equivalent to twice the atmospheric carbon storage. Hence, permafrost degradation under global warming may induce a release of a substantial amount of additional greenhouse gases, leading to further warming. In addition to gradual degradation through heat conduction, the importance of abrupt thawing or erosion of ice-rich permafrost has recently been recognized. Such ice-rich permafrost has evolved over a long timescale (i.e., tens to hundreds of thousands of years). Although important, knowledge on the distribution of vulnerability to degradation, i.e., location and stored amount of ground ice and soil carbon in ice-rich permafrost, is still limited largely due to the scarcity of accessible in situ data. Improving the future projections for the Arctic using the Earth System Models will lead to a better understanding of the current vulnerability distribution, which is a prerequisite for conducting climatic and biogeochemical assessment that currently constitutes a large source of uncertainty. In this study, present-day circum-Arctic distributions (north of 50° N) in ground ice and organic soil carbon content are produced by a new approach to combine a newly developed conceptual carbon-ice balance model, and a downscaling technique with the topographical and hydrological information derived from a high-resolution digital elevation model (ETOPO1). The model simulated the evolution of ground ice and carbon for the recent 125 thousand years (from the Last Interglacial to the present) at 1° resolution. The 0.2° high-resolution circum-Arctic maps of the present-day ground ice and soil organic carbon, downscaled from the 1° simulations, were reasonable compared to the observation-based previous maps. These data, together with a map of vulnerability of ice-rich permafrost to degradation served as initial and boundary condition data for model improvement and the future projection of additional greenhouse gas release potentially caused by permafrost degradation.