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Sulfur, with its highly varying stable isotope ratio and involvement in numerous biogeochemical processes, is one of the most widely used elements as an isotopic paleoenvironmental proxy, yet the sulfur isotope ratios of ice‐wedges and their insoluble fraction remain unexplored. This study first presents the sulfur isotopic compositions of soluble sulfate, particulate organic matter (POM), and lithic particles recovered from East Siberian ice‐wedges. Soluble sulfate, primarily representing atmospheric sulfate deposition, shows comparable sulfur isotope ranges in Zyryanka and Batagay, while in Central Yakutia, ice‐wedge sulfate is more enriched in 34S, consistent with the orogenic and cratonic terranes in East Siberia. Given the wedge growth during the inland winter, it is likely that sulfate aerosols were derived mainly from erosion and weathering of regional basement rocks rather than from sea salt spray or biogenic emissions. Within individual ice‐wedges, however, the sulfur isotopic composition of soluble sulfate varies by as much as 7‰, possibly reflecting changes in the relative contributions of sulfur‐isotopically distinct source regions. Beyond the origin of sulfate, greater sulfur isotope fractionations between POM and sulfate during the last glaciation suggest that sulfate may have been anaerobically reduced to sulfide and vice versa in the adjacent root zone. [ABSTRACT FROM AUTHOR]

Permafrost thawing as a result of global warming is expected to foster the biological remineralization of intact organic carbon and nitrogen and release greenhouse gas (GHG) into the atmosphere, which will have positive feedback for future global warming. However, GHG budgets and their controls in permafrost ground ice are not yet fully understood. This study aims to better understand the control mechanisms of GHG in ground ice by using new gas and chemistry data. In this study, we present new data on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) mixing ratios in three different ice wedges, Churapcha, Syrdakh, and Cyuie, located in central Yakutia, Siberia. The GHG mixing ratios in the studied ice wedges range from 0.0% to 13.8% CO2, 1.3–91.2 ppm CH4, and 0% and 0–1414 N2O. In particular, all three ice wedges demonstrate that ice‐wedge samples enriched in CH4 were depleted in N2O mixing ratios and vice versa. N2–O2–Ar compositions indicate that the studied ice wedges were most likely formed by dry snow or hoarfrost, not by freezing of snow meltwater, and the O2‐consuming biological metabolism was active. Most of the observed GHG mixing ratios cannot be explained without microbial metabolism. The inhibitory impact of denitrification products of nitrate (including N2O) could be an important control of the ice‐wedge CH4 mixing ratio. [ABSTRACT FROM AUTHOR]

Forest fires significantly impact permafrost degradation in the subarctic regions. However, interannual and seasonal variations in surface deformation due to permafrost thawing in burned areas were poorly understood. Measuring the ground surface displacement in fire scars helps us understand the freeze‐thaw dynamics of near‐surface ground and predict the future state, particularly in ice‐rich permafrost regions. This study used the L‐ and C‐band interferometric synthetic aperture radar technique to reveal interannual subsidence and seasonal thaw settlement/frost heave in a fire scar near Mayya, Sakha Republic in Eastern Siberia burned in 2013. We found that the cumulative subsidence was up to 7 cm between 2014 and 2020, most of which had occurred by 2016. The magnitude of seasonal thaw settlement and frost heave varied each year from 2017 to 2020 after the fire, but the interannual change in frost heave corresponded to the temporal variation in precipitation during the thawing season from 2017 to 2020. This suggests that the precipitation amount during the thawing season is related to the magnitude of segregation‐ice formation in the sediments, which determines the frost heave amount. The observed seasonal displacements could not be quantitatively explained by models inferred from the Stefan's equation and volume changes associated with ice‐water phase change. This implies that other models associated with segregated ice (ice lens) formation/thaw are required to explain the observed seasonal displacement. Plain Language Summary: Forest fires in permafrost regions significantly affect regional landscape changes and ecosystems through permafrost degradation and subsequent ground deformation. However, the number of observations of post forest fire surface displacement is extremely limited. We calculated surface displacement in a fire scar in Eastern Siberia from spaceborne radar images captured using interferometric synthetic aperture radar. Our observed data will help us understand permafrost degradation processes in forest fire scars. Key Points: Ground subsidence was primarily associated with the severity of forest fires, and slope orientation was likely an additional factorSeasonal frost heave measured by interferometric synthetic aperture radar was correlated to precipitation amount in thawing seasonExisting phase change model could not explain observed seasonal displacement quantitatively [ABSTRACT FROM AUTHOR]

Arctic precipitation (PG) that occurs as rainfall (Prain) or snowfall (Psnow) depending on the prevailing climatic conditions results in seasonally specific hydrological events. Climate change can affect the PG‐ and permafrost‐originated water (Pice) regimes, resulting in change to ecohydrological processes. However, the relative influences of source waters (i.e., Prain, Psnow, and Pice) on terrestrial hydrological processes have not yet been fully established. Here, we report the development and implementation of a numerical water tracer model designed to quantify changes in the storages and fluxes of the source waters and the hydrogen and oxygen isotopic tracers associated with hydrometeorological events. The presented tracer model was used to illustrate the spatiotemporal variability of the tracers in the surface–subsurface system of a deciduous needleleaf boreal forest and to separate the contribution rates of the tracer waters to evapotranspiration (ET). Although Psnow accounted for 22%–57% of ET and the subcomponents, the contribution rates to soil evaporation and transpiration were significant only during spring. The major source water for soil moisture was Prain, which accounted for 69.2% of ET and showed an increasing trend during 1980–2016. Additionally, Prain also accounted for 77.2% of transpiration. Under the present conditions of warming permafrost, Pice demonstrated negligibly low impact on ET. The tracer model was shown capable of quantifying the contribution rates of tracer waters to ET, highlighting the advantages of the tracer model for a similar quantitative separation regarding future climate change. Plain Language Summary: Although snowfall and rainfall are seasonally different processes, their influence on hydrological processes (i.e., evapotranspiration and river discharge) occurs mainly during the growing season. Quantification of their contributions to hydrological processes is an ongoing scientific problem in the field of Arctic hydrology. Thus, we developed a tracer model, which includes isotopic processes, to separate the contributions of snowfall, rainfall, and permafrost‐originated water to evapotranspiration and applied it to a boreal forest. The model simulation suggested that summer rainfall has the greatest impact on evapotranspiration, while water from snowfall is strongly implicated in springtime evaporation. Permafrost‐originated water is not connected directly to evapotranspiration at the study site. However, future warming climate could potentially increase the role of permafrost‐related water in ecohydrological processes. Thus, the presented water tracer model could potentially provide a quantitative assessment of the changes in the physics of water dynamics caused by climate change. Key Points: Tracer model separates contributions of precipitation‐ and permafrost‐originated waters to evapotranspiration in deciduous boreal forestRainfall is the primary contributor to seasonal and interannual variability of evapotranspirationPermafrost‐originated water has negligibly low impact on evapotranspiration [ABSTRACT FROM AUTHOR]

Cryopeg is a layer within permafrost containing a significant amount of cryotic unfrozen water due to dissolved salts. To explore the origin and development of cryopeg and associated brines found near Utqiaġvik, we sampled extensively within the Barrow Permafrost Tunnel. We found two types of cryopeg brines based on their distinctive locations: (a) intra‐ice brine (IiB), entirely bounded by massive ground ice, and not previously observed in the Northern Hemisphere; and (b) intra‐sediment brine (IsB), found as expected in unfrozen sediments within permafrost. The encountered IiBs were situated in small ellipsoidal or more complex shaped pockets within the massive ice at roughly atmospheric pressure. Radiocarbon dating suggests that the IiB segregated from IsB‐bearing cryopeg beneath the massive ice at about 11 ka BP, at the earliest. From geochemical analyses, IsB lenses were interpreted as having developed through repeated evaporation and cryoconcentration of seawater in a lagoonal environment, then isolated when the surrounding sediment froze and became covered by an upper sediment unit around 40 ka BP or earlier. The discovery of IiB and development of origin scenarios for both brine types validate the importance of high‐resolution sampling as enabled by the unique facility of a permafrost tunnel. [ABSTRACT FROM AUTHOR]

Keywords: Arctic; cave; climate change; microhabitat; permafrost; thermokarst; wolverine EN Arctic cave climate change microhabitat permafrost thermokarst wolverine 1 4 4 05/05/21 20210501 NES 210501 The Arctic is changing rapidly, introducing new challenges and opportunities for animals. The first site (Cave A) was used once (April 5) by a single wolverine for 12 h, and the second site (Cave B, 37 km from Cave A) was used twice (April 15 and May 3) by the same wolverine for 1-3 h during each visit. Abundant wolverine scat was present in the vicinity of the cave entrance, including in the trench, suggesting that the wolverines used both the cave and the snowdrifts formed in the trench for their den. Arctic, cave, climate change, microhabitat, permafrost, thermokarst, wolverine. [Extracted from the article]

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]

The larch ( Larix spp.) forest in eastern Siberia is the world's largest coniferous forest. Its persistence is considered to depend on near-surface permafrost, and thus, forecast warming over the 21st century and consequent degradation of near-surface permafrost is expected to affect the larch forest in Siberia. However, predictions of these effects vary greatly, and many uncertainties remain about land - atmosphere interactions within the ecosystem. We developed an integrated land surface model to analyze how the Siberian larch forest will react to current warming trends. This model analyzed interactions between vegetation dynamics and thermo-hydrology, although it does not consider many processes those are considered to affect productivity response to a changing climate (e.g., nitrogen limitation, waterlogged soil, heat stress, and change in species composition). The model showed that, under climatic conditions predicted under gradual and rapid warming, the annual net primary production of larch increased about 2 and 3 times, respectively, by the end of the 21st century compared with that in the previous century. Soil water content during the larch-growing season showed no obvious trend, even when surface permafrost was allowed to decay and result in subsurface runoff. A sensitivity test showed that the forecast temperature and precipitation trends extended larch leafing days and reduced water shortages during the growing season, thereby increasing productivity. The integrated model also satisfactorily reconstructed latitudinal gradients in permafrost presence, soil moisture, tree leaf area index, and biomass over the entire larch-dominated area in eastern Siberia. Projected changes to ecosystem hydrology and larch productivity at this geographical scale were consistent with those from site-level simulation. This study reduces the uncertainty surrounding the impact of current climate trends on this globally important carbon reservoir, and it demonstrates the need to consider complex ecological processes to make accurate predictions. [ABSTRACT FROM AUTHOR]

ABSTRACT Perennial frost mounds are present near the edges of ponds located on the terrace between the mountain flank and a valley-bottom lake in the Akkol valley of the Russian Altai Mountains. These mounds are 10-50 m in diameter and 3-6 m in height. We describe one mound, identified as a lithalsa, which had been eroded so as to expose almost its entire vertical cross-section, revealing its internal structure. The frozen core consisted mainly of soil segments suspended in reticulate ice lenses with a mean thickness of 11-48 mm and a maximum thickness of about 160 mm. The shapes of the soil segments matched their neighbours. Other features included soil segments suspended in the ice veins shaped like 'En echelon gash veins', and the presence of a radial structure of ice-rich and sediment-rich frozen bands. These features all suggest the greater importance of a differential stress field during heaving of the mound and after ice segregation, compared to the thermal gradient and water supply. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]