Understanding long-term interactions between climate, permafrost, and vegetation provides an essential context for interpreting current Arctic greening. Using 65 fossil pollen records from northern Siberia and a Random Forest model trained on a dataset of 835 modern pollen-climate assemblages, we quantitatively reconstructed mean temperature of the warmest month (Mtwa: mean July temperature) anomalies over the past 40 thousand years (ka) and assessed associated vegetation changes. During the Last Glacial Period, herbaceous taxa overwhelmingly dominated, and warming of similar to 1 degrees C during similar to 40-35 cal ka BP was insufficient to deepen the active layer beyond the threshold required for tree establishment, leaving woody cover minimal. In the early Holocene, sustained warming of nearly 2 degrees C triggered permafrost degradation and active-layer thickening, enabling forest expansion, although tree taxa lagged shrubs by several millennia. These results reveal a clear threshold effect in vegetation-permafrost interactions and show that only sustained warming can overcome permafrost constraints. By providing quantitative temperature estimates, our reconstruction offers critical benchmarks for predicting how ongoing Arctic warming may transform vegetation patterns and permafrost stability.

Accurate soil thermal conductivity (STC) data and their spatiotemporal variability are critical for the accurate simulation of future changes in Arctic permafrost. However, in-situ measured STC data remain scarce in the Arctic permafrost region, and the STC parameterization schemes commonly used in current land surface process models (LSMs) fail to meet the actual needs of accurate simulation of hydrothermal processes in permafrost, leading to considerable errors in the simulation results of Arctic permafrost. This study used the XGBoost method to simulate the spatial-temporal variability of the STC in the upper 5 cm active layer of Arctic permafrost during thawing and freezing periods from 1980 to 2020. The findings indicated STC variations between the thawing and freezing periods across different years, with values ranging from-0.4 to 0.28 W & sdot;m-1 & sdot;K-1. The mean STC during the freezing period was higher than that during the thawing period. Tundra, forest, and barren land exhibited the greatest sensitivity of STC to freeze-thaw transitions. This is the first study to explore the long-term spatiotemporal variations of STC in Arctic permafrost, and these findings and datasets can provide useful support for future research on Arctic permafrost evolution simulations.

Permafrost thawing is mobilizing dissolved organic carbon (DOC) stored in Arctic frozen soils into rivers, but vertical transport mechanisms within soil columns remain unclear, hindering accurate estimation of soil-derived DOC export. Through leaching experiments on active-layer organic soils and underlying mineral permafrost, this study reveals that mineral permafrost exhibits high soil carbon loss as DOC (3.27%-11.42%). However, 11.17%-46.42% of active-layer DOC is retained by mineral permafrost during vertical transport, forming an internal soil carbon sink. The sink selectively retains aromatic compounds, acting as a molecular filter that alters DOC composition and bioavailability. This internal retention complicates interpretations of active-layer DOC transport dynamics and alters the chemistry of both thawed permafrost and exported DOC. The findings emphasize the critical role of intra-soil DOC transformations in Arctic carbon cycling.

Brown carbon (BrC) aerosols play a significant role in atmospheric radiative forcing, particularly in the Arctic where they could potentially contribute to surface warming. However, their regional variability and sources in the open ocean remain poorly understood. To address this, we conducted ship-based aerosol measurements aboard the R/V Mirai during the MR18-05C research cruise (October-December 2018), spanning the western North Pacific, Bering Sea, and Arctic Ocean. We examined BrC optical properties alongside PM2.5 chemical composition, trace gases, and meteorological conditions to assess its variability and sources. Our results reveal a drastic northward decline in BrC levels, with light absorption capability in the Bering Sea and the Arctic approximately 50% lower than those in the western North Pacific. The strongest BrC absorption was observed in regions influenced by crop residue burning in Northeast China. In the Arctic, BrC remained low as the main footprint is within the Arctic alongside limited BrC sources, although occasionally affected by long-range transport. Chemical composition analysis highlights biomass burning and fossil fuel emissions as dominant BrC sources in the western North Pacific. Solubility analysis indicated that BrC in the Arctic was predominantly water soluble, increasing its susceptibility to wet scavenging. A strong high-pressure system (1027 +/- 6.2 hPa) over the Arctic (November 9-17) led to aerosol accumulation, although BrC remained low. This study underscores the complex interplay between regional emissions, long-range transport, and atmospheric processing in regulating BrC distributions across latitudinal gradients. Our findings highlight the importance of source-region emissions and transport pathways in determining BrC fate in the Arctic, with implications for understanding its role in climate forcing.

Massive stores of ancient soil organic carbon (SOC) in permafrost can decompose with Arctic warming and accelerate global climate change. Declining SOC stocks are central to the permafrost carbon feedback, but direct measures of SOC loss are extremely rare due to methodological challenges related to subsidence in the Arctic. To fully capture changing SOC dynamics during thaw, we directly measured SOC stock and bulk soil radiocarbon (C-14) changes, while accounting for subsidence, during 13 years of permafrost thaw in a warming experiment in Interior Alaska. We found significant declines in SOC stocks: 14% (+/- 6%) in ambient plots that experienced regional warming and 23% (+/- 5%) in snow fence warmed plots, entirely in deep, mineral soil layers. Losses were largely driven by winter soil warming but were mediated by changing soil moisture and vegetation conditions. Plots with low shrub biomass had greater SOC losses, suggesting that vegetation community composition may play an important role in SOC storage. Surface soil C-14 measurements suggest that carbon inputs were three times greater in warming plots compared to ambient plots, but that decomposition increased proportionally leading to no detectable change in surface organic layers. We observed significant SOC losses of 5.2-8.1 kg C m(-2) from deeper soil layers where carbon was sequestered similar to 2400 to similar to 4500 years ago. Our findings indicate that warmer soils in the winter will accelerate SOC losses, but that increasing density of shrub species through shrub expansion could help to mitigate SOC losses in deep soils. The significant loss of SOC from deep, mineral soils observed over just 13 years of ambient and experimental permafrost thaw highlights the vulnerability of this old C pool as it enters the active global carbon cycle.

Arctic ecosystems are highly vulnerable to ongoing and projected climate change. Rapid warming and growing anthropogenic pressure are driving a profound transformation of these regions, increasingly positioning the Arctic as a persistent, globally significant source of greenhouse gases. In the Russian Arctic-a critical zone for national economic growth and transport infrastructure-intensive development is replacing natural ecosystems with anthropogenically modified ones. In this context, Nature-based Solutions (NbS) represent a vital tool for climate change adaptation and mitigation. However, many NbS successfully applied globally have limited applicability in the Arctic due to its inaccessibility, short growing season, low temperatures, and permafrost. This review demonstrates the potential for adapting existing NbS and developing new ones tailored to the Arctic's environmental and socioeconomic conditions. We analyze five key NbS pathways: forest management, sustainable grazing, rewilding, wetland conservation, and ecosystem restoration. Our findings indicate that protective and restorative measures are the most promising; these can deliver measurable benefits for both climate, biodiversity and traditional land-use. Combining NbS with biodiversity offset mechanisms appears optimal for preserving ecosystems while enhancing carbon sequestration in biomass and soil organic matter and reducing soil emissions. The study identifies critical knowledge gaps and proposes priority research areas to advance Arctic-specific NbS, emphasizing the need for multidisciplinary carbon cycle studies, integrated field and remote sensing data, and predictive modeling under various land-use scenarios.

The recent large reduction in anthropogenic aerosol emissions across China has improved China's air quality but has potential consequences for climate forcing. This sharp reduction in anthropogenic emissions has occurred against a background influenced by changing regional biomass burning emissions over a similar period of time. Here, we use the UK Earth System Model (UKESM) to estimate aerosol instantaneous radiative forcing (IRF) due to changes in emissions of aerosols and precursors from biomass burning and anthropogenic sources (separately and in combination) over 2008-2016, with a focus on China and regions downwind. We also separately quantify the IRF due to changes in anthropogenic aerosol emissions inside China (CHN) and the Rest Of the World (ROW). Reductions in Chinese anthropogenic emissions of BC, SO2 and OC contributed -0.30 +/- 0.01, +1.00 +/- 0.04, and +0.05 +/- 0.01 W m-2, respectively to IRF over China, accounting for similar to 97% of the total local anthropogenic aerosol IRF. These emission changes contributed a remote regional IRF of 0.22 +/- 0.04 W m-2 over the North Pacific Ocean. The reduction in SO2 emissions from China contributed a global IRF of equal magnitude to that from SO2 emissions from ROW (similar to 0.08 W m-2). Changes in global biomass burning emissions contributed 0.03 W m-2 (equivalent to over 20% of the magnitude of anthropogenic aerosol IRF), enhancing the global anthropogenic aerosol IRF, whereas they partly offset the anthropogenic IRF over China. Meanwhile, biomass burning emissions dominated the total IRF (around 98%) over the Arctic.

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.

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.