Study region The eastern Qilian Mountains, located on the northeastern margin of the Tibetan Plateau, span elevations from similar to 2600 to 5300 m around the Menyuan area. It is characterized by cold, alpine climatic conditions and hosts both permafrost and seasonally frozen ground, which are highly sensitive to climate change and have important hydrological and ecological implications. Study focus This study develops an enhanced multi-temporal InSAR framework to monitor frozen ground dynamics in the eastern Qilian Mountains using Sentinel-1 data from 2014 to 2024, with a particular focus on the permafrost-seasonally frozen ground transition zone around Menyuan. It addresses key challenges in permafrost monitoring by implementing a co-seismic deformation separation model, a Common Scene Stack (CSS)-based atmospheric correction method, and a time-series decomposition model with linearly varying annual amplitude to capture evolving freeze-thaw behavior under climate change. New hydrological insights for the region The results reveal clear hydrological and thermal contrasts between permafrost and seasonally frozen ground. Seasonally frozen ground exhibits higher seasonal deformation amplitudes, more rapid interannual changes, and shorter thermal response lags compared to permafrost, reflecting its more dynamic hydrothermal regime. The estimated freeze-thaw layer thickness ranges from 0 to 5.3 m, with thinning trends in seasonally frozen ground at lower elevations and slight thickening of active layers in high-elevation permafrost. These findings highlight ongoing frozen ground degradation and provide new insights into subsurface water-energy interactions and long-term cryospheric responses to climate warming in alpine environments.

Black carbon (BC) mixed with non-BC components strongly absorbs visible light and leads to uncertainty in assessing the absorption enhancement (Eabs) and thus radiative forcing. Traditional Single-Particle Soot Photometer (SP2) combined with the leading-edge only fitting (the only-SP2 method) derives BC's mixing states through Mie scattering calculations. However, errors exist in retrieved optical diameter (Dopt) and MR due to the assumption of the ideal spherical core-shell structure and the selection of the calculation parameters like density and refractive index (RI) of the components. Here, we employed a custom-developed tandem CPMA-SP2 system, which classifies fixed-mass BC to characterize the mixing state, then compared with the only-SP2 method in quantifying the mixing state and Eabs. The field measurements show that the SP2 demonstrates variability in assessing the mixing state of BC in different aging states. The thickly-coated particles with small core approaching the internally mixed state are more sensitive to the change of calculated RI. The Dopt decreases with the RI increasing, indicating that this method accurately measures both Dopt and Eabs when a reasonable refractive index is selected for calculation. However, for thinly-coated particles with moderate or large core, this method results in significant deviations in the computed Eabs (errors up to 15 %). These deviations may be caused by the various shapes of BC and systematic errors. Our results provide valuable insights into the accuracy of the SP2-retrieved Dopt and MR based on Mie calculations and highlight the importance of employing advanced techniques for further assessment of BC's mixing state.

Permafrost soils contain approximately twice the amount of carbon as the atmosphere and this carbon could be released with Arctic warming, further impacting climate. Mosses are major component of Arctic tundra ecosystems, but the environmental drivers controlling heat penetration though the moss layer and into the soil and permafrost are still debated, especially at fine spatial scales where microtopography impacts both vegetation and soil moisture. This study measured soil temperature profiles (1-15 cm), summer thaw depth, water table depth, soil moisture, and moss thickness at a fine spatial scale (2 m) together with meteorological variables to identify the most important controls on the development of the thaw depth during two Arctic summers. We found a negative relationship between the green moss thickness (up to 3 cm) and the soil temperatures at 15 cm, suggesting that mosses insulated the soil even at high volumetric water contents (>70%) in the top 5 cm. A drier top (2-3 cm) green moss layer better insulated deep (15 cm) soil layers by reducing soil thermal conductivity, even if the moss layers immediately below the top layer were saturated. The thickness of the top green moss layer had the strongest relationships with deeper soil temperatures, suggesting that the top layer had the most relevant role in regulating heat transfer into deeper soils. Further drying of the top green moss layer could better insulate the soil and prevent permafrost thawing, representing a negative feedback on climate warming, but damage or loss of the moss layer due to drought or fire could reduce its insulating effects and release carbon stored in the permafrost, representing a positive feedback to climate warming.

Soil organic matter (SOM) stability in Arctic soils is a key factor influencing carbon sequestration and greenhouse gas emissions, particularly in the context of climate change. Despite numerous studies on carbon stocks in the Arctic, a significant knowledge gap remains regarding the mechanisms of SOM stabilization and their impact on the quantity and quality of SOM across different tundra vegetation types. The main aim of this study was to determine SOM characteristics in surface horizons of permafrost-affected soils covered with different tundra vegetation types (pioneer tundra, arctic meadow, moss tundra, and heath tundra) in the central part of Spitsbergen (Svalbard). Physical fractionation was used to separate SOM into POM (particulate organic matter) and MAOM (mineral-associated organic matter) fractions, while particle-size fractionation was applied to evaluate SOM distribution and composition in sand, silt, and clay fractions. The results indicate that in topsoils under heath tundra POM fractions dominate the carbon and nitrogen pools, whereas in pioneer tundra topsoils, the majority of the carbon and nitrogen are stored in MAOM fractions. Moreover, a substantial proportion of SOM is occluded within macro-and microaggregates. Furthermore, the results obtained from FTIR analysis revealed substantial differences in the chemical properties of individual soil fractions, both concerning the degree of occlusion in aggregates and across particle size fractions. This study provides clear evidence that tundra vegetation types significantly influence both the spatial distribution and chemical composition of SOM in the topsoils of central Spitsbergen.

At high elevations, tree saplings and shrubs are usually protected by mid-winter snow cover, although climate change is expected to extend the snow-free (SF) period. Exposure to winter drought, freeze-thaw events and freezing temperatures will therefore increase, inducing damages to the hydraulic system and to living cells, resulting in reduced growth and increased mortality. A snow removal experiment was carried out at 1700 m. above sea level on saplings of five different species (Acer pseudoplatanus, Juniperus communis, Larix decidua, Picea abies and Sorbus aucuparia). Stem diameter was continuously monitored and compared with spring hydraulic conductivity (PLCspring), living cell mortality (PLDspring), nonstructural carbohydrates (NSCs), growth and survival rates. Under SF conditions, saplings had higher PLCspring and higher PLDspring, and thus experienced greater winter dehydration, resulting in lower growth compared with snow-covered saplings. Summer mortality was strongly correlated with PLCspring and PLDspring. These two key ecophysiological parameters predicted the risk of mortality in all species, whereas only PLDspring reduced growth. By monitoring stem diameter during winter, we have defined indices to quantify resistance and recovery of woody plants under increased frost pressure. Recovery strategies such as resprouting or embolism repair were critical for survival, highlighting the potential vulnerability of saplings to climate change at high elevations.

The thermal stability of permafrost, a foundation for engineering infrastructure in cold regions, is increasingly threatened by the dual stressors of climate change and anthropogenic disturbance. This study investigates the dynamics of the crushed rock revetted embankment at the Kunlun Mountain Section of the Qinghai-Tibet Railway, systematically investigating the coupled impacts of climate warming and engineering activities on permafrost thermal stability using borehole temperature monitoring data (2008-2024) and climatic parameter analysis. Results show that under climate-driven effects, the study area experienced an air temperature increase of 0.2 degrees C per decade over the 2015-2024. Concurrently, the mean annual air thawing degree-days (TDD) rose by 13.8 degrees C center dot d/a, leading to active-layer thickening at a rate of 3.8 cm center dot a- 1at natural ground sites. From 2008 to 2024, the active layer had thickened by 0.7-0.8 m. At the embankment toe (BH 5), the active-layer thickening rate (3.3 cm center dot a- 1) was 25 % lower than that at the natural ground borehole (3.8 cm center dot a- 1); correspondingly, the underlying permafrost temperature increase rate at the toe (0.3 degrees C per decade) was lower than that at the natural borehole (0.5-0.6 degrees C per decade). Permafrost warming rates decreased with depth. Shallow layers (above -2 m) were significantly influenced by climate, with warming rates of 0.3-0.6 degrees C per decade. In contrast, deep layers (below -10 m) showed warming rates converging with the background atmospheric temperature trend (0.2 degrees C per decade). Thermal regime disturbance was most pronounced at horizontal distances of 3.0-5.0 m from the embankment. Nevertheless, the crushed-rock revetment maintained a permafrost table 0.6 m shallower than that of natural ground, confirming its thermal diode effect (facilitating convective cooling in winter), which partially offset climate warming impacts. This study provides critical empirical data and validates the cooling mechanism of crushed-rock revetment, which is essential for predicting the long-term thermal stability and informing adaptive maintenance strategies for railway infrastructure in warming permafrost regions.

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.

Carbonaceous aerosols (CA) strongly impact regional and global climate through their light-absorbing and scattering properties, yet their effects remain uncertain in dust-influenced regions. We investigated the optical properties, source contributions, and radiative impacts of CA at two climatically distinct regions in northwestern India: an arid region (AR, Jodhpur; post-monsoon) and a semi-arid region (SAR, Kota; winter). Mean absorption & Aring;ngstr & ouml;m exponent (AAE) values were comparable between the two regions (AR: 1.416 +/- 0.173; SAR: 1.395 +/- 0.069), but temporal cluster analysis revealed source-specific variability, with lower AAE during traffic-dominated periods (similar to 1.30) and elevated AAE during solid fuel and biomass combustion (1.68 in AR and 1.52 in SAR). While equivalent BC (eBC) levels were higher in AR with a relatively uniform liquid-fuel contribution (BClf = 80.06 +/- 1.98 %), the mass absorption cross- of BC (MAC(BC)) in SAR was similar to 4.5X greater, driven by local solid fuel combustion and transported biomass burning emissions (BCsf = 34.61 +/- 6.88 %). Mie modelling indicated higher SSA in AR due to higher contribution of mineral dust, in contrast to SAR, where carbonaceous aerosols caused stronger absorption, forward scattering, and higher imaginary refractive index (k(OBD)). Although absorption enhancement (E-lambda) was slightly higher in AR (similar to 1.11 vs. similar to 0.99), SAR aerosols nearly doubled the warming potential (Delta RFE), with RFE values of similar to 0.87 W/m(2) in SAR versus similar to 0.43 W/m(2) in AR. These findings highlight strong source-specific and site-specific variability in aerosol absorption and radiative, emphasizing the need to integrate region-specific parameters into climate models and air quality assessments for data-scarce arid and semi-arid South Asian environments.

The response of Arctic vegetation to climate warming exhibits pronounced spatial heterogeneity, driven partly by widespread permafrost degradation. However, the role of thermokarst lake development in mediating vegetation-climate interactions remains poorly understood, particularly across heterogeneous landscapes of northeastern Siberia. This study integrated multi-source remote sensing data (2001-2021) with trend analysis, partial correlation, and a Shapley Additive Explanation (SHAP)-interpreted random forest model to examine the drivers of normalized difference vegetation index (NDVI) variability across five levels of thermokarst lake coverage (none, low, moderate, high, very high) and two vegetation types (forest, tundra). The results show that although greening dominates the region, browning is disproportionately observed in areas with high thermokarst lake coverage (>30%), highlighting the localized reversal of regional greening trends under intensified thermokarst activity. Air temperature was identified as the dominant driver of NDVI change, whereas soil temperature and soil moisture exerted secondary but critical influences, especially in tundra ecosystems with extensive thermokarst lake development. The relative importance of these factors shifted across thermokarst lake coverage gradients, underscoring the modulatory effect of thermokarst processes on vegetation-climate feedbacks. These findings emphasize the necessity of incorporating thermokarst dynamics and landscape heterogeneity into predictive models of Arctic vegetation change, with important implications for understanding cryospheric hydrology and ecosystem responses to ongoing climate warming.