Ze Zhang

Lake and pond water surfaces in thermokarst-affected Arctic permafrost lowlands are important for hydrological, habitat, and carbon-cycle studies. Existing inland-water products rarely provide georeferenced image-mask pairs designed for supervised segmentation of small Arctic water bodies. We present a Sentinel-2 semantic segmentation dataset for thermokarst-associated lake and pond water surfaces across 23 selected permafrost-lowland areas of interest (AOIs) spanning Alaska, northwestern Canada, European Russia, Yamal, and Siberia. The supervised target is visible summer lake and pond water, while separate tile-level fields record thermokarst relevance and non-target-water risk. The dataset contains 5513 image-mask pairs derived from summer 2023 Sentinel-2 Level-2A surface-reflectance composites. Each image is a 256 by 256 pixel GeoTIFF with five bands (B2, B3, B4, B8, and B11), accompanied by a binary water mask and a quality-assurance (QA) mask for invalid observations and ambiguous margins. The train, validation, and test splits contain 3982, 739, and 792 tiles, respectively. The masks contain 29,141,595 positive pixels, representing 8.07 % of all pixels and a pixel-count-equivalent area of approximately 2914.2 km2; 88.35 % of target-water pixels lie north of or on the Arctic Circle at 66°34′ N. The package includes 16539 image, water-mask and QA GeoTIFF files, with sample metadata, source records, processing settings, split definitions and a 150-tile low-water subset index. A geometry audit identified cross-split overlap in the legacy development split and in the original Mackenzie Delta holdout. After removing overlapping and nearby development samples and retraining with QA-aware loss, the Mackenzie Delta experiment reached a target-agreement intersection-over-union (IoU) of 0.659 (spatial-cluster bootstrap interval 0.587–0.728). The Yamal and European Russia holdout had no detected test–development footprint overlap and retained its previously reported target-agreement IoU of 0.936. These values measure agreement with the released supervision targets; independent human-reference accuracy remains to be established. The release is designed for supervised segmentation and controlled model comparison within the represented 2023 Arctic permafrost-lowland settings. The dataset is available from the National Cryosphere Desert Data Center at https://doi.org/10.12072/ncdc.permafrost.db7645.2026 (Guo, 2026). The accompanying model-output dataset is available on Zenodo at https://doi.org/10.5281/zenodo.22965055 (Zhang et al., 2026).

Climate warming and wetting accelerate permafrost degradation in the Xiao Xing’anling Mountains, Northeast China at the southern limit of Eurasian latitudinal permafrost. Conventional interferometric synthetic aperture radar (InSAR) retrievals of active-layer thickness (ALT) assume vertically uniform soil properties, potentially biasing estimates in layered soils. We developed a depth-stratified InSAR framework combining the amplitude of seasonal deformation (ASD) with layer-specific ERA5 soil moisture and USDA soil texture. We applied it to 149 Sentinel-1B acquisitions from October 2016 to December 2021. Long-term linear deformation rates ranged from -47 to +53 mm/year, ASD reached 140 mm, and retrieved thaw depths ranged from 0.4 to 6.5 m. Against borehole observations, soil stratification reduced mean absolute error from 1.023 to 0.853 m (16.6%), with the largest improvement where thin active layer overlies warm permafrost. Deep thaw occurred preferentially at elevations of 250–400 m a.s.l., on slopes (<5°), and on shaded aspects. ASD varied linearly with the E-factor, an edaphic index integrating soil moisture and texture, consistent with their coupled control on seasonal deformation. The sensitivity resembled that of poorly drained, near-saturated Arctic lowlands but exceeded that of the drier, coarser substrates of the Qinghai–Tibet Plateau. In this climatic transition zone, extreme retrieved depths likely represent the depth of the permafrost table rather than ALT, indicating active-layer–permafrost decoupling/detachment associated with supra-permafrost talik development. Low ASD combined with persistent subsidence may therefore indicate talik initiation. The framework improves thaw-depth retrieval in heterogeneous patchy permafrost regions and enables scalable monitoring of permafrost degradation and infrastructure risk.

To reveal the degradation patterns and damage mechanisms of loess microstructure under freeze–thaw cycles (FTCs), this study investigates typical loess from the Fuping area at the southeastern edge of the Loess Plateau. Using scanning electron microscopy combined with multifractal analysis, a multiscale quantitative study was conducted on the pore and fracture structures after varying FTCs (0–100 cycles). Results indicate that FTCs significantly alter the spatial distribution characteristics of loess pore networks. Macropores (50–500 μm) and mesopores (10–50 μm) are the most sensitive to FTCs, exhibiting rapid expansion and interconnection, whereas micropores (1–10 μm) maintain structural stability with negligible variation. The generalized fractal dimension D(q) exhibits a “first-rise-then-stabilization” pattern with increasing FTCs, where the volume dimension D0 peaks at approximately 1.85 after 50 FTCs and subsequently stabilizes. The information dimension D1 and correlation dimension D2 exhibit consistent changes, reflecting enhanced pore connectivity and structural reorganization. The spectral width Δα increased from an initial value of 0.545 to a peak of 0.621, then decreased to 0.472 at approximately 100 FTCs, demonstrating a three-stage evolution pattern of “enhancement-homogenization-stabilization.” At the microscopic level, the freeze–thaw action promotes pore expansion and crack initiation through ice crystal growth and frost heave pressure. Subsequent thawing leads to water redistribution and cementation weakening, thereby enhancing pore connectivity and structural homogeneity. The coupled hydro-thermal-mechanical processes during freeze–thaw control the multifractal evolution of loess microstructure. These findings provide a new analytical perspective for structural degradation assessment and stability analysis in cold region loess engineering.

This research was conducted on mountain summits in South Yakutia, Russia. The findings indicate that within the goltsy altitudinal belt (comparable to the alpine zone), the weathering intensity of rocks above 1400 m depends on the development of snow-ice formations, particularly snowpatches. Snowpatches promote physical rock weathering along their edges by up to 1.5–4 times more intensely compared to baseline levels. The ground temperature at the edges was examined in relation to air temperatures. The conditions that facilitate rock weathering at the snowpatch edge during the summer months are characterized by diurnal air temperatures below 10–15 °C, with minimum temperatures below 5 °C. Nivation processes in the goltsy altitudinal belt of South Yakutia are considered as one of the dominant geomorphic agents. However, future changes are expected in the existing nival-glacial belts, as snowpatches respond rapidly to climate change, with the mean annual air temperature in South Yakutia exhibiting a rising trend.