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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]

The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Ωm and above 700 Ωm, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures.

The degradation of permafrost poses severe environmental threats to communities in cold regions. As near-surface permafrost warms, extensive topographic variability is prevalent in the Arctic and Sub-Arctic communities. Geologic hazards such as thermokarst are formed due to varying rates of permafrost degradation, resulting in ground subsidence. This gradual subsidence or abrupt collapse of the earth causes a danger to existing infrastructure and the economic activities of communities in cold regions. Understanding the causes of thermokarst development and its dynamics requires imaging its underground morpho-structures and characterizing the surface and subsurface controls. In this study, we conducted a two-dimensional (2D) electrical resistivity tomography (ERT) survey to characterize the permafrost conditions in a thermokarst prone site located in Fairbanks, Alaska. To increase the reliability in the interpretability of the ERT data, borehole data and the depth-of-investigation (DOI) methods were applied. By using the 2D and three-dimensional (3D) ERT methods, we gained valuable information on the spatial variability of transient processes, such as the movement of freezing and thawing fronts. Resistivity imaging across the site exhibited distinct variations in permafrost conditions, with both low and high resistive anomalies observed along the transects. These anomalies, representing taliks and ice wedges, were characterized by resistivity values ranging from 50 Om and above 700 Om, respectively. The results from this study showed the effectiveness of ERT to characterize permafrost conditions and thermokarst subsurface morpho-structures. The insights gained from this research contribute to a better understanding of the causes and dynamics of thermokarst, which can be instrumental for engineers in developing feasible remedial measures. [ABSTRACT FROM AUTHOR]

The Nihewan Basin is a rift basin at the junction of northern Shanxi Province and northwestern Hebei Province in north China. The basin is known for its rich paleontological fossils and ancient human remains. There are also abundant soft-sediment deformation structures (SSDS) in the thick lacustrine sediments. Previously, most SSDS have been interpreted as ice-edge features or ignored entirely. Recently, the authors have carried out several field surveys in the Nihewan Basin and found that many SSDS are sandwiched between normal lacustrine strata at multiple sections. In the excavation pit at the 10th Locality of Maliang Site (ML10), 10 horizontal SSDS layers and two vertically developed geological features have been identified. Based on genesis analysis and related criteria, these features are divided into two categories: cryoturbation-triggered SSDS and earthquake-triggered SSDS. Among them, a special type of ancient ice-wedge pseudomorph (SSDS-8) of ML10 is recognized in the basin for the first time. The other 9 horizontal SSDS are mainly caused by earthquake-triggered liquefaction and slumping. They can be further divided into 14 seismic event layers. These findings indicate that the tectonic activity in the Nihewan Basin is very strong and frequent, and there were cold periods in the geological history of the basin. At the same time, the SSDS with distinct morphological characteristics and stable horizontal distribution in the basin can be used as an important indicator of stratigraphic correlation. [ABSTRACT FROM AUTHOR]

Permafrost thaw exhibits an array of spatially heterogenous patterns. As the Arctic continues to warm, those spatial patterns of permafrost thaw, or degradation, are becoming increasingly intricate and dynamic. In particular, ice-wedge permafrost degradation contains a high degree of spatial heterogeneity as ice wedges transition through undegraded, degraded, and stabilized stages. Developing accurate remote sensing methods for characterizing degradation will better allow us to monitor and forecast Arctic landscape evolution and associated land-atmosphere carbon-climate interactions. In this study, we (i) characterized ice-wedge degradation stages across a regional scale using a novel hydrogeomorphic approach. Then, we (ii) assessed the heterogeneity of degradation from meter- to kilometer-scales, and (iii) identified landscape properties associated with degradation patterns. We leveraged the unique spectral and geometric properties of ice-wedge degradation stages to map those stages across 366 km2 of the Arctic Coastal Plain near Prudhoe Bay, Alaska in sub-meter resolution Worldview-2 satellite imagery. Then, we validated the maps with in-situ observations, airborne LIDAR, and drone multispectral surveys. We evaluated spatial heterogeneity in ice-wedge degradation through a clustering approach. Specifically, we grouped regions into hydrogeomorphic clusters defined by similarities in trough widths and flooding, which reflect distinct degradation stages. This analysis revealed that ice-wedge degradation is heterogeneous across both meter and kilometer scales. At the meter scale, a single ice-wedge polygon is generally bounded by varied degradation stages. In addition, the most advanced stages of degradation occur in areas of low trough relative elevation and at the junctions between troughs. At the kilometer-scale, distinct clustering of degradation stages was identified across the region and linked to spatial patterns in topography: regional clusters of advanced degradation occurred in higher elevation areas. The millennial-scale evolution of the landscape has resulted in heterogeneous topographic, hydrologic, and cryogenic characteristics; these varied features exhibit diverse responses to warming events, which reflect the dynamic interplay that occurs between permafrost landscapes and climate change. • We used spectral and geometric properties to assess stages of ice-wedge degradation. • Ice-wedge degradation is heterogeneous at both meter- and kilometer-scales. • A single polygon is generally bounded by multiple stages of ice-wedge degradation. • Km-scale degradation clusters follow patterns in topography and landscape morphology. [ABSTRACT FROM AUTHOR]