Subarctic palsa mires are natural indicators of the status of permafrost in its sporadic distribution zone. Estimation of the rate of their thawing can become an auxiliary indicator to predict climate shifts. The formation, growth, and degradation of palsas are dynamic processes that depend on seasonal weather fluctuations and local environmental factors. Therefore, accurate forecasts of palsas conditions and related ecosystem shifts must be based on a broad set of attributes of palsas from different regions of the Northern Hemisphere. With this in mind, we studied two palsa mires sites on the Kola Peninsula, for which no thorough descriptions were previously available. The first site, Chavanga, is at the southern limit of the permafrost zone under unfavorable climatic conditions and is a collapsing relic. The second site, Ponoy, in contrast, is within the sporadic permafrost zone with relatively cold and dry conditions. Our dataset was created by combining several methods to produce detailed spatial models of permafrost for the studied palsa mires. We used 3D ground-penetrating radar (GPR) survey, UAV-based orthophoto maps, peat thermometry, time-domain reflectometry, and manual sampling. We developed two integrated geospatial models that describe the active layer, the configuration of the palsa frozen core, and its thermal state and identify the zones of the most intense thawing. These observations revealed a significant thermal effect of the groundwater flow and its critical role in the palsas segmentation and rapid collapse. We have investigated a regulating effect of micromorphological features of palsa mounds such as heights, slope, depressions, and mire mineral bed through groundwater drainage. As a result, two new scenarios for the palsa degradation process have been developed, emphasizing the influence of environmental factors on the permafrost condition.

Climate change drives disturbance in hydrology and geomorphology in terrestrial polar landscapes underlain by permafrost, yet measurements of, and theories to understand, these changes are limited. Water flowing from permafrost hillslopes to channels is often modulated by water tracks, zones of enhanced soil moisture in unchannelized depressions that concentrate water flow downslope. Water tracks, which dominate hillslope hydrology in some permafrost landscapes, lack a consistent definition and identification method, and their global occurrence, morphology, climate relationships, and geomorphic roles remain understudied despite their role in the permafrost carbon cycle. Combining a literature review with a synthesis of prior work, we identify uniting and distinguishing characteristics between water tracks from disparate polar sites with a toolkit for future field and remotely sensed identification of water tracks. We place previous studies within a quantitative framework of top-down climate and bottom-up geology controls on track morphology and hydrogeomorphic function. We find the term water track is applied to a broad category of concentrated suprapermafrost flowpaths exhibiting varying morphology, degrees of self-organization, hydraulic characteristics, subsurface composition, vegetation, relationships to thaw tables, and stream order/hillslope position. We propose that the widespread occurrence of water tracks on both poles across varying geologic, ecologic, and climatic factors implies that water tracks are in dynamic equilibrium with the permafrost environment but that they may experience change as the climate continues to warm. Current knowledge gaps include these features' trajectories in the face of ongoing climate change and their role as an analog landform for an active Martian hydrosphere.

Black carbon (BC) aerosol is one of the most important factor in global warming. BC radiative forcing remains unconstrained, mainly because of the uncertain parameterizations of its absorption and scattering properties in the atmosphere. The single sphere model is widely used in current climate assessment of BC aerosols due to its computational convenience, however, their complex morphologies in particle level are excessively simplified which leads to computed inaccuracy. In this study, we present a dynamic model for optical calculations of BC aerosol ensembles considering their complex fractal aggregate morphologies with the constraint of max monomer numbers (N s, max) and radius (a max). We show that the simulation accuracy of the dynamic model with suitable values of N s, max and a max may achieve similar to 95% while the computation time may reduce to similar to 6%. We find that optical properties of BC aerosol ensembles can be simulated for higher accuracy or faster calculation by performing different selections of monomer numbers and radius in their size distributions. This method enables extensive and accurate optical calculations of BC particles with complex morphologies, which would be useful for the remote sensing inversion and the assessment of climate.

The areas covered by permafrost in the polar regions are vulnerable to rapid changes in the current climate. The well-studied near-surface active layer and permafrost zone are in contrast to the unknown exact shape of the bottom permafrost boundary. Therefore, the entire shape of permafrost between the upper and lower boundaries is not identified with sufficient accuracy. Since most of the factors affecting deep cryotic structures are subsurface in nature, their evolution in deeper layers is also relatively unclear. Here, we propose a hypothesis based on the results of geophysical studies regarding the shape of the permafrost in the coastal area of Svalbard, Southern Spitsbergen. In the article, we emphasize the importance of recognizing not only the uppermost active layer but also the bottom boundary of permafrost along with its transition zone, due to the underestimated potential role of its continuity in observing climate change. The lower permafrost boundary is estimated to range from 70 m below the surface in areas close to the shore to 180 m inland, while a continuous layer of an entirely frozen matrix can be identified with a thickness between 40 m and 100 m. We also hypothesized the presence of the possible subsea permafrost in the Hornsund. The influence of seawater intrusions, isostatic uplift of deglaciated areas, and surface-related processes that affect permafrost evolution may lead to extensive changes in the hy-drology and geology of the polar regions in the future. For all these reasons, monitoring, geophysical imaging and understanding the characteristics and evolution of deep permafrost structures requires global attention and scientific efforts.

Ground ice distribution and abundance have wide-ranging effects on periglacial environments and possible impacts on climate change scenarios. In contrast, very few studies measure ground ice in the High Arctic, especially in polar deserts and where coarse surficial material complicates coring operations. Ground ice volumes and cryostructures were determined for eight sites in a polar desert, near Resolute Bay, Nunavut, chosen for their hydrogeomorphic classification. Dry, unvegetated polar desert sites exhibited ice content close to soil porosity, with a <45 cm thick ice-enriched transition zone. In wetland sites, suspended cryostructures and ice dominated cryofacies (ice content at least 2x soil porosity values) were prevalent in the upper similar to 2 m of permafrost. Average ground ice saturation at those locations exceeded porosity values by a factor between 1.8 and 20.1 and by up to two orders of magnitude at the similar to 10 cm vertical scale. Sites with the highest ice contents were historically submerged wetlands with a history of sediment supply, sustained water availability, and syngenetic and quasi-syngenetic permafrost aggradation. Ice enrichment in those environments were mainly caused by the strong upward freezing potential beneath the thaw front, which, combined with abundant water supply, caused ice aggradation and frost heaving to form lithalsa plateaus. Most of the sites already expressed cryostratigraphic evidence of permafrost degradation. Permafrost degradation carries important ecological ramifications, as wetland locations are the most productive, life-supporting oases in the otherwise relatively barren landscape, carrying essential functions linked with hydrological processes and nutrient and contaminant cycling.

Arctic permafrost is degrading and is thus releasing nutrients, solutes, sediment and water into soils and freshwater ecosystems. The impacts of this degradation depends on the geochemical characteristics and in large part on the spatial distribution of ground ice and solutes, which is not well-known in the High Arctic polar desert ecosystems. This research links ground ice and solute concentrations, to establish a framework for identifying locations vulnerable to permafrost degradation. It builds on landscape classifications and cryostratigraphic interpretations of permafrost history. Well-vegetated wetland sites with syngenetic permafrost aggradation show a different geochemical signature from polar desert and epigenetic sites. In wetlands, where ground ice contents were high (<97% volume), total dissolved solute concentrations were relatively low (mean 283.0 +/- 327.8 ppm), reflecting a carbonate terrestrial/freshwater setting. In drier sites with epigenetic origin, such as polar deserts, ice contents are low (<47% volume), solute concentrations were high (mean 3248.5 +/- 1907.0 ppm, max 12055 ppm) and dominated by Na+ and Cl- ions, reflecting a post-glacial marine inundation during permafrost formation. Dissolved organic carbon and total dissolved nitrogen concentrations usually increased at the top of permafrost and could not be as clearly associated with permafrost history. The research shows that the geochemistry of polar desert permafrost is highly dependent on permafrost history, and it can be estimated using hydrogeomorphological terrain classifications. The lower ice content of polar desert sites indicates that these areas are more vulnerable to thaw relative to the ice-rich wetland sites, and the elevated solute concentrations indicate that these areas could mobilise substantial solutes to downstream environments, should they become hydrologically connected with future warming.

Effective density (peff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of peff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. peff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass.

Anthropogenic climate change threatens water storage and supply in the periglacial critical zone. Rock glaciers are widely distributed alpine aquifers with slower response to temperature increases, that provide the summer water flow of many alpine streams. Knowing the extent and makeup of rock glaciers is necessary to evaluate their potential for water supply. We used non-invasive methods, integrating geological, geomorphological, meteoro-logical, and geophysical information to characterize the internal structure and hydrology of the Upper Camp Bird rock glacier (UCBRG) located on level 3 of Camp Bird Mine in Ouray, Colorado, and assessed the applicability of two electromagnetic induction systems in this highly heterogeneous landform with a history of anthropogenic activity. The time-domain (G-TEMTM) system achieved deep subsurface penetration (similar to 100 m) and realistic modeling of the internal structure of the UCBRG: a shell of volcanic rock fragments (< 3 m thick; 1-100 Ohm-m), a meltwater component (10(2)-10(3) Ohm-m), located between 50 and 100 m near the toe (subpermafrost flow), and 1-30 m in the soundings farthest from the toe (suprapermafrost flow within the active layer), and a frozen component (permafrost 50-80 m thick; 10(3)-10(6) Ohm-m). The frequency-domain system, however, was highly susceptible to local environmental conditions, including anthropogenic objects (i.e., mine carts, lamp posts, tunnel tracks, etc.) and was unable to resolve UCBRG's internal makeup. The non-invasive methodology and general conceptual framework presented here can be used to characterize other alpine aquifers, contributing to the quantification of global water resources, and highlighting the importance of preserving rock glaciers as storage for critical water supply in the future.

Black carbon (BC) is an important aerosol species due to its strong heating of the atmosphere accompanied by cooling of the Earth's surface, but its radiative forcing is poorly constrained by different regional size distributions due to uncertain reproductions of a morphologically simplified model. Here, we quantify the BC morphological effect on measuring the particle size using an aggregate model. We show that the size distributions of loose BC particles could account for up to 45% underestimation by morphological simplification, leading to up to 25% differences, by relying on a simplified model to estimate radiative forcing. We find that the BC particle size is remarkably amplified for looser and larger BC aggregates by angular scattering observations. We suggest that the BC morphological diversity can be neglected in forward scattering angles (<30 degrees), which is a useful supplement to reduce the uncertainty of radiative forcing assessment.

Accurate estimates of regional and global glacier mass require many field-based sample measurements that are widely distributed across an area of interest. The Sawir Mountains are an isolated mountain system in Central Asia and changes in glacier mass balance from this region have rarely been reported. In this study, we provide a comprehensive analysis of mass changes of the Muz Taw Glacier in the Sawir Mountains based on glaciological and geodetic measurements. The glaciological mass balance exhibited a strong variability during the period 2016-2020, with a range of values between - 1.29 and - 0.31 m water equivalent (w.e.) and a mean value of - 0.86 +/- 0.16 m w.e. Differences in the surface elevation of the Muz Taw Glacier were determined from analysis of a topographic map (1:100,000 scale) and terrestrial laser scanning (TLS) point-cloud data, with these data sources indicating an average surface elevation change of approximately - 33.36 +/- 9.39 m or - 0.54 +/- 0.15 m a(-1) during 1959-2021. This thickness is roughly equivalent to half of the mean thickness of the glacier terminus, which has contributed to the negative geodetic mass balance of - 28.36 +/- 8.23 m w.e. or - 0.46 +/- 0.13 m w.e. a(-1). Approximately twice as much mass has been lost from the Muz Taw Glacier during the past 5 years (2016-2020) than estimated by geodetic data, indicating that the mass loss of Muz Taw Glacier has continued unabated.