Abstract Active layer increase may contribute to greenhouse gas emissions, ecosystem change, and increased hazards. Here, we show the results of field measurements of active-layer thickness from 156 monitoring sites in Arctic, Antarctic and mountain permafrost regions. Active layer thickness increased significantly at 55% and 38% of sites in the Arctic and Antarctic regions, at more than 90% European mountain and high elevation Asian sites, and at sites in South America, demonstrating worldwide permafrost degradation during the first quarter of this century (2000–2024). The largest changes were observed in mountain regions where active layer doubled at several sites. The smallest changes were observed at sites with thick surficial organic horizons and high ground ice content. In continuous permafrost, sites generally exhibited smaller increases compared to sites in discontinuous permafrost. Regression analysis indicates Arctic active layer changes are attributable to increasing thawing degree-days, followed by increases in total rainfall. Other permafrost regions require more sites and longer time-series to draw conclusions regarding active layer change attribution.

In 2023, the Batagay megaslump exposure was studied and monoliths of composite and ice wedges were sampled from five cryostratigraphic units: the Lower Ice Complex of Marine Isotope Stage (MIS) 16 or older, the Lower Sand of MIS 6 or older, the Upper Ice Complex of MIS 4-3, the Upper Sand of MIS 3-2, and the uppermost permafrost layer of MIS 1. The main aim was to investigate the formation mechanism of wedge structures in connection with paleoenvironmental conditions. The study of composite wedges' structure indicated crystals of segregated ice between and within sand veins. The segregated ice was formed in the thermal-contraction cracks infilled by unfrozen sediments from an active layer. Water separated and migrated to two cold walls providing ice lens formation. Stable O-H isotope values of most samples from the wedge structures are located between the global and local meteoric water lines and indicate extremely cold and dry conditions. Some of the samples, especially from composite wedges, have high dexc values that can be related to fractionation during evaporation in thin snow cover. Primary mineralization in ground ice can be related to extremely continental climatic conditions with associated evaporation, as well as secondary processes.

The degradation of modern and ancient permafrost-affected soils and organic-rich sediments and the release of relict soil organic matter from the frozen state are critical for understanding the global carbon cycle in a changing climate. The molecular structure of humic acids isolated from modern Cryosols and paleosoils from the Ice Complex deposits in the Batagay megaslump area was investigated. The elemental composition analysis was performed using a CHN analyzer, and molecular composition analysis was determined by CP/MAS 13C-NMR spectroscopy. Analysis of the molecular structure of humic acids showed that MIS 5e paleosoils are characterized by a relatively high content of aliphatic structural fragments (C,H-AL—29–36%) and a low content of aromatic structural fragments (AR/AL—0.49–0.43), which reveals low humification rates in this time period. The composition of humic acids from MIS 7 paleosoils shows a relatively high content of aromatic structural fragments compared to modern soils (AR/AL—0.47) and MIS 5e deposits (AR/AL—0.67–0.54), indicating a longer humification process in heterogenic conditions (warm and cold periods). The results indicate that the molecular structure of humic acids is a dynamic parameter of the environment that reflects the local conditions of pedogenesis and organic matter formation. Permafrost thawing leads to the release of organic matter (including matter that is relatively weakly resistant to biodegradation where aliphatic structural fragments dominate the composition of humic acids) that may strengthen the emission of climate-active gases into the atmosphere and boost climate change.

Изучены строение и свойства отложений крупнейшей регрессивной термоденудационной котловины Батагай. Стратиграфическая последовательность многолетнемерзлых отложений предположительно непрерывно накоплена за период среднего-позднего неоплейстоцена (~700-11 тыс. лет назад) и частично трансформирована в течение голоцена. На основе палеопочвенных, палеонтологических и геокриологических данных получены новые представления об историческом развитии почвенно-растительного покрова и позднеледниковой фауны Янского плоскогорья. Подтверждены два благоприятных климатических периода формирования почвенно-растительного покрова: первый по различным методам датирования относится к эпохам МИС 15-17 (600-700 тыс. лет) либо к эпохе МИС 7е (230-250 тыс. лет); второй более уверенно датируется эпохой МИС 5е (110-130 тыс. лет). The morphology and properties of frozen strata were studied in the area of the largest retrogressive thermal thaw slump Batagay (Yakutia). A presumably continuous stratigraphic sequence of permafrost sediments accumulated during the Middle and Late Pleistocene (~700-11 ka) and was partially transformed during the Holocene. Based on paleopedological, paleontological, and geocryological data, new suggestions have been made regarding the historical development of the soil-vegetation cover and late glacial fauna in the Yana Plateau region. Two extensive and relatively warm climatic periods favoring the formation of developed soil-vegetation cover have been identified: the first one belongs to MIS 15-17 (600-700 ka) or (depending on the dating method) to MIS 7e (230-250 ka); the second one is more certainly dates back to MIS 5e (110-130 ka).

Retrogressive thaw slumps (RTS) are an important landform of rapid permafrost degradation in regions with very high ground ice contents. RTS mobilize significant amounts of sediment, meltwater and organic carbon and impact downstream hydrological systems by directly affecting topography and water quality. The term megaslump has previously been coined for RTS exceeding 20 ha in size. The Batagay megaslump in the Yana highlands of NE Siberia with an area of 87.6 ha (in 2023, including the bowl-shaped part and the erosional outlet) has been identified as the largest megaslump on Earth. We use very high resolution remote sensing from satellite data and drones, geological structure modeling, and field data to assess how much and what material is thawed and mobilized in the Batagay megaslump. The total volume of permafrost thaw and material loss from the Batagay RTS amounts to about 1 million m 3 per year. The material is by one third composed of thawed sediments and by two thirds of melted ground ice. About 4000 to 5000 tons of previously permafrost-locked organic carbon is released every year. Organic carbon content has been measured as Total Organic Carbon (TOC) of sediments and as Dissolved Organic Carbon (DOC) of ground ice. From its formation in the 1970s until 2023, the Batagay RTS - due to thermal denudation and headwalls retreat - mobilized a total volume of about 34.7 million m 3 of which 23.4 million m 3 were melted ground ice and 11.3 million m 3 were thawed deposits including a total of about 169,500 t organic carbon. With these rates of sediment and carbon mobilization, the Batagay megaslump is not only a prominent local feature of rapid permafrost thaw, but offers excellent conditions to study rates and mechanisms of rapid permafrost degradations and to calculate the stock and release of, e.g., organic matter.

Soils of the Arctic sea coasts are one of the least studied due to the complex logistical accessibility of the region, as well as the severe climatic conditions. The genesis of these soils is determined by several factors of soil formation simultaneously—cryogenesis, the influence of river alluvial processes, as well as the tidal influence of the sea. The paper presents data on the morphological structure of soils formed on the seacoast of the East-Siberian Sea (Kolyma Lowland, North Yakutia). Under the influence of cryogenesis and sea water tidal input, marsh soils are formed, with a relatively high level of salinity and the development of gleyization. Autochthonous and allochthonous soil organic matter play a leading role in marsh soil formation here, including the possible accumulation and biochemical transformation of incoming pollutants (e.g., hydrocarbons). The main objective of the study was to evaluate the soil organic matter genesis and alteration under the influence of tidal processes in coastal permafrost-affected soils as well as to obtain the previously unknown characteristics of the structural and elemental composition of different fractions of organic matter. The elemental composition and 13C NMR spectroscopy of humic acids were analyzed. It was revealed that humic acids extracted from the studied marsh soils accumulate up to 50% C and 4% N. Active processes of dehydrogenation are noted in HAs molecules, which indicates a relatively low degree of aliphatic structure development. According to 13C NMR spectroscopy, it was revealed that up to 45% of aromatic structural fragments accumulate in marsh soils, indicating a relatively high degree of organic matter stabilization and resistance to biodegradation.

One of the most important problems of cryopedology is the interaction of pedogenic processes with the processes that form the structure of the uppermost layers of the near‐surface permafrost. The thickness, structure, spatial variability, and other features are responsible for the reaction of the soil‐permafrost system to the bioclimatic fluctuations as well as the contemporary anthropogenic pressure. Together the soil profile and the upper layers of permafrost form the natural body of the “soil–cryogenic complex,” which is the result of simultaneous late Pleistocene–Holocene soil and permafrost coevolution. Pedogenic and cryogenic processes together form organic‐accumulative horizons above the permafrost table that have often been described in the profiles of Cryosols in different regions of Arctic. The multiannual dynamics of summer thawing depth determine the involvement of the material of these shielding horizons into the zone of active modern pedogenesis or its exclusion from it in case of their frozen state. Soil surface microrelief, complexity of the vegetation, and spatial differences of thermal properties of the suprapermafrost soil horizons and the transient layer of permafrost are responsible for the complicated pattern of permafrost table microrelief. Thus, the long‐term study of cryogenic soils that are developed on the close underlying permafrost provides improved understanding of the natural‐historical body—soil‐cryogenic complex.

The study of microbial complexes in organo-accumulative horizons of Antarctic soils (Cryosols, Leptosols) at the Larsemann Hills and Schirmacher oases and on King George Island has been carried out by the fouling glass method. This method allows one to study the taxonomic composition of microorganisms, features of their morphology, inter-organism interactions, and spatial organization of the complex of microorganisms, as well as to simulate the processes of colonization of mineral surfaces. The investigated microbial complexes can be subdivided into four groups with respect to dominant microorganisms: (1) diverse microbial complexes of King George Island with a considerable portion of diatoms among algae and with a predominance of mycelium in the fungal biomass; (2) complexes of lichen–moss, moss, and algal–moss associations in lake basins with a greater proportion of eukaryotic and coccoid cyanobacteria and with mycelium and sporous forms of micromycetes; (3) complexes of moss and algal–moss associations in the bottoms of wet valleys with a higher proportion of filamentous cyanobacteria and with the absence of fungi, or their presence in the form of short chains of chlamydospores; and (4) hypolithic microbial complexes of rock baths in dry rocky habitats, where the fouling of glasses did not take place. The microbial complexes in different glass samples taken in February–March in different years proved to be at different stages of development. Microscopic mycelium of fungi was not abundant in all algae and moss associations; in some, it was practically absent. Among algae, not cyanobacteria, but eukaryotic algae dominated in a number of habitats: diatoms, green algae, and streptophytes. The totality of the complex features indicated the extremity of the habitat: one morphotype of melanized fungal mycelium dominated in a particular sample; there was no diversity of spore forms, which indirectly indicates a low taxonomic diversity of fungi; multiple chlamydospore formation and microcycles of development were common. Among cyanobacteria, brown and reddish coloration was often found, and the formation of biofilms on glasses was limited to microcolonies, while algal biofilms abundantly covered the soil of the studied horizons. Apparently, extended biofilms were formed over time exceeding the exposure time of the glasses. Hypolithic communities did not colonize new habitats (glasses) for several years of exposure, unlike the bottoms of hydromorphic valleys and lake basins in oases (glasses overgrown in a year) and King George Island (glasses overgrown in 10 days).

Cryosols of the Antarctic maritime area are much different from the continental ones. The relatively moderate climate conditions in Maritime Antarctica and a strong interaction between the biotic and abiotic environment are drivers for more intensive soil formation processes than in the continental regions. Soil formation studies from the Maritime Antarctica are, however, rather rare. Therefore, micromorphological investigations on polar soils can contribute to more comprehensive information on soil genesis in Antarctica. In this study, we applied the micromorphological study of thin sections from soil micromonoliths to assess the intensity and trends of the pedogenic processes in selected soils from two adjacent islands of the South-Shetland archipelago: King George Island and Livingston Island. The results obtained show that regional lithology and the origin of the incoming organic matter mainly determine the micromorphological structure of the local soils. Soil matrix micromorphological properties and features (mineralogical content, weathering stage and even partly grain-size distribution) are mainly defined by pyroclastic particles due to recent and ancient volcanic eruptions. The presence of rounded grains and aggregated mineral particles is the evidence of marine origin of the sediments. Ornithogenic soils show the clear evidence of the organic plasma formation and mineral particles aggregation via the zoogenic organic substances provided by penguins which is a unique specifics of the maritime Antarctic soils.

A specific group of diverse marsh soils forming on sea coasts in the permafrost zone is proposed to be included into the Russian soil classification system. These soils are affected both by cryogenic and sea processes. At present, there are several regional classifications of marsh soils forming in the European north and Far East of Russia and in northern Europe. We have developed a classification scheme for these soils at four higher taxonomic levels (from soil trunks to soil subtypes) of the Russian soil classification system using the data of soil studies on the accumulative seashores in the eastern sector of Russian Arctic. The studied soils are preliminary named as Thalassosols. According to the proposed scheme, they are categorized within three soil trunks, for which new orders are introduced. The order of initial marsh soils is suggested for the trunk of initial pedogenesis. In the trunk of organogenic soils, marsh soils can be separated at the type level within the newly proposed order of allochthonous organic soils. A new order of marsh soils is also suggested for the trunk of synlithogenic soils. Approaches to further subdivision of marsh soils at the lower (type and subtype) levels of the Russian soil classification system are discussed. A new symbol (؉) is suggested to single out the soil layers and horizons of synlithogenic marsh soils. Specific diagnostic features of the profiles of marsh soils in the permafrost zone are related to the shallow embedding by permafrost and to the activity of cryogenic processes; these soils also have specific features related to soil salinization on seashores against the background of the activity of cryogenesis and soil waterlogging.

Thalassosols developing on the accumulative coasts of the East Siberian Sea include initial soils of regularly flooded tidal flats with sparse vegetation, episodically flooded marsh soils with different degrees of salinization, and maritime soils that are morphologically close to the zonal soils but are affected by salts transferred by wind with seawater drops and organomineral matter from the non-vegetated seashores. Weakly developed marsh soils have the initial features and structure of the marine sediments combined with the processes of salinization; sulfate reduction; gleyzation; cryogenic mass exchange; as well as the transfer, accumulation, and weak biochemical transformation of the raw organic matter. Soils with different degrees of salinization are formed on tidal marshes and are characterized by some redistribution of salts in the soil profile with weak accumulation of salts in the uppermost organic horizons and in the suprapermafrost layers along with pronounced sulfate reduction. Slightly saline organogenic and peaty gleyic soils predominate in the areas of sedge marshes. The majority of studied marsh soils form under the conditions of distinct cryogenic polygonal microtopography, waterlogging, and relatively shallow permafrost.

Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.

The role of ornithogenic factor in the formation of soils and soil cover patterns in continental and maritime Antarctica is considered. The results of long-term soil studies at key sites in coastal oases of East Antarctica (Larsemann Hills, the Haswell Islands) and on the Subantarctic islands (King George Island, Livingston Island, the Argentine Islands) are summarized. The influence of the penguin rookeries on the morphology and physicochemical properties of soils is shown. These rookeries determine the vast spatial zones of biogeochemical influence on the environment around themselves. Special attention is paid to the phenomenon of ornithochory, which is maintained by the flying seabirds (skuas, albatrosses, terns, petrels, etc.) and is manifested in redistribution of vegetation, soil material, and meso- and microbiota to the areas that were previously free of vegetation and soil cover (periglacial areas, fresh moraines, rocky outcrops, etc.).

Изучение более чем 40 профилей криогенных почв на четырёх ключевых участках в различных районах криолитозоны показало, что процессы криогенного массообмена, проявляющиеся в профилях (криотурбации, пучение, пятнообразование, мерзлотная солифлюкция в т.ч., в сочетании с флювиальными процессами), способны приводить к миграции и аккумуляции различных локальных и глобальных загрязнителей (нефтепродуктов, подвижных форм тяжелых металлов, ПАУ, техногенных радионуклидов и пр.) в срединных и надмерзлотных горизонтах. Установлена необходимость всестороннего и полнопрофильного аналитического исследования мерзлотных почв с морфологически выраженными процессами криогенного массообмена, особенно при характеристике экологического состояния почв, подверженных в настоящее время (или подвергавшихся в прошлом) антропогенному воздействию.

The warming and an increase in the amount of solid precipitation, which became apparent in North Yakutia on the threshold of the 21st century, have led to an increase of soil temperature in winter season and of the permafrost. The heat fluxes measured in the taiga soil on the Kolyma Lowland reveal an imbalance in the annual heat gain and loss in the cryogenic ecosystem amounting to 26.3–56.1% of the incoming energy. An increase in the summer air temperatures of the 2000th caused a universal increase in the depth of seasonal soil thawing. After the drop in high summer temperatures, the active layer thickness (ALT) either continued to grow or stabilized at higher levels in the watershed ecosystems of the Kolyma Lowland; however, ALT returned to its initial values in the tundra of the Yana-Indigirka Lowland. As for the floodplain landscapes, ALT increased near-linearly over the 24 years of monitoring. The waterlogged tundra and taiga soils as well as the upland gleyzem of the Bykovsky Peninsula differed only by a temporary increase in the thawing depth. The degree of the soil and permafrost thermal regime transformation tends to increase from west to east, fitting the heterogeneity of climate changes.

Data on the morphology and major physical and chemical properties of 130 pedons sampled in the ice-free area of the Fildes Peninsula and adjacent Ardley Island (King George Island, West Antarctica) are analyzed, and the soil-geomorphological map of the surveyed area on the scale of 1:10 000 is presented. The soils have been classified according to the WRB (2014/2015) system. The map provides information on the soil cover patterns in relation to geomorphic elements and also reflects the degree of anthropogenic load on the studied territory. Nearly half (42.9%) of the total area is covered by different subgroups of Cryosols. Flat watersheds are mainly occupied by Protic Arenosols (Turbic) (22.9%). Leptosols are mainly represented by the Lithic (Ochric) subgroup covering 13.8% of the area. Fluvisols are locally developed in the tidal zone (3.3% of the total area) and are represented by the Tidalic (Skeletic) subgroup. The unique area of Fibric Cryic Histosol (0.02%) is separately delineated. Various Hyperskeletic Technosols (Toxic, Transportic, and Urbic) are formed under the influence of human loads and cover about 0.9% of the Fildes Peninsula and Ardley Island. The map as the main result of the study can be used for monitoring and forecasting the environmental changes of soil cover pattern under the global climate change and local anthropogenic impact.