Строение верхней части криолитозоны и рельеф северо-востока Западной Сибири обусловлены изменением природной обстановки в позднем неоплейстоцене и голоцене. В 2016–2021 гг. изучены разрезы отложений на разных элементах рельефа III озерно-аллювиальной равнины Пур-Тазовского междуречья – увалах и термокарстово-эрозионных ложбинах. В строении верхней части равнины выделены каргинско-сартанские аллювиальные, озерные, склоновые отложения и голоценовые торфяники. На основе стратиграфии и новых геохронологических данных на Пур-Тазовском междуречье выявлены последствия активизации неотектонических процессов в сартанский период и влияния климатических факторов на дифференциацию аккумулятивных и денудационных процессов в голоцене. The structure of the upper part of permafrost and the topographic features in the northeast of Western Siberia were shaped by changes in the natural environment in the Late Pleistocene and Holocene. In 2016–2021, sections of different landforms – ridges and thermokarst-erosional hollows – were studied within the third lacustrine-alluvial plain of the Pur–Taz interfluve. The upper part of the plain includes the Kargin–Sartan alluvial, lacustrine, and slope sediments and Holocene peatlands. Based on the stratigraphy and new geochronological data on the Pur–Taz interfluve, the consequences of the activation of neotectonic processes in the Sartan period and the influence of climatic factors on the differentiation of accumulative and denudation processes in the Holocene were identified.

Link for citation: Butakov V.I., Slagoda E.A., Zavatsky M.D., Ivanov V.I. Gas composition and microorganisms of ground ice in Russian Arctic. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 63-75. In Rus. Relevance. The increase in the concentration of greenhouse gases in the atmosphere is a fundamental problem on a planetary scale. The source of greenhouse gases in the subsurface horizon of soil can be both deep deposits of hydrocarbons and organic matter processed by microorganisms during the thawing of the ice-rich soil. To determine the source of the gas it is necessary to examine both its quantity and composition and the microorganism content in the subsurface ice. Taking into account the dynamic development of the energy complex in the north of Western Siberia it is necessary to take into account the geotechnical risks associated with the release of greenhouse gases from frozen deposits. Purpose: to study the composition and identify the sources of greenhouse gases in the ice and the ice-rich soil on account of the ice formation conditions and the microorganism content. Objects: ice wedge, hydrogenic and segregational genesis of ice, ice-rich soil of northern Western Siberia and Central Yakutia, collected by expeditions Earth Cryosphere Institute, Tyumen scientific center SB RAS in 2011–2021. Methods of research and interpretation of chemical composition. The structure of frozen deposits has been investigated by cryolitological methods. The monoliths of the ice and the frozen deposits were stored at –18 °C. Gas was extracted from the monoliths with the determination of volume fraction by thermovacuum degassing method. The composition of gases is determined by gas chromatography. Normalization of the gas composition with solubility values in water was carried out. Volume fractions of gas in free and dissolved forms was calculated. The data processing were implemented by means of «Geochem Anomaly» program. Cultivated psychrophilic microorganisms were studied by seeding on nutrient media; the total number of microorganisms was determined by epifluorescent microscopy. Results. The contents of N2 (74,9–87,8 %), O2 (11,7–20,3 %), CO2 (0,01–3,28 %), CH4 (0,003–7, 35 %), H2 (0,001–0,035 %) and hydrocarbons with an atom content from 2 to 6 (2,0×10–5–2,8×10–3 %) are determined in ice and ice-rich soil. The value of N2 and O2 in the gas composition of ice is close to atmospheric air. The ice has wide variations in gas saturation (1,1–21,1 %), CH4 and CO2 content. The freezing of gas-saturated solution occurred for the ice formation, part of the air was in a free form (from 30 to 75 %). Calculated indexes CH4/(C2H6+C3H8) and C2H6/C2H4 indicate biogenic hydrocarbon genesis. The composition of gas bubbles is recalculated for the volume of the entire sample: CH4 content is insignificant in ice wedge, closed-cavity ice and icing (averages 51, 81 and 1 ppmV, respectively). The low amounts of CH4 could be produced by forming these types of ice from the sediments of the active layer, as the dependence of the gas composition on the peat element amount is established. CH4, CO2 and H2 contents increased in samples with peat elements. In interbedding ice the CH4 content is high (216 ppmV). CO2 (up to 3007 ppmV) was accumulated in the texturing ice, and hydrogenic wedge-shaped ice showed high levels of CH4 (up to 4032 ppmV) as the ice was frozen in an enclosed volume. The ice of peat mound has a maximum content of CH4 (15545 ppmV) and high CO2 (2466 ppmV); inclosing sediments flooded with marginal-marine waters are the source of high values of CH4 and CO2. The cultivated psychrophilic microorganisms were identified in the surface ice, and their maximum quantities were identified in segregated formations – up to 1680 KOU/ml, in textural ice – up to 1032 KOU/ml. High concentrations of greenhouse gases are found in frozen peat – CO2 (1075 ppmV), H2 (9 ppmV), CH4 (262 ppmV) and other hydrocarbons due to activity of microorganisms, which results in accumulation of these gases. High gas saturation and CH4 and CO2 levels indicate the formation of gaseous composition by both aerobic and anaerobic microorganisms.

The permafrost properties and cryostructure of Holocene peatlands and underlying the Pre-Holocene deposits within Pur-Taz interfluve in the Northern West Siberia were studied. The cryolithological description, particle size, botanical compositions based on plant macro-fossils, and radiocarbon age from 8500 +/- 240 cal BC to 1810 +/- 150 cal AD were defined. The polygonal peatlands were formed in lacustrine-bog basins. The "arboreal" horizon at the bottom of the peat, which is characteristic of Northern West Siberia, was identified. This "arboreal" horizon dates to the Boreal and Atlantic periods of the Holocene - 8500 +/- 240 cal BC and 7390 +/- 210 cal BC, which explains the occurrence of forest tundra in the area of typical modern tundra during the Holocene Climatic Optimum. The vegetation composition of peat-forming plants, the ash content, and the decomposition degree of organic matter were controlled by changing natural conditions and dynamics of peat accumulation during the Holocene: flooding and burial of woody vegetation, overgrowing and eutrophication of water bodies, the gradual accumulation of peat and syngenetic ice-wedge polygon formation, peat accumulation slowing caused by drainage of drained lake basin surface. Organic frost boils on the peatland surface indicate modern deepening of the permafrost Table and are related to an increase of the microorganism activity in the thawed, poorly decomposed peat. The peat accumulation rate was about 1 mm per year. A 2-m peat layer containing ground ice has accumulated over 2500 years. The purpose of the present work is study of the history of the vegetation on the northern limits of treeline. Examination of the peat, macrofossil, decomposition degree, and ash content history of a peat sections on the Pur-Taz Interfluve in North-Western Siberia, provides a long-term view of vegetation dynamics, peatland change, and climate history during the Holocene at the Arctic treeline.

The species distribution of plants, phytocenoses, and biotopes in the peatlands of the southern tundra is necessary for the reconstruction of natural landscapes and ecological conditions in the Holocene. Changes in the floristic composition, degree of decomposition, ash content, and radiocarbon age of peat have been determined in the peat bogs of the Tazovsky district of the Yamal-Nenets Autonomous Okrug. It has been established that the diversity of vegetation during the period of peat formation depended both on global climatic fluctuations in the Holocene and on local environmental conditions that determine the type of plant nutrition in khasyreys - their hypsometric position, watering and dryness. Keywords: PEAT, FLORISTIC COMPOSITION, ENVIRONMENTAL CONDITIONS, HOLOCENE, WESTERN SIBERIA

Heterogeneous ice wedges were studied within the peatland of the drained lake on the Pur‐Taz interfluve (67°20′14.8″, 078°55′47.1″, Northwest Siberia). The elements of the ice‐wedge structure were identified: young ice wedge, shoulders, selvages, closed‐cavity ices, and ice lenses in a peatland. Different genetic types of ice (ice vein, congelation ice, and segregated ice) were revealed by analyzing the elements of the ice‐wedge structure under polarized light and analyzing their chemical compositions. Genetic types of the ice indicate the different mechanisms of ice‐wedge formation. The ice vein forms due to fast bilateral freezing of primarily meltwater in a thermal contraction crack. The congelation ice forms due to the slow freezing of free water that has accumulated into a thermokarst cavity. The segregated ice forms due to pore water migration to the freezing zone. The elements of the ice‐wedge structure have variable stable isotope values (δ18O from −13.5‰ to −21.9‰ and δD from −87.7‰ to −154.6‰). The high range of deuterium excess values (13.8‰ to 32‰) indicates fractionation at condensation. The mean winter paleotemperature calculated using Vasil’chuk’s equations for the ice‐wedge pats formed by the ice veins varied in the range of −18 to −22°C, which is not very different from current values and is consistent with the isotopic data of ice wedges from nearby regions of Northwest Siberia. The paleotemperature average error can equal 4.5°C if we ignore the data on the ice petrographic analysis. The error depends on where and how the ice wedges are sampled, because of varying genetic types within the ground ice. This could lead to different palaeoclimatological interpretations.

The texture, structure, ionic and trace element composition of samples of fast (coastal-sea) and lake ice collected in 2014 in the area of Cape Marre-Sale (the North-Western Siberia) were analyzed. The following main types of the ice structure were identified in ice sections: firn ice with randomly oriented small crystals; lake large- and small-crystalline bubble ice; layered fast sea ice with small isometric and vertically elongated crystals. The upper part of the lake ice is formed by recrystallized snow containing marine aerosols and lake water. The coefficient of involvement of the main ions from the solution during the ice formation varies for lake ice from 0.02 to 1.51, for sea ice - from 0.10 to 0.23, and for coastal-marine - from 0.03 to 0.04. The difference in the degree of ion involvement into the lake ice is related to the sources of components entering the process of formation of firn and large ice crystals from lake water. Coastal sea ice has high concentrations of trace elements relative to the darks of sea waters. The income of trace elements into the coastal sea ice is probably determined by continental runoff. It is established that the mineralization of seasonal ice increases with a decrease in the size of crystals. The dependence of the values of the Europium anomaly on the rate of ice formation was revealed. The Europium anomaly in coastal sea ice is inherited from seawater, and the upper part of lake ice is inherited from precipitation.

The upper part of the subsurface component of the Earth’s cryosphere—polygonal peatlands—are considered in this paper. The polygonal peatlands are widespread in the cryolithozone in northwestern Siberia. When the upper permafrost layer thaws under the influence of climatic fluctuations, the ice-bearing transition and intermediate layers in the polygonal peatlands serve as a buffer zone. Therefore, the identification of these layers is a crucial task. The specific features of the layers, their relationship with ice of various origins, and the properties of peat have been determined. The differences in the structure of the intermediate layer, associated with polygonal microrelief of the surface, have been revealed. Thawing of the transitional layer against the background of modern warming has been recorded on the basis of monitoring of a seasonally thawed layer. To identify the transitional and intermediate layers, the indicators—the cryogenic structure, degree of preservation, color, water content, and density of peat—have been determined.

В 2021 г. продолжен мониторинг глубины сезонного протаивания, температуры многолетнемерзлых пород, активности криогенных процессов, связанных с вытаиванием подземных льдов, и изменений, происходящих с полигональными торфяниками на полуострове Ямал, севере Пур-Тазовского междуречья и Гыданского полуострова. Представлены основные результаты исследований.

The relevance. The greenhouse effect is often associated with methane and carbon dioxide emission from the thawing gas-saturated icy deposits. The relationship between the increase in concentrations of greenhouse gases in the atmosphere and their content in underground ice and frozen deposits has not been sufficiently studied. Different and incomparable methods of gas sampling from frozen deposits and ice are used to assess the content of gases in sediments and ice, the volume of gases entering the atmosphere. When generalizing the data on carbon emissions in the Arctic zone, it is necessary to take into account both the methods of determining the content and composition of gases and the different chemical composition, the presence of organic and mineral inclusions in genetic types of underground ice. The aim of the research is to determine the results of different methods of gas sampling from ice and to establish the relationship between the content and composition of gases in common genetic types of ground ice. Objects: genesis types of ice (segregated, closed-cavity, and ice wedge), icy frozen deposits of the north of Western Siberia: on the Bely island, on Western Yamal, on the north of Gydan and the Pur-Taz interfiuve, collected in expeditions of the Earth Cryosphere Institute, Tyumen scientific center SB RAS in 2014-2019. Research methods and interpretation of chemical composition. The thermal vacuum degassing method and the "headspace" method were used for gas extraction from frozen monoliths and ice. The thermal vacuum degassing method in laboratory conditions with the determination of the gas volume in the ice sample was used as a reference. The method of gas chromatography was applied to determine the composition of atmospheric and greenhouse gases. Gas content in ice and gas content in frozen peat that contains gas in the atmosphere, and the values of the gas solubility in water were compared. The correlation analysis of the gas content in common types of underground ice, as well as frozen peat, was carried out. Results. It was established that gas entrapped in ground ice and frozen peat was similar to atmospheric gas in terms of the relative content of nitrogen and oxygen. It was found out the large variations in methane content from 4 to 1,7 - 10(4) ppmV and carbon dioxide from 7 to 2,7 - 10(3) ppmV in samples are associated with different conditions for production and accumulation of greenhouse gases in the permafrost. The prevalence of carbon dioxide content over methane in segregated ice and ice wedge was established, and maximum methane concentrations (from 1,1 - 10(3) to 1,7 - 10(4) ppmV) in segregated-migration ice of heaving mound and wedge-shaped ice. An excess of methane in the near-surface segregated-migration ice is associated with its accumulation in thawed talik deposits and subsequent ice formation during freezing in a closed system. High concentrations of carbon dioxide (up to 1,1 -10(3) ppmV) and methane (up to 222 ppmV) in segregated ice in peat were found; their source is organic matter degradation under variable aerobic and anaerobic conditions under the action of bacteria. As a result, the peatlands are a significant source of carbon dioxide emissions into the atmosphere. Assessing reproducibility and comparability of the methods of thermal vacuum degassing and "headspace" was carried out in the study of ice and frozen sediments in the cross section of peat bog in the area of the village Gaz-Sale. It was found that methane concentrations during testing by the "headspace" method are overestimated by 3-70 times in comparison with the values determined by the method of thermal vacuum degassing. This is due to the low solubility of methane and its predominance in bubbles, while carbon dioxide and some oxygen remain dissolved in water and do not pass into the gas sample. Consequently, the data on the gas content determined by the "headspace" method is insufficient to estimate the volumes of greenhouse gas emissions, since these values characterize the qualitative composition of the gas in the bubbles. Thermal vacuum degassing method allows calculating and estimating the volumes of gas receipts from thawing permafrost.

The advantages and limitations of the petrography method and the relevance of its use for the study of natural ice are reviewed in the present work. The petrographic method of ground ice study is often used for solving paleogeographic issues. The petrofabric analysis of ground ice is not only useful for descriptive purposes but, like the study of cryostructures, helps to infer growth processes and conditions. Different types of natural ice have specific features that can help us to determine ice genesis. Surface ice, such as glacier ice is often presented by foliation formed by large crystals (50-60 mm); lake ice is characterised by the upper zone of small (6 mm x 3 mm) dendritic and equigranular crystals, which change with increasing depth to large (may exceed 200 mm) columnar and prismatic crystals; segregated ice is composed by crystals forming foliation. Ground ice, such as ice wedge is presented by vertical-band appearance and small crystals (2-2.5 mm); closed-cavity ice is often distinguished by radial-ray appearance produced by elongated ice crystals; injection ice is composed by anhedral crystals, showing the movement of water; snowbank ice is presented by a high concentration of circular bubbles and small (0.1-1 mm) equigranular crystals; icing is described by foliation and mostly columnar crystals. Identification of the origin of ground ice is a complicated task for geocryology because it is difficult to distinguish different types of ground ice based on only visual explorations. The simplest way to get an ice texture pattern is by using polarized light. Distinctions between genetic types of ground ice are not always made in studies, and that can produce erroneous inferences. Petrography studies of an ice object are helpful to clarify the data interpretation, e.g., of isotopic analyses. It is particularly relevant for heterogeneous ice wedges’ study.

Updated long-term series of average values of climatic parameters included in the equation of radiation balance were compiled for the warm and cold half-year periods to clarify the regional climate change in the north of Western Siberia.The initial data were time series of the values measured from 1966 to 2017 for the following parameters: total solar radiation, air and surface temperatures, cloudiness, and elasticity of water vapor.Surfaces of the spatial distribution of the listed climatic parameters and radiation balance in the north of Western Siberia (64°-74° N and 64°-88° E) were constructed on a 1×1° grid.The main calculations were performed using the Mathcad program; data visualization was implemented in the QGIS program.Climatic parameters increase uniformly from north to south in the warm period.The calculated parameters vary unevenly in the region in the cold period.Total radiation, cloud cover, and radiation balance decrease from north to south; air and surface temperatures and water vapor elasticityfrom west to east.The modeling results correspond to the current climate characteristics in the north of Western Siberia.K e y w o r d s : climate, climatic parameters, air temperature, solar radiation, Western Siberia.

Remote sensing methods make it possible to evaluate the reaction of the cryolithozone and tundra landscapes in hard-to-reach Arctic areas based on the indicators of modern climate changes. In 2016–2019, numerous organic frost boils were discovered on the peatland surfaces of drained lakes in the southern tundra of the Pur-Taz interfluve in the northern part of West Siberia and studied. It is established that the formation of frost boils caused by organic mass injections occurs in the summertime and that they indicate local deepening of seasonal thawing. Frost boils emerging at peatlands in summertime was identified after analysis of UAV survey in 2019. Local deepening of seasonal thaw layer on polygonal peatlands is evidence of permafrost reaction to global warming.

Structure of arctic peatlands with massive ice and structure-forming ice were studied in drained lake ("khasyrey") of the Pur-Taz interfluves (the north of West Siberia). The period of accumulation of two-meter thickness of the peat was established to be changed from 8413 +/- 90 to 897 +/- 90 years BR Composition of the peat deposits is represented by Betula nana, Sphagnum sp., Vaccinium oxycoccos, Eriophorum sp., Equiseturn sp. The massive ice is represented by ice wedges with large shoulders and young ice wedges. The central part of the ice wedge is composed by recrystallized crystals of ice veins. Melting zones (elongated crystals of segregated ice and closed-cavity ice) were found in the shoulders of the ice wedge and in the upper part of the young ice wedge. Young ice wedges in the central and lateral parts the main wedge have a similar structure in the cross-section, but they are built by different genetic types of ice: the ice veins or closed-cavity ice with segregated ice. Ice-rich peat contains different types of ice inclusions and subhorizontal ice belts and ice lenses. Ice lenses in the peat can be formed by the segregated ice and/or infiltrated-segregated ice. The hydrochemical composition of the ice wedges, ice lenses, surface water samples and the aqueous extract from peat was analyzed. Hydrochemical analysis did show that polygonal-core ice has basically similar composition with the present-day atmospheric precipitation and surface waters of the polygonal bath; in the area of the shoulder - the composition is intermediate between the ground waters of peat and the central part of the vein. The hydrochemical composition of the ice lenses is similar to the composition of the lake water and peat underlying the active layer. The methane concentrations and its distribution within the ice wedges, peat and lens ice were determined. The closed-cavity ice doesn't contain methane; the ice wedges with ice veins have minimal methane concentrations; large ice lenses have differentiation of methane concentrations. High concentrations of methane are typical for the frozen peat with inclusions of closed-cavity ice in the uppermost part of permafrost layer; the maximum methane concentration was determined inside the peat with ice lenses. The heterogeneous ices inside the ice wedges, distribution of hydrochemical compounds and methane distribution were conditioned by dynamics of the melting depth during the peatland formation under changing climate of the Holocene in the Arctic.

Structure of arctic peatlands with massive ice and structure-forming ice were studied in drained lake («khasyrey») of the Pur-Taz interfluves (the north of West Siberia). The period of accumulation of two-meter thickness of the peat was established to be changed from 8413±90 to 897±90 years BP. Composition of the peat deposits is represented by Betula nana, Sphagnum sp., Vaccinium oxycoccos, Eriophorum sp., Equisetum sp. The massive ice is represented by ice wedges with large shoulders and young ice wedges. The central part of the ice wedge is composed by recrystallized crystals of ice veins. Melting zones (elongated crystals of segregated ice and closed-cavity ice) were found in the shoulders of the ice wedge and in the upper part of the young ice wedge. Young ice wedges in the central and lateral parts the main wedge have a similar structure in the cross-section, but they are built by different genetic types of ice: the ice veins or closed-cavity ice with segregated ice. Ice-rich peat contains different types of ice inclusions and subhorizontal ice belts and ice lenses. Ice lenses in the peat can be formed by the segregated ice and/or infiltrated-segregated ice. The hydrochemical composition of the ice wedges, ice lenses, surface water samples and the aqueous extract from peat was analyzed. Hydrochemical analysis did show that polygonal-core ice has basically similar composition with the present-day atmospheric precipitation and surface waters of the polygonal bath; in the area of the shoulder – the composition is intermediate between the ground waters of peat and the central part of the vein. The hydrochemical composition of the ice lenses is similar to the composition of the lake water and peat underlying the active layer. The methane concentrations and its distribution within the ice wedges, peat and lens ice were determined. The closed-cavity ice doesn’t contain methane; the ice wedges with ice veins have minimal methane concentrations; large ice lenses have differentiation of methane concentrations. High concentrations of methane are typical for the frozen peat with inclusions of closed-cavity ice in the uppermost part of permafrost layer; the maximum methane concentration was determined inside the peat with ice lenses. The heterogeneous ices inside the ice wedges, distribution of hydrochemical compounds and methane distribution were conditioned by dynamics of the melting depth during the peatland formation under changing climate of the Holocene in the Arctic.

Relevance of the research. Information on composition, ice content and geochemical characteristics of frozen rocks is necessary for exploration of oil and gas condensate fields of Yamal, Gydan and Taimyr. Among the factors determining the tundra landscapes ecology of the cryolithozone, underground ice and their melting have great importance. The hydrochemical composition and rare-earth elements content in syngenetic ice wedge retain the information on the moisture sources and conditions of their formation. The main ions correlation and rare-earth elements distribution in the ice composition can be used to estimate the influence of such natural factors as precipitation, sea and volcanic aerosols and anthropogenic pollution. The main aim of the research is to identify chemical elements sources and to assess the impact of the ice type on hydrochemical composition and rare-earth elements distribution in different genetic types of ice - wedge, seasonal and firn ice. Objects: ice wedge, sediments rocks, seasonal ice, surface water, taken in expeditions Earth Cryosphere Institute, Tyumen scientific centre SB RAS in 2009-2014. Methods of chemical research: inductively coupled plasma mass spectrometry, atomic absorption spectrometry, emission photometry, chromatography. Results. It is established that marine and continental aerosols influenced the chemical composition of ice wedge studied in the coastal zone of the key areas of Belyj island, Sibiryakova island, Western Yamal and Western Taimyr. Fresh and ultrafresh syngenetic ice wedge is formed by freezing melt water, which contains snow-sorbed sea aerosols - suspended in the atmosphere solid and liquid particles. Ice wedge in the lake Sokhonto area long-distanced from the sea has no signs of marine influence according to the main ions content. Ice wedge with mineral inclusions was formed not only due to snow melt water with aerosols of continental origin, but also due to the suprapermafrost water. It was found out that lanthanide content in water-soluble form has increased in comparison with both clark values and the content in the modern surface ice. In the most of examined syngenetic ice wedge the participation of marine aerosols is confirmed taking into account the cerium anomaly. Moreover according to the distribution of rare-earth elements the correlation between light and heavy rare-earth elements typical for ice wedge, equal to 0,9, and correlation between lanthanum and the other lanthanides, equal to 0,2, are observed. Sea ice inherits the mineralization and composition of sea water. Lake ice varies in depth and reflects seasonal changes in hydrochemical composition of ice and increases in concentration of marine aerosols in the snow covering the lake ice. Firn ice of the polar Urals has a very low mineralization, there are no impurities of sea aerosol. The natural mechanism of rare earth elements accumulation in water-soluble form in combination with iron, thorium and yttrium is implemented in ice wedge of the Holocene and Neopleistocene. Melting out ice wedge may lead to the flow of rare-earth elements in the surface water.

In 2016-2017, we have detected numerous organic frost boils on the surface of khasyrey peat plateau in the southern tundra part of Pur-Taz interfluve (the north of West Siberia). They are related to the microrelief depressions in polygons and to the swales between tussocks. Cross-sections, cryogenic structure, properties of peat in active layer (moisture, density, heaving, chemical composition) and peat distribution within the khasyreys were studied. In the active layer, we distinguished soil and vegetation cover, upper and middle solid layers of weakly decomposed peat, lower layer of a well decomposed peat. Under the microrelief depressions, the top of permafrost is lowered, thickness and moisture of decomposed peat is increased due to the recent thawing in comparison to the elevated parts of polygons. In the cross-sections of seasonally thawing peat, we determined injections of organic matter from the lower layer of peat to the surface. We propose the mechanism of organic frost boils formation in peat plateau due to the injections during the summer seasons of 2016-2018 against the increase of a thaw depth without freezing. During the observation period, the amount of frost boils on polygonal peat plateau was found to increase.

В 2018 году продолжены комплексные исследования криолитозоны, начатые в 2016 г. в северо- восточной части Пур-Тазовского междуречья. Проводится мониторинг глубины сезонного протаивания в различных ландшафтных условиях от дренированных водоразделов до полигональных торфяников. На одном из торфяников отслеживаются изменения рельефа за счет вытаивания полигонально-жильного льда, изучается морфология льда и криолитологическогостроениявмещающихотложений. Вовремяполевойкампании 2018 г. заложеныдополнительные площадки мониторинга глубины протаивания. Для изучения детальной пространственной дифференциации глубины протаиванияиопределениятехногенногоиестественноговоздействиянаучасткахсполигонально-жильнымильдами выполнены георадиолокационные исследования. Продолжено сопоставление ботанического состава современной растительности и многолетнемерзлого торфа, изучение почв пятен-медальонов в контуре торфяника. Начаты работы по оценке дефляционного влияния на осадконакопление минеральных пород в пределах торфяника. Started in 2016 complex studies of the cryolithozone in northeastern part of the Pur-Taz interfluve continue in 2018. Seasonal thaw depth in different landscapes from drained watersheds to polygonal peatlands is monitored. On one of the peatlands, the relief changes due to the melting of polygonal-wedge ice are observed, the morphology of ice and the cryolithological structure of the enclosing sediments are studied. During the field campaign of 2018 additional sites for thaw depth monitoring were established. To study the detailed spatial differentiation of thaw depth and to determine technogenic and natural impacts in the areas with polygonal-wedge ice georadar survey was performed. We continued the comparison of modern vegetation botanical composition with a permafrost peat and the study of spot-medallions soil in the peatland was carried on. We carried out the first stage assessment of the deflation impact on the mineral sedimentation within the peatland.