The article presents the results of a comprehensive geochemical monitoring of the underwater gas seep Vostochnoe (the Gulf of Patience, Sea of Okhotsk) in 2022–2025. Based on the analysis of the molecular and isotopic composition (δ13C) of hydrocarbon gases, the distribution of inorganic gases (He, CO₂) and trace elements (Zn, Hg, Cu, Co, Ni, etc.) in bottom sediments, the nature of the fluid system of this feature is characterized for the first time. The composition of gases and sediments of the site is consistent with potential genetic links to the processes feeding the Pugachevsky mud volcano on land, suggesting that the Vostochnoe site may represent its submarine continuation. However, key geochemical indicators (gas dryness coefficient K1, paraversity index K4, helium and mercury contents) suggest possible differences in the discharge mechanism: Vostochnoe is characterized by high thermodynamic maturity of gases, the absence of a typical hydrothermal trace element load, and episodic pulses of deep fluid enriched in helium. Particularly noteworthy is the 2024 anomaly, when a sharp increase in He concentrations (up to 184 ppm) and the appearance of thermogenic methane with δ13С up to −35.6‰ were recorded at several stations, suggesting possible short-term activation of a deep fault. However, these interpretations remain provisional; alternative explanations involving different reservoirs, regional source rocks, or mixing-fractionation effects cannot be excluded without further isotopic and structural studies.

Brief results of oceanological studies in the south-eastern Baltic Sea and Gulf of Finland on cruise 54 of the R/V Akademik Sergey Vavilov (2022) are presented. Hydrological, hydro- and geochemical, hydrobiological, geoecological, geological, and geophysical studies were carried out. New data on the state and dynamics of the Baltic Sea natural complexes under conditions of increasing anthropogenic pressure and climate change were obtained.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070395

Climate-induced changes contribute to the thawing of ice-rich permafrost in the Arctic, which leads to the release of large amounts of organic carbon into the atmosphere in the form of greenhouse gases, mainly carbon dioxide and methane. Ground ice constitutes a considerable volume of the cryogenically sequestered labile dissolved organic carbon (DOC) subjected to fast mineralization upon thawing. In this work, we collected a unique geochemical database of the ground and glacier ice comprising the samples from various geographic locations in the Russian Arctic characterized by a variety of key parameters, including ion composition, carbon-bearing gases (methane and carbon dioxide), bulk biogeochemical indicators, and fluorescent dissolved organic matter (DOM) fractions. Our results show that interaction with solid material—such as sediments, detritus, and vegetation—is likely the overriding process in enrichment of the ground ice in all the dissolved compounds. Terrigenous humic-like dissolved organic matter was predominant in all the analyzed ice samples except for glacier ice from Bolshevik Island (the Severnaya Zemlya archipelago) and pure (with low sediment content) tabular ground ice from western Yamal. The labile protein-like DOM showed no correlation to humic components and was probably linked to microbial abundance in the ground ice. The sum of the fluorophores deconvoluted by PARAFAC strongly correlates to DOC, which proves the potential of using this approach for differentiation of bulk DOC into fractions with various origins and biogeochemical behaviors. The pure tabular ground ice samples exhibit the highest rate of fresh easily degradable DOM in the bulk DOC, which may be responsible for the amplification of permafrost organic matter decomposition upon thawing.

The study of massive ices is of interest both for the purposes of paleogeographic reconstructions, and for solving engineering and geocryological problems. Despite the widespread distribution of massive ice beds in the cryolithozone, the problem of spatial identification of them and mapping has not yet been resolved, which is mainly due to the difficulty of determining and understanding the processes of their formation. The paper presents the results of studying the methane content as a genetic trait in massive ice beds along the coast of Eastern Chukotka. In 2016-2022, our team studied variations in the methane content in 4 massive ice beds and host deposits using the "headspace" method. The CH4 concentration in ice and air bubbles ranged from 1 to 1582 ppmv, which made it possible to suggest the genesis of each bed and compare it with previously proposed hypotheses of their formation based on the earlier made cryolithological and oxygen isotope analyses. The study has confirmed the intra-ground (median methane concentration of 432 ppmv) and buried (2 ppmv) genesis for two beds. For the third one, the issue of its genesis remained debatable, and in the fourth bed, the obtained results have thrown doubt on the previous hypothesis about the intra-ground genesis of ice, since the recorded methane concentration was found to be close to the atmospheric one. Despite the limitations of the "headspace" method shown in the paper, it was manifested as the adequate way for the field studies when transportation of frozen samples to the laboratory is impossible.

The article provides new data on the structure of the Laptev Sea flank of the Gakkel Ridge. The intensive supply of clastic material from the Laptev Sea shelf leads to the development of a thick alluvial fan at the continental rise, which determines the structure of the bottom topography. In the northwestern direction, the influence of the fan decreases and tectonics becomes the main relief-forming factor. The bathymetric survey traced the asymmetrical rift valley of the Gakkel Ridge, the western flank of which is complicated by terraces. The presence of fault structures, bottom subsidence, extensive sediment supply, and the widespread development of subaqueous slump processes indicate the high neotectonic activity of the Laptev Sea flank of the Gakkel Ridge. For the first time in this region, numerous carbonate rocks have been discovered, the authigenic cement of which is represented by magnesian calcite or aragonite with an admixture of terrigenous material. The palynological and micropaleontological analysis of the carbonate rocks indicates the Quaternary formation of authigenic carbonate cement. An important role in the formation of authigenic carbonates was played by diagenetic solutions coming from the sedimentary cover together with methane and oxidation products of gases and organic matter. The authigenic carbonates were precipitated mainly in an isotopic equilibrium with bottom water at a temperature of about 0°C. The negative correlation between 87Sr/86Sr and δ13C indicates the presence of at least two different sources of carbonate-forming solutions.

The article describes the first find of authigenic carbonates on the southern flank of the Gakkel Ridge in the zone of its junction with the Laptev Sea continental margin of the Russian Federation. The samples are represented by dense magnesian calcites and aragonites, including rounded and angular fragments of terrigenous material, as well as microphytoplankton of different ages, spores and pollen of terrestrial and aquatic plants. Elemental and organochemical characteristics indicate the predominance of oxidizing or intermediate between oxidizing and reducing conditions of carbonate crystallization, which may be a consequence of their formation near the bottom surface. The isotopic composition of O, C, and Sr allows us to conclude that the diagenetic carbonates of the Gakkel Ridge were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C, which corresponds to measurements from the ship. A wide range of δ13С (–23.5 до –37.3) indicates that methane was an important, but not the only source of carbon in carbonates. The wide variations in the 87Sr/86Sr (0.70906–0.70933), which correlate with the δ13С values, show that the carbonate-forming fluid was not only modern sea water, but also diagenetic solutions coming from the sedimentary cover together with methane and the products of methane and organic matter oxidation. Intense discharge of heterogeneous methane-bearing fluids may be related to the high modern tectonic activity of the studied region.

Outcrops of the coal-bearing Tankhoi Formation (Oligocene–Pliocene), traced along the southern shore of Lake Baikal, submerge under its Southern Basin, where several hydrate-bearing zones of the focused hydrocarbon fluid discharge have been found. To test the hypothesis that coals of the Tankhoi Formation can be the sources of hydrocarbon gases in these zones, we collected coal samples from the Shakhterskaya Gorka outcrop. Experiment on gas generation from the selected samples was carried out in a special autoclave at a temperature of 90°C for eight months. This paper presents the obtained results, which confirm an important role of the process of gas generation from coals in the formation of fluids in the Kedr mud volcano. The further migration of gases was accompanied by the biodegradation and formation of secondary microbial methane due to CO2 reduction. This was one of the reasons for the carbon isotopic pattern observed in methane (heavier than –50‰ VPDB) and carbon dioxide (positive values) taken from the near-surface sediments and hydrates of the Kedr mud volcano, as well as for the significant enrichment of authigenic siderites in the heavy 13C isotope.

Understanding paleoenvironmental conditions of the permafrost formation allows us to estimate the permafrost carbon pool and its behavior upon thawing in a changing climate. In order to classify different types of ground ice and to reconstruct paleoenvironments, we examined geochemical data of ice wedges (IWs), tabular ground ice (TGI), and lens ice from the eastern coast of the Faddeevsky Peninsula (East Siberian Arctic). We analyzed isotope and ion composition, molecular composition of the gas phase, bulk biogeochemical parameters and dissolved organic matter (DOM) composition in ground ice samples. IWs formed in the Late Pleistocene under the coldest winter conditions and in the Holocene in proximity to the sea. The Holocene IWs have the highest mean d-excess (11–13‰) and a heavier isotope composition by an average of 6‰ compared with the Late Pleistocene IWs. We observe predominance of sea-salt fractions in ion composition of the Holocene IWs, while the Late Pleistocene IW shows enrichment in non-sea-salt component of SO42− (nssSO42−), which is probably associated with mineral leaching of deposits. Higher dissolved organic carbon (DOC) content in the Late Pleistocene IW (to 17.7 mg/L) may indicate more favorable vegetation conditions or lower degree of organic matter mineralization compared to Holocene IWs and TGI. CH4 concentrations were relatively low with a maximum value of 2.27 μmol/L. DOM composition, supposed to record the paleoenvironment of the freezing process, was for the first time tried as a biomarker for paleoenvironmental reconstructions of ground ice formation. Parallel factor (PARAFAC) analysis of EEM (Excitation-Emission matrix) of fluorescent DOM decomposes four components: P1–P3, which are related to allochthonous humic-like constituents, and P4, which is relevant to autochthonous fraction associated with microbial activity. The distribution of fluorescent DOM tracked the variability in both paleoclimate conditions of the IW formation (discriminating the Holocene and the Late Pleistocene IWs) and types of ground ice (IW and TGI), which demonstrates the potential of the used approach.

This paper performs a detailed study of a wide set of organic-geochemical proxies in 15 sediment cores collected from the main basins of Lake Baikal (the northern, the central and the southern) where processes of focused fluid discharge were detected. A variety of studied zones includes sites with gas and hydrothermal seepage, mud volcanoes with or without gas-oil fluid discharge, gas hydrates and authigenic carbonates. The composition of the dispersed organic matter and individual hydrocarbon molecular markers (n-alkanes, dimethyl alkanes, isoprenoids, steranes, terpanes and polycyclic aromatic hydrocarbons) testify to the input from predominantly allochthonous terrestrial and autochthonous microbial and algal sources. The studied sources, maturity and biodegradation parameters of organic matter vary significantly for areas with different fluid discharge. The composition of specific biomarkers including isoprenoids and immature hopanoids reflects the lateral and vertical changes of microbial activity in sediments associated with various environmental conditions. The identified types of terpanes distribution (mature, mixed and immature) correlate well with types of fluid discharge and attest to the development of various methanogenic and methanotrophic microbial communities in sediments. Moreover, the revealed specificity of microbial molecular markers distribution allowed us to suggest the fluid discharge processes in zones where they were not previously detected.

EDITORIAL article Front. Environ. Sci., 13 December 2022Sec. Biogeochemical Dynamics Volume 10 - 2022 | https://doi.org/10.3389/fenvs.2022.1101196

Permafrost thawing leads to mobilization of the vast carbon pool into modern biogeochemical cycling through the enhanced release of dissolved organic matter (DOM) and production of greenhouse gases (CO2 and CH4). In this work, we focus on the study of methane and DOM distribution and genesis in the ground ice samples of thermodenudational exposure in the Central Yamal (Russian Arctic). We propose that the liberation of the ice-trapped CH4 and generation of CO2 by DOM mineralization are the earliest factors of atmospheric greenhouse gases emission as a result of permafrost thawing. The observed enormously “light ” isotope signatures of methane (δ13C < −80‰, δD < −390‰) found in the tabular ground ice units significantly divergent in morphology and localization within the exposuremay be related to subzero (cryogenic) carbonate reduction a as significant factor of the local methane enrichment. DOM is mainly formed (>88%) by biochemically refractory humic acids. Distribution of the labile protein-like DOM reflects the specific features of carbon and nitrogen cycles in the tabular ground ice and ice wedge samples. Tabular ground ice units are shown to be a significant source of methane and high quality organic matter as well as dissolved inorganic nitrogen (DIN). Ice wedges express a high variation in DOM composition and lability.

Driven by rising bottom water temperatures, the thawing of subsea permafrost leads to an increase in fluid flow intensity in shallow marine sediments and results in the emission of methane into the water column. Limiting the release of permafrost-related gas hydrates and permafrost-sequestered methane into the global carbon cycle are of primary importance to the prevention of future Arctic Ocean acidification. Previous studies in the South Kara Sea showed that abundant hydro-acoustic anomalies (gas flares) induced by seafloor gas discharge into the water column occur in water whose depth is >= 20 m. This distribution of gas flares could indicate the outer extent to which continuous permafrost restricts upward fluid flow. This paper reports on a geochemical analysis of a 1.1m long sediment core located in an area of shallow fluid flow off of the Yamal Peninsula coast (South Kara Sea) using high-resolution seismic data. Our results reveal a thin zone of Anaerobic Oxidation of Methane (AOM), a sharp shallow sulfate-methane transition (SMT) located at a sub-bottom depth of 0.3 m, and significant temporal variation in methane discharge confirmed by the pyrite (FeS2) distribution in the core sample. A concave up pore water chloride profile depicts upward fresh/brakish water advection in subsurface sediments. The terrestrial/fresh water genesis of methane from the sampled core is deduced from the stable isotopic signatures (delta C-13 and delta D). We propose two mechanisms for the observed fluid flow: i) convection of thaw water from subsea permafrost; and/or ii) lateral sub-permafrost ground water discharge marking the outer extent of continuous permafrost off of the central Yamal Peninsula coast at (similar to)45m water depth.

Authigenic carbonates are crystallized in subaquatic and subaerial settings at various stages of sedimentary rock formation, and are often found in both ancient and modern deposits. The explanation of their genesis may be problematic. However, in most cases the study of stable isotopes makes it possible to reconstruct the authigenic carbonates crystallization mechanism. The fact of the frequent genetic association of authigenic carbonates with hydrocarbons determines the importance of the development of methods for the reliable identification of their genesis.

We present the results of studies of the methane content in soils of the active layer and underlying permafrost, as well as data on the emission of methane into the atmosphere in the dominant landscapes of typical tundra of the western coast of the Yamal Peninsula. A detailed landscape map of the study area was compiled, the dominant types of landscapes were determined, and vegetation cover was described. We determined that a high methane content is characteristic of the wet landscapes: peat bogs within the floodplains, water tracks, and lake basins. Average values of the methane content in the active layer for such landscapes varied from 2.4 to 3.5 mL (CH4)/kg, with a maximum of 9.0 mL (CH4)/kg. The distribution of methane in studied sections is characterized by an increase in its concentration with depth. This confirms the diffuse mechanism of methane transport in the active layer and emission of methane into the atmosphere. The transition zone of the upper permafrost contains 2.5–5-times more methane than the active layer and may become a significant source of methane during the anticipated permafrost degradation. Significant fluxes of methane into the atmosphere of 2.6 mg (CH4) * m−2 * h−1 are characteristic of the flooded landscapes of peat bogs, water tracks, and lake basins, which occupy approximately 45% of the typical tundra area.

Study of the molecular composition of the dispersed organic matter (OM) in bottom sediments of Lake Baikal was conducted (supported by RSF #19-17-00226). Sediments (11 gravity cores - 28 samples) were collected during research expeditions of the R/V “G.U. Vereschagin” (LIN SB RAS, Irkutsk) in 2016-2018. Variations in composition and ratios of aliphatic and aromatic components reflect changes of OM sources. Most n-alkane profiles show the distinguishable predominance of terrigenous components C27-C31. The highest biodegradation degree and increased content of isoprenoids is detected near the Gorevoy cliff where the active oil discharge was observed. Biogenic hopanes (ββ-hopanes and hopenes) predominate in most samples and diagenetic type of distribution is identified only in sediments with oil inclusions. Steranes are the minor components with ethylcholestanes as the main peaks attesting to the input of land plants. Increased values of perylene and phenanthrene in polycyclic aromatic HCs composition indicate the mixed biogenic-petrogenic nature of OM of the studied Lake Baikal sediments, while the oily samples contain only trace amounts of perylene. The branched 2,7-dimethyl alkanes (m/z 127) have been identified in mudstone samples from the Vendian Marna Formation from the Sayan-adjacent Biryusa area and in Permian and Upper Carboniferous coal-bearing rocks from superdeep well SV-27 (Vilui syneclise) [1]. Their precursors most likely are the analogues of branched methylenated acids detected in lipids of modern bacteria (9,10-methylene hexadecane, 9,10-methylene octadecane, and 11,12-methylene octadecane acids). Decarboxylation of the methylenated acids branched at the second and seventh carbon atoms during diagenesis and catagenesis should have resulted in 2,7-dimethyl alkanes that were detected in all immersed sediments of the southern, central and northern parts of Lake Baikal. Trace amounts of the other poorly studied group of compounds – monoaromatic steroids (MAS) were identified in bottom sediments near the mud volcano Kedr in the southern part of the lake. These structures can be formed during diagenetic transformations of sediments at the contacts of OM with clays (catalyzers) together with the formation of regular steranes and diasteranes (C27-C29). They have been previously detected in apocatagenetic rocks of the East Siberian sedimentary basin (ultradeep hole SV-27 from the Middle Vilyui area of the Vilyui syneclise) [2]. The absence of the main fragmental ion m/z 253 in the analyzed samples points to the migration of methyl alternate from C-17 to C-23 alkyl-chain position and agrees with distribution of the similar structures (m/z 281, 309, 366) in rocks of the hole SV-27. The detected 17-desmethyl-23-methylmonoaromatic steroids appear and exist at high temperatures and pressures and are very thermodynamically stable. Thus, the input of the OM of catagenetic maturity degree to the bottom sediments of Lake Baikal is likely associated with the deep fluid migration and mud volcanic breccia uplift to the surface. References [1] Kashirtsev V.A. et al., 2009. New homologous series of biomarker molecules from Vendian deposits of the Sayan-adjacent Biryusa area. Russian Geology and Geophysics 50, 541–545. [2] Kashirtsev V.A. et al., 2016. New monoaromatic steroids in organic matter of the apocatagenesis zone. Doklady Earth Sciences 469, 815–818.