The heavy metals (Cu, Ni, Zn, As, Pb, and Cd) in 93 bottom sediment samples collected from shelf northwestern Bering Sea were studied due to this area is very important for the fishing and is strategically vital sections of the Northern Sea Route. For the first time in this region the sediment quality indices, ecological and human health risk assessments of metals were determined. The mean Cu, Ni, Zn, Pb, and As contents were 11.32, 13.4, 49.7, 14.54, and 11.4 ppm, respectively. The maximal Cd, Pb and As concentrations were observed on several stations from the Kresta Bay and the Mechigmenskiy Gulf where demonstrated higher values of environmental indicators that could be deal with industrial exploitation of ore deposits or lithogenic factors. Nevertheless, the results of hazard index and carcinogenic risks for all HM from ingestion and dermal pathways indicated a no potential health risk.

Gornostay Bay, located near the city of Vladivostok (Far East of Russia), has long served as a site for the placement and operation of a solid domestic waste landfill. The functioning of the landfill resulted in extensive and complex pollution of the coastal water area. Remediation and closure measures in 2010 were expected to improve the ecological condition of the bay. This study demonstrates the application of biochemical markers of oxidative stress as indicators of metabolic recovery processes in marine invertebrates, using bivalves as a model group. The results demonstrated a time-dependent decrease in the concentrations of potentially toxic elements in mussel tissues and a reduction in oxidative lipid degradation to control levels. These findings indicate an improvement in the quality of the marine environment in the years following the 2010 landfill remediation activities. Based on molecular indicators of oxidative stress and the content of heavy metals in the digestive gland and gills of Crenomytilus grayanus from polluted Gornostay Bay, the study concludes that a gradual restoration of the marine environment has occurred.

The western Aleutian Trench remains one of the least characterized hadal environments with respect to trace metal biogeochemistry. Here we present the first dataset of mercury (Hg) concentrations, Hg fluxes, and sedimentation rates derived from excess 210Pb in three hadal sediment cores collected during a 2024 China-Russia collaborative expedition. Surface sediment Hg concentrations range from 59 to 172 ng g- 1, comparable to other Pacific trench systems. Down-core profiles reveal a strong coupling between Hg and total organic carbon (TOC) in two cores, indicating organic matter as the primary carrier phase, whereas a decoupled Hg-TOC relationship at the trench junction suggests enhanced lithogenic control under dynamic hydrodynamic conditions. Calculated Hg fluxes (15.8-22.7 mu g m-2 yr- 1) exceed global deep-sea averages, with substantially higher values (up to 208 mu g m- 2 yr- 1) at the trench junction, reflecting intensified sedimentation and material focusing. Thermodesorption analysis indicates that Hg predominantly occurs in sulfide-bound and mineral-associated forms. We infer that Hg accumulation in the western Aleutian Trench is governed by the interplay between organic matter deposition, tectonically enhanced sediment focusing, and additional inputs from cold seeps and regional volcanism. Despite elevated fluxes, Hg concentrations remain below thresholds associated with significant ecological risk.

Ferromanganese formations (FMF) are one of the major types of mineral deposits on the Eastern Arctic Shelf; however, there is no consensus on the mechanism of concretion formation and the source of ore and microelements to the FMF. Therefore, it is important to conduct a comprehensive study of the patterns of changes in the composition of FMF as a function of environmental conditions. Four representative ferromanganese formations collected from the shallow semi-enclosed Chaunskaya Bay (East Siberian Sea) were studied by inductively coupled plasma mass-spectrometry and X-ray powder diffraction to determine the origin and correlation of their composition with the regional conditions of sedimentation. The formations are completely composed of an iron X-ray amorphous phase (up to 90-95

In the changing Arctic, permafrost thaw is shifting from gradual to abrupt. Although iron-bound organic carbon (OC-FeR) critically modulates permafrost carbon-climate feedbacks, its decadal-scale variability and response to this regime shift remain poorly constrained. Focusing on the East Siberian Arctic, a hotspot of land-to-ocean permafrost carbon transfer, we established critical linkages between marine sedimentary OC-FeR burial records and terrestrial permafrost-climate dynamics. Results revealed that coastal OC-FeR reservoirs exhibited temporally-distinct responses to permafrost thawing dynamics. During the pre-2000s, the progressive decline in OC-FeR coincided with watershed-scale soil moisture redistribution driven by gradual active-layer deepening, which preferentially retained OC-FeR in permafrost, attenuating its land-to-ocean fluxes. Since 2000s, although abrupt thaw has rapidly mobilized OC, similar to 19% of sedimentary OC remained stabilized as OC-FeR, thus partially decoupling abrupt thaw from immediate permafrost carbon-climate feedbacks. Therefore, this mineralogical buffering mechanism can attenuate the net climate impact of accelerating abrupt thaw across the Northern Hemisphere cryosphere.

The processes that occur with mercury under the ice covering different water areas are among the least studied ones in the global mercury cycle. In the winter of 2016, we measured total and dissolved mercury concentrations in water, total mercury levels in suspended particulate matter, determined phytoplankton species, and measured the main hydrological parameters (water temperature, salinity, chlorophyll a concentration) in the ice-covered Partizanskaya River Estuary (Primorsky Territory, Russia). The data obtained indicate the mercury accumulation by diatoms under the ice during the bloom. We assume that a similar process occurs in the Arctic Ocean, leading to the redistribution of mercury species in water and the accumulation of dissolved gaseous elemental mercury under the ice.

Arctic climate changes have profoundly influenced the polar environmental changes in recent years. The Arctic Oscillation (AO), as a key component of the Arctic climate system’s internal variability, affects the source to sink processes and interactions across the multilayer Arctic system by regulating the land, ocean, sea ice, and atmospheric processes. The East Siberian Arctic Shelf (ESAS) has experienced significant changes in the input, transport, and burial of sedimentary organic carbon (OC) due to climate warming and shifts in the AO phase in recent decades. This study analyzes grain size, total organic carbon (TOC), total nitrogen (TN), and stable carbon isotope (δ13C) in two sediment cores from the ESAS to reconstruct the burial record of OC over the past few decades and examine the response mechanism of sedimentary OC records to regional-scale climate forcing. The results show that the OC in the two sediment cores originates from mixed sources with a dominant terrestrial contribution. In the LV83-28 core from the Laptev Sea, the TOC and TN contents have increased at an accelerated rate since the 1990s, with a noticeable rise in the contribution of terrestrial OC. This trend is linked to an increase in terrigenous input caused by the positive AO phase. Core LV83-39 in the East Siberian Sea could have accumulated more terrestrial OC transported along the continental shelf during the positive AO. This implies that, under the interannual regulation of the AO regime, the input and cross-shelf transport of terrigenous OC in the ESAS showed consistent sedimentary responses. This finding could enhance the understanding of the burial mechanism of sedimentary OC and its environmental response to regional climate change.

This work presents new data on the composition and concentrations of hydrocarbon gases in the upper horizons of bottom sediments of Avacha Bay and the adjacent zone of the Pacific Ocean. The established concentrations of methane and the sums of its homologues are highly variable, from 0.0003 to 120.9385 and from 0.00005 to 0.00753 cm3/kg. Gas anomalies are formed in the sediments of the shallow shelf (Avacha Bay, Russkaya Bay, Vilyuchinskaya Bay and Listvennichnaya Bay) and in the outer shelf and the continental slope at sea depths of 14–800 m and sampling depths of 3–50 cm. The data on the isotopic composition of carbon δ13C–CH4 from –78.1 to –33.4‰ and δ13C–CO2 from –19.8 to –11.1‰ indicate the formation of natural gases of various polygenetic (mixed) origin in the bottom sediments of the region and, with a high probability, their significant influx from the underlying sediments.

The Bering Sea shelf is a transit zone for water masses moving from the Pacific Ocean to the Arctic Ocean. Mercury geochemistry in bottom sediments of the northwestern Bering Sea shelf has been practically unstudied, whereas the Arctic seas are constantly being explored. Hg concentrations ranged from 6 ppb to 65 ppb in the bottom sediments of the study area. Based on the dating of sediment cores, the background concentration was 34 ppb. The concentration of Hg in fine sediment fractions was 60 ppb, in sandy fractions (>63 μm) varied from 17 to 43 μg ppb. In recent decades, a stable increase of mercury fluxes to bottom sediments has been observed. We used the Hg/TOC ratio as an indicator of mercury input to marine waters from natural terrigenous sources.

The results of gas-geochemical and lithogeochemical studies of modern bottom sediments sampled in the South Tatar sedimentary basin (Sea of Japan) during a comprehensive geological and geophysical expedition on the R/V AkademikOparin (OP-54) are presented. Anomalies of hydrocarbon gases (УВГ) and chemical elements in surface bottom sediments were estimated. Sediments hosting hydrocarbons are mainly represented by aleuritic varieties with psammitic (up to 46%) and pelitic (up to 43%) components. The maximum contents of Si, Ti, K, Ca, Sr, Zr, Y are noted in the bottom sediments of coastal shelf zones; the concentrations of S, Ni, Cu, Zn, Pb, V, Fe, Mn, Rb increase in the shelf-bathyal direction. Sediments with anomalous methane contents are significantly enriched in S, Mn, V, Cu, Ni, Zn, Pb. The data obtained allows to suggest the presence of sources of hydrocarbon migration and further consider the prospects for conducting detailed work to assess the oil, gas and gas hydrate content in the southern part of the Tatar Strait.

The paper presents brief results of gas-geochemical and hydrometeorological studies of the outer water area of Peter the Great Bay (Sea of Japan), obtained as a result of a marine expedition study on the R/V Professor Gagarinskiy (cruise 83) in October–November 2022. Areal atmochemical measurements of climatically active gases (CH4, CO2, H2O vapor) and Hg(0) in the near layer of the atmosphere of the outer water area of Peter the Great Bay were performed for the first time. Gas geochemical fields in bottom sediments and water column are detailed. The current position of gas flares within the outer shelf of Posyet Bay is determined. Long-term stations for marine daily monitoring were carried out.

For the first time the grain size, contents of major (Al, Ti, Fe, Mn, Ca, Mg, Na, and K) and trace elements (Mo, Ni, and Cu), total organic carbon, and stable carbon isotope were studied in the sediment cores collected at a water depth of approximately 9500 m from the Kuril-Kamchatka Trench. This study determined the factors of sedimentary environment. The quantitative content and species composition of diatoms were also studied. We have estimated the sedimentation rate based on the excess Pb-210 data. According to age models, the sedimentation rate was similar to 1.64 mm/year. Paleoconstructions were formed on comparing the distribution of chemical and biological parameters in deep-sea basin sediments. The studied sediments were characterized by the high content of the bioproductivity indicators and chemical elements (Fe, Ca, and Cu) corresponding to a period of increased supply of nutrients that stimulated the production of diatoms. Based on the study of chemical indicators and characteristics of nutrient utilization by phytoplankton, a period of outbreak of diatom productivity due to the introduction of volcanic ash into the sediment in the period 1860-1883 was marked. New data will complement existing information and helpful for further understanding of sedimentary geochemical characteristics in this hadal area, and allow us to relate abiotic conditions to productivity.

Thawing Arctic permafrost is releasing massive amounts of terrestrial mercury (Hg) into the Arctic shelf, which is expected to form a Hg sink in sediments. Here we analyzed the coupling roles of terrestrial input and biological processes in varying mineral/organic matrix-related Hg sequestration and deposition on the East Siberian Arctic shelf (ESAS), using Pearson and partial correlation analysis. Results show that the occurrence of Hg in the Laptev Sea under the Lena River-dominated input exhibits strong correlations with the organic carbon (OC) content and sediment specific surface area. This indicates that the prolonged riverine loading processes facilitate Hg sequestration by organic/mineral matrices and these land-derived mineral-OC-Hg complexes remain stable during cross-shelf transportation. By contrast, the comparative samples with coastal erosion-dominated Hg input in the western East Siberian Sea shows limited Hg complexation, primarily due to the absence of regulation by riverine processes and/or the high sedimentation rates. The correlations between Hg and OC source proxies (delta C-13 and lignin) indicate that these matrix-free Hg could be more readily sequestrated by the marine OC, which facilitates its deposition via the biological pump. While unexpectedly low Hg abundance in the Chukchi Sea may indicate that the effective biological scavenging of Hg sequestration could be constrained by insufficient terrestrial Hg input. Our findings of the matrix-related Hg sequestration by mineral and/or OC association in this study may shed light on the biogeochemical cycle of Hg in the Arctic aquatic regime, which could reduce the methylmercury formation in water column, and the methylation within sediments needs further exploration.

Information is provided on the results of gas geochemical and hydrometeorological studies of Amur and Ussuri bays, Sea of Japan, on cruises 84 and 85 of the R/V Professor Gagarinskiy in December 2022. For the first time for the winter period, synchronous measurements of greenhouse gases and atomic mercury were carried out in the surface marine boundary layer of Peter the Great Gulf, and new information was obtained on the seasonal characteristics of gas geochemical fields in the water column and bottom sediments.

Reconstruction of ice conditions and climate of the East Siberian Sea during the Late Middle Holocene was implemented for the first time using a transfer function method based on marine sedimentation proxies. Transfer functions were developed based on a hydrometeorological time series of changes in mean annual air temperature (ΔT10) and the ice-free period (IF10) for the last 70–90 years and a geochemical time series of bottom sediments accumulated during this time, which were obtained using a submillimeter scanning of the core in the X-ray fluorescence analysis of synchrotron radiation. Geochemical time series of Holocene deposits were obtained from X-ray fluorescence analysis of the core in a step of 1–2 cm. Reconstruction of ice conditions and average annual air temperature revealed a decreasing trend of ΔT10 and IF10, which started from the middle Holocene up to the Little Ice Age due to an orbitally determined decrease in insolation. A synchronous periodicity of changes in ice cover and air temperature was revealed and approximated by periods of 1600 years for IF10 and 1740 years for ΔT10, which are comparable to Bond’s climatic cycles. These results indicates the telecommunication of the Atlantic processes, climate of the East Siberian Sea, and predominance of the cyclonic type of atmospheric circulation during the Holocene.

The objective of the work was a comprehensive study of Late Holocene bottom sediments from the southern Chukchi Sea and reconstruction of their accumulation conditions. Analytical methods included macroscopic description with smear slides, 210Pb dating of sediments, determination of biogenic components, magnetic susceptibility measurements, and grain size distribution, palynological, and mineral analyses. The modern sedimentation rate established at the study point is 8–10 mm/year. Sediments are mainly represented by silts. In the upper part of the core, there are elevated concentrations of SiO2biog, Corg, and Ntot and decreased magnetic susceptibility values. This is probably due to the increased bioproductivity of the Chukchi Sea in recent years, caused by current climate warming. The palynological composition of the studied deposits reflects the tundra and forest–tundra vegetation on land adjacent to the Chukchi Sea. The presence of Neogene pollen in Late Holocene sediments is evidence of their transfer from eroded ancient sediments.

Mercury (Hg) having a high migration capacity reach the Arctic region via the atmosphere. The absorbers for Hg are sea bottom sediments. Sedimentation in the Chukchi Sea occurs under the influence of highly productive Pacific waters entering through the Bering Strait and the inflow of a terrigenous component from the western direction with the Siberian Coastal Current. The Hg concentrations ranged from 12 mu g kg -1 to 39 mu g kg(-1) in bottom sediments of study polygon. Based on dating sediment core the background concentration was 29 mu g kg(-1). Concentration of Hg in fine sediment fractions was 82 mu g kg(-1), in sandy fractions (> 63 mu m) varied from 8 to12 mu g kg( -1). In recent decades the Hg accumulation in bottom sediments has been controlled by the biogenic component. The Hg in the studied sediments presents as sulfide form.

On the basis of lithological and gas geochemical studies and a comprehensive interpretation of the available materials, the main factors of the formation and distribution of grain size distribution, water-physical properties, organic saturation, concentrations and geochemical parameters of hydrocarbon gases in seafloor sediments of geostructures of the western part of the East Siberian Sea are summarized and analyzed. It has been established that the sediments of the northern and central parts of the study area are represented by aleurite-pelites, the southern ‒ by aleurite-pelite-psamites with variations in Corg values ‒ 0.6–2.0%, natural humidity and density ‒ 18–43% and 1.5–2.0 g/cm3, open porosity ‒ 17–33%, the concentrations of methane and its homologues are 0.001–5.934 and 0.00003–0.0312 cm3/kg, the molecular mass of the hydrocarbons fraction, the “wetness”, “dryness” coefficients, and the coefficients of the transformation are 16.05–22.6 g/mol, 0.2–51%, 1–1999, 0.2–50.8 and δ13С‒СН4 (–82.7…–38.4‰). Based on the values of gas geochemical parameters, eleven types of gas sources were identified in bottom sediments. In the process of research, it was found that the formation of hydrocarbon anomalies in sediments is mainly associated with their reservoir properties, Corg content and depths of their sampling, as well as with the complex influence of geological factors, the main of which are the gas saturation of the underlying sediments and the type of gas sources, discontinuous and plicative tectonics, geostructures position, thickness of Quaternary deposits, coal and gas content and age of the folded base. To a lesser extent, anomalies of hydrocarbon gases are associated with the lithological composition and density parameters of sediments.

For the first time, data on the mercury content and its forms in the ferromanganese and ferruginous formations of the Chaun Bay (East Siberian Sea) were obtained. According to the geochemical classification, the studied formations belong to diagenetic. The mercury content ranges from 8 to 26 µg/kg, which is two to five times lower than the bulk content in the Upper continental crust. The isomorphic (mineral) form of mercury is predominant in ferromanganese and ferruginous formations.

Layers accumulated in the pre-industrial period were selected using dated bottom sediment cores. They determine the mercury concentrations that are the geochemical background for the selected water basins. The variability of the mercury concentrations in the sediments of the inner shelf is low (20–30 μg/kg) and can be used as a basis for ecological assessment during the economic development of the Arctic regions.