Mercury is a persistent global pollutant, and the Arctic remains a region of special concern due to rapid warming and complex mercury cycling. This study presents continuous measurements of atmospheric gaseous elemental mercury (GEM) during a cruise from the Kara Sea to the East Siberian Sea (September-October 2024). GEM concentrations ranged from 0.73 to 1.32 ng m-3 (mean 0.97 ng m-3), below the Northern Hemisphere background, but consistent with the global trend of decreasing atmospheric GEM concentrations. The Kara Sea exhibited a slightly elevated mean GEM concentration (1.00 ng m-3) compared to the other seas. Backward trajectory and concentration-weighted trajectory analyses identified three major potential source regions: the central Arctic Ocean (suggesting re-emission from ice-free waters); the West Siberian Plain (industrial cities including Surgut and Novosibirsk); and northern Europe and the Baltic region (long-range transport). Preliminary sea-air GEM evasion flux measurements over active methane seeps reached 3.5 ng m-2 h-1, substantially above regional background. Control experiments showed that ship thruster operation artificially enhanced measured fluxes by a factor of 1.3-1.7. While these results suggest that methane seep areas may warrant further investigation as potential sites of enhanced GEM evasion, the present measurements should be considered exploratory. The possibility of thruster-induced artifacts and the absence of direct geochemical characterization at the seep sites preclude definitive attribution. The findings are consistent with the Arctic Ocean playing a role as an active secondary mercury source and underscore the need for flux studies accounting for hydrodynamic artifacts.

The paper summarises the results of gamma-spectrometric determination of the activity concentration of the major natural radionuclides (226Ra, 232Th, and 40K) in the surface bottom sediments (84 samples) and a single sample of ferromanganese nodules collected in the East Siberian Sea and the Laptev Sea in 2008-2020. Radium equivalent activity, external and internal hazard, and gamma activity concentration indices were calculated in order to assess the natural pollution and risk level of radionuclides. Activity concentrations ranged 16.5-70.4 (mean 31.0) Bq kg-1 of 226Ra, 21.4-77.9 (mean 40.2) Bq kg-1 of 232Th, and 298-991 (mean 543) Bq kg-1 of 40K for the East Siberian Sea samples. The Laptev Sea samples exhibited ranges 15.5-54.0 (mean 32.9) Bq kg-1 of 226Ra, 23.1-66.4 (mean 41.8) Bq kg-1 of 232Th, and 328-546 (mean 441) Bq kg-1 of 40K. In the case of the ferromanganese nodule sample, the measured activity concentrations were 262 ± 42 Bq kg-1 of 226Ra, 137 ± 35 Bq kg-1 of 232Th, and 323 ± 45 Bq kg-1 of 40K. The activity concentrations of natural radionuclides in the sediments were found to be in close proximity to the global average. Activity concentrations of 226Ra and 232Th in ferromanganese nodules were 8 and 3 times higher, respectively. The subsequent radiological risk assessment indicated that the observed values for the sediments were below the specified threshold values. The values for the ferromanganese nodule sample exceeded these thresholds indicating a potential radiological hazard associated with mining of such deposits.

The paper presents data on the spatial distribution of activity concentration of natural (232Th, 226Ra, 40K) and anthropogenic (137Cs) radionuclides in the surface layer of bottom sediments of the Chaun Bay of the East Siberian Sea. The measured activity of 232Th and 226Ra is typical for bottom sediments of the Arctic coastal zone and corresponds to the global level. The level of 137Cs activity in bottom sediments showed the absence of local sources of anthropogenic contamination in Chaun Bay, while the mean 40K activity concentration was 1.8 times higher than the global average. The results of statistical analysis showed that the dynamics of riverine run-off, thermoabrasion and currents, as well as aeolian and sea ice transport of sedimentary matter, are the main factors that determined the differences in the behaviour of the studied radionuclides in the surface bottom sediments of the Chaun Bay.

Relevance. Dictated by the need to assess functioning of the biogeochemical regime of the Arctic region by studying geochemical properties of organic matter of bottom sediments on the example of the Chaunskaya Bay (East-Siberian Sea). Aim. To study the spatial variability of geochemical parameters of organic matter of bottom sediments of the Chaunskaya Bay using the Rock-Eval method, as well as to identify a possible relationship between the parameter TOC and the pelite fraction. Objects. Samples of bottom sediments of the Chaunskaya Bay (East Siberian Sea). Sampling took place in stages from three horizons (upper 0–2 cm, intermediate 2–5 cm, lower 5–10 cm) during a comprehensive scientific expedition to the R/V "Academician Oparin" in September–October 2020. Methods. Granulometric composition of bottom sediments was determined using the Analysette 22 NanoTec particle analyzer (Fritsch, Germany). The analysis of hydrocarbon compounds of organic matter was performed using pyrolytic analysis on the device (Rock Eval 6 Turbo of Vinci Technologies, France). Results. The results of pyrolytic analysis considered by the authors have shown that such factors as the primary productivity of the waters of the studied water area and the processes of erosion of the coastal zone play a decisive role in the formation of the composition of the TOC in bottom sediments of the Chaunskaya Bay. We also do not exclude the contribution of river runoff to the composition of the TOC in bottom sediments; however, we consider it small due to the insignificant inflow of river sediments into the waters of the studied area. The pyrolytic data obtained by us indicate that both the marine component (primary productivity) and the terrigenous component (erosion of the coastal complex) are present in the composition of the TOC in bottom sediments of the studied area.

Based on the results of an analysis of 174 samples of bottom sediments collected at 48 stations in the Chaun Bay during the cruise 60 of the R/V Akademik Oparin (October 2020), it was found that their grain size distribution varies from poorly sorted silty clay to well sorted sand. The results of the study led to conclusion that the main sedimentation mechanisms in Chaun Bay are thermal abrasion, river runoff, and abrasion, as well as ice rafting and aeolian transport. The zoning of grain size types of bottom sediments is related to the bottom topography and consistent with areas affected by riverine runoff, abrasion, and thermal coastal abrasion, as well as with the direction of currents. The high occurrence of coarse clastic matter in sediments is evidence of abrasion of the coastal zone and active ice rafting of large (up to 15 cm) rock fragments. The vertical variability of the grain size parameters of the studied bottom sediments within the upper 20 cm layer reflects gradual Late Holocene intensification of terrigenous (fluvial and thermal abrasion) fluxes with the current effects of climate change in the Arctic.

Chaun Bay, located on the fringe of the East Siberian Sea, has been described since the mid-20th century to support a unique marine ecosystem that is atypical for the local Siberian Arctic. Here we use ship-board physical, biogeochemical and geological measurements taken in October 2020, along with hydrographic observations taken from land-fast ice in April 2023, to demonstrate that these warm-water biological communities are supported by hydrothermal submarine groundwater discharge that delivers heat, salinity, nutrients, and trace elements to the bay. We identify a cyclonic eddy that mixes the warm nutrient-rich groundwater with oxygen-rich surface water, resulting in a water mass within Chaun Bay that has similar physical and chemical properties to the highly productive waters of the North Pacific and Southern Chukchi Sea. The bay showed elevated concentrations of chlorophyll-a and zooplankton, and the abundance and species diversity of epibenthos significantly exceeded values observed elsewhere in the East Siberian Sea. The benthic communities contained a number of boreal species that are not typically found in the Arctic Ocean. We also observed Thysanoessa krill populations, a pelagic species generally considered an expatriate in Arctic waters.

The paper provides information on integrated oceanological studies in the Bering, Chukchi, and East Siberian Seas during the cruise 69 of the R/V Akademik Oparin in September–October 2023. Preliminary results of the scientific expedition are discussed.

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.

The interaction of surface water and groundwater is important in the ecology of coastal basins, affecting hydrological conditions, oxygen regime, carbon, and nutrient exchange. This study demonstrates a dynamic connection between the salt-wedge region and its underlying aquifer in the eutrophic estuary. In winter, this estuary is covered with ice, and the river flow is at its lowest; that is why the specific response to groundwater discharge is best marked in this season. Groundwater admixture was detected in the salt-wedge region by highly active radium isotopes: 223Ra—4.80 ± 0.42 dpm 100 L−1, 224Ra—55.37 ± 1.1 dpm 100 L−1, and 228Ra—189.71 ± 4.66 dpm 100 L−1. The temperature of groundwater and river water was about +4 °C and 0 °C, respectively; that of seawater was −1.6 °C, and temperature increased up to +2.3 °C in the surface water–groundwater interaction region. Groundwater admixture is accompanied by a lower level of oxygen concentration of 52 μmol/kg; at that time, the maximum oxygen concentration in the salt-wedge region was 567 μmol/kg. In waters with a high activity of radium isotopes, there was a maximum partial pressure of CO2—4454 μatm at the range 100–150 μatm in the salt-wedge region and also observed extremum of NH4+, NO2−, and dissolved phosphorus. The surface water–groundwater interaction through anoxic sediment can form localized anaerobic areas despite the general oxygen supersaturation of eutrophic estuary waters and also cause local recycling of nutrients from bottom sediments.

Ссылка для цитирования: Особенности состава органического вещества донных осадков Чаунской губы (Восточно-Сибирское море) / Н.А. Полтавская, Е.В. Гершелис, И.А. Оберемок, А.А. Гринько, А.Н. Чаркин, Е.И. Ярощук, О.В. Дударев, Н.А. Смирнова, Н.В. Гусева, И.П. Семилетов // Известия Томского политехнического университета. Инжиниринг георесурсов. – 2023. – Т. 334. – № 2. – С. 130-146. Актуальность исследования определяется необходимостью оценки региональных особенностей транспорта и преобразования органического вещества в различных седиментационных и биогеохимических обстановках, действующих на Восточно-Сибирском арктическом шельфе, в том числе в Восточно-Сибирском море – наиболее ледовитом и наименее изученном море Российской Арктики. Цель исследования заключается в определении состава и источников органического вещества донных осадков Чаунской губы (Восточно-Сибирское море). Объекты: 25 проб поверхностных донных осадков, отобранных по профилю от прибрежной зоны Чаунской губы до внутренней части шельфа Восточно-Сибирского моря в ходе комплексной научно-исследовательской морской экспедиции на борту НИС «Академик Опарин» в сентябре–октябре 2020 г. Методы. Для анализа групп углеводородных соединений ОВ донных осадков был применен пиролитический анализ по методу Rock-Eval; оценка распределения н-алканов проводилась на основе результатов газовой хромато-масс-спектрометрии. Гранулометрический анализ осадков выполнялся на лазерном анализаторе частиц. Результаты. Состав осадочного материала в Чаунской губе преимущественно определяется особенностями подводного рельефа и гравитационными потоками поступающего терригенного материала – продуктов локальной термоабразии береговой зоны (о. Айон) и речного аллювия в юго-восточной части губы. Определенную роль в формировании седиментационного облика губы, предположительно, играют процессы вытаивания криозоля в результате разрушения областей припайного льда. Данные пиролиза и анализ распределения н-алканов для поверхностных осадков указывают на смешанный генезис органического вещества в поверхностных осадках с доминирующим вкладом наземного органического вещества высокой степени преобразованности и высокое содержание трудноразлагаемых гуминовых веществ и фульвокислот. Присутствие автохтонного органического вещества отражает высокую продуктивность вод Чаунской губы.

Natural radioactive isotopes serve as a useful proxy of geological and geochemical processes in marine environment, while radiocesium serves as an indicator of man-made contamination. Monitoring of natural and anthropogenic radioactivity under conditions of the climate changes in the Arctic region is of high importance in investigations of this natural system. For the first time, we report the data on spatial distribution of natural (232Th, 226Ra, 40K) and anthropogenic (137Cs) radionuclide activities in the marine sediments from Chaun Bay (East Siberian Sea). The measured activity concentrations varied in the range 23.7-77.9 (mean 39.2) Bq kg-1 for 232Th, 16.5-39.3 (mean 26.6) Bq kg-1 for 226Ra, 535-991 (mean 726) Bq kg-1 for 40K, and 0.5-4.7 (mean 2.0) Bq kg-1 for 137Cs. The radiocesium level in the sediments showed no local sources of anthropogenic pollution in the Chaun Bay, while the average activity concentration of 40K was 1.8 times higher than worldwide.

The article provides a data on 160 samples of bottom sediments obtained from 48 stations during 60th cruise of R/V Akademik Oparin in the East Siberian Sea in Autumn 2020 (26 September – 11 November). It contains mean diameter of the particles, sorting coefficient, standard deviation, skewness, and kurtosis, values of percentiles (p5, p10, p16, p25, p50, p75, p84, p90, p95), lithology and mass percentage of >2 mm, 1-2 mm, 0.5-1 mm, 250-500 µm, 125-250 µm, 63-125 µm, 31-63 µm, 10-31 µm, 2-10 µm, and <2 µm fractions. The bottom sediments have been sampled in Chaun Bay of the East Siberian Sea from 9 to 21 October 2020 with Ekman (0.25 m2) and Van Veen (0.05 m2) samplers. The grain size data was obtained from laser diffraction method using a SHIMADZU SALD 2300 particle analyser. The data provides an overview on lithology and grain size properties of bottom sediments that will be useful to understand risks for climate changes in the Arctic. The data will help the researchers who work on the Arctic to assess a relationship between grain size properties of the bottom sediments and it sorption potential. A principal component analysis (PCA) can be performed to identify key parameters of the bottom sediments in assessment of sedimentation rates and it changes in the Arctic. Additionally, the data can be used in mapping a spatial distribution of above mentioned parameters for better understanding sedimentation rate changes in the East Siberian Sea and adjacent seas as well.

In the present paper a high-resolution gamma-spectrometry data processing algorithm aimed at locating hydrothermal alteration haloes is discussed. On the first stage a cluster model of spatial variation of radioactive background is created using information on natural radioactive elements (NRE) concentrations and numerical geomorphological characteristics. This model allows for good terrain differentiation in terms of its lithological and landscape variability. Mathematical procedure for removal of NRE distribution variance, related to variability of lithology and elementary landscapes, improved radiometry data for mapping zones of hydrothermal alterations. On the second stage we integrated the "corrected" gamma-ray spectrometry data using principal component analysis (PCA). Comparing the acquired factor model with a priori radioactive models of hydrothermal alterations allowed us to differentiate quartz-hydromica and quartz-pyrite-sericite alteration haloes.

Transport and accumulation of radionuclides in the Arctic depends on many biogeochemical processes, which are changing at accelerated rates due to climate change and human economic activity. We present the results of a study on the features distribution of some natural radionuclides in the marine sediments on the East Siberian Arctic Shelf collected during several expeditions from 2008 to 2019. Average activity concentration of 232Th, 40K and 226Ra under the influence of different sedimentation regime increases from 40.7, 418 and 30.8 Bq/kg to 41.6, 423 and 34.9 Bq/kg respectively from coastal shelf marine sediments (<50% clay) to outer shelf marine sediments (>50% clay). Sediment particle size has a greater impact on radionuclides in the coastal shelf. An increase in the activity concentrations of 232Th and 226Ra with the increasing clay particles were found. On the outer shelf with a change in the sedimentation regime, the influence of the size composition decreased, at the same time, there is a correlation between the organic carbon concentration and the radionuclide activity concentration. Absolute maximums of natural radionuclide activity concentration (232Th = 70.9, 226Ra = 70.4, 40K = 591 Bq/kg) were detected in the Chaun Bay. The highest activity concentration of 226Ra was found in paleo-river valleys marine sediments. A low 232Th/226Ra activity concentration ratio indicates the enrichment of paleo-river valleys marine sediments with 226Ra. In the deep-sea sediments of the shelf slope on the contrary paleo-river valleys, this ratio is greatly increased.

The East Siberian Sea (ESS) is the largest, shallowest and most icebound Arctic marginal sea. It receives sub-stantial input of terrigenous material and climate-vulnerable old organic carbon from both coastal erosion and rivers draining the extensive permafrost-covered watersheds. This study focuses on the interannual variability and spatial distribution of suspended particulate matter (SPM) in the surface and bottom waters of the ESS during the ice-free period in 2000, 2003, 2004, 2005 and 2008. We report on the composition and variability of par-ticulate organic carbon (POC), total nitrogen (TN), POC/TN ratios, carbon and nitrogen isotopes (delta 13C, delta 15N) and provide estimates of the contribution of terrestrial organic carbon (terrOC) based on the delta 13C isotopic values.The results show that interannual SPM distribution and elemental-isotopic characteristics of POC differ significantly between the western biogeochemical province (WBP; West of 165oE) and the eastern biogeo-chemical province (EBP; East of 165oE) of the ESS. The SPM mean concentration in the WBP is almost an order of magnitude higher than in the EBP. From west-to-east of the ESS, SPM tends to become more depleted in delta 15N, while the delta 13C becomes isotopically heavier. This trend can be explained by a shift in organic matter sources from terrigenous origin (erosion of the coastal ice complex and riverine POC) to becoming dominantly from marine plankton.The maximum contribution of terrOC to POC reached 99% in parts of the WBP, but accounts for as low as 1% in parts of the EBP. At the same time, the type of atmospheric circulation and its associated regime of both water circulation and ice transport control a displacement of the semi-stable biogeochemical border between WBP and EBP to the east or to the west if compared to its long-term average position near 165oE. Our multi-year inves-tigation provides a robust observational basis for better understanding of the transport and fate of terrigenous material upon entering the ESS shelf waters. Our results also provide deeper insights into the interaction in the land-shelf sea system of the largest shelf sea system of the World Ocean, the East Siberian Arctic Shelf system.

Abstract The study demonstrates a dynamic connection between the saltwater wedge region and its underlying aquifer. In winter, this estuary is covered with ice and the river flow is at its lowest; that is why its hydrological and oxygen-specific response to groundwater discharge is best marked in this season. Groundwater discharge was detected in the saltwater wedge region by highly active radium isotopes: 224Ra — 66.32 ± 0.60 dpm 100L−1, 223Ra — 2.85 ± 0.17 dpm 100L−1, 228Ra — 159.15 ± 0.13 dpm 100L− 1. The temperature of ground and river waters was +4.3 °С and +0.09 °С, respectively, that of sea water −1.2 °С, and the near-bottom layer temperature increased up to +1.2 °С in the water discharge region. According to the data provided by an anchored autonomous station installed in the area of saltwater discharge influence during the freeze-up period, the temperature reaches 2.5 °С in the saltwater wedge. Groundwater discharge is accompanied by a lower level of oxygen saturation – 67%, at that time oxygen saturation in sea water was 151%. Thus, we present evidence documenting the natural process that may result in a lower level of oxygen saturation in an estuary irrespective of man-induced effects, supply of nutrients and further intensification of production-destruction processes.

The East Siberian Arctic Shelf (ESAS), the world’s widest and shallow continental shelf, plays a crucial role in the climate system of our planet holding huge amounts of organic carbon (OC) in the permafrost deposits which are remobilized upon accelerating permafrost thaw. To get more detailed insights into the sources of OC and compare the mechanisms of its transformation in the different ESAS zones, we investigate a scarcely studied coastal area of the East Siberian Sea – Chaun Bay (CB), a semi-closed accumulative area, where the influence of river discharge is limited and the coastline deposits are composed mainly of the rocky formations, which is contrasting to the permafrost-dominated Arctic bays. In this study, we analyzed 25 surface sediments collected along the profile from the coastal zone of CB to the midshelf of East Siberian Sea. To characterize the OC composition, we used Rock-Eval indicators along with traditional molecular markers (n-alkanes; n-alkanoic acids). Detailed grain size composition was also performed in order to assess the sedimentation environment operating in the study area. Sediments are mostly represented by sortable silt (7.61-62.48% on average 43.5%), fine silt (1.98-60.9% on average 34.63%) with a certain proportion of clay (average 11.13%) predominantly in the inner shelf areas, and sand (average 10.73%) deposited in the eastern, southern, and western (Aion Island) parts of the CB. OC content along the studied profile ranged from 0.49 to 1.76%. Hydrogen index along the studied profile ranged from 111 to 232 mg/g, Oxygen index varied from 134 to 239 mg/g. The relationship between HI and OI indicated roughly equal contributions of terrestrial and marine sources to the OC composition. Meanwhile, variable distribution of n-alkanes is observed with a pronounced presence of high-molecular-weight n-alkanes, which are recognized as higher terrestrial vegetation markers. These data will be further combined with more detailed biomarker analysis to reveal the OM sources proportions in the CB sediments and to understand the dominating mechanisms of OC transformation within this area. This analytical studies were financially supported by RSF (Project # 21-77-00075).

The Chaunskaya Bay, a large Arctic estuary with a surface of about nine thousand km(2), is poorly studied in terms of ichthyology, although there is a transit hub of the Northern Sea Route on its coast, the seaport of Pevek, and its southeastern coast is a part of the state natural reserve "Chaunskaya Guba ". Only 10 marine fish species have been recorded in the bay previously. The paper presents the results of studying fish (125 specimens from 20 stations) caught during the benthic survey at depths of 9-27 m in autumn 2020. The collections include demersal juveniles of 11 species from 7 families, 8 of which were recorded in the Chaunskaya Bay for the first time: Gymnocanthus tricuspis, Triglops pingelii, Aspidophoroides olrikii, Liparis tunicatus, Gymnelus barsukovi, Lycodes polaris, Lumpenus medius and Lumpenus fabricii. Juvenile Arctic cod Boreogadus saida, Artediellus scaber and Ammodytes hexapterus were also caught. L. fabricii and L. tunicatus were the most common species in catches, accounting for 65.6% of all individuals and 66% of the total biomass. The distribution of juvenile demersal fish across the bay's water area is provided. The largest species diversity and the maximum fish abundance were recorded in the apex of the bay opposite the mouth of the Chaun River. Thus, 18 species of marine fish (excluding anadromous salmonids, whitefish and smelts) have been recorded from the Chaunskaya Bay in total. (C)& nbsp;2022 Elsevier B.V. All rights reserved.

Ongoing climate warming in the Arctic accelerates mobilization of freeze-locked carbon from the coastal and subsea permafrost deposits, affecting transport, accumulation and transformation of organic carbon (OC) in the permafrost-dominated land-shelf system of the Eastern Arctic. The mineral matrix is believed to exert a first-order control on OC degradation state and thereby on its potential degradation and release as CO2 and CH4 to the atmosphere. To understand the interactions between organic matter and mineral composition, we investigated four sediment cores obtained from contrasting sedimentation areas: coastal (Buor-Khaya Bay, BK; 20 cm) and outer part (LS; 17 cm) of the Laptev Sea, Dmitry Laptev Strait (DLS; 14 cm), Chaunsky Bay (CB; 14 cm) of the East Siberian Sea. This study presents preliminary results of the sedimentary organic matter composition analyzed with both Pyrolysis-GCMS and Rock Eval pyrolysis, along with the clay mineral composition and grain size distribution. By combining these mineralogical and macromolecular data, we aim to get new insights into the interactions between the mineral matrix and OM and evaluate how the physical properties of the sediments affect the OM fate in the different areas of the East Siberian Arctic shelf. The variability in the OC and mineral composition observed for the different sampling sites, as well as for different sampling horizons, reflects the dominance of diverse hydrodynamic regimes. The greatest variations with sampling depth were observed in sediments of the DLS system characterized by transit/transport bottoms. DLS sediments were generally enriched in aromatics (up to 44.6%), lipids (up to 34.2%) and lignin markers (up to 34.3%). A relatively uniform distribution is observed for the samples from CB, a predominantly accumulative system with a semi-closed water exchange, where proportions of lipids and lignin markers where also high. Rock Eval pyrolysis also revealed significant variability between the studied sites: hydrogen index values generally were within the range of 74-164 mg HC/g TOC with higher average values in the CB samples. Oxygen index values were between 150 and 241 CO2/g TOC: the highest values were observed in the BK sediments. The average clay mineral contents in the studied sediment cores vary as follows: illite from 46.1 % in DLS to 58.7 in BK; illite-montmorillonite from 6.6% in CB to 17.6% in DLS; montmorillonite from 3.1% in CB and BK to 5.3% in LS; chlorite from 6.5% in CB to 9.2% in LS; kaolinite from 19.7 % in LS to 29.7 % in CB. Analytical studies were financially supported by RSF (Project # 21-77-00075). Research cruises were also performed with support of RSF (Project # 21-77-30001).