The current levels of aliphatic (20 μ g/L, IR method) and polycyclic aromatic (90 ng/L, fluorescence method) hydrocarbons in suspended particulate matter of surface water and in bottom sediments have been determined in the coastal areas of the Caucasian sector of the Black Sea within the boundaries of the Russian Federation (in September 2021, May and September 2022). Despite the decrease in hydrocarbon concentrations in surface water over recent years, the Kerch Strait belongs to the most polluted area, as before. Accumulation of hydrocarbons occurs in bottom sediments, which leads to an increase in their content in C _org (for aliphatic hydrocarbons, up to 14.2

Data on the content and composition of hydrocarbons, like aliphatic and polycyclic aromatic hydrocarbons, in Holocene sediments (undisturbed cores 0–30 cm) are presented. The samples were collected in the southwestern region of the Kara Sea during the first part of cruise 89 of the R/V Akademik Mstislav Keldysh in September 2022. It has been established that the distribution of hydrocarbons, unlike organic carbon, does not depend on the lithotype of bottom sediments, because, along with methane, high molecular weight hydrocarbons are formed in the gas-saturated zone. This leads to an increase in the proportions of aliphatic (>1

The concentrations and composition of hydrocarbons (aliphatic, AHCs, and polycyclic aromatic, PAHs) are determined using molecular markers in bottom sediments of the Greenland–Norwegian basin and the Barents Sea (during the 84th cruise of the R/V Akademik Mstislav Keldysh in 2021). The research covered the deep-sea part of the Greenland Basin, the northern part of the East Greenland Ridge, the near-fault zone in the area of the junction of the Mohns and Knipovich ridges, the Western and Northwestern extremities of the Svalbard continental shelf (the Vestnes Ridge, the Ermak Plateau, the Sofia Basin, and the Hinlopen Trough), the Fram Strait, the Orly trough area with the intersection of the Erik-Eriksen trough, and the central part of the Barents Sea. The surface bottom sediments are found to contain a wide range of concentrations of Corg (0.25

The current level of aliphatic and polycyclic aromatic hydrocarbons was determined in suspended particulate matter of waters (mainly in surface waters) and in upper layer of bottom sediments of coastal areas in the Caucasian sector of the Black Sea of the Russian Federation (September 2021, May and September 2022, March 2023). IR method was used to determine the aliphatic hydrocarbons, and the method of high performance liquid chromatography was employed for PAHs. The average concentration of aliphatic hydrocarbons was ≈20 μg/L and for polycyclic aromatic hydrocarbons ≈130 ng/L in suspended particulate matter in open surface waters of Gelendzhik and Golubaya bays. Their content naturally increased as they approached the coast. Despite the decrease in hydrocarbon concentrations in surface waters in recent years, the Kerch Strait and Novorossiysk remain the most polluted areas as before. Higher concentrations in the waters of the Taman Peninsula may be caused by the seepage of hydrocarbons from the sedimentary layer. Hydrocarbons are accumulated in bottom sediments, that leads to their rising portion in total organic carbon (e.g., aliphatic hydrocarbons up to 14.2 % in the Tuapse region and 13.1 % in the Novorossiysk region). Along with contamination from anthropogenic sources, natural processes also affect the hydrocarbon levels such as high biological productivity of the area and fluid flows from the sediment layer.

The concentrations and composition of hydrocarbons - HCs (aliphatic - AHCs and polycyclic aromatic hydro- carbons - PAHs) in the Barents and Kara Seas (cruises 80, 83 and 89 of the R/V << Akademik Mstislav Keldysh >>, August 2020, June 2021, September 2022 respectively) are analyzed in the paper. The concentrations of the HC dissolved and suspended forms were measured in the surface microlayer (SML, 100-1000 mu m thick), melting ice and surface waters. Higher concentration of HCs in SML was found in suspended particulate matter (SPM). AHC concentration in SPM in the Barents Sea were lower (31-96, on average 68 mu g/L) than in the Kara Sea in June 2021 (187-1051, 573 mu g/L on average), where the studies were carried out in the early summer season. The concentrations of AHCs in the SPM in the SML of the Kara Sea were 3.6 times higher than in the dissolved form (127-217, on average 187 mu g/L), and they were almost 15 times higher than those in the surface waters. The accumulation of organic compounds also occurs in ice, but to a lesser extent than in the SML. The composition of alkanes in SML and melting ice mainly indicates the slight influence of autochthonous processes shaping HCs. The average content of PAHs in SPM was also 4.8 times higher than that in the dissolved form. According to the markers, the influence of combustion products of marine fuel was traced in the composition of PAHs. In September 2022, AHC and PAH concentrations in the Kara Sea were lower than in June 2021: on average, 159 mu g/L and 492 ng/L accordingly, that is due to a decrease in the content of SPM from an average of 1.89 to 1.21 mg/L.

The organic compounds in a suspension of surface water and sediments of the shallow Chernavka River flowing into self-sustaining Lake Elton are studied: Corg and aliphatic (AHCs) and polycyclic aromatic (PAHs) hydrocarbons (HCs). The surface waters are characterized by high contents of lipids, AHCs, and PAHs: 692, 80, and 0.79 µg/L, respectively. The alkane composition of the water suspension corresponded to weathered oil HCs. The HCs are transformed at the water–sediment boundary rather than upon sedimentation. As a result, the AHC composition of sediments differs from that of the suspension in the presence of planktonogenic low molecular homologues of n-С15–С17 and a strong increase in the series of odd high molecular alkanes, whereas the PAH composition has a higher amount of naphthalene.

The concentrations and composition of hydrocarbons (HCs), aliphatic (AHCs), and polycyclic aromatic hydrocarbons (PAHs) in the Barents and Kara seas were determined in the surface microlayer (SML, about 300 µm thick), melting ice, and surface waters. Field material was collected on cruises 80 and 83 of the R/V Akademik Mstislav Keldysh in August 2020 and June 2021, respectively. In the SML, HCs occur primarily in suspension. In the Barents Sea, the AHC content in suspension was lower (31–96, 68 µg/L on average) compared to the Kara Sea (187–1051, 693 µg/L on average), where research was carried out in early summer. In the Kara Sea, the AHC concentrations in the SML were 3.6 times higher than in dissolved form (89–270, 158 μg/L on average), while compared to the suspension of surface waters, they were almost 15 times higher. Organic compounds also accumulate in ice, but to a lesser extent than in the SML. From the alkane composition, the influence of autochthonous processes on HC generation in melting ice is insignificant. The PAH contents in suspension were also 4.8 times higher on average than in dissolved form. The influence of the combustion products of ship fuel on the PAH composition was traced by markers, which showed that, in addition to phenanthrene, fluoranthene and pyrene dominated in all samples.

The concentrations and composition of hydrocarbons (HCs), including aliphatic hydrocarbons (AHCs) and polycyclic aromatic hydrocarbons (PAHs), were defined in the sea surface microlayer (SML) about 300 μm thick, ice, and surface waters in the Kara Sea during the 83rd cruise of R/V Academic Mstislav Keldysh in June 2021. AHCs are concentrated in the SML in suspended particulate matter (SPM), where their content varied in the range of 197–1051 μg/L, on average, 621 μg/L. This amount was almost four times higher than in the dissolved form at 89–270 μg/L (on average, 158 μg/L) and almost 22 times higher than in a suspended form of surface waters (33 μg/L, on average). AHCs are also accumulated in ice, but to a lesser extent than in the SML. According to the composition of alkanes, autochthonous processes have an insignificant impact on the formation of AHCs in SML and thawing ice and differ from their composition in forming ice. The impact of the autochthonous processes on the AHCs composition was observed only in the frontal zone in the St. Anna Trough. The content of PAHs in the SPM was also 4.8 times higher, on average, than in the dissolved form. In spite of different sources of these hydrocarbon classes, a dependence in the distribution of AHCs and PAHs in SPM (r = 0.79, n = 52, at p < 0.01) was observed for all samples collected. According to the markers, the impact of fuel combustion products is traced in the composition of PAHs, because, in addition to phenanthrene, fluoranthene and pyrene dominated in all samples.

The current level and origin of hydrocarbons (HCs) was determined: aliphatic – AHCs and polycyclic aromatic – PAHs (September 2021, May and September 2022) in suspended particulate of surface waters (for AHCs – 20 µg/l; PAHs – 130 ng/l, fluorescent method) and in the bottom sediments of the coastal areas of the Caucasian sector of the Black Sea of the Russian Federation. Despite the decrease in HC concentrations in surface waters in recent years, the most polluted areas include, as before, the Kerch Strait. HC accumulate in bottom sediments, which leads to an increase in their content in the composition of Corg (up to 14.2% in the Tuapse region and 13.1% in the Novorossiysk region). It has been established that, along with pollution, HC levels are greatly influenced by natural processes (the productivity of the area, fluid flows from the sedimentary mass).

—The distribution of hydrocarbons (HCs): aliphatic–AHCs and polycyclic aromatic hydrocarbons–PAHs is examined in waters and bottom sediments sampled during cruises 75 and 80 of the R/V Akademik Mstislav Keldysh in 2019 and 2020 in the Norwegian–Barents Sea Basin: Mohns Ridge, shelf of the Svalbard Archipelago, Storfjord, Medvezhinsky trench, central part of the Barents Sea, Novaya Zemlya shelf, and Franz Victoria Trough. An increase in AHCs content, on average, up to 20–23 μg/L in the suspended particulate matter (SPM) in surface waters compared to those of 2016–2017 is caused by phytoplankton bloom near the ice edge. In bottom sediments, the distribution of AHCs (3–186 μg/g) and PAHs (3–9934 ng/g) depends not only on the sedimentation conditions and particle size composition of sediments, but also on the variability of redox conditions in the sedimentary sequence and molecular diffusion of HCs from productive horizons.

The results on the content and composition of aliphatic (AHCs) and polycyclic aromatic hydrocarbons (PAHs) at the geochemical barrier between the Kara Sea and the Ob and Yenisei Rivers are discussed in comparison with those in the mouth areas of the Lena, Khatanga, Indigirka and Kolyma. It has been established that hydrocarbon concentrations sharply decrease in the river-sea mixing zones, and their composition, and the ratio of their dissolved and suspended forms change. Besides, the research season plays a great role, as the highest content of hydrocarbons and particulate matter was found in the Ob Gulf during the flood, when the concentrations of AHCs in surface waters reached 325 mu g/L, PAHs-15 ng/L, particulate matter-15.5 mg/L. In the Kara Sea itself, AHC concentrations increased on average from 20 to 59 mu g/L, that is most likely associated with the melting of seasonal ice and floods. Anthropogenic influence was found in river waters, where the proportion of naphtha-lenes, which marks oil products, and pyrene, which marks pyrogenic PAHs, is increased. In the Ob Gulf is linked to an increase in navigation along the Northern Sea Route and the functioning of the port of Sabetta. In the mouth area of the Yenisei, the concentrations of both AHC and PAH in surface waters and sediments varied in a smaller range than in the mouth area of the Ob, which is due to the nature of the rocks that make up the catchment areas of these rivers, as well as the regulation of the Yenisei runoff. The hydrological features of the estuarine areas can lead to increased AHC concentrations (the mouth of the Khatanga, up to 189 mu g/L, 2.6 mu g/mg SPM). The minimum AHC content in SPM and sediments in the river transects was established in the East Si-berian rivers (Indigirka, Kolyma), associated with the decreasing productivity in waters from the Western Arctic seas to the Eastern.

Hydrocarbons in water, suspended matter and bottom sediments of the Barents Sea were studied based on materials from expeditions to the RV Akademik Mstislav Keldysh in 2016–2019. It is shown that at present there is no oil pollution in open areas of the Barents Sea. With the transition from early summer (2019) to autumn (2016), there was a decrease in hydrocarbon concentrations in surface waters, caused by a change in the biochemical composition of organic matter (possibly due to a decrease in the area of ice). With depth, the HC content decreased mainly. An exception was observed in the area of gutters and deposits, where in the bottom nepheloid layers there was an increase in the concentration of hydrocarbons in suspension and in the surface layer of bottom sediments, and in the thickness of the sediments there was no dependence on their distribution and organic carbon.

The results of long-term studies of organic compounds in separated water bodies in two regions: Lake Stepped, Prydz Bay, Commonwealth Sea, (Antarctica) and lakes of the periphery of the Kandalaksha Gulf of the White Sea (the Arctic) are presented. It is established that the eutrophication of these reservoirs largely depends on the connection of these lakes with the sea. Coastal anthropogenic activity affects to a lesser extent. The restoration of the ecosystem of these lakes occurs at the launch of sea waters. The greatest differences between organic compounds in the Arctic and Antarctic waters are established in hydrocarbons. In Antarctica, due to the lack of vegetation, alkanes are dominated by autochthonous compounds, and in the Arctic along with autochthonous, allochthonous.

The first data on the content of organic compounds (OCs), i.e., Corg, lipids, and hydrocarbons (aliphatic (AHCs) and polycyclic aromatic (PAHs)) in the suspended particulate matter of the surface waters and bottom sediments in the western Kara Sea and the Gulf of Ob during the period of seasonal ice melting (July 2019) are considered. The highest content of OCs and suspended particulate matter in surface waters was found in the Gulf of Ob: AHCs up to 325 μg/L, PAHs up to 15 ng/L, and suspended particulate matter up to 15.5 mg/L. In the sea basin, the AHC concentrations increased, on average, from 20 to 59 μg/L, which was associated with flooding. A sharp decrease in all OC components supplied by the river runoff is observed at the geochemical barrier between the Gulf of Ob and the Kara Sea. The production of hydrocarbons and intensification of navigation in the southern part of the Kara Sea affect the AHC and PAH composition. The decomposition of autochthonous suspended particulate matter including the suspended OCs during sedimentation leads to the absence of increasing concentrations of Corg, AHCs, and PAHs in the bottom sediments, unlike those in the surface waters.

The results of the study of hydrocarbons (HCs): aliphatic (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in bottom sediments (2019 and 2020, cruises 75 and 80 of the R/V Akademik Mstislav Keldysh) in the Norwegian-Barents Sea basin: Mohns Ridge, shelf Svalbard archipelago, Sturfiord, Medvezhinsky trench, central part of the Barents Sea, Novaya Zemlya shelf, Franz Victoria trough are presented. It has been established that the organo-geochemical background of the Holocene sediments was formed due to the flow of sedimentary material in the coastal regions of the Barents Sea on shipping routes. The anthropogenic input of HCs into bottom sediments leads to an increase in their content in the composition of Corg (in the sandy sediments of the Kaninsky Bank at an AHC concentration up to 64 μg/g, when its proportion in the composition of Corg reaches 11.7%). The endogenous influence on the of the Svalbard archipelago shelf in Sturfiord and in the Medvezhinsky Trench determines the specificity of local anomalies in the content and composition of HCs. This is reflected in the absence of a correlation between HCs and the grain size composition of sediments and Corg content, as well as a change in hydrocarbon molecular markers. At the same time, the sedimentary section is enriched in light alkanes and naphthalene’s that may be due to emission during point discharge of gas fluid from sedimentary rocks of the lower stratigraphic horizons and/or sipping migration.

The article gives the results of studies of the concentration and composition of aliphatic hydrocarbons in suspension in surface water and in the surface layer of bottom sediments in April and September 2019 in Kerch Strait compared with other regions of the Black Sea. Notwithstanding the high concentrations of aliphatic hydrocarbons (especially, in the water of the strait itself, i.e., 110–160 µg/L and in sand sediments, i.e., 16–63 µg/g), the composition of alkanes was not of petroleum type because of the rapid transformation of petroleum hydrocarbons. The pollution of water and sediments in the strait manifested itself in a higher concentration of hydrocarbons in the composition of lipids and Corg, in the presence of naphthene-aromatic compounds in alkane composition, and in the predominance of phytane over pristine.

The results of long-term studies of the distribution and composition of hydrocarbons (HCs) in the suspended particulate matter and bottom sediments of the Norwegian and Barents Seas during cruises of the research vessel Akademik Mstislav Keldysh in 2016–2020 are presented. An increase in HCs concentrations in surface water from an average of 2.8–8.3 (2016–2017) to 20–23 μg/L (2019–2020) was detected, which was due to climate change. In bottom sediments, the distribution of HCs depends not only on the conditions of sedimentation and the particle size composition, but also on the variability of redox conditions and endogenous flows from sedimentary strata.

The results of studying the content and composition of aliphatic hydrocarbons (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in the suspended particulate matter of the surface water layer and in the surface layer of bottom sediments in Kerch Strait in April and September 2019 are given in comparison with other areas of the Black Sea. In spite of the high concentrations of AHCs, in waters of the strait (110–160 μg/L) and in sandy sediments (16–63 μg/g) in particular, the composition of alkanes does not correspond to oil because of the rapid transformation of oil AHCs. The contamination of water and sediments in the strait by oil HCs results in the presence of naphthenic-aromatic compounds in alkanes, the domination of phytane over pristine, and the domination of pyrogenic and to a smaller rate of oil HCs in the composition of PAHs.