The paper discusses the consequences of the accidents with tankers Volgoneft-212 and Volgoneft-239 in the Black Sea on December 15, 2024. The post-emergency study had showed that the water area near Anapa had been the most polluted. The decrease in hydrocarbon concentrations observed 2.5 months after the accident was due to both their physical weathering on the shore and in the water, and the bacterial degradation. As a result, the concentration of chloroform-extractable bitumen decreased, as well as low-molecular alkanes and polyaromatic hydrocarbons (PAHs) in its composition. However, the composition of hydrocarbons remained dominated by oil-derived compounds in the suspended matter of bottom waters and in surface sediments. After 3.5 months, light n-alkanes up to n-C17 and naphthalenes were almost negligible in the oil lumps. In the surface sediments, the concentrations of aliphatic hydrocarbons also declined. In the Kerch Strait, they decreased from 71 to 53 μg/g (dry weight) and from 1.15 to 0.86 % Corg normalized; in the Anapa area, they dropped from 31 to 25 μg/g (dry weight) and from 5.63 to 3.06 % Corg-normalized. The content of n-C17 and odd high molecular weight homologues increased. In contrast, PAH concentrations slightly rose in the Anapa area mainly because of the increase in phenanthrene content. In the area of the Kerch Strait and Crimean Peninsula, they went up driven by pyrogenic PAHs. This suggests inputs from vessel traffic and shipping related activities as these areas are high traffic maritime routes. The toxicity index in the sediments of Anapa area decreased from an average of 82 % in March to 63 % in April 2025, while the total toxicity level declined from 0.33 to 0.07. Concentrations of individual PAHs did not exceed the Canadian interim quality guidelines for marine surface sediments.

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

One year after the emergency diesel fuel spill in Norilsk, hydrocarbon concentrations in bottom sediments of the Norilsk-Pyasina water system decreased. However the average concentrations of hydrocarbons in surface sediments decreased in the same sequence (mu g/g) as in 2020: the mouth of the Ambarnaya R. (835, sigma = 1788) > Bezymyanny Cr.-the Daldykan R.-the Ambarnaya R. (306, sigma = 273) > the Pyasina R. (23, sigma = 20) > the Pyasino Lake (12, sigma = 8). Concentrations decreased due to degradation of low molecular weight hydrocarbons. The content of polycyclic aromatic hydrocarbons in 2021 also changed in a smaller range (0-1027 ng/g) than in 2020 (0-3865 ng/g). Petroleum origin of polycyclic aromatic hydrocarbons in the sediments of the Ambarnaya R. (including the mouth), Bezymyanny Cr. and the Daldykan R. is confirmed by the dominance of alkylated naphthalene homologues in their composition. Hydrocarbons accumulation in some layers of the sedimentary column is caused not only by the spill of diesel fuel, but also by the organic matter from the surrounding swamps, from wetlands and floodplain lakes, as well as by the burial of the surface layer by the 2021 flood.

The study analyzes polycyclic aromatic hydrocarbons (PAHs) isolated from bottom sediments of the Barents and Norwegian seas (2019–2021 cruises of the R/V Akademik Mstislav Keldysh). Elevated PAH concentrations (up to 16 900 ng/g) are recorded in the coastal region of the Svalbard archipelago, and low ones, in the Greenland Basin and the eponymous ridge (up to 80 ng/g), as well as on the continental slope of the Barents Sea (up to 240 ng/g on average). Among cata-condensed PAHs, 2–3 ring polyarenes are the most common: naphthalene, 1- and 2-methylnaphthalenes, and phenanthrene, while among peri-condensed PAHs, 4–6 ring polyarenes are the most typical: fluoranthene, pyrene, and benz(a)anthracene. Anthropogenic sources in the bottom sediments of the study area are of subordinate importance compared to their natural input from the sedimentary stratum with fluid fluxes and erosion.

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

Using the remote sensing data obtained by the Sentinel-1A and Sentinel-1B satellites in the years 2016–2021, a local accumulation of oil slicks in the Barents Sea in 53 synthetic aperture radar images is delineated in the area with coordinates 75.2°–75.3° N and 31.5°–31.8° E. The study of an undisturbed core in this area (station 7105, 84th cruise of the R/V Akademik Mstislav Keldysh) has shown an anomalous distribution of polycyclic aromatic hydrocarbons, PAHs, the concentrations of which increased at the lower horizons of the column, and 2-methylnaphthalene, a marker of oil genesis, dominated in their composition; at the same time, the share of light homologs in the composition of alkanes increased. All this points to the natural formation of hydrocarbons in the sea bottom sediments, and it is definite that the group of oil slicks detected from the satellite radar data is a natural oil seep.

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.

Several geochemical characteristics ((La/Yb)N, Eu/Eu*, and Th content) of gray silts of the Volga River, suspended particulate matter of the Lena River, and silt–pelite fraction of bottom sediments in the Yangtze River are analyzed. It has been established that the above parameters of the chondrite-normalized lanthanide spectra and the Th content turn out in almost all cases to be comparable with their values determined for the specially prepared (removal of nonterrigenous carriers of rare earth elements (carbonate minerals, Fe–Mn oxyhydroxides, and organic components) pelite fractions of bottom sediments deposited near the mouths of named major rivers, and are retained over thousands of kilometers upstream from their deltas/mouths. The regulation of the Volga and Yangtze flows does not have a significant impact on parameters of the suspended particulate matter and bottom sediments under consideration.

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.

Results of a joint Russian-Brazilian expedition to study the dynamics of continental river runoff in the ocean associated with the Amazon plume are presented. The stations of the study region covered the seaward part of the Amazon plume. The work was carried out in the dry season (November). The data of in situ measurements and satellite data show that the most desalinated and rich in suspended particulate matter and chlorophyll-a waters were localized on the shallow inner shelf. The horizontal and vertical structure of the thermohaline fields indicates the presence of a well-pronounced river plume about 15 m thick. The decrease in salinity in the plume relative to the background values exceeded 6 PSU even at 300–400 km from the river mouth. The plume waters were characterized by increased concentrations of suspended matter. The best approximation to the in situ measurements is provided by the SMOS satellite salinity data and reanalysis GLORYS12. Chemical determinations in the surface layer in the area of the plume reveal elevated concentrations of silicates, phosphates, and nitrites compared to the seaward part.

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).

—It is shown that a large number of organic compounds of autochthonous and allochthonous nature are formed in the bottom sediments of separating waterbodies in the Kandalaksha Gulf of the White Sea, despite their subarctic position. The average content of C org , N tot , S tot , aliphatic hydrocarbons, and polycyclic aromatic hydrocarbons in the bottom sediments are 5.33, 0.78, 0.53%, 817 μg/g, and 261 ng/g, respectively, which are significantly higher than in sediments of the open areas of the White Sea. The eutrophication of these waterbodies depends on their connection with the sea. It was found that anoxic pelitic sediments of separating lakes are enriched in Cu, Cd, Mo, Hg and U compared to sediments of the open sea bays in Kandalaksha Gulf. Thereby, the Hg and Mo contents are 2 and 14 times higher than their maximum permissible concentrations (MPC) (0.3 and 3 µg/g, respectively). A positive correlation with total sulfur ( r > 0.8, р < 0.01) indicates the prevailing occurrence of these metals in form of poorly soluble sulfides.

One year after the emergency diesel fuel spill in Norilsk, the hydrocarbon concentrations in bottom sediments of the Norilo-Pyasinsk water system decreased. However, the average decrease in the areas occurred in the same sequence (µg/g) as in 2020: the mouth of the Ambarnaya River (835, σ = 1788) > Bezymyannyi Creek–Daldykan River–Ambarnaya River (306, σ = 273) > the Pyasina River (23, σ = 20) > Pyasino Lake (12, σ = 8). The concentrations decreased due to degradation of low molecular weight hydrocarbons. The content of polycyclic aromatic hydrocarbons also changed in a smaller range (0–1027 ng/g) in 2021 than in 2020 (0–3865 ng/g). The petroleum origin of polycyclic aromatic hydrocarbons in the sediments of the Ambarnaya River (including the mouth), Bezymyannyi Creek, and the Daldykan River confirms the dominance of alkylated naphthalene homologs in their composition. Hydrocarbon accumulation in certain horizons of the sedimentary stratum is caused not only by seepage of diesel fuel, but also by the input of organic matter from the surrounding swamps and floodplain lakes, as well as by the burial of the surface layer by the 2021 flood.

—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.

One year after an emergency spill of diesel fuel in Norilsk, hydrocarbon concentrations in bottom sediments of the Norilo-Pyasinskaya Water System decreased, but, on the average over the regions, they decreased in the surface layer in the same order as in 2020: Ambarnaya River mouth (835 µg/g, σ = 1788) > Bezymyannyi Creek—Daldykan River—Ambarnaya River (306 µg/g, σ = 273) > Pyasina River (23 µg/g, σ = 20) > Pyasino Lake (12 µg/g, σ = 8). The decrease in the concentrations was due to the degradation of low-molecular hydrocarbons. The concentration of polycyclic aromatic hydrocarbons in 2021 also varied within a narrower interval (0–1027 ng/g) than in 2020 (0–3865 ng/g). The oil origin of the hydrocarbons in the sediments of the Bezymyannyi Creek and the rivers of Daldykan and Ambarnaya is confirmed by their high content of alkylied naphthalene homologues. The accumulation of hydrocarbons in some horizons of the sedimentary stratum is due not only to the seepage of diesel fuel, but also to the input of organic matter from swampy areas and floodplain lakes, as well as to the burial of the surface layer by the flood of 2021.

The study of the particle size distribution in the near-water aerosol, as well as suspended particulate matter (SPM) and organic compounds (OCs) in SPM in the surface waters of the South and Atlantic oceans showed that in the near-water atmosphere the minimum number of particles was found in the coastal regions of Antarctica due to the ice cover on the continent (for 0.3–1 μm particles, on average, 6182 particles/L). The maximum amount of aerosols (on average 28186, maximum 55389 particles/L) confined to coastal Europe is related to their influx from industrial areas and shipping. The latter led to a chaotic change in the concentrations of aerosols and OCs in surface waters (up to 70 μg/L, 214 μg/mg SPM for hydrocarbons in the English Channel). The fluxes from Patagonia and the African deserts lead to an increase of aerosols up to 33 824–34 893 particles/L, where they have the greatest effect, due to the mineral nature, on the SPM distribution in surface waters. The distribution of aerosols on the Africa–Antarctica section was mainly controlled by the frontal zones of surface waters; therefore, their content correlated with the speed of the wind blowing them out from the sea surface: r = 0.82. The La Plata River–Atlantic Ocean geochemical barrier affects the variability of the OCs and SPM concentrations in the surface water of the Montevideo area, where the SPM content varied from 0.23 to 1.3 mg/L, and HCs, from 7 to 48 μg/L (up to 37 μg/mg SPM).