This paper is the first focused study of gas bubble emissions at the Crimean shelf in the northern Black Sea. During R/V Professor Vodianickiy 125/1 Cruise in November 2022 hydroacoustic and geochemical studies were carried out to detect gas seepage along Crimean coastline to assess methane-related processes taking place in the local hydrosphere. More than 200 bubble-induced hydroacoustic anomalies in the water column were found at 7.1 km2. We allocated 4 seepage areas which are arranged in the west of the study area and included most of the identified flares located primarily along 35-45 m isobaths. Vertical profiles of temperature, salinity, dissolved oxygen content were measured, and a video survey of the seafloor was conducted. The spatial and temporal variability of the flares was examined at Martyan seep site by multiple hydroacoustic surveys on a hours-and days-scales. The observations of the flare appearance showed that most flares are temporally variable. Calculated gas flow rate from individual flare ranged from 4.1 (0.04) to 88.6 (0.101) L center dot day-1 (t center dot year-1), while the average value was 38 (0.07) L center dot day-1 (t center dot year-1). Distinct methane transport from the seep sites into the hydrosphere was observed only for Martyan seep area by relative enrichments of dissolved methane in near-bottom waters. Sediments from the active seep area were significantly enriched in mercury (87 +/- 21 ng g-1) compared to the reference sites (26 +/- 7 ng g-1). Our analyses provide one of the first interdisciplinary descriptions of shallow gas seeps sites within the Black Sea seep system.

During cruise 71 of the R/V Akademik Oparinm the radioecological state of the Pacific Ocean east of Japan and the Kuril Islands, as well as the seas of Okhotsk and Japan, was assessed in connection with polluted water discharge from the Fukushima-1 NPP. The results of the first samples of surface analysis showed a tritium content of 0.36–0.78 tritium units (0.04–0.09 Bq/L). The highest concentrations were found in the jet of the Kuroshio Current and in the area of the Southern Kuril Islands. Meanwhile, it is ten thousands time lower than the radio security norm. On the cruise, samples of water, bottom sediments, and marine biota were prepared to analyze radio isotopes of cesium, strontium, lead, radium, etc. A large volume of hydrographic, chemical, biological, gas-geochemical, and mercury measurements and samplings was obtained. Mooring systems were recovered and redeployed. New data on the water state and dynamics of the study region were obtained, as well as biogeochemical parameters and their interannual variability in association with climate change and increasing anthropogenic load.

The peculiarities of the distribution of rare-earth elements (REEs) in the surface bottom sediments in the Gulf of Tonkin (South China Sea) are considered. According to the results of granulometric analysis, the sediments are mainly represented by pelitic silt, silty pelite, and miktites. The REE contents normalized to the chondrite composition show the absence of cerium anomaly, the presence of negative europium anomaly and significant fractionation of light and heavy REEs. The values of indicator ratios LaN/YbN, Cr/Th, Th/Co, La/Sc, and Th/Sc indicate the predominance of rocks of intermediate and acidic composition in the erosion areas, due to which sediments were formed. The values of the Ce/La and (Fe + Mn)/Ti ratios characterize the surface sediments as typically terrigenous without the admixture of endogenous exhalative material. The Eu/Sm ratio values indicate low permeability of the sediments for upward fluid flows, which is consistent with the measured methane concentrations. The analysis of correlations indicates the dominance of the terrigenous source of REEs and that clay minerals and iron hydroxides play a significant role in the migration and accumulation of REEs.

Investigation of the interannual and short-term variability of the water parameters in the seas of Japan and Okhotsk and their ecological state were continued on cruises 77 of the R/V Professor Gagarinskiy and 97 of the R/V Akademik M.A. Lavrentyev in fall–winter 2021. CTD profiling and water sampling for chemical analyses, including methane and radioisotopes, were carried out. Autonomous bottom stations were moored for 2.5 months. Long-term trends of bottom water warming, eutrophication, and acidification of the Sea of Japan have been confirmed. The specific features of fall–winter restructuring of the field of currents in the northern Sea of Japan, multifrontality of the Sakhalin upwelling structure, and bimodality of the Primorye Current are shown.

The paper presents brief results of comprehensive studies of waters of the Tatar Strait and Sea of Japan, obtained on cruise 79 of the R/V Professor Gagarinsky in May–June 2022. The distribution of geophysical fields was obtained, the block’s divisibility of the bottom of the water area was confirmed, and new data was obtained on the distribution of gases in the sedimentary sequence, bottom, and surface water. The electrokinetic parameters of microorganisms for evaluating their relationship with methane concentration was obtained, and micropalentological analysis of sedimentary deposits was performed.

The bioindication of oil and gas fields is a field of geomicrobiology that is mainly devoted to the detection of hydrocarbon-oxidizing microbial indicator species or functional genes in total DNA. However, it appears promising to use the physiological properties of microorganisms detection deposit type of hydrocarbons, in particular their ability to oxidize hydrocarbons under aerobic and anaerobic conditions. In this study, the most promising approach in this area was the method used for assessing the anaerobic degradation of hydrocarbons. When comparing molecular genetics and cultured methods of bioindication, it can be concluded that molecular biomarkers of functional genes for the anaerobic destruction of hydrocarbons (masD) make it possible to separate areas with traditional and gas-hydrate types of deposits. Using cultured methods, we found that representatives of the Nocardiaceae family of the phylum Actinomycetota were tied to the areas where gas hydrates were found. The ability of aerobic and facultative anaerobic hydrocarbon-oxidizing microorganisms to anaerobically utilize hydrocarbons was determined with cultured methods. For the first time, this ability was revealed for the genera Stenotrophomonas, Psychrobacter, Micrococcus and Peribacillus. The wide distribution of this ability that we found in strains isolated from both study regions suggests its prominent role in the destruction of hydrocarbons in marine sediments.

During the joint Russian-Vietnamese studies in the East Vietnam Sea (known as Bien Dong or the South China Sea), manifestations of new hydrocarbon-accumulating zones were discovered; evidences of the presence of mineral indicators for solid minerals in shelf deposits were obtained; a unique zone, where accumulations of ferromanganese crusts and nodules have been formed, was revealed for the first time; evidence of unique properties of deep-water fine-dispersed carbonate sediments (which makes it possible to attribute them to an independent type of mineral resources of the East Vietnam Sea) were obtained; the ikaite mineral (that serves as an indicator of methane migration zones and cold marine paleo-conditions) was discovered in the Phu Khanh basin; heavy concentrates with indicators of rare forms of ore mineralization were collected; features of methane and mercury fluxes into the atmosphere, cultures of methane-oxidizing, oil-oxidizing and sulfate-reducing bacteria were registered for the first time within the study areas. New data on gravity and magnetic field anomalies along the shelf and slope of Vietnam have been obtained. The article presents the results of coastal geophysical and gasgeochemical research obtained in 2010–2020 within the Joint Russian-Vietnamese Laboratory for Marine Geosciences (POI FEB RAS - IMGG VAST). For the first time, anomalous methane fields (comparable to anomalies on the oil- and gas-bearing shelf and the gas hydrate-bearing slope of Sakhalin Island) were registered in the water column. The gravimagnetic survey was carried out on the central and southern shelf and the continental slope of Vietnam; the executed works supplemented the geophysical data, which had been obtained in the 80s–90s of the preceding century. The paper contributes to the Russia-Vietnamese program within the UN Decade of Ocean Sciences for Sustainable Development framework.

The paper presents the results of studying the authigenic sulfide aggregates (pyrite) from sediments in the southwestern South China Sea. Materials for the study were obtained during a comprehensive geological-geophysical expedition aboard the R/V Akademik M.A. Lavrentyev (Cruise 88) (Shakirov et al., 2021). The morphology and microstructure of pyrite were studied. Isotopic studies of sulfur in pyrite were performed to elucidate the genesis of sulfides, and the abiogenic nature of their formation was substantiated for the first time in the Fu Han Basin. The biogenic origin of most other sulfide formations was confirmed by geomicrobiological investigations. The study of the composition and admixtures in pyrite revealed a high Ni content in this mineral.

The paper presents brief results of comprehensive studies of the water area of the Tatar Strait and Sea of Japan obtained on cruise 61 of the R/V "Akademik Oparin" in November-December 2020. The bottom relief and geophysical and gas-geochemical fields were refined, and new features of the geochemistry and mineralogy of bottom sediments were revealed.

The review is devoted to the biodiversity of microorganisms capable of degrading oil hydrocarbons in sea deep sediments and their relationship with the accompanying microbiota, which includes sulfate-reducing and denitrifying prokaryotes. Particular attention is paid to the biodiversity of hydrocarbon-oxidizing bacteria, in particular thermo- and hyperthermophilic bacteria, in the areas of oil fields. Sulfate-reducing microorganisms are widespread in them. Some of them are capable not only of sulfate reduction, but also of hydrocarbon oxidation. Such microorganisms were generally classified in the Deltaproteobacterium class. The relationship between the number of oil-oxidizing and denitrifying microorganisms is most often presented in areas with a high anthropogenic load and in the coastal zone. Possible mechanisms of anaerobic oxidation of hydrocarbons and the coexistence of aerobic and anaerobic microorganisms in a single community are briefly considered.

Abstract —The paper gives brief results of comprehensive studies in the South China Sea obtained from a joint Russian–Vietnamese expedition in November 2019 (cruise 88 of the R/V “Akademik M.A. Lavrentyev”). The set of methods included acoustics, geophysics, geology, mineralogy,geochemistry, paleogeography, geomicrobiology, hydrooptics and hydrology. The seafloor relief, geophysical and gasgeochemical fields have been refined; new features of the geochemistry and mineralogy of the continental shelf of Vietnam and the adjacent deep-sea basins have been revealed.

According to the Plan of Complex Scientific Research of the World Ocean for 2017–2022, the V.I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, continues to study the northern part of the Sea of Japan and the Tatar Strait, carrying out a three-year plan of expeditionary research of this region. The expedition aboard the R/V Akademik Oparin (cruise no. 55) spanned from October 2 to 19, 2018. Geophysical and gas-geological study of the water area in the central and southern parts of the Tatar Strait was continued. On the rookery of Tyuleny Island, in the Sea of Okhotsk, information on sea lions and larghas were recorded, three individuals of northern fur seal were tagged with satellite trackers to study their migration routes. CTD observations of the upper layer (down to 600 m) were made on transects across mesoscale eddies in the northern part of the Sea of Japan. Expeditionary research was supported by the Council of the Earth’s Hydorsphere of the Ministry of Science and Higher Education of the Russian Federation.

В ноябре 2019 г. в Южно-Китайском море (исключительная экономическая зона СРВ) впервые за последние 30 лет была проведена крупная комплексная геолого-геофизическая совместная экспедиция ТОИ ДВО РАН и Вьетнамской академии наук и технологий (88-й рейс НИС «Академик М.А. Лаврентьев»). Области изучения – геофизика, геология, гидроакустика, газогеохимия, гидрооптика, геомикробиология, палеогеография и гидрология. В толще вод и донных отложениях впервые обнаружены газогеохимические аномалии, сравнимые с аномалиями над нефтегазоносным шельфом о-ва Сахалин. Впервые в районе исследований выявлены геомикробиологические индикаторы углеводородных скоплений. Уточнены рельеф, геофизические поля, гидрологическая структура, особенности седиментации, палеогеографии и минералогии континентального шельфа Вьетнама и прилегающих глубоководных бассейнов. Предложено выделить тонкодисперсные карбонатно-глинистые осадочные отложения в самостоятельный минеральный ресурс. Выявлены районы, перспективные для поисков новых залежей нефти и газа, газогидратов, скоплений железо-марганцевых образований и др. Более 70 % научного состава экспедиции составляли молодые ученые. In November 2019, for the first time in 30 years, an integrated geological and geophysical joint expedition of the POI FEB RAS and the Vietnamese Academy of Science and Technology was carried out in the South China Sea (EEZ Vietnam) (88 cruise of the R/V “Akademik M.A. Lavrent’yev”). The set of methods consisted of geophysics, geology, hydroacoustics, gasgeochemistry, hydrooptics, geomicrobiology, paleogeography and hydrology. Gasgeochemical anomalies were found in the water column and bottom sediments, comparable with the anomalies over the oil and gas deposits along the Sea of Okhotsk shelf of Sakhalin Island. For the first time in the study area, deep water geomicrobiological indicators of hydrocarbon accumulations have been identified. The relief, geophysical fields, hydrological structure, features of sedimentation, paleogeography and mineralogy of the continental shelf of Vietnam and the adjacent deep sea basins are refined. Finely dispersed carbonate-clay sediments were proposed as a new mineral resource. Areas that are promising for the search for new deposits of oil and gas, gashydrates, accumulations of iron-manganese formations, and others are identified. Young scientists occupied more than 60 % of the scientific expedition staff.

Наиболее оперативную информацию о состоянии океана дает проведение комплексных исследований (гравиметрические наблюдения, измерения интенсивности флуоресценции, концентрации метана и хлорофилла-а в приповерхностном слое воды, ртути и газов в атмосферном воздухе) непосредственно во время следования судна. Наши исследования проводились на переходе Владивосток–Нячанг в период с 27 по 29 октября 2019 г. в Японском море в рамках рейса LV88 на НИС «Академик М.А. Лаврентьев». Полученные данные отличаются высокой сходимостью с результатами прошлых экспедиций (например, рейс LV84, 2018 г.). Нами выявлены зоны аномальных концентраций метана (8,3 нмоль/л), углекислого газа (2,3 ppm) и ртути (4 нг/м3), а также отмечены гравитационные аномалии в Корейском проливе. The study of the ocean by complex methods using a flow system and atmospheric air is currently one of the universal methods of obtaining express results (such as gravimetric observations, fluorescence intensity measurements, methane and chlorophyll-a concentrations in near-surface water, mercury and various gases in open air) directly during the vessel’s sailing. The studies were conducted on the Vladivostok – Nha Trang traverse during October 27–29, 2019 in the Sea of Japan as a part of the LV88 voyage aboard the R/V “Academic M.A. Lavrent’yev”. According to the results of the study, abnormal zones of concentrations of methane (8.3 nM/l), carbon dioxide (2.3 ppm) and mercury (4 ng/m3) were identified. We have also noted gravitation anomalies in the Korean Strait.

This paper reports the results of the third Russian–Vietnamese expedition (POI FEB RAS and the Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology) in the Gulf of Tonkin, South China Sea (April 2016) and field work outcomes from 2016-2017. The studies revealed new specific features of the distribution and origin of gas-geochemical fields in sediments within the rift zone of the Red River along a 150-km profile. Four zones with high amplitude anomalies of hydrocarbon gases, helium, hydrogen, carbon dioxide, and carbon monoxide were revealed. The distribution of the anomalies reflects the tectonic structure of the area and points to the presence of several lithospheric sources of gases including gases of deep origin. The studies were carried out within the scope of the Joint Vietnamese–Russian Laboratory for Marine Geosciences (POI FEB RAS and the Institute of Marine Geology and Geophysics, Vietnam Academy of Science and Technology). The article is dedicated to the year of friendship between Russia and Vietnam.

The interrelation of microbial processes in marine sediments of two areas in the Sea of Japan was studied. The southern area is located in the north of the Central (Japan) Basin; the northern area covers the southern part of the Tatar Trough near the La Perouse Strait. It is shown that microbial processes are less dependent on each other in the southern area than in the northern area, which allows us to conclude that the carbon source is more diversified in the southern area. In the northern area, the processes of methanotrophy and methanogenesis are more balanced relative to each other than in the southern area. A high correlation between microbial methane oxidation and sulfate reduction is revealed in the northern area. The study was conducted during the expedition of POI FEB RAS on the R/V "Akademik M.A. Lavrentyev" (Cruise No 81, 2018).