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 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.

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.

Geochemical data are presented on the Pleistocene sediments from the central part of the outer shelf of the East Siberian Sea, the continental slope and Podvodnikov Basin of the Arctic Ocean. The studied sediments of the outer shelf and continental slope belong to the aleuropelitic type, while those of the shelf edge and the Podvodnikov Basin, to the pelitoaleuritic type. The contents of the psammitic fraction and stone material do not exceed 10 and 1%, respectively. These features predetermine the distribution of the maximum sediment density and median diameters in the sediments of the outer shelf, and the minimum values in the Podvodnikov Basin. The distribution of Corg and Сcarb contents in the studied sediments is characterized by a similar variability. The average wetness content in the bottom sediments in the study area systematically increases in the “shelf–pelagial” direction. The study of the chemical and gas composition of the bottom sediments in the same direction made it possible to distinguish four main groups of geochemical associations in the Pleistocene sediments of the study area. The bottom sediments of the outer shelf are characterized by the maximum concentrations of the first group of chemical elements (Si, Sr, Ba) and methane (up to 0.102 cm3/kg), those of the shelf edge, by the maximum concentrations of the second group (Cd, Hg, U, K, Ca) and the minimum content of methane (up to 0.002 cm3/kg). The sediments of the continental slope have the maximum concentrations of the third group (Cu, Zn, Ti, Be, Nb, Ag, Tl, Pb, Lu, Tm, Tb, Ho, Eu, Yb, Er, Dy), while those of the Podvodnikov Basin, the fourth group (Mn, Fe, Al, Cr, P, Mg, Mo, Ni, Sb, Sn, As, Th, Co, Ga, W, Hf, Rb, V, Cs, Sc, Li, Gd, Sm, Pr, Nd, La, and Ce) and intermediate contents of methane (up to 0.051 cm3/kg). The maximum total concentration of methane homologues (up to С5 including, 0.006 cm3/kg), δ13С-СН4 (up to –36.0‰), δ13С-С2Н6 (up to –17.2‰), molecular mass of the hydrocarbon fraction (up to 27.5 g/mol), coefficient of transformation and “wetness” of the hydrocarbon fraction were found in the Pleistocene sediments of the continental slope and the foot of the Podvodnikov Basin, while the lowest concentrations of these parameters were determined in the outer shelf. The established isotope-gas-geochemical indicators point to the predominance of epigenetic hydrocarbon gases from various gas sources in the studied sediments. The positive and negative correlations between geochemical and isotopic-gas-geochemical indicators have been established. Obtained data were used to estimate the oil and gas prospects of the study area.

This paper reports new data on the composition of hydrocarbon gases in bottom sediments of the Laptev–East Siberian marginal shelf transition zone, the continental slope of the Lomonosov Ridge, and Podvodnikov Basin of the Arctic Ocean. Anomalous concentrations of methane and hydrocarbon gases (up to C5 inclusive) have been established. Gas-geochemical indicators of eight genetic groups of hydrocarbon gases have been determined. The oil-and-gas content of the study area has been predicted based on the data obtained.

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.

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.

The brief results of integrated research in the southern part of the Tatar Strait and the northern part of the Sea of Japan obtained during the 85th cruise of the R/V Akademik M. A. Lavrentyev are presented. The characteristics of the bathymetric, gravimetric, magnetometric, hydrological, lithological, microbiological, and gas-geochemical studies are given. The bottom topography has been refined, new distributions of the geophysical fields were obtained, the gas-geochemical background has been specified, foraminifera species in bottom sediments were identified, bioindicator (bacterial) species were discovered and the distribution of the main ecotrophic groups is described. An abnormal water distribution was found in the southern part of the Tatar Strait and a large amount of hydrological, meteorological, and atmochemical observations in the water area of the study region were carried out.

Preliminary results of integrated oceanographic and geophysical observations in the profile of Peter the Great Bay – Tsushima Strait (the Sea of Japan, October 2019). A.А. LEGKODIMOV1, M.A. BOVSUN1,2, D.A. SHVALOV1, G.I. MISHUKOVA1, M.V. IVANOV1, N.A. LIPINSKAYA1, M.V. SHAPOVALOVA1 (1V.I. Il’ichev Pacific Oceanological Institute, FEB RAS, Vladivostok, 2Far Eastern Federal University, Vladivostok), A.G. SHIYANOV3 (3Ural State Mining University, Ekaterinburg). 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.

According to the results of the 55-th cruise of R/V “Akademik Oparin”, methane fluxes from the Tatar Strait water area of the Sea of Japan were calculated and spatial variability of its emission into air was explored. The revealed variability of methane fluxes is consistent with the results of previous expeditions that confidently allow identifying the correlation of gas geochemical data with the geological structure of the Tatar Strait and the adjacent water areas. For the first time the ranking of directions and intensity of the values of methane fluxes for interpretation of their distribution and origin was proposed.