The South China Sea is a fairly well researched area. Areas of the continental shelf have been studied to a lesser extent. They are characterized by places of gas, hydrocarbon sources and oil and gas fields. The studies were carried out during the Russian-Vietnamese geological and geophysical expedition of the POI FEB RAS during the 88th cruise of the R/V “Akademik M.A. Lavrent’yev” (October 25 – December 08, 2019). The area of work included about the Vietnamese water area of the South China Sea (the area of the Nam Con Son basin, the area of the central Vietnamese shelf and slope (Fu Han basin), and the area of the sedimentary basin of the Red River). Geological sampling of bottom sediments was carried out at sea depths from 50 to 2400 m. We studied the distribution and abundance of methanotrophic, hydrocarbon-oxidizing and sulfate-reducing microorganisms in different horizons in core of bottom sediments. The dependence of the distribution of indicator groups of microorganisms on the sampling depth is considered. The studies carried out allowed us to conclude that there is a high degree of correlation between the number of microorganisms and changes in the concentration of methane in the core. The features of the growth of the studied groups of microorganisms at different temperatures of cultivation are noted. It is shown that the possible participation of sulfate-reducing microorganisms in the formation of sulfide mineralization (hydrotroilite and marcasite) in the sediment.

Eskova Alena Igorevna, Researcher, Laboratory of Comprehensive Study of the Environment and Mineral Resources, V.I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: alena-esya@mail.ru 

Ponomareva Anna Leonidovna, Candidate of Sciences (Biology), Senior Research Scientist, Laboratory of Comprehensive Study of the Environment and Mineral Resources, V.I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: giston@list.ru 

Legkodimov Aleksey Aleksandrovich, Postgraduate, V. I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: alexey.legkodimov@gmail.com 

Kalgin Vladislav Yur’evich, Postgraduate, V.I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: kalgin.vladislav@yandex.ru 

Shakirov Renat Belalovich, Doctor of Sciences (Geology and Mineralogy), Head, Laboratory of Gas Geochemistry, V.I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: ren@poi.dvo.ru 

Obzhirov Anatoly Ivanovich, Doctor of Sciences (Geology and Mineralogy), Head, Laboratory a Comprehensive Study of the Environment and Mineral Resources, V.I. Il'ichev Pacific Oceanological Institute FEB RAS, 43, Baltiyskaya st., Vladivostok, 690041, Russian Federation, e-mail: obzhirov@poi.dvo.ru

Eskova A.I., Ponomareva A.L., Legkodimov A.A., Kalgin V.Yu., Shakirov R.B., Obzhirov A.I. The Characteristics and Distribution of Indicator Microorganisms in the Marine Sediments from the South-China Sea. The Bulletin of Irkutsk State University. Series Earth Sciences, 2020, vol. 33, pp. 33-43. https://doi.org/10.26516/2073-3402.2020.33.33 (in Russian)

Rodnikov A.G., Zabarinskaja L.P., Rashidov V.A., Sergeeva N.A., Nisilevich M.V. Glubinnoe stroenie kontinentalnyh okrain regiona Juzhno-Kitajskogomorja [Deep structure of the continental margins of the South China sea region]. Vestnik KRAUNC. Nauki o Zemle, 2011, no. 2, iss.18, pp. 52-72 (in Russian)

Shakirov R.B., Sorochinskaja A.V., Jacuk A.V., Aksentov K.I., Karabcov A.A., Vovna V.I., Osmushko I.S., Korochencev V.V. Ikait v zone metanovoj anomalii na kontinentalnom sklone Japonskogo morja [Ikait in the zone of methane anomaly on the continental slope of the sea of Japan]. Vestnik Kamchatskoj regionalnoj organizacii uchebno-nauchnyj centr. serija: Nauki o Zemle, 2020, no. 2 (46), pp. 72-84 (in Russian)

Egorov N.S. Praktikum po mikrobiologii [Workshop on Microbiology]. Moscow, Mosсow State Univ. Publ., 1976, 307 р. (in Russian)

Rukovodstvo po metodam biologicheskogo analiza morskoi vody i donnykh otlozhenii [A guide to the methods of biological analysis of sea water and bottom sediments]. Ed. A.V. Tsyban. Leningrad, Gidrometeoizdat Publ., 1980, 192 p. (in Russian)

Graw M.F., D'Angelo G., Borchers M., Thurber A.R., Johnson J.E., Zhang C., Liu H.,  Colwell F.S. Energy Gradients Structure Microbial Communities Across Sediment Horizons in Deep Marine Sediments of the South China Sea. Front. Microbiol., 2018, vol. 9, pp. 1-12. https://doi.org/10.3389/fmicb.2018.00729

Jochum L.M., Chen X., Lever M.A., Loy A., Jørgensen B.B., Schramm A., Kjeldsen K.U. Depth Distribution and Assembly of Sulfate-Reducing Microbial Communities in Marine Sediments of Aarhus Bay. Applied and environmental microbiology, 2017, vol. 83, no. 23, pp. 01547-17. https://doi.org/10.1128/AEM.01547-17

Jilan S. Overview of the South China Sea circulation and its influence on the coastal physical oceanography outside the Pearl River Estuary. Continental Shelf Research, 2004, vol. 24, no. 16, pp. 1746-1760. https://doi.org/10.1016/j.csr.2004.06.005

Wu J.-M. A history of oil and gas exploration in the central and northern parts of the South China Sea. Energy, 1985, vol. 10, no. 3-4, pp. 413-419. https://doi.org/10.1016/0360-5442(85)90057-X