Study of Oceanographic Conditions in the Area of the Avachinskiy Bay, Kamchatka, in Winter during an Expedition on the R/V Akademik Oparin (Cruise 65).

During cruise 65 of the R/V Akademik Oparin from November 26 to December 29, 2022, research was continued in the area of Avachinskiy Bay, Kamchatka, to study the possible factors that caused the mass mortality of marine organisms in fall 2020, and perform integrated hydrographic and hydrochemical surveys on the northeastern shelf of Sakhalin Island to monitor the environmental situation in areas of oil and gas production and in the southern Sea of Okhotsk. According to data from two autonomous moorings deployed in the coastal zone of Avachinskiy Bay with an exposure of 169 days, relatively calm water dynamics in the bay were noted throughout the entire summer–fall season of 2022, which contributed to enrichment of waters in nutrients necessary for plankton development. No noticeable decrease in oxygen content was recorded. A survey of the southern part of the East Kamchatka Current was carried out, the evolution and the structure of the anticyclonic eddy of Avachinskiy Bay at the time of its splitting was traced. Studies have been carried out on the hydrochemical characteristics of coastal bays and rivers during the freeze-up period. Samples of plankton and bottom sediments were taken for special analyses in the laboratories of the Pacific Institute of Bioorganic Chemistry and National Center for Marine Biology, Far Eastern Branch, Russian Academy of Sciences. [ABSTRACT FROM AUTHOR]