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Within the program "Marine Ecosystems of the Siberian Arctic," based on materials collected during cruises 69 and 72 of the R/V Akademik Mstislav Keldysh, the distribution of chemical elements (As, Ba, Bi, Co, Cr, Cr, Cd, Co, Cu, Cr, Mn, Ni, Pb, Sc, Ti, Tl, Th, V, U, and Zn) and organic carbon in the benthic mass taxa of methane seepage fields in the Laptev Sea and outside of them was examined. For the first time, the bioaccumulation potential (BP) was quantified, taking into account, in addition to the concentrations of elements in organisms, their biomass. On the C-15 methane field, the ophiuroid population accumulates each element per square meter of seafloor up to 40 times greater than at the background station. Ophiuroids and bivalves exhibited elevated BP for Ni, As, Ba, Cu, Ti, V, Mn, and Zn compared to other elements. At the same time, the BP of ophiuroids significantly exceeds that of bivalves. It is suggested that the increased bioaccumulation of some heavy metals and metalloids is related to greater bioavailability of organic matter in the bottom sediments of methane seeps. Organic carbon revealed the highest BP, which was especially pronounced in the C-15 methane field. At the background station, taxa accumulate a significantly smaller (by a factor of 10) amount of carbon in their biomass. As a result of the detritus feeders' activity, bottom sediments are enriched in organic carbon, which indicates an important contribution of benthic organisms to the carbon cycle in the Arctic seas. [ABSTRACT FROM AUTHOR] more...

From 2019 to 2021, integrated studies of new shallow-water methane bubble gas seeps were carried out in the coastal zone near Cape Fiolent (Southwest Coast of Crimea). The studies included determination of the hydrocarbon and isotope composition of bubble gas, measurement of the methane and nutrient concentration in the water in the areas of gas seeps, estimation of the value of bubble flows, and measurement of the hydrophysical parameters over the seep sites compared to background areas. A seasonal type of Cape Fiolent methane seeps was noted, and the durations of its active gas emission phases differed in different years. The increased pore water silica concentration at the seep sites and their localization in the vicinity of freshwater slope springs may indicate its association with submarine freshwater discharge in the area. However, no significant desalination of either pore water or the bottom water layer above the seeps was recorded. Dissolved methane concentrations in pore water at seep sites were two orders of magnitude higher compared to the background areas, reaching 448 μmol/L. High values were also obtained for surface water directly above the bubble gas emission points (maximum 353 nmol/L). Multihour monitoring of the hydrophysical parameters above the active seeps showed a decrease in dissolved oxygen compared to the background sites. The maximum difference in O2 concentrations was 3 mg/L. The carbon isotope composition of bubble gas methane δ13C-CH4 (–62.84 to –38.27‰) and carbon dioxide δ13C-CO2 (–16.83 to –10.17‰) corresponded to a mixture of isotopically heavy gas and near-surface isotopically light gas of microbial origin. The question remains open: what are the reasons for the change in the summer active and cold season passive gas emission phases? [ABSTRACT FROM AUTHOR] more...

On cruise 93 of the R/V Akademik M.A. Lavrentyev (2021), we studied benthic communities in the Gamov Canyon (Sea of Japan), off the eastern coast of Kamchatka, and methane seep communities of the Koryak slope (Bering Sea); in addition, data were obtained on the sea-air mercury flux. The studies confirm the potential of the Gamov Canyon as a model site for long-term monitoring. We document significant changes in the structure and composition of the fauna compared to 2018 in the background and methane seep communities of the Koryak slope. [ABSTRACT FROM AUTHOR] more...

On cruise 82 voyage of the R/V Akademik M.A. Lavrentyev, comprehensive studies of ecosystems associated with hydrothermal vents and cold seeps in the Bering Sea were carried out. New data on the composition and structure of benthic communities of the Piip volcano were obtained. A new area of cold seeps has been discovered on the Chukchi slope of the Bering Sea. At present, the chemosynthesis communities of the Chukchi slope are the northernmost of their kind known in Pacific, and the Chukotka population of Calyptogena is the northernmost Recent population of pliocardiines in the World Ocean. [ABSTRACT FROM AUTHOR] more...