Microbial processes of the carbon and sulfur cycles in the Kara Sea

The results of microbiological, biogeochemical, and isotope geochemical studies in the Kara Sea are described. The samples for these studies were obtained during the 54th voyage of the research vessel Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Gulf of Ob. The quantitative characteristics of the total bacterial population and the activity of the microbial processes in the water column and bottom sediments were obtained. The total population of the bacterioplankton (BP) varied from 250000 cells/ml in the northern water area to 3000000 cells/ml in the Gulf of Ob. The BP population depended on the content of the water suspension. The net BP production was minimal in the central water area, amounting to 0.15–0.2 μg C/(l day), and maximal (0.5–0.75 μg C/(l day)) in the Gulf of Ob. The organic material at the majority of the stations in the Ob transect predominantly contained light carbon isotopes (−28.0 to −30.18‰) of terrigenous origin. The methane content in the surface water layer varied from 0.18 to 2.0 μl CH₄/l, and the methane oxidation rate changed in the range of 0.1–100 nl CH₄/(l day). The methane concentration in the upper sediment layer varied from 30 to 300 μl CH₄/dm³; the rate of the methanogenesis was 44 to 500 nl CH₄/(dm³ day) and that of the methane oxidation, 30 to 2000 nl CH₄/(dm³ day). The rate of the sulfate reduction varied from 4 to 184 μg S/(dm³ day).