Sulfur and carbon in mIcrobial processes in waters and sediments of the Kara Sea in September 2007

Results of microbiological, biogeochemical and isotope geochemical studies in the Kara Sea are described. Samples for these studies were obtained during Cruise 54 of R/V Akademik Mstislav Keldysh in September 2007. The studied area covered the northern, central, and southwestern parts of the Kara Sea and the Obskaya Guba (Ob River estuary). Quantitative characteristics of total bacterial population and activity of microbial processes in the water column and bottom sediments were obtained. Total abundance of bacterioplankton (BP) varied from 250000 cells/ml in the northern Kara Sea to 3000000 cells/ml in the Obskaya Guba. BP abundance depended on concentration of suspensded matter. Net BP production was minimal in the central Kara Sea (up to 0.15-0.2 µg C/l/day) and maximal (0.5-0.75 µg C/l/day) in the Obskaya Guba. Organic material at the majority of stations at the Ob transect predominantly contained light carbon isotopes (-28.0 to -30.18 per mil) of terrigenous origin. Methane concentration in the surface water layer varied from 0.18 to 2.0 µl CH4/l, and methane oxidation rate varied from 0.1 to 100 nl CH4/l/day. Methane concentration in the upper sediment layer varied from 30 to 300 µl CH4/dm**3; rate of methane formation was varied from 44 to 500 nl CH4/dm**3/day and rate of methane oxidation - from 30 to 2000 nl CH4/dm**3/day. Rate of sulfate reduction varied from 4 to 184 µg S/dm**3/day

(Table 1) Characteristics of suspended particulate matter, its mass concentration, and total number of microorganisms in surface waters of the Severnaya Dvina River marginal filter in August 2005

During summer periods of 2003-2005, spatial and vertical distributions of suspended particulate matter and bacteria in stratified and homogeneous waters of the White Sea was studied. Results of the study of various quantitative characteristics of the suspended particulate matter (first of all, area of surface and volumetric and mass concentrations) and abundance of microorganisms in water are discussed. A direct correlation between the value of the surface area of the suspended particulate matter and the total number of bacteria in water is revealed. However, it was manifested only during the early summer period of observations and was not expressed at the end of summer. Enhanced surface area of the suspended particulate matter can indicate the higher biochemical activity of its particles. Influence of pelitic (<0.01 mm) size fraction on bacteria abundance in different parts of the sea during summer is estimated