(Table) Carbon, nitrogen and n-alkane content and isotopic composition of bottom sediments obtained in the East Siberian Sea

The chemical composition of organic matter (Corg, Norg, d13C, d1SN, and n-alkanes) was studied in the top layer of bottom sediments of the East Siberian Sea. Possible ways were proposed to estimate the amount of the terrigenous component in their organic matter (OM). The fraction of terrigenous OM estimated by the combined use of genetic indicators varied from 15% in the eastern part of the sea, near the Long Strait, to 95% in the estuaries of the Indigirka and Kolyma rivers, averaging 62% over the sea area.

Nutrients of pore water in sediments of the central equatorial Pacific

Shipboard whole-core squeezing was used to measure pore water concentration vs depth profiles of [NO3]-, O2 and SiO2 at 12 stations in the equatorial Pacific along a transect from 15°S to 11°N at 135°W. The [NO3]- and SiO2 profiles were combined with fine-scale resistivity and porosity measurements to calculate benthic fluxes. After using O2 profiles, coupled with the [NO3]- profiles, to constrain the C:N of the degrading organic matter, the [NO3]- fluxes were converted to benthic organic carbon degradation rates. The range in benthic organic carbon degradation rates is 7-30 ?mol cm**-2 y**-1, with maximum values at the equator and minimum values at the southern end of the transect. The zonal trend of benthic degradation rates, with its equatorial maximum and with elevated values skewed to the north of the equator, is similar to the pattern of primary production observed in the region. Benthic organic carbon degradation is 1-2% of primary production. The range of benthic biogenic silica dissolution rates is 6.9-20 µmol cm**-2 y**-1, representing 2.5-5% of silicon fixation in the surface ocean of the region. Its zonal pattern is distinctly different from that of organic carbon degradation: the range in the ratio of silica dissolution to carbon degradation along the transect is 0.44-1.7 mol Si mol C**-1, with maximum values occurring between 12°S and 2°S, and with fairly constant values of 0.5-0.7 north of the equator. A box model calculation of the average lifetime of the organic carbon in the upper 1 cm of the sediments, where 80 +/- 11% of benthic organic carbon degradation occurs, indicates that it is short: from 3.1 years at high flux stations to 11 years at low flux stations. The reactive component of the organic matter must have a shorter lifetime than this average value. In contrast, the average lifetime of biogenic silica in the upper centimeter of these sediments is 55 +/- 28 years, and shows no systematic variations with benthic flux.

Data on the biogeochemical cycle of methane in the ocean

Geological, mineralogical and microbiological aspects of the methane cycle in water and sediments of different areas in the oceans are under consideration in the monograph. Original and published estimations of formation- and oxidation rates of methane with use of radioisotope and isotopic methods are given. The role of aerobic and anaerobic microbial oxidation of methane in production of organic matter and in formation of authigenic carbonates is considered. Particular attention is paid to processes of methane transformation in areas of its intensive input to the water column from deep-sea hydrothermal sources, mud volcanoes, and cold methane seeps.