Methane as a source of organic matter and carbon dioxide of carbonates at a cold seep in the Norway sea

The survey carried out with manned submersibles Mir in the area of gas-satu rated and gas hydrate (CH4) vents at an arctic mud volcano (72 degrees N) a llowed us to ascertain the specific features typical of most methane seeps, i.e., the carbonate chimneys, up to 30 cm high, the methane plume in the n ear-bottom water layer (0-25 cm) with active anaerobic methane oxidation, t he development of bacterial mats with a predominance of filamentous colorle ss sulfur bacteria, the development of a benthic symbiotrophic community wi th prevailing pogonoforas, the mixing of deep CH4 fluid with porous and sea water, the active anaerobic oxidation of migrating methane in surface depo sits (0-20 cm) presumably with the paticipation of methane-forming and sulf ate-reducing bacteria, and the depletion of carbonate and organic carbon in C-13. About 0.15 l of methane are oxidized each day in one square meter of sediment cover, 0-20 cm thick. The rate of methane-derived carbon incorpor ation into the bacterial biomass is 11 mg/m(2) per day. The carbone dioxide that is resulted from methane oxidation (similar to 83% of oxidized methan e volume) is consumed for the formation of carbonate illite-calcite-barite chimneys, crusts, and nodules.