Carbon dioxide assimilation and methane oxidation in various zones of the rainbow hydrothermal field

Rates of carbon dioxide assimilation and methane oxidation were determined in various zones of the Rainbow Hydrothermal Field (36 degreesN) of the Mid -Atlantic Ridge. In the plume above the hydrothermal field, anomalously hig h methane content was recorded, the microbial population density (up to 10( 5) cells/ml) was an order of magnitude higher than the background values, a nd the CO2 assimilation rate varied from 0.01 to 1.1 mug C/(1 day). Based o n the data on CO2 assimilation, the production of organic carbon due to bac terial chemosynthesis in the plume was calculated to be 930 kg/day or 340 t ons/year (about 29% of the organic carbon production in the photic zone). I n the black smoke above active smokers, the microbial population density wa s as high as 10(6) cells/ml, the rate of CO2 assimilation made up 5-10 mug C/(1 day), the methane oxidation rate varied from 0.15 to 12.7 mul/(1 day), and the methane concentration ranged from 1.05 to 70.6 mul/l. In bottom se diments enriched with sulfides, the rare of CO2 assimilation was at least a n order of magnitude higher than in oxidized metal-hearing sediments. At th e base of an active construction, whitish sediment was found, which was cha racterized by a high methane content (92 mul/dm(3)) and a high rate of meth ane oxidation (1.7 mul/(dm(3) day)).