Microbial processes at the aerobic-anaerobic interface in the deep-water zone of the Black Sea

Chemical and key microbiological processes (assimilation of carbon dioxide, oxidation and formation of methane. and sulfate reduction) occurring at th e aerobic-anaerobic interface in the deep-water zone of the Black Sea were investigated. Measurements were taken at depths from 90 to 300 m at interva ls of 5-10 m. The integral rate of the dark assimilation of carbon dioxide varied from 120 to 207 mg C/(m(2) day) with a maximum at the boundary of cy clonic currents. The organic matter (OM) formed from methane comprised less than 5% of the OM formed from carbon dioxide. A comparison between the rat es of methane oxidation and methane production suggests that methane that i s oxidized at depths from 100 to 300 m was formed in deeper water horizons. The maximum rate of sulfate reduction (1230 mg S/(m(2) day)) was observed in the western halistatic region, and the minimum rate (490 mg S/(m(2) day) ), in the eastern halistatic region. The average rate of hydrogen sulfide p roduction measured at three deep-sea stations amounted to 755 mg S/(m(2) da y), or 276 g S/(m(2) year).