Microbial Processes of the Methane Cycle at the North-western Shelf of the Black Sea

During expeditions in August 1995 and May 1997, the distribution of methane and the rates of its production and oxidation were studied in water and bottom sediments of the north-western shelf of the Black Sea. Experiments that involved the addition of 14CH3COOH and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 560–680 mol m 2 day 1) were found in coastal sediments in summer-time. In spring, methane production in the same sediments did not exceed 3·6 mol m 2 day 1. The 13C values of methane ranged from 70·7 to 81·8‰, demonstrating its microbial origin and contradicting the concept of the migration of methane from the oilfields located on the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of the methane (from 20 to 235 mol m 2 day 1) arrives at the atmosphere.