VARIABILITY OF OXIC/ANOXIC CONDITIONS OVER THE FIELDS OF METHANE SEEPS AT THE NW BLACK SEA SHELF SLOPE
Keywords:
The Black Sea, oxic/anoxic interface, temporal and spatial variability, gas seep microbial mats and reefs, control of oxidation of methaneAbstract
CTD data, H2S water column samples and detailed bathymetric survey of the underwater Dnieper paleo-delta were analyzed to study of temporal and spatial fluctuations of oxic/anoxic interface over the gas seepage area, where methane-related microbial mats and carbonate reefs are highly developed. Time-series CTD measurements have allowed to estimate temporal variability of the isopycnal surfaces with sigma-theta (σ) values 15.4 (oxycline encased with the permanent pycnocline) and 16.2 (oxic/anoxic interface). In the investigated region quasi-periodical vertical fluctuations of the H2S-waters upper boundary (σ = 16.2) between 130 and 165 m depths, i.e. up to 35 meters, have been observed. At the area of massive microbial reefs within this depths range a seabed slope angles have been changed from 1.5o to 13.0o. Accordingly, a specific belt–like zone of periodic near-bottom water redox-changes could to cover a great distance across the shelf slope – up to 1100 m. In view of fact that microbial control of methane oxidation and control of CH4-fluxes it can be both aerobic or anaerobic process, it should to influence on the type, pathways and activity of microbial oxidation of methane within the gas seep fields.
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