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Abstract:
This study focuses on the influence of gas seepage on methane sources and sinks, aerobic and anaerobic oxidation of methane and the mediating microbial organisms in the Black Sea. We present data from two cruises that took place in 2001 and 2003. Seven stations (two from the shelf, four from the upper and lower slope, and one from the central basin) were compared with respect to methane concentration and isotope signature. The stations differed in methane concentration depending on the location on the slope. A strong change in the concentration and isotopic composition of methane was observed below the oxic/anoxic interface, coinciding with increased levels of archaeal biomarkers (archaeol and sn-2-hydroxy-archaeol). Concentration and isotopic composition of methane in the water column and sediments indicate that sediments from the shelf, slope, and deep basin are only minor sources of methane. The main methane sources are seeps located on the shelf and upper slope, but also in the deep basin. The comparison of two shelf stations with and without methane seepage showed a difference in methane concentrations, isotopic composition and oxidation rates, but the presence of similar methanotrophic microbial assemblages. Also two deep stations at a seep and outside of a seep area were compared, but here methane concentrations and oxidation rates were not different from each other. Anaerobic methane oxidizers (ANME-1 and ANME-2 group) were observed at both stations with slightly higher cell counts at the seep station.
