Methane emission from high-intensity marine gas seeps in the Black Sea into the atmosphere

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Abstract

[1] Submarine high-intensity methane seeps have been surveyed in the Sorokin Trough and Paleo Dnepr Area in the Black Sea from May to June, 2003 to estimate the sea-air methane flux. The Sorokin Trough mud volcano area in around 2080 m water depth shows no direct effects on the methane concentration in the surface water and the atmosphere (average methane saturation ratios (SR) of 143%). The average sea-air methane flux can be determined as 0.2–0.57 nmol m−2 s−1, using two different sea-air gas exchange models; mean wind speed were extraordinary low throughout the cruise (1.16 m s−1). The investigations in the Paleo Dnepr Area (60 to 800 m water depth) reflects a more diverse pattern. Spots of high methane concentrations in the surface water have been recorded above a seep location in around 90 m water depth (SR up to 294%). The air-sea methane flux above this seep site (0.96–2.32 nmol m−2 s−1) is 3 times higher than calculated for the surrounding shelf (0.32–0.77 nmol m−2 s−1) and 5 times higher than assessed for open Black Sea waters (water depth > 200 m, 0.19–0.47 nmol m−2 s−1).

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