文摘
Methane concentrations and carbon stable isotopic ratios (δ<sup>13sup>C<sub>CH4sub>), oxygen concentrations and hydrographic parameters (CTD) were investigated in the water column of the north-western Black Sea during the summers of 2003 and 2004. Water samples were collected along a transect which crosses three methane seep areas in 90, 220, and 600 m water depth. These active seeps strongly influence methane distribution in the overlying anoxic and oxic water column. Methane concentration and stable isotope (δ<sup>13sup>C<sub>CH4sub>) patterns indicate that water column stratification and microbial methane oxidation efficiently hamper the transfer of methane to the sea surface. Only the shelf seep site in 90 m water depth acts as a direct source of atmospheric methane. Microbial methane oxidation and/or gas stripping seem to cause oxygen depletion above the two shallower seep areas. The methane flux from the 90 m site into the water column is estimated to have been 0.599 × 10<sup>6sup> mol yr<sup>− 1sup> (9.6 t yr<sup>− 1sup>) in 2003 and 0.347 × 10<sup>6sup> mol yr<sup>− 1sup> (5.6 t yr<sup>− 1sup>) in 2004. Comparison of results from the two years shows different water column methane inventories in the deep part of the transect, implying a variable methane source strength at the 600 m deep site. The flux from this area is estimated to have been 11.35 × 10<sup>6sup> mol yr<sup>− 1sup> in 2003.