Gas seepage in the Dnepr paleo-delta area (NW-Black Sea) and its regional impact on the water column methane cycle

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• 作者：O. Schmale ; S.E. Beaubien ; G. Rehder ; J. Greinert ; S. Lombardi
• 关键词：Methane ; Gas seepages ; Marginal seas ; Anoxic basins ; Carbon isotope ratio ; Oxygen depletion
• 刊名：Journal of Marine Systems
• 出版年：2010
• 出版时间：20 February 2010
• 年：2010
• 卷：80
• 期：1-2
• 页码：90-100
• 全文大小：1691 K

文摘

Methane concentrations and carbon stable isotopic ratios (δ¹³C_CH4), 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 (δ¹³C_CH4) 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 × 10⁶ mol yr^− 1 (9.6 t yr^− 1) in 2003 and 0.347 × 10⁶ mol yr^− 1 (5.6 t yr^− 1) 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 × 10⁶ mol yr^− 1 in 2003.