Carbon isotopic characterization for the origin of excess methane in subsurface seawater
Carbon isotopic characterization for the origin of excess methane in subsurface seawater
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DOI：
10.1029/2007jc004217
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发表时间：
2008-03
影响因子：
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通讯作者：
M. Sasakawa;U. Tsunogai;S. Kameyama;F. Nakagawa;Y. Nojiri;A. Tsuda
中科院分区：
文献类型：
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作者：
M. Sasakawa;U. Tsunogai;S. Kameyama;F. Nakagawa;Y. Nojiri;A. Tsuda
我们收集了北太平洋西北部的海水、浮游动物和下沉颗粒样本，利用稳定碳同位素作为示踪剂，确定了氧合开放海洋中超过大气CH4平衡饱和值的过量CH4的来源。我们发现，地下（~ 100 m深度）海水与大气平衡的表层海水（- 47‰）相比，13c -富集CH4（高达- 33.1‰）的过饱和（高达12%），表明13c -富集CH4的原位添加可能是深度处CH4富集的原因。沉降颗粒释放的CH4 δ13C值（−36.7±1.2‰~ +5.9±7.5‰）与海水中过量CH4 δ13C值范围内，表明地下过量CH4的主要来源是沉降颗粒。沉降颗粒释放出的CH4 δ13C组成异常富集，表明微生物活跃的CH4氧化发生在这些颗粒的氧/缺氧边界内。根据Rayleigh方程，我们估计沉降颗粒缺氧中心内产生的CH4至少有62%在地表100 m范围内被氧化。
[1] We collected samples of seawater, zooplankton, and sinking particles in the northwestern North Pacific to determine the source of excess CH4 over the saturation value in equilibrium with the atmospheric CH4 in the oxygenated open ocean, using stable carbon isotope as a tracer. We found that subsurface (∼100 m depth) seawater is supersaturated (up to 12%) with 13C-enriched CH4 (up to −33.1‰) relative to surface seawater in equilibrium with the atmosphere (−47‰), suggesting that in situ addition of 13C-enriched CH4 must be responsible for CH4 enrichment at depth. The δ13C of CH4 emitted from sinking particles (from −36.7 ± 1.2‰ to +5.9 ± 7.5‰) is within the range of that of excess CH4 in seawater, suggesting that the major source of subsurface excess CH4 is sinking particles. The unusually 13C-enriched δ13C composition of CH4 emitted from sinking particles suggests that active microbial CH4 oxidation occurs within the oxic/anoxic boundary of these particles. On the basis of the Rayleigh equation, we estimated that at least 62% of CH4 produced within the anoxic center of sinking particles is oxidized within 100 m of the surface.