The stable carbon isotope biogeochemistry of acetate and other dissolved carbon species in deep subseafloor sediments at the northern Cascadia Margin
The stable carbon isotope biogeochemistry of acetate and other dissolved carbon species in deep subseafloor sediments at the northern Cascadia Margin
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DOI：
10.1016/j.gca.2009.03.001
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发表时间：
2009-06-01
影响因子：
5
通讯作者：
Hinrichs, Kai-Uwe
中科院分区：
文献类型：
--
作者：
Heuer, Verena B.;Pohlman, John W.;Hinrichs, Kai-Uwe
海洋钻探揭示了深海海底存在大量微生物种群，但迄今为止对它们的代谢活动知之甚少。为了更好地了解深层生物圈中的地球化学过程，我们研究了沉积物孔隙水中乙酸盐和其他含碳代谢产物的稳定碳同位素化学。乙酸盐是缺氧沉积物中碳循环的关键代谢产物。其稳定的碳同位素组成提供了信息的代谢过程中占主导地位的乙酸周转原位。本研究报告了我们的研究结果，在北方卡斯卡迪亚边缘（东北太平洋）的综合大洋钻探计划（IODP）的远征311采样的沉积物上部190米的甲烷丰富的网站。在现场U1329，醋酸盐的δ（13）C值范围很广，相对于VPDB，从-46.0 ppm到-11.0 ppm，并随沉积物深度发生系统性变化。相比之下，大量溶解有机碳（DOC）（-21.6 +/-1.3ppm vs. VPDB）和低分子量化合物乳酸盐（-20.9 +/-1.8ppm vs. VPDB）的δ（13）C值显示出很小的变化性。这些物种被解释为代表发酵产物的碳同位素组成。相对于DOC，乙酸盐的贫化率高达千分之23.1，（13）C的富集率高达千分之9.1。概括地说，（13）相对于DOC的醋酸盐碳消耗表明来自醋酸生成的碳通量进入醋酸盐池，而（13）相对于DOC的孔隙水醋酸盐碳富集表明醋酸分解甲烷生成消耗醋酸盐。乙酸盐和乳酸盐或DOC之间的同位素关系提供了新的信息，碳流和特定功能微生物群落的存在和活动在不同的沉积物地球化学视野。特别是，他们认为产乙酸CO（2）-还原可以与产甲烷CO（2）-还原共存，这一观点与氢水平由化学上最有利的电子接受过程控制的假设相反。此外，同位素的关系表明，相对增加的乙酸流，乙酸碎屑产甲烷与深度，虽然它的总产甲烷的贡献可能是小的。我们的研究表明，乙酸盐的稳定碳同位素地球化学可用于确定地下环境中微生物碳周转的途径。我们的观察也提出了新的问题，控制海洋沉积物中的乙酸周转的因素。(C)2009爱思唯尔有限公司保留所有权利。
Ocean drilling has revealed the existence of vast microbial populations in the deep subscafloor, but to date little is known about their metabolic activities. To better understand the biogeochemical processes in the deep biosphere, we investigate the stable carbon isotope chemistry of acetate and other carbon-bearing metabolites in sediment pore-waters. Acetate is a key metabolite in the cycling of carbon in anoxic sediments. Its stable carbon isotopic composition provides information on the metabolic processes dominating acetate turnover in situ. This study reports our findings for a methane-rich site at the northern Cascadia Margin (NE Pacific) where Expedition 311 of the Integrated Ocean Drilling Program (IODP) sampled the upper 190 m of sediment. At Site U1329, delta(13)C values of acetate span a wide range from -46.0 parts per thousand to -11.0 parts per thousand vs. VPDB and change systematically with sediment depth. In contrast, delta(13)C values of both the bulk dissolved organic carbon (DOC) (-21.6 +/- 1.3 parts per thousand vs. VPDB) and the low-molecular-weight compound lactate (-20.9 +/- 1.8 parts per thousand vs. VPDB) show little variability. These species are interpreted to represent the carbon isotopic composition of fermentation products. Relative to DOC, acetate is up to 23.1 parts per thousand depleted and up to 9.1 parts per thousand enriched in (13)C. Broadly, (13)C-depletions of acetate relative to DOC indicate flux of carbon from acetogenesis into the acetate pool while (13)C-enrichments of pore-water acetate relative to DOC suggest consumption of acetate by acetoclastic methanogenesis. Isotopic relationships between acetate and lactate or DOC provide new information on the carbon flow and the presence and activity of specific functional microbial communities in distinct biogeochemical horizons of the sediment. In particular, they suggest that acetogenic CO(2)-reduction can coexist with methanogenic CO(2)-reduction, a notion contrary to the hypothesis that hydrogen levels are controlled by the thermodynamically most favorable electron-accepting process. Further, the isotopic relationship suggests a relative increase in acetate flow to acetoclastic methanogenesis with depth although its contribution to total methanogenesis is probably small. Our study demonstrates how the stable carbon isotope biogeochemistry of acetate can be used to identify pathways of microbial carbon turnover in subsurface environments. Our observations also raise new questions regarding the factors controlling acetate turnover in marine sediments. (C) 2009 Elsevier Ltd. All rights reserved.