Deep Sulfate-Methane-Transition and sediment diagenesis in the Gulf of Alaska (IODP Site U1417)
Deep Sulfate-Methane-Transition and sediment diagenesis in the Gulf of Alaska (IODP Site U1417)
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DOI：
10.1016/j.margeo.2019.105986
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发表时间：
2019-11
期刊：
影响因子：
2.9
通讯作者：
M. Zindorf;C. März;T. Wagner;S. Gulick;H. Strauss;J. Benowitz;J. Jaeger;B. Schnetger;L. Childress;L. Levay;C. Land;Michelle La Rosa
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文献类型：
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作者：
M. Zindorf;C. März;T. Wagner;S. Gulick;H. Strauss;J. Benowitz;J. Jaeger;B. Schnetger;L. Childress;L. Levay;C. Land;Michelle La Rosa
对阿拉斯加湾(果阿，IODP探险341，U1417站点)的沉积物样品进行了分析，以了解现在和过去的成岩过程，这些过程覆盖了原始沉积物成分。在硫酸盐枯竭带没有观察到硫酸盐-甲烷过渡带，但在硫酸盐枯竭深度(~200 m)到开始产甲烷(~440 m)之间存在一个厚达200 m的硫酸盐和无甲烷沉积区间。我们认为，有机质生物地球化学过程中的这种明显差距是由于富甲烷层上边界重晶石溶解时释放的硫酸盐对甲烷的厌氧氧化造成的。在产甲烷带之下，在~650SMTZ深度，孔隙水硫酸盐浓度再次增加，这表明硫酸盐从更深的深度进入了一个深的反向 区。对U1417深海海底硫酸盐有效性的一个可能解释是，存在与板块弯曲断裂有关的深层含水层，它积极地将富含硫酸盐的水输送到沉积物和洋壳之间的界面，并有可能沿界面输送。这种逆成岩分带以前曾在海洋沉积物中观察到，但尚未与俯冲相关的板块弯曲联系起来。随着在大洋内部板块环境中发现了深部反向SMTZ，以及自生重晶石溶解释放的硫酸盐阻止了甲烷的向上扩散，U1417站点提供了对海底以下孔隙-流体和气体动力学的新见解，及其对全球元素循环和深层生物圈的影响。
Sediment samples from the Gulf of Alaska (GOA, IODP Expedition 341, Site U1417) have been analyzed to understand present and past diagenetic processes that overprint the primary sediment composition. No Sulfate-Methane Transition Zone (SMTZ) was observed at the zone of sulfate depletion, but a >200 m thick sulfate- and methane-free sediment interval occurred between the depth of sulfate depletion (~200 m) and the onset of methanogenesis (~440 m). We suggest that this apparent gap in biogeochemical processing of organic matter is caused by anaerobic oxidation of methane fueled by sulfate which is released during dissolution of barites at the upper boundary of the methane rich layer. Beneath the methanogenic zone, at ~650 m depth, pore-water sulfate concentrations increase again, indicating sulfate supply from greater depth feeding into a deep, inverse SMTZ. A likely explanation for the availability of sulfate in the deep sub-seafloor at U1417 is the existence of a deep aquifer related to plate bending fractures, which actively transports sulfate-rich water to, and potentially along, the interface between sediments and oceanic crust. Such inverse diagenetic zonations have been previously observed in marine sediments, but have not yet been linked to subduction-related plate bending. With the discovery of a deep inverse SMTZ in an intra-oceanic plate setting and the blocking of upward methane diffusion by sulfate released from authigenic barite dissolution, Site U1417 provides new insights into sub-seafloor pore-fluid and gas dynamics, and their implications for global element cycling and the deep biosphere.