Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial
Silicate weathering in anoxic marine sediment as a requirement for authigenic carbonate burial
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DOI：
10.1016/j.earscirev.2019.102960
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发表时间：
2020
影响因子：
12.1
通讯作者：
M. Torres;W. Hong;E. Solomon;K. Milliken;Ji-hoon Kim;J. Sample;B. Teichert;K. Wallmann
中科院分区：
文献类型：
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作者：
M. Torres;W. Hong;E. Solomon;K. Milliken;Ji-hoon Kim;J. Sample;B. Teichert;K. Wallmann
我们强调海洋硅酸盐风化（MSiW）反应在缺氧沉积物中的重要性，作为产生碳酸盐沉淀和保存沿着大陆边缘所需的碱性和阳离子的基础。我们使用的模型，耦合热力学与水的地球化学表明，在甲烷生成过程中释放的CO2导致pH值下降到6.0，除非这些质子被MSiW缓冲，碳酸盐矿物将溶解。我们目前的数据来自两个地区：印度被动边缘和日本，火山灰和/或河流供应的活性硅酸盐相，反映在锶同位素数据的主动俯冲带。在印度和韩国近海，陆源硅酸盐的蚀变导致孔隙水富含放射性87 Sr，87 Sr/86 Sr比值分别高达0.7095和0.7104。在日本近海，受火山灰蚀变影响的孔隙水中锶以87 Sr亏损，87 Sr/86 Sr低至0.7065。由碱度和通过MSiW产生的阳离子形成的碳酸盐矿物携带这些锶同位素信号，并且通常是白云石、菱铁矿和富铁方解石。这些与文石和高镁方解石甲烷厌氧氧化过程中形成的对比，并纳入同时代的海水87 Sr/86 Sr信号。我们表明，MSiW对于沿着大陆边缘的自生碳酸盐形成和保存是必要的，它以之前估计的至少1012摩尔/年的速率从地球表面去除碳。此外，这些自生碳酸盐岩与深部生物圈、流体流动、地震成因、斜坡稳定性和储层特征的研究有关。
We emphasize the importance of marine silicate weathering (MSiW) reactions in anoxic sediment as fundamental in generating alkalinity and cations needed for carbonate precipitation and preservation along continental margins. We use a model that couples thermodynamics with aqueous geochemistry to show that the CO2released during methanogenesis results in a drop in pH to 6.0; unless these protons are buffered by MSiW, carbonate minerals will dissolve. We present data from two regions: the India passive margin and the active subduction zone off Japan, where ash and/or rivers supply the reactive silicate phase, as reflected in strontium isotope data. Offshore India and Korea, alteration of continent-derived silicates results in pore water enriched in radiogenic87Sr, with87Sr/86Sr ratios as high as 0.7095 and 0.7104, respectively. Off Japan, strontium in pore water influenced by ash alteration is depleted in87Sr, with87Sr/86Sr as low as 0.7065. Carbonate minerals formed by alkalinity and cations generated through MSiW carry these strontium isotopic signals, and are typically dolomite, siderite, and Fe-rich calcite. These contrast with the aragonite and high-magnesium calcite that form during anaerobic oxidation of methane and incorporate the coeval seawater87Sr/86Sr signal. We show that MSiW is necessary for authigenic carbonate formation and preservation along continental margins, which remove carbon from Earth’s surface at rates previously estimated to be at least 1012mol yr−1. In addition, these authigenic carbonates are of relevance to studies of the deep biosphere, fluid flow, seismogenesis, slope stability, and reservoir characteristics.