Serpentine alteration as source of high dissolved silicon and elevated δ(30)Si values to the marine Si cycle.
Serpentine alteration as source of high dissolved silicon and elevated δ(30)Si values to the marine Si cycle.
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DOI：
10.1038/s41467-020-18804-y
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发表时间：
2020-10-12
影响因子：
16.6
通讯作者：
Menzies CD
中科院分区：
文献类型：
--
作者：
Geilert S;Grasse P;Wallmann K;Liebetrau V;Menzies CD
绢云母蚀变是元素循环的重要过程，但有关硅通量的研究还不清楚。对IODP Expedition 366期间在马里亚纳弧前区域采集的蛇纹岩海山孔隙流体的Si、B和Sr同位素特征（分别为δ 30 Si、δ 11 B和87 Sr/86 Sr）进行了研究，以研究地幔楔中的蛇纹岩化和海水对自生粘土的浅部蛇纹岩蚀变。地幔楔中的蛇纹石化作用没有引起明显的硅同位素分馏，这意味着封闭系统的条件，海水对蛇纹石的蚀变导致了自生层状硅酸盐的形成，导致了迄今为止测量到的最高天然流体δ 30 Si值（高达+5.2 ± 0.2‰）。在这里，我们表明，海底蚀变的蛇纹岩是硅的来源，海洋具有极高的流体δ 30硅值，这可以解释异常的海洋硅预算，如在卡斯卡迪亚盆地，必须考虑在未来的调查全球海洋硅循环。硅循环对海洋生产力和养分循环很重要，但全球收支存在不确定性。在这里，作者对海底沉积物和孔隙流体使用了多同位素方法，发现海底蛇纹岩的降解是海洋中硅的一个未被重视的来源。
Serpentine alteration is recognized as an important process for element cycling, however, related silicon fluxes are unknown. Pore fluids from serpentinite seamounts sampled in the Mariana forearc region during IODP Expedition 366 were investigated for their Si, B, and Sr isotope signatures (δ30Si, δ11B, and 87Sr/86Sr, respectively) to study serpentinization in the mantle wedge and shallow serpentine alteration to authigenic clays by seawater. While serpentinization in the mantle wedge caused no significant Si isotope fractionation, implying closed system conditions, serpentine alteration by seawater led to the formation of authigenic phyllosilicates, causing the highest natural fluid δ30Si values measured to date (up to +5.2 ± 0.2‰). Here we show that seafloor alteration of serpentinites is a source of Si to the ocean with extremely high fluid δ30Si values, which can explain anomalies in the marine Si budget like in the Cascadia Basin and which has to be considered in future investigations of the global marine Si cycle. The Si cycle is important to ocean productivity and nutrient cycling, however there are uncertainties in global budgets. Here the authors use a multi-isotope approach on seafloor sediments and pore fluids, finding that an unappreciated source of Si to the ocean is the degradation of seafloor serpentinites.
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