Reactive-transport modeling of neodymium and its radiogenic isotope in deep-sea sediments: The roles of authigenesis, marine silicate weathering and reverse weathering
Reactive-transport modeling of neodymium and its radiogenic isotope in deep-sea sediments: The roles of authigenesis, marine silicate weathering and reverse weathering
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DOI：
10.1016/j.epsl.2022.117792
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发表时间：
2022-09-08
影响因子：
5.3
通讯作者：
Vance, Derek
中科院分区：
文献类型：
--
作者：
Du, Jianghui;Haley, Brian A.;Vance, Derek
海水中溶解稀土元素（REE）和放射性钕（Nd）同位素组成（ENd）是研究海洋作用的重要地球化学工具，但对它们的现代海洋收支却知之甚少。近年来，特别是在深海沉积物中发现了具有独特的稀土元素特征的大的底栖稀土通量，并提出了“自下而上”的假说，即沉积物-水界面（SWI）以下的早期成岩作用控制着海洋的稀土元素和钕（Nd）收支。为了研究这种沉积过程，我们建立了一个反应传输模式的海洋沉积物中的Nd和Nd（Nd）的地球化学循环。在此，我们试图量化的作用，自生，海洋硅酸盐风化和逆风化在成岩循环中的Nd和Nd（Nd）在深海（3000米）的站点在俄勒冈州边缘。我们的模型预测，在这个网站上，Nd携带的Fe/Mn氧化物进入沉积物最终转化为自生Nd-磷酸盐，在此期间，接近9%的进入固体Nd通量作为溶解的底栖通量释放回上覆的底层水。我们还发现，经典的可逆清除配方适用于钕共循环与铁/锰氧化物是不一致的数据。相反，共沉淀配方，假设钕结构纳入铁/锰氧化物，成功地模拟数据。该模型还表明，自生作用不能单独解释孔隙水和自生钕，这都是放射性比底层水在这个网站。然而，来自当地俯冲带的火山硅酸盐的风化作用可以成功地解释Nd。我们认为，由于自生粘土形成的逆风化保持了孔隙水中原生硅酸盐的不饱和度，海洋硅酸盐风化可以进行。我们模拟的过程可能会影响许多其他微量元素和同位素的沉积循环，对海洋地球化学的理解具有更广泛的意义。(C)2022作者。由爱思唯尔公司出版
Dissolved Rare Earth Elements (REE) and radiogenic neodymium (epsilon(Nd)) isotope composition (ENd) of seawater are widely used geochemical tools in studying marine processes, but their modern ocean budgets are poorly understood. Recent discoveries of large benthic fluxes of REE with unique epsilon(Nd) signatures from marine sediments, particularly in the deep-sea, have led to a "bottom-up" hypothesis, which suggests that early diagenesis below the sediment-water interface (SWI) controls the ocean's REE and epsilon(Nd) budgets. To investigate such sedimentary processes, we created a reactive-transport model for the biogeochemical cycling of Nd and epsilon(Nd) in marine sediments. Here, we attempt to quantify the roles of authigenesis, marine silicate weathering and reverse weathering in the diagenetic cycling of Nd and epsilon(Nd) at a deep-sea (3000 m) site on the Oregon margin.Our model predicts that, at this site, Nd carried by Fe/Mn oxides into sediments eventually transforms to authigenic Nd-phosphate, during which similar to 9% of the incoming solid Nd flux is released as a dissolved benthic flux back to the overlying bottom water. We also find that the classic reversible scavenging formulation applied to Nd co-cycling with Fe/Mn oxides is inconsistent with the data. Rather, a co-precipitation formulation, assuming Nd is structurally incorporated into Fe/Mn oxides, successfully simulates the data. The model also shows that authigenesis alone cannot explain the pore water and authigenic epsilon(Nd), which are both more radiogenic than bottom water at this site. However, the weathering of volcanic silicates sourced from the local subduction zone can successfully explain epsilon(Nd). We suggest that, because reverse weathering by authigenic clay formation maintains the under-saturation of primary silicates in pore water, marine silicate weathering can proceed. The processes we model likely affect the sedimentary cycling of many other trace elements and isotopes, with much broader implications for the understanding of ocean biogeochemistry. (C) 2022 The Author(s). Published by Elsevier B.V.