Altervalent substitution of sodium for calcium in biogenic calcite and aragonite
Altervalent substitution of sodium for calcium in biogenic calcite and aragonite
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生物方解石和文石中钠替代钙
DOI：
10.1016/j.gca.2016.12.003
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发表时间：
2017
影响因子：
5
通讯作者：
N.,
中科院分区：
文献类型：
--
作者：
Yoshimura;T.;Tamenori;Y.;Suzuki;A.;Kawahata;H.;Iwasaki;N.;Hasegawa;H.;Nguyen;L.T.;Kuroyanagi;A.;Yamazaki;T.;Kuroda;J.;Ohkouchi;N.,
钠在生物碳酸钙中的浓度为百万分之几千，以摩尔计，钠是这些碳酸盐中含量最丰富的微量元素之一。然而，CaCO3中Na的化学形式并没有得到很好的限制。我们用同步辐射X射线光谱，以确定占主导地位的分子主机网站钠在生物方解石和文石沉淀珊瑚，双壳类，有孔虫。我们还利用K边X射线吸收近边结构研究了Na在生物碳酸钙中的化学环境，并确定了Na在方解石和文石晶格结构中对Ca位的交替取代。生物CaCO3中的次要阳离子和阴离子浓度表明，主要的取代机制涉及通过产生CO32−空位进行电荷补偿。我们研究的各种生物群的骨骼微结构中的大多数均匀的Na浓度表明，环境和生物控制，如温度，骨骼微结构和钙化率，骨骼Na浓度只有轻微的影响。从第四纪沉积物岩心中挑选的有孔虫壳随着年龄的增加，Na：Ca比值下降，表明Na的逐步释放，这表明生物CaCO3中结构取代的Na在埋藏成岩作用过程中很容易被沥滤。而经历成岩作用的沉积物释放一些钠回水柱，钠共沉淀在生物碳酸钙作为一个潜在的钠汇的海洋。
Sodium concentrations in biogenic CaCO3are several thousands of parts per million, and, on a molar basis, Na is among the most abundant constituent minor element in these carbonates. Nevertheless, the chemical form of Na in CaCO3is not well constrained. We used synchrotron X-ray spectroscopy to identify the dominant molecular host sites for Na in biogenic calcite and aragonite precipitated by corals, bivalves, and foraminifera. We also used theK-edge X-ray absorption near-edge structure to investigate the chemical environment of Na in biogenic calcium carbonates and identify the altervalent substitution of Na into Ca sites in the lattice structures of calcite and aragonite. Minor cation and anion concentrations in biogenic CaCO3suggest that the principal substitution mechanism involves charge compensation through the creation of CO32−vacancies. The mostly homogeneous Na concentrations in the skeletal microstructures of the various biota we examined indicate that environmental and biological controls, such as temperature, skeletal microstructure, and calcification rates, have only minor influences on skeletal Na concentrations. A decrease of Na:Ca ratios with increasing age of foraminiferal shells picked from a Quaternary sediment core, indicates progressive release of Na, which suggests that structurally-substituted Na in biogenic CaCO3is readily leached during burial diagenesis. Whereas the sediment that undergo diagenesis release some Na back to the water column, sodium co-precipitation in biogenic CaCO3serves as a potential sink of Na for the ocean.