The distribution and coordination of trace elements in Krithe ostracods and their implications for paleothermometry
The distribution and coordination of trace elements in Krithe ostracods and their implications for paleothermometry
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DOI：
10.1016/j.gca.2017.12.005
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发表时间：
2018-09-01
影响因子：
5
通讯作者：
Elderfield, Henry
中科院分区：
文献类型：
--
作者：
Branson, Oscar;Redfern, Simon A. T.;Elderfield, Henry
介形虫阀的Mg和Sr含量已被用来重建过去的温度和盐度，其稳定同位素已被用来揭示海洋，湖泊和河口水文方面。然而，介形虫的钙化过程，微量元素的掺入机制，以及代理示踪剂复杂的混杂因素的敏感性，显着的不确定性。大多数介形虫的瓣由嵌入有机基质中的微米级晶粒组成。这些结构的细尺度地球化学以及生物矿化过程对阀化学影响的性质仍然受到很大的限制。我们已经进行了亚微米分辨率的X射线显微镜的海洋Krithe介形虫阀，并确定了镁的化学配位，和Mg，Na和S的分布在整个晶体有机阀结构。这些微量元素显示系统的亚微米尺度的组成变化内的矿物颗粒和颗粒间基质的阀门超微结构。这些模式意味着Krithe生物矿化过程显着调制微量元素掺入在亚微米尺度。因此，Krithe的化学成分可能在某种程度上与它们钙化的水脱钩。最重要的是，镁K边近边X射线吸收精细结构（NEXAFS）光谱，高镁地区与富含硫的有机层的重合表明，镁主要不是托管在方解石结构的阀门。我们的研究结果强调，需要了解的过程，驱动这种精细尺度的化学异质性和外部环境和阀门地球化学之间的连接，如果介形虫被用作古环境代理源的影响。(C)2018作者出版社：Elsevier Ltd
The Mg and Sr content of ostracod valves have been used to reconstruct past temperature and salinity, and their stable isotopes have been used to reveal aspects of marine, lake and estuary hydrology. However, significant uncertainties surround ostracod calcification processes, the incorporation mechanisms of trace elements, and the sensitivity of proxy tracers to complex confounding factors. The valves of most ostracods are composed of micron-scale crystalline grains embedded in an organic matrix. The fine-scale geochemistry of these structures, and the nature of the influence of biological mineralisation processes on valve chemistry, remain poorly constrained. We have performed sub-micron resolution X-ray microscopy of a marine Krithe ostracod valve, and determined the chemical coordination of Mg, and the distribution of Mg, Na and S throughout the crystal-organic valve structure. These trace elements display systematic sub-micron-scale compositional variations within the mineral grains and inter-granular matrix of the valve ultrastructure. These patterns imply that Krithe biomineralisation processes significantly modulate trace element incorporation at the sub-micron scale. Thus Krithe chemical composition is likely to be decoupled to some extent from the water in which they calcified. Most importantly, Mg K-edge Near-Edge X-Ray Absorption Fine Structure (NEXAFS) spectra, and the coincidence of high-Mg regions with S-rich organic layers reveal that Mg is not primarily hosted in the calcite structure in the valve. Our results highlight the need to understand the processes that drive this fine-scale chemical heterogeneity and their influence on connections between the external environment and valve geochemistry, if ostracods are to be used as sources of paleoenvironmental proxies. (C) 2018 The Authors. Published by Elsevier Ltd.