Barite formation in the ocean: Origin of amorphous and crystalline precipitates
Barite formation in the ocean: Origin of amorphous and crystalline precipitates
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DOI：
10.1016/j.chemgeo.2018.09.011
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发表时间：
2019-04
期刊：
影响因子：
3.9
通讯作者：
F. Martínez-Ruiz;A. Paytan;M. T. González-Muñoz;F. Jroundi;M. M. Abad-M.;P. Lam;J. Bishop;T. Horner;P. Morton;M. Kastner
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文献类型：
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作者：
F. Martínez-Ruiz;A. Paytan;M. T. González-Muñoz;F. Jroundi;M. M. Abad-M.;P. Lam;J. Bishop;T. Horner;P. Morton;M. Kastner
海洋出口生产是影响气候的全球碳循环的一个关键组成部分。过去的海洋出口产量通常是通过重晶石和钡代用指标来估计的。然而，不饱和海水柱中重晶石沉淀的确切机制尚未完全了解。在这里，我们提出了一个详细的矿物学和晶体学分析的重晶石从粒度分级颗粒材料收集使用多个单元大体积原位过滤系统在北大西洋和南大洋。我们的数据表明，海洋重晶石的形式从一个初始的无定形富磷相，结合钡，演变成重晶石晶体，其中磷酸盐基团被硫酸盐取代。扫描电子显微镜观察还显示了重晶石颗粒与有机物聚集体和胞外聚合物（EPS）的关联。这些结果与实验工作一致，表明在细菌生物膜中Ba与细胞和EPS中的磷酸盐基团结合，这促进了局部高浓度的Ba，导致有利于重晶石沉淀的饱和微环境。这些结果强烈表明，在海洋中，这是一致的细菌生产和丰富的富钡颗粒在水柱之间的密切联系，类似的沉淀机制。我们认为，EPS在介导的重晶石形成在不饱和的海洋水柱中发挥了重要作用，具体而言，生产力的提高和有机质降解的中层区将需要更广泛的EPS生产，从而促进钡生物积累和适当的微环境的重晶石沉淀。这一观察有助于更好地理解Ba替代物及其重建过去海洋出口生产力的效用。本文是由Tim M. Conway，Tristan Horner，Yves Plancherel，and Aridane G.冈萨雷斯
Ocean export production is a key constituent in the global carbon cycle impacting climate. Past ocean export production is commonly estimated by means of barite and Barium proxies. However, the precise mechanisms underlying barite precipitation in the undersaturated marine water column are not fully understood. Here we present a detailed mineralogical and crystallographic analysis of barite from size-fractionated particulate material collected using multiple unit large volume in-situ filtration systems in the North Atlantic and the Southern Ocean. Our data suggest that marine barite forms from an initial amorphous phosphorus-rich phase that binds Ba, which evolves into barite crystals whereby phosphate groups are substituted by sulfate. Scanning electron microscopy observations also show the association of barite particles with organic matter aggregates and with extracellular polymeric substances (EPS). These results are consistent with experimental work showing that in bacterial biofilms Ba binds to phosphate groups in both cells and EPS, which promotes locally high concentrations of Ba leading to saturated microenvironments favoring barite precipitation. These results strongly suggest a similar precipitation mechanism in the ocean, which is consistent with the close link between bacterial production and abundance of Ba-rich particulates in the water column. We argue that EPS play a major role in mediating barite formation in the undersaturated oceanic water column; specifically, increased productivity and organic matter degradation in the mesopelagic zone would entail more extensive EPS production, thereby promoting Ba bioaccumulation and appropriate microenvironments for barite precipitation. This observation contributes toward better understanding of Ba proxies and their utility for reconstructing past ocean export productivity.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean – GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.