Weaving of biomineralization framework in rotaliid foraminifera: implications for paleoceanographic proxies
Weaving of biomineralization framework in rotaliid foraminifera: implications for paleoceanographic proxies
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DOI：
10.5194/bg-15-6773-2018
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发表时间：
2018-11
期刊：
影响因子：
4.9
通讯作者：
Y. Nagai;K. Uematsu;Chong Chen;Ryoji Wani;J. Tyszka;T. Toyofuku
中科院分区：
文献类型：
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作者：
Y. Nagai;K. Uematsu;Chong Chen;Ryoji Wani;J. Tyszka;T. Toyofuku
抽象的。有孔虫钙质测试的元素和/或同位素特征通常用于重建古环境条件。一个主要的问题，通常被称为“生命效应”，是这种地球化学特征存储在无机碳酸钙在相同的环境条件下，以及类群，物种，个人等之间的差异很大，这种影响以前被解释为被动与主动离子传输模式之间的相对贡献，但其细节仍在调查中。在这项研究中，伪足结构在室形成过程中的功能作用，阐明了详细的观察氨beccarii（林奈，1758）使用延时光学成像系统和高分辨率电子显微镜。我们首次记录了覆盖碳酸盐沉淀场地的三重有机层。三个主要的有机层（外有机层、初级有机层和内有机层）由伪足的初始框架与进一步的层状伪足重叠而形成。初级有机片似乎促进早期碳酸钙成核，然后被双沉淀位点捕获。我们进一步表明，钙化开始时，外部或内部的有机层仍然表现出微小的差距（框架内的孔），可以作为被动离子交换（如Mg 2+）之间的海水和有限的降水空间的途径。然而，大多数壁增厚发生时，降水网站是完全隔离的海水，这意味着活跃的离子交换。这可能解释了在以前的研究中观察到的早期和晚期钙化的镁scinCa比率的差异。我们的研究通过培养实验和对活体动物的深入观察，为解决理解有孔虫钙化过程中的关键“缺失部分”提供了见解。我们的研究结果有助于解释和理解的“生命效应”，特别是元素和同位素比值沿着室壁，是直接联系到时空组织的“生物矿化三明治”控制的三个主要有机层的地球化学代理。
Abstract. Elemental and/or isotopic signatures of calcareous tests of foraminifera are commonly used to reconstruct paleoenvironmental conditions. A major problem, often referred to as the “vital effect”, is that such geochemical signatures stored in inorganic calcium carbonates differ greatly under the same environmental conditions, as well as between taxa, species, individuals, etc. This effect was previously explained by relative contributions between passive vs. active ion transport patterns, but their details are still under investigation. In this study, the functional role of pseudopodial structures during chamber formation is elucidated by detailed observation of Ammonia beccarii (Linnaeus, 1758) using a time-lapse optical imaging system and high-resolution electron microscopy. We document triple organic layers sandwiching carbonate precipitation sites for the first time. The three major organic layers (outer organic layer, primary organic sheet, and inner organic layer) are formed by an initial framework of pseudopodia overlaid with further layer-like pseudopodia. The primary organic sheet seems to facilitate early calcium carbonate nucleation, then entrapped by double precipitation sites. We further show that calcification starts when outer or inner organic layers still exhibit tiny gaps (holes within the framework) that may serve as pathways for passive ion exchange (e.g. Mg2+) between seawater and the confined precipitation space. Nevertheless, the majority of wall thickening occurs when the precipitation site is completely isolated from seawater, which implies active ion exchange. This may explain the differences in Mg ∕ Ca ratios in early and later stages of calcification observed in previous studies. Our study provides insight into resolving a key “missing piece” in understanding foraminiferal calcification through culture experiments and in-depth observations of living animals. Our findings contribute to interpreting and understanding biogeochemical proxies by showing that the “vital effect”, specifically elemental and isotopic ratios along chamber walls, is directly linked to spatio-temporal organization of the “biomineralization sandwich” controlled by the three major organic layers.