Coccolithophores are biogeochemically and ecologically important phytoplankton that produce a composite calcium carbonate-based exoskeleton – the coccosphere – comprised of individual platelets, known as coccoliths. Coccoliths are stunning examples of biomineralization; their formation featuring exceptional control over both biomineral chemistry and shape. Understanding how coccoliths are formed requires information about minor element distribution and chemical environment. Here, the first high-resolution 3D synchrotron X-ray fluorescence (XRF) mapping of a coccolith is presented, showing that the lopadoliths of Scyphosphaera apsteinii display stripes of different Sr concentration. The presence of Sr stripes is unaffected by elevated Sr in the culture medium, macro-nutrient concentration, and light intensity, indicating that the observed stripiness is an expression of the fundamental coccolith formation process in this species. Current Sr fractionation models, by contrast, predict an even Sr distribution and will have to be modified to account for this stripiness. Additionally, nano-XANES analyses show that Sr resides in a Ca site in the calcite lattice in both high and low Sr stripes, confirming a central assumption of current Sr fractionation models.

中文翻译：

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纳米级 X 射线荧光断层扫描揭示了球石藻 Scyphosphaera apsteinii 中锶的不均匀分布

颗石藻是生物地球化学和生态学上重要的浮游植物，它产生复合的碳酸钙外骨骼——颗石球——由单个血小板组成，称为颗石藻。颗石藻是生物矿化的惊人例子。它们的形成具有对生物矿物化学和形状的卓越控制。了解球石是如何形成的需要有关微量元素分布和化学环境的信息。在这里，首次展示了颗石石的高分辨率 3D 同步加速器 X 射线荧光 (XRF) 绘图，显示Scyphosphaera apsteinii的石柱石显示出不同 Sr 浓度的条纹。 Sr 条纹的存在不受培养基中 Sr 升高、常量营养物浓度和光强度的影响，表明观察到的条纹是该物种中基本球石形成过程的表达。相比之下，当前的 Sr 分馏模型预测 Sr 分布均匀，因此必须进行修改以解决这种条纹问题。此外，纳米 XANES 分析表明，Sr 位于高 Sr 条带和低 Sr 条带中方解石晶格的 Ca 位点上，证实了当前 Sr 分馏模型的中心假设。