Collaborative Research: Calibration of Raman Spectroscopy for calcite saturation state in marine biogenic calcification

释放到大气中的人为二氧化碳大部分被海洋吸收，海洋起到了缓冲全球变暖和快速气候变化的作用。但这会使海水对CaCO3矿物质更具酸性和腐蚀性(称为海洋酸化：OA)，这预计会损害用CaCO3(海洋钙化剂)建造骨骼或贝壳的海洋生物。海洋钙化剂通常通过从海水中改变其化学成分来提高CaCO_3饱和度(Ω)，从而在微尺度的“钙化流体(CF)”中生长其CaCO_3硬质部分。这一过程可能会使钙化剂至少在一定程度上应对骨性关节炎。本研究旨在建立利用拉曼光谱(RS)来限制碳纤维Ω的方法。与其他方法相比，该方法具有简单、快速、对生物体和碳酸钙样品无破坏等优点。这项工作将成为一种重要方法的基石，该方法可以促进对海洋钙化机制和海洋钙化物质对OA的复原力的了解。在较高的Ω水平下，CaCO_3的快速沉淀导致矿物晶格中更大的结构无序，这是由于缺陷增加和动力学驱动的次要/痕量元素(例如，镁)的吸收。因此，由拉曼峰的位置移位和宽度确定的晶格无序程度应该是Ω的函数。这一概念已在文石中得到验证，RS已被广泛用于限制文石类钙化剂中CF的Ω。但在方解石中，通过取代钙而形成的镁包裹体也对结构无序有显著的贡献。这需要对镁驱动的晶格紊乱进行纠正，以便在钙化生物体上有效地使用RS，这是目前所缺乏的。这项研究将产生一套广泛的非生物方解石样品，这些样品在镁含量和用于降水的溶液Ω方面存在显着差异，这些样品是基于使用人工海水进行的实验室实验。这些样品将解开镁包裹体和Ω对方解石结构无序的重叠作用。这项研究将首次产生适用于海洋生物源方解石的镁含量和Ω的拉曼定标。该项目由地球生物学和低温地球化学计划(GG)、既定的促进竞争性研究计划(EPSCoR)和海洋地质和地球化学计划(MGG)联合资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Much of the anthropogenic CO2 released into the atmosphere has been absorbed by the ocean, which acts as a buffer against global warming and rapid climate change. But this makes seawater more acidic and corrosive to CaCO3 minerals (known as ocean acidification: OA), which is expected to harm marine organisms that build skeletons or shells from CaCO3 (marine calcifiers). Marine calcifiers typically grow their CaCO3 hard parts in a micro-scale “calcifying fluid (CF)” by modifying its chemistry from seawater to elevate the degrees of CaCO3 saturation (Ω). This process potentially enables calcifiers to cope with OA, at least to some extent. This research aims to establish the use of Raman Spectroscopy (RS) to constrain Ω of CF. Compared to other methods, this approach will be simple, rapid, and non-destructive to organisms and CaCO3 samples. This work will be a cornerstone for an important methodology that can advance knowledge on calcification mechanisms and resilience of marine calcifiers against OA. Rapid precipitation of CaCO3 at higher Ω levels leads to greater structural disorder in the mineral lattice due to increased defects and kinetically-driven uptake of minor/trace elements (e.g., Mg). Thus, the degree of lattice disorder determined from the positional shift in and width of Raman peaks should be a function of Ω. This concept has been validated for aragonites and RS has been extensively used to constrain Ω of CF in aragonitic calcifiers. But in calcites, Mg inclusion by substitution of Ca also contributes to structural disorder significantly. This necessitates a correction for Mg-driven lattice disorder for effective use of RS on calcitic organisms, which is currently lacking. This research will produce an extensive set of abiogenic calcite samples that vary significantly in Mg contents and solution Ω for precipitation based on laboratory experiments using artificial seawater. These samples will disentangle the overlapping effect of Mg inclusion and Ω on calcite structural disorder. This investigation will for the first time generate Raman calibrations for Mg contents and Ω that are applicable to marine biogenic calcites. This project is jointly funded by the Geobiology and Low-Temperature Geochemistry Program (GG), the Established Program to Stimulate Competitive Research (EPSCoR), and the Marine Geology and Geochemistry Program (MGG).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.