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

大部分释放到大气中的人类活动产生的二氧化碳都被海洋吸收了，海洋起到了缓冲全球变暖和快速气候变化的作用。但这使得海水对CaCO 3矿物质更具酸性和腐蚀性（称为海洋酸化：OA），预计这将损害由CaCO 3（海洋钙化物）构建骨骼或外壳的海洋生物。海洋钙化生物通常在微尺度的“钙化流体（CF）”中通过改变其来自海水的化学性质来提高CaCO 3饱和度（Ω）来生长其CaCO 3硬质部分。该过程可能使钙化器能够至少在一定程度上科普OA。本研究旨在建立利用拉曼光谱（RS）来限制CF的Ω。与其他方法相比，该方法简单，快速，对生物体和CaCO 3样品无破坏性。这项工作将是一个重要方法的基石，可以提高对钙化机制和海洋钙化对OA的弹性的认识。CaCO 3在较高Ω水平下的快速沉淀导致矿物晶格中更大的结构无序，这是由于增加的缺陷和动力学驱动的微量/痕量元素（例如，Mg）。因此，由拉曼峰的位置偏移和宽度确定的晶格无序度应该是Ω的函数。这一概念已经在文石中得到验证，RS已被广泛用于限制文石钙化物中CF的Ω。但方解石中Mg替代Ca包裹体也是结构无序的重要原因。这就需要对镁驱动的晶格无序进行校正，以有效地使用RS对方解石生物体，这是目前缺乏的。这项研究将产生一套广泛的非生物成因的方解石样品，在镁含量和溶液Ω显着变化的基础上，使用人工海水的实验室实验沉淀。这些样品将解开Mg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成因方解石的Mg含量和Ω的拉曼校准。该项目由地球生物学和低温地球化学计划（GG）、激励竞争性研究的既定计划（EPSCoR）和海洋地质学和地球化学计划（MGG）共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.