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

人类释放到大气中的大部分二氧化碳已经被海洋吸收，海洋起到了减缓全球变暖和快速气候变化的缓冲作用。但这使得海水变得更酸，对CaCO3矿物具有更强的腐蚀性（称为海洋酸化：OA），这预计会损害用CaCO3（海洋钙化剂）构建骨骼或外壳的海洋生物。海洋钙化剂通常在微尺度的“钙化流体（CF）”中生长CaCO3硬部分，通过改变海水中的化学成分来提高CaCO3的饱和度（Ω）。这个过程可能使钙化者至少在一定程度上应对OA。本研究旨在建立利用拉曼光谱（RS）来约束CF的Ω。与其他方法相比，该方法简单，快速，对生物体和CaCO3样品无破坏性。这项工作将成为一种重要方法的基石，该方法可以促进对钙化机制和海洋钙化剂对OA的恢复能力的了解。在较高Ω水平下CaCO3的快速沉淀会导致矿物晶格中更大的结构紊乱，这是由于缺陷增加和微量元素（如Mg）的动力学驱动吸收。因此，由拉曼峰的位置位移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已被广泛用于约束文石钙化剂中CF的Ω。但在方解石中，钙取代镁包合也会导致结构紊乱。这需要对镁驱动的晶格紊乱进行校正，以便有效地利用RS对钙化生物，这是目前缺乏的。本研究将产生一套广泛的非生物成因方解石样品，这些样品在Mg含量和沉淀溶液Ω上变化显著，基于人工海水的实验室实验。这些样品将解开镁包裹体和Ω对方解石结构紊乱的重叠效应。这项研究将首次产生适用于海洋生物方解石的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）、刺激竞争性研究的既定计划（EPSCoR）和海洋地质和地球化学计划（MGG）共同资助。该奖项反映了美国国家科学基金会的法定使命，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.