Biogenic Calcium Carbonate Solubilities and Reaction Rates by Lab and Field Saturometry

海洋积极地与大气交换二氧化碳，目前正在吸收人类通过燃烧化石燃料排放的大约三分之一的二氧化碳。由于二氧化碳是酸性的，海洋的pH值在吸收二氧化碳的过程中会下降，这一过程被称为“海洋酸化”。海洋酸化使生物更难生长碳酸钙壳，从而对海洋生态系统的健康产生负面影响。然而，这些碳酸钙壳在深海中的溶解有助于中和我们作为人类排放的二氧化碳。这一过程发生的程度是海洋碳酸钙溶解度的函数。该项目将评估温度和压力对生物生产的碳酸钙矿物稳定性的影响。这项研究的结果将使我们能够更好地预测二氧化碳将在哪里、多少和多快地被中和并储存在世界海洋中。我们还将研究碳酸钙外壳化学成分的微小变化--如镁的加入--对其稳定性的影响。该项目还将对微生物的外壳进行微型计算机断层扫描，以更好地显示它们的三维细节。我们将打印这些三维扫描，作为课堂和伍兹霍尔游客中心的教育工具。此外，每年还将为高中教师举办关于海洋酸化和海洋钙化重要性的专业发展研讨会。海洋是大多数人为二氧化碳排放的最终储存库，这反过来又使海洋化学不利于通过海洋酸化过程的生物碳酸盐沉淀。海洋酸化降低了海水的pH值，但主要是生物成因的碳酸盐矿物的溶解具有缓冲这种酸化的能力，并在几千年的时间里将整个海洋的pH值和大气二氧化碳推向工业化前的值。不幸的是，海水化学、碳酸盐矿物溶解度和控制碳酸盐溶解和沉淀的动力学之间的关系还没有完全了解。目前，很明显，仅基于无机方解石的关系不足以描述海洋中生物源方解石的循环。该项目将在实验室和野外使用pH饱和度分光光度法系统地测定三种最常见的生物碳酸盐(球藻、有孔虫和翼足类)的溶解度和反应动力学。饱和度计在封闭系统中将碳酸钙与海水孵化。在每次运行过程中，当系统接近平衡时，饱和仪内的pH变化跟踪碳酸钙溶解/沉淀的进程。因此，该饱和度计有可能在一次实验中将矿物溶解/沉淀动力学的机械解释与溶解度的测量联系起来。PH分光光度法使用校准良好的指示剂染料，允许将溶解度和数据与现代pH校准和参考材料捆绑在一起，可以在实验室使用或部署在海上的水线上。现场实验将在多个深度进行，阐明对溶解度和动力学的现场控制，以及生物源方解石的溶解度对温度和压力的敏感性。实验将从平衡的两个方面进行，允许可靠地确定无机和生物来源的溶解性。这一奖项反映了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。

The ocean actively exchanges carbon dioxide with the atmosphere and is currently absorbing about a third of the carbon dioxide humans emit through fossil fuel burning. Because carbon dioxide is acidic, ocean pH drops as it takes up carbon dioxide, a process known as "ocean acidification". Ocean acidification negatively affects the health of marine ecosystems by making it harder for organisms to grow their calcium carbonate shells. Yet, the dissolution of these calcium carbonate shells in the deep ocean helps neutralize the carbon dioxide we emit as humans. The extent to which this process takes place is a function of the solubility of marine calcium carbonate. This project will evaluate the temperature and pressure effects on the stability of biologically produced calcium carbonate minerals. The results from this study will allow us to better predict where, how much, and how fast, carbon dioxide will be neutralized and stored in the world's ocean. We will also investigate the ways in which small changes in the chemical composition of calcium carbonate shells - such as the incorporation of magnesium - influence their stability. This project will also conduct micro-computed tomography scans of microorganisms' shells to better visualize them in 3-dimensional detail. We will print these 3-dimensional scans for use as educational tools in the classroom and in the Woods Hole Visitor Center. In addition, professional development workshops for high school teacher on ocean acidification and the importance of marine calcification will be held yearly.The ocean is the ultimate repository for most of anthropogenic carbon dioxide emissions, which in turn is making ocean chemistry less favorable for biogenic carbonate precipitation through the process of ocean acidification. Ocean acidification decreases seawater pH but dissolution of primarily biogenic carbonate minerals has the capacity to buffer this acidification and over thousands of years push whole-ocean pH and atmospheric carbon dioxide to their preindustrial values. Unfortunately, the relationship between seawater chemistry, carbonate mineral solubility, and the kinetics that govern carbonate dissolution and precipitation are not fully understood. Currently, it is clear that relationships based solely on inorganic calcite are insufficient to describe the cycling of biogenic calcites in the ocean. This project will conduct a systematic determination of the solubilities and reaction kinetics of the three most common biogenic carbonates (coccoliths, foraminifera, and pteropods), both in the laboratory and in the field, using spectrophotometric pH saturometry. The saturometer incubates calcium carbonate with seawater in a closed system. During each run, the change in pH within the saturometer traces the progression of calcium carbonate dissolution/precipitation as the system approaches equilibrium. The saturometer therefore has the potential to link mechanistic interpretations of mineral dissolution/precipitation kinetics to measurements of solubility in a single experiment. The spectrophotometric pH method uses well-calibrated indicator dyes, allows solubility and data to be tied to modern pH calibrations and reference materials, and can be used in the laboratory or deployed on a hydrowire at sea. Field experiments will be conducted at multiple depths, elucidating in-situ controls on solubility and kinetics, as well as the sensitivity of biogenic calcite solubility to temperature and pressure. Experiments will be conducted from both sides of equilibrium, allowing for robust determinations of inorganic and biogenic solubilities.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.