Characterization of aragonite and calcite solubility products in seawater using modern CO2 system measurement techniques

碳酸钙是一种矿物（固体），由经济和环境重要的海洋生物（包括蛤和牡蛎）产生，用于结构支撑和防止捕食。由于海洋从大气中吸收二氧化碳，碳酸钙是珊瑚礁的结构矿物，变得越来越容易溶解（化学诱导分解）。该项目致力于提高对海洋生态系统特别重要的不同形式碳酸钙稳定性的预测和解释的准确性。海水中固体碳酸钙的稳定性或不稳定性通常通过（a）测量收集的海水样品中溶解的化学成分的浓度和（b）计算（数学模型）海水中防止固体碳酸钙溶解所需的溶解钙和溶解碳酸盐的量来评估。用于模拟碳酸钙稳定性的必要计算是从实验中产生的，其中将固体碳酸钙颗粒添加到海水样品中，并允许颗粒溶解，直到溶解结束并且此后观察不到颗粒的进一步变化。通过此类实验产生的海水中碳酸钙稳定性模型对于贝类产业很重要，并且对于了解作为具有重要经济意义的海洋生物的食物的含碳酸盐生物的自然化学循环也很重要。在过去的十年中，贝类行业的经济利益刺激了监测工作，以评估孵化水域中碳酸钙稳定性的日常变化。人们还认识到，碳酸钙稳定性模型对于了解表层海洋中非常小的生物体的可用性非常重要，这些生物体是生命早期阶段鲑鱼的必需食物。当前海水中固体碳酸钙的稳定性模型已经有超过 35 年的历史，并且是使用现代标准认为过时的测量技术生成的。该项目将使用现代最先进的方法来确定海水中固体碳酸钙稳定性所需的化学条件，然后将这些测量结果用于创建碳酸钙在各种盐度和温度下稳定性的定量模型。对于外展活动，这位科学家计划通过圣彼得堡科学节和女孩海洋学营的互动模块向公众传达研究结果，并为圣彼得堡 SciCafe 系列准备一个关于该项目及其与海洋酸化的关系的演示。 这项研究将支持一名研究生和一名本科生暑期实习生的论文研究。 该项目是对碳酸钙 (CaCO3) 溶解度的最先进研究，碳酸钙是全球海洋中一种独特的重要矿物质。陆地 CaCO3 矿物的风化以碳酸氢盐 (HCO3-) 和碳酸盐 [CO3(2-)] 的形式增加海水的碱度。海洋表面的海洋钙化剂会沉淀出固体 CaCO3，以提供结构支撑并防止被捕食。海洋钙化剂产生的生物碳酸钙沉淀并溶解在更深的水域中。这些过程有时称为碳酸钙泵，对于将碳从表层海洋转移到深处非常重要。因此，碳酸钙，无论是固体形式还是溶解成分，在全球碳循环中都发挥着不可或缺的作用。海洋 CaCO3 溶解度的评估对于定量理解和解释固体 CaCO3 与其溶解成分之间的转化至关重要。 CaCO3 溶解度以海水中溶解的 Ca2 和 CO3(2-) 浓度（mol/kg 海水）的乘积 (Ksp) 定量表示，与指定的 CaCO3 结晶多晶型物达到平衡。 Ksp 受海水温度 (T)、盐度 (S) 和压力 (P) 的影响，用于量化饱和状态 (Ω)，即海水中溶解的 Ca2 和 CO3(2-) 欠饱和或过饱和的程度。鉴于海洋酸化导致全球海洋中 CaCO3 的饱和度不断降低，对 Ksp 进行准确的定量评估至关重要。除了 Ksp 表征在海洋碳循环模型中的重要性之外，Ksp 参数化对于贝类行业水化学的评估也至关重要。在过去的十年中，贝类养殖者的经济利益刺激了对 Ω 对贝类健康影响的研究。 CaCO3 溶解度对于评估某些渔业的经济效益也很重要。碳酸钙稳定性模型对于了解表层海洋中含碳酸盐生物的可用性非常重要，这些生物是生命早期阶段鲑鱼的必需食物。当前海水中固体碳酸钙的稳定性模型已经有超过 35 年的历史，并且是使用现代标准认为过时的测量技术生成的。在该项目中，将使用现代最先进的 pH、碱度和碳酸根离子浓度测量程序来确定 Ksp。然后，这些测量结果将用于创建各种盐度和温度下的 Ksp 定量模型。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Calcium carbonate is a mineral (solid) produced by economically and environmentally important types of marine organisms (including clams and oysters) for structural support and protection from predation. Calcium carbonate, the structural mineral of coral reefs, is becoming increasingly susceptible to dissolution (chemically-induced decomposition) due to the ocean’s uptake of carbon dioxide from the atmosphere. This project is devoted to improving the accuracy of predictions and interpretations of the stability of different forms of calcium carbonate that are uniquely important to the oceanic ecosystem. The stability or instability of solid calcium carbonate in seawater is routinely evaluated from (a) measurements of the concentrations of dissolved chemical components in collected seawater samples and (b) calculations (mathematical models) of the amounts of dissolved calcium and dissolved carbonate in seawater that are required to prevent solid calcium carbonate from dissolving. The necessary calculations for modeling calcium carbonate stability are generated from experiments in which solid calcium carbonate particles are added to seawater samples and the particles are allowed to dissolve until dissolution ends and no further changes in the particles are observed thereafter. The models of calcium carbonate stability in seawater produced through such experiments are important to the shellfish industry and are important to understanding the natural chemical cycles of carbonate-bearing organisms that serve as food for economically-important marine organisms. Over the past decade, the economic interests of the shellfish industry have stimulated monitoring efforts to assess day-to-day changes in the stability of calcium carbonate in hatchery waters. It is also recognized that models of calcium carbonate stability are important to understanding the availability of very small organisms in the surface ocean that serve as an essential food for early-life-stage salmon. Current models of the stability of solid calcium carbonate in seawater are more than thirty-five years old and were generated using measurement techniques that are considered antiquated by modern standards. Modern state-of-the-art methods will be used in this project to determine the chemical conditions required for stability of solid calcium carbonate in seawater, and these measurements will then be used to create quantitative models of calcium carbonate stability over a wide range of salinities and temperatures. For outreach activities, the scientist plans to communicate results from the study to the public via interactive modules at the St. Petersburg Science Festival and the Oceanography Camp for Girls, as well as prepare a presentation for the St. Petersburg SciCafe series about this project and how it relates to ocean acidification. This research will support the dissertation research of one graduate student and an undergraduate summer intern. This project is a state-of-the-art investigation of the solubility of calcium carbonate (CaCO3), a uniquely important mineral in the global ocean. Weathering of terrestrial CaCO3 minerals adds alkalinity to seawater in the form of bicarbonate (HCO3-) and carbonate [CO3(2-)]. Marine calcifiers at the ocean surface precipitate solid CaCO3 for structural support and protection from predation. The biogenic CaCO3 produced by marine calcifiers settles into and dissolves within deeper waters. These processes, sometimes called the calcium carbonate pump, are important for transferring carbon from the surface ocean to depth. As such, calcium carbonate, in both its solid form and dissolved components, plays an integral role in the global carbon cycle. Assessments of marine CaCO3 solubility are essential for a quantitative understanding and interpretation of transformations between solid CaCO3 and its dissolved components. CaCO3 solubility is quantitatively expressed in terms of the product (Ksp) of the dissolved Ca2+ and CO3(2-)concentrations (mol/kg seawater) in seawater at equilibrium with a specified crystalline polymorph of CaCO3. Ksp is influenced by seawater temperature (T), salinity (S), and pressure (P) and is used to quantify saturation state (Ω), the degree to which seawater is under- or over-saturated with dissolved Ca2+ and CO3(2-). In view of the decreasing saturation states of CaCO3 in the global ocean, a consequence of ocean acidification, accurate quantitative assessments of Ksp are essential. In addition to the importance of Ksp characterizations in models of oceanic carbon cycling, Ksp parameterizations are essential to assessments of water chemistry in the shellfish industry. Over the past decade, the economic interests of shellfish growers have stimulated research into the effects of Ω on shellfish health. CaCO3 solubility is also important to assessing the economics of certain fisheries. Models of calcium carbonate stability are important to understanding the availability of carbonate-bearing organisms in the surface ocean that serve as an essential food for early-life-stage salmon. Current models of the stability of solid calcium carbonate in seawater are more than thirty-five years old and were generated using measurement techniques that are considered antiquated by modern standards. In this project, Ksp will be determined using modern state-of-the-art procedures for measurements of pH, alkalinity, and carbonate ion concentrations. These measurements will then be used to create quantitative models of Ksp over a wide range of salinities and temperatures.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.