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），由经济上和环境上重要的海洋生物（包括蛤蜊和牡蛎）产生，用于结构支撑和保护免受捕食。由于海洋从大气中吸收二氧化碳，构成珊瑚礁的结构性矿物碳酸钙越来越容易被溶解（化学诱发的分解）。该项目致力于提高预测和解释对海洋生态系统具有独特重要性的不同形式碳酸钙稳定性的准确性。固体碳酸钙在海水中的稳定性或不稳定性通常通过(a)收集的海水样品中溶解化学成分浓度的测量和(b)防止固体碳酸钙溶解所需的海水中溶解钙和溶解碳酸钙量的计算（数学模型）来评估。模拟碳酸钙稳定性的必要计算是由实验产生的，实验中，将固体碳酸钙颗粒添加到海水样品中，并允许这些颗粒溶解直到溶解结束，此后没有观察到颗粒的进一步变化。通过这些实验产生的海水中碳酸钙稳定性模型对贝类产业很重要，对理解作为经济上重要的海洋生物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，贝类产业的经济利益刺激了监测工作，以评估孵化场水域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海洋表面非常小的生物的可用性非常重要，这些生物是早期生命阶段鲑鱼的基本食物。目前关于海水中固体碳酸钙稳定性的模型已有35年以上的历史，使用的测量技术被现代标准认为是过时的。该项目将使用现代最先进的方法来确定固体碳酸钙在海水中稳定性所需的化学条件，然后这些测量结果将用于创建碳酸钙在广泛的盐度和温度范围内稳定性的定量模型。在外联活动方面，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播研究结果，并为圣彼得堡科学咖啡馆系列准备一份关于该项目及其与海洋酸化的关系的报告。本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）溶解度的最新研究，碳酸钙是全球海洋中一种独特的重要矿物。陆地CaCO3矿物的风化作用以碳酸氢盐（HCO3-）和碳酸盐[CO3(2-)]的形式增加了海水的碱性。海洋表面的海洋钙化剂沉淀固体碳酸钙，用于结构支撑和保护免受捕食。海洋钙化剂产生的生物源CaCO3在较深的水域中沉淀和溶解。这些过程有时被称为碳酸钙泵，对于将碳从海洋表面转移到海洋深处非常重要。因此，碳酸钙，无论是固体形式还是溶解成分，都在全球碳循环中发挥着不可或缺的作用。评估海洋CaCO3的溶解度对于定量理解和解释固体CaCO3及其溶解组分之间的转化至关重要。CaCO3的溶解度定量表示为海水中溶解的Ca2+和CO3（2-）浓度（mol/kg海水）的乘积（Ksp），具有特定的CaCO3晶型。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），即海水溶解Ca2+和CO3（2-）的过饱和或过饱和程度。由于海洋酸化导致全球海洋中CaCO3的饱和状态下降，因此对Ksp进行准确的定量评估至关重要。除了海洋碳循环模型中Ksp表征的重要性之外，Ksp参数化对于评估贝类行业的水化学也至关重要。在过去的十年中，贝类养殖者的经济利益刺激了Ω对贝类健康影响的研究。碳酸钙的溶解度对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海洋表层含碳酸盐生物的可用性非常重要，这些生物是早期生命阶段鲑鱼的基本食物。目前关于海水中固体碳酸钙稳定性的模型已有35年以上的历史，使用的测量技术被现代标准认为是过时的。在这个项目中，Ksp将使用最先进的方法来测量pH值、碱度和碳酸盐离子浓度。然后，这些测量结果将用于在广泛的盐度和温度范围内创建Ksp的定量模型。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。

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.