Carbonic acid dissociation and calcite solubility in seawater of non-standard major ion composition

海洋酸化的过程是通过一系列化学反应发生的，首先是溶解在海洋中的二氧化碳与水反应产生碳酸。碳酸的化学分解是海洋酸化过程中的一个关键步骤。此外，矿物方解石的溶解度对于受海洋酸化影响的矿物的稳定性和溶解性至关重要。这很重要，因为像方解石这样的碳酸盐矿物会随着海洋变得更酸而溶解，因此，这对构建碳酸盐外壳的生物具有重要意义。这个项目将提供对碳酸解离和方解石矿物溶解度的基本见解-化学海洋学领域内外的研究人员广泛感兴趣的现象。它将解决数据可用性和对碳酸系统内主要海水化学相互作用的理解方面的一个重要空白。需要这些信息，以便为公众、科学领袖和政策制定者更好地了解不减碳排放对公海、河口、珊瑚礁等海洋化学和海洋生态系统的影响。该项目将海洋酸化和气候变化的研究和教育活动结合起来，将这些信息直接引入中学、大学课程和科学期刊。该项目促进了夏威夷大学来自不同种族的本科生和研究生的教育，同时进行了前沿研究。除了支持、教育和指导研究生之外，夏威夷大学全球环境科学项目的两名本科生每年也将得到支持。该项目将与当地一家电视台合作，制作一集关于海洋酸化的电视节目。调查人员还将协调各种公共教育活动和机构外展活动，并与檀香山的当地学校、教育中心和博物馆合作。该项目关于海洋化学和气候的成果将引起海洋学家、广大科学听众和普通公众的注意。碳酸的解离和方解石在离子介质（如海水）中的沉淀是海洋环境中普遍存在的现象，对从咸淡水到盐水的溶液中的许多过程以及从海洋酸化到碳封存的应用都至关重要。碳酸解离和方解石在稀溶液、简单NaCl介质和恒定主离子比（包括Na、Mg、Ca、K、Cl、SO4）下的溶解度相对较好地了解，并且化学计量解离常数/溶解度产物是已知的。然而，对于碳酸解离和方解石在非标准海水溶液中的溶解度的热力学，特别是对于复杂溶液和不同浓度的Mg、Ca、K和SO4，人们的基本理解还存在很大的差距。目前还缺少这类溶液的精确热力学数据。然而，这些数据对许多现代海洋系统至关重要，包括边缘海和河口、沉积物孔隙水、某些缺氧盆地/热液环境、海冰盐水、海洋生物的细胞室等。此外，海洋的主要离子组成在过去发生了很大的变化。本项目将精确测量非标准主要离子组成的海水溶液中的碳酸解离，确定相同溶液组成下方解石的溶解度，并在此基础上推导和实现化学形态模型（离子配对模型、Pitzer模型等）的关键参数。在受控的实验室条件下进行酸碱滴定，以确定碳酸在不同离子强度、温度和组成（Mg、Ca、K和SO4）的水溶液中的第一和第二化学计量解离常数（K* s），以及相同溶液组成下方解石溶解度的测量。从这些数据中，将提取用于改进现有化学形态模型的参数，从而可以计算各种成分的K*和方解石溶解度。项目成果的影响和应用非常广泛，涉及化学海洋学、海洋生物学、地球化学、古海洋学、物理化学、医学等领域。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。

The process of ocean acidification occurs through a series of chemical reactions, beginning when carbon dioxide that has been dissolved in the ocean reacts with water to produce carbonic acid. The chemical break down of carbonic acid represents a critical step in the process of ocean acidification. Additionally, the solubility of the mineral calcite is essential for the stability and dissolution of minerals affected by ocean acidification. This is important because carbonate minerals like calcite will dissolve as the oceans become more acidic, therefore, this has significant implications for organisms that build carbonate shells. This project will provide fundamental insight into carbonic acid dissociation and calcite mineral solubility - phenomena of wide interest to researchers within and beyond the field of chemical oceanography. It will address an important gap in data availability and understanding of major seawater chemical interactions within the carbonic acid system. Such information is needed to provide the public, scientific leaders, and policymakers with a better understanding of the consequences of unabated carbon emissions for ocean chemistry and marine ecosystems in the open ocean, estuaries, coral reefs, and more. The project integrates research and educational activities on ocean acidification and climate change by introducing this information directly into secondary school, college curricula, and scientific journals. The project fosters education for undergraduate and graduate students from the ethnically diverse population at the University of Hawaii, while conducting cutting-edge research at the same time. In addition to supporting, educating, and mentoring graduate students, two undergraduate students from the Global Environmental Science program at the University of Hawaii will be supported each year. The project will work with a local TV broadcast to produce a TV episode on ocean acidification. The investigators will also coordinate various public educational activities and outreach events at institutions and in collaboration with local schools, educational centers, and Museums in Honolulu. The project results on ocean chemistry and climate will capture the attention of oceanographers, a broad scientific audience, and the general public alike.The dissociation of carbonic acid and calcite precipitation in ionic media such as seawater are ubiquitous phenomena in the marine environment and are critical to numerous processes in solutions ranging from brackish waters to brines and to applications from ocean acidification to carbon sequestration. Carbonic acid dissociation and calcite solubility in dilute solutions, simple NaCl media, and seawater at constant major ion ratios (including Na, Mg, Ca, K, Cl, SO4) is relatively well understood and the stoichiometric dissociation constants/solubility products are well known. However, there is a significant gap in the fundamental understanding of the thermodynamics of carbonic acid dissociation and calcite solubility in non-standard seawater solutions, particularly for complex solutions and varying concentrations of Mg, Ca, K, and SO4. Accurate thermodynamic data for such solutions are presently missing. Yet, the data is critical for numerous modern marine systems, including marginal seas and estuaries, sediment porewaters, certain anoxic basins/hydrothermal environments, sea ice brines, cell compartments in marine organisms, etc. Moreover, the ocean's major ion composition has varied substantially in the past. This project will accurately measure carbonic acid dissociation in seawater solutions of non-standard major ion compositions, determine calcite solubility for the same solution composition, and derive and implement critical parameters for chemical speciation models (ion-pairing models, Pitzer models, etc.) based on the measurements. Acid-base titrations under controlled laboratory conditions will be conducted to determine the first and second stoichiometric dissociation constant (K*'s) of carbonic acid in aqueous solutions of varying ionic strength, temperature, and composition (Mg, Ca, K, and SO4), as well as measurements of calcite solubility for the same solution composition. From the data, parameters to improve existing chemical speciation models will be extracted, allowing computation of K*'s and calcite solubility over a wide range of compositions. The implications and applications of the project results are very broad and relevant to chemical oceanography, marine biology, geochemistry, paleoceanography, physical chemistry, medicine, and more.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.