NSFGEO-NERC: A Thermodynamic Chemical Speciation Model for the Oceans, Seas, and Estuaries

人为二氧化碳溶解造成的海洋酸化以及累积压力因素（包括酸化、污染、变暖和缺氧）的影响是海洋研究的重中之重，需要在地球仪范围内进行准确和一致的测量，以监测和了解目前的影响，并建立模型，以评估未来的情景和补救方法。观测科学家和模型制作者的工作与需要准确了解天然沃茨和用于仪器校准的参考材料和溶液中无机碳酸盐系统的化学形态、pH值、营养物和污染物痕量金属有关。化学形态定义为海水中化学元素在不同分子和离子形式之间的分布，并决定其反应性和生物利用度。形态取决于相关热力学平衡常数的值，以及每个溶解离子和分子的活性。这些都是温度、压力和盐度（或者更一般地说，溶液成分）的复杂函数，无法从理论上预测。海水中的许多重要反应都涉及酸碱平衡，这就引入了pH值作为一个额外的变量。尽管化学形态的重要性，现有的计算工具往往只是简单的经验公式，产生的反应作为盐度和温度的函数的平衡常数。这样的方程不能用于许多重要的天然沃茨，其组成与正常海水的组成不同（例如，极地卤水、河口、孔隙水、封闭海和古海洋）。此外，由于富营养化、上升流、河水中溶解的溶质以及伴随pH值变化的金属毒性变化的影响，陆架海和河口海水pH值和碳酸盐化学的人为变化变得复杂。因此，尽管物理化学家在过去几十年中做出了最大的努力，但仍然没有能力计算控制影响贝类和许多河口和海岸典型的半咸水/中盐环境中更广泛的海洋动物的化学因素的平衡。我们将在海洋科学家测量，解释，并通过建立一个基于Pitzer方程计算溶质和水活度的物种形成模型，预测不同组成的天然沃茨中的化学物种形成和pH值。这种方法在地球化学领域有着长期的成功记录。该方程是基于这样的概念，即溶解的溶质物种的控制活动之间的相互作用对和三胞胎。这些相互作用的参数的值是从溶液性质的广泛测量确定的。这个项目的工作将包括测量活动和热容量，并利用最近的文献数据来改进和检验模型;对模型进行计算机编码和验证，并制定方法来量化模型预测的物种形成的不确定性与基本测量结果的不确定性之间的关系;与国际海洋学家合作，帮助设计实用的物种形成模型工具和具体应用的相关指南。完成的模型将使所有海水成分的活性和形态能够在一个统一的框架内进行计算，该框架（i）包括海水及其与淡水的混合物中的主要和微量元素，（ii）包括其他不同组成的盐水环境，以及（iii）包括用于校准pH值和其他仪器的缓冲液。我们的研究结果将促进对化学形态的定量理解-从海洋测量到生态系统模型-扩大自然水体和海洋环境的范围。

Ocean acidification due to the dissolution of anthropogenic CO2, and the effects of cumulative stressors (including acidification, pollution, warming, and anoxia) are among the top priorities for ocean research, requiring accurate and consistent measurements across the globe to monitor and understand present effects, and modelling to evaluate future scenarios and methods of remediation. The work of observational scientists and modellers is linked by the need for an accurate knowledge of the chemical speciation of the inorganic carbonate system, pH, and nutrient and contaminate trace metals, in both natural waters and the reference materials and solutions used for instrument calibration.Chemical speciation is defined as the distribution of a chemical element between different molecular and ionic forms in seawater, and determines its reactivity and bioavailability. Speciation depends on the value of the relevant thermodynamic equilibrium constant, and on the activities of each of the dissolved ions and molecules. These are complex functions of temperature, pressure, and salinity (or, more generally, solution composition), and cannot be predicted from theory. Many of the important reactions in seawater involve acid-base equilibria, which introduces pH as an additional variable. Despite the importance of chemical speciation, the available calculation tools are often only simple empirical equations that yield equilibrium constants for reactions as functions of salinity and temperature. Such equations cannot be used for many important natural waters whose composition differs from that of normal seawater (e.g., polar brines, estuaries, pore-waters, enclosed seas, and paleo-oceans). Furthermore, human-driven changes in seawater pH and carbonate chemistry in shelf seas and estuaries are complicated by the effects of eutrophication, upwelling, the dissolved solutes contained in river water, and changes in metal toxicity accompanying pH change. Consequently, despite the best efforts of physical chemists over the last several decades, there is not yet the ability to calculate the equilibria controlling the chemical factors impacting shellfish and a broader range of marine fauna in the brackish/mesohaline environments typical of many estuaries and coasts.We will create a step change in the capability of marine scientists to measure, interpret, and predict chemical speciation and pH in natural waters of varying composition by creating a speciation model based upon the Pitzer equations for the calculation of solute and water activities. The approach has a long track record of success in geochemistry. The equations are based upon the concept that interactions between pairs and triplets of dissolved solute species control activities. The values of the parameters for these interactions are determined from a wide range of measurements of solution properties. Work in this project will include measuring activities and heat capacities, and using recent literature data, to improve and test the model; the computer coding and validation of the model and the development of methods to quantify the relationship between uncertainties in model-predicted speciation and those in the underlying measurements; and engagement with oceanographers internationally to help design practical speciation modelling tools and associated guidance for specific applications. The completed model will enable the activities and speciation of all seawater components to be calculated within a unified framework that, (i) includes the major and trace elements in seawater and its mixtures with freshwaters, (ii) includes other saline environments of differing composition, and (iii) encompasses the buffers that are used to calibrate pH and other instruments, and. Our results will this advance the quantitative understanding of chemical speciation - from ocean measurements to ecosystem models - for an expanded range of natural water bodies and marine environments.