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

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Ocean acidification due to increasing dissolution of carbon dioxide in seawater, and the effects of cumulative stressors (including acidification, pollution, warming, and anoxia) are among the top priorities for ocean research. Scientific progress requires 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 modelers 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. In this collaborative project between investigators in the U.S. and the United Kingdom, a team of scientists will work to create a thoroughly updated modeling tool for determining the detailed chemical composition, or "speciation," of seawater. The investigators propose to 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 result of this project will be a critically-evaluated thermodynamic model of natural waters containing (in any proportion) the major and minor ions of seawater, seawater-related pH buffers, and the trace metals iron, zinc, copper, and cadmium, to be made available to the wider community through a project web site. The academic beneficiaries will be chemical oceanographers, aquatic scientists, and others working in the following areas: ocean acidification including polar brines (in seasonal ice); pore water chemistry diagenetic reactions; paleoceanography; metrology of pH in saline solutions such as seawater. A postdoctoral researcher will be supported and trained through this project.