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.
