Award: OCE-1558699

The chemical reaction of carbon dioxide with water in the marine environment is a fundamental process that creates carbonic acid and all of the associated chemical ions (carbonate ions, hydrogen ions, and bicarbonate ions) that serve as the dominant buffer for pH in the ocean. Dehydration refers to the opposite reaction that releases carbon dioxide gas. By entering into important reactions and serving to control pH, these species govern a wide variety of chemical and biological processes in the ocean. Surprisingly, while the important reactions that involve carbon dioxide hydration and its resulting products have been extensively studied in the ocean, some of the fundamental mechanisms remain poorly understood and datasets are sparse. In particular, very little is known about how the natural isotopes (same chemical element but different masses) of the carbon and oxygen atoms are involved and this is critically needed to explain observed changes in chemical species and solid calcium carbonate such as that created by corals and other marine organisms. This research has carefully produced novel experimental data that includes critical measurements of carbon and oxygen isotopes before and after the hydration of carbon dioxide in the ocean. The kinetic isotope effects found in this study are the largest values compared to previously reported experimental values, suggesting that the effects found here are closest to the full isotope disequilibrium during carbon dioxide hydration. This research has provided a consistent data set on carbon and oxygen isotope fractionation that will be widely used in the ocean sciences. While hydration/dehydration of carbon dioxide in the ocean critically influences a variety of marine chemical and biological processes, there are certain aspects of the reaction that are poorly understood. Kinetic isotope effects during carbon dioxide hydration have not been well studied, and the data regarding this topic is inconsistent. This study has overcome the main challenge of separating the reaction product, bicarbonate ions, from carbon dioxide before re-equilibration by rapidly precipitating dissolved carbon as carbonate. Since carbonates formed from the process of hydration are considered critical indicators of water chemistry, biological processes, and the inorganic carbon cycle as a whole and are used in a wide variety of oceanographic research, particularly as paleo-proxies, this research has provided fundamental mechanistic data that greatly advances studies reaching beyond the physico-chemical measurements made here. Because the carbonate species affected by the isotope effects are used widely in studies in the ocean sciences, particularly those examining past climates, this research has far-reaching consequences. Additionally, the results provide new fundamental insight on exactly how the ocean will take up and respond to changing concentrations of atmospheric carbon dioxide in a changing climate. The results of this study are also critical in re-evaluating kinetic isotope effects observed in many ocean processes, will help to improve the reliability of paleo-proxies, and our understanding of biogeochemical processes. Furthermore, the results will help to improve paleoclimate reconstructions and hence aid in constraining future climate projections. This project is therefore relevant to the general public and policy makers. The research has funded a PI and an early-career scientist dedicated to graduate and undergraduate education as well as scientific outreach to the community. Graduate students have been trained in the areas of seawater chemistry, carbon cycling, paleoclimatology, and future climate change. Last Modified: 04/07/2020 Submitted by: Richard E Zeebe