Carbonate chemistry dynamics along the U.S. eastern continental shelf

Abstract

The uptake of carbon dioxide (CO2) from the atmosphere by seawater has caused ocean acidification globally. In addition to anthropogenic CO2 uptake, the coastal ocean experiences enhanced acidification due to freshwater discharge, eutrophication, upwelling, etc. This coastal acidification affects the health of calcifying species and has a harmful impact on commercial fisheries and the marine ecosystem. It is critical to monitor coastal acidification and determine the spatial and temporal trends of related parameters. This dissertation focuses on the carbonate/bicarbonate buffering system, which is a chemical buffer system that regulates seawater pH. I analyze the carbonate chemistry dynamics and buffer capacities for the east coast using four shipboard datasets, satellite remote sensing data, and model outputs. Results suggest that total dissolved inorganic carbon and the aragonite saturation state along the U.S. eastern continental shelf have patterns that agree with predictions based on carbon dioxide equilibrium with the atmosphere. This indicates a solubility control mechanism that leads to low carbonate ion concentrations and aragonite saturation state in cold northern waters and the opposite in warm southern waters. In terms of short-term variability of aragonite state in the central Mid-Atlantic Bight, quantitative analyses show that physical advection and mixing processes are the dominant forces for a higher aragonite saturation state in slope waters while biological carbon removal and carbon dioxide degassing contribute to higher aragonite state in shelf waters. On decadal and longer time scales, dissolved inorganic carbon has increased while aragonite saturation state and pH have decreased along the U.S. eastern continental shelf. However, dissolved inorganic carbon increase and aragonite saturation state decrease were dampened in the Mid-Atlantic Bight because of seawater temperature increase. The analyses of carbonate chemistry parameters in various spatial and temporal scales help us to better understand the processes that can alter carbonate chemistry in coastal waters. In addition, with specific regional-scale ocean models, the community can extend our ability of quantitative understanding carbonate chemistry dynamics and take necessary efforts to prevent the occurrence of low pH or undersaturation conditions in the future.