Marsh-Dominated Ocean Margins as a Source of CO2 to the Atmosphere and Open Oceans: A Field Study in the U.S. Southeastern Continental Shelf

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ABSTRACTOCE-0425153Recent studies in several large continental shelves located in mid-to-high latitude areas indicate significant air-to-sea CO2 transfer. Presumably the absorbed CO2 is transferred into the open ocean. If this conclusion is globally applicable, such a continental shelf CO2 sink would be very important in the study of global carbon cycling. In this project, researchers at the University of Georgia will test this hypothesis by quantifying air-sea CO2 fluxes in a low-to-mid latitude ocean margin, the U.S. Southeastern Continental Shelf (also known as the South Atlantic Bight, SAB), where preliminary evidence indicates an opposite (sea-to-air) CO2 flux. The researchers hypothesize that the SAB is a source of CO2 to the atmosphere and to the open ocean and that this CO2-release is driven by the respiration of organic carbon (OC) exported from intertidal salt marshes. Shelf-wide distributions of surface pCO2 and water column total dissolved inorganic carbon (DIC) and alkalinity (Alk) will be determined with four cross-shelf transects and one alongshore transect covering the entire SAB and through five quarterly cruises. The seaward export fluxes of DIC will be estimated based on an area-integrated excess DIC inventory and the shelf water residence time determined by freshwater balance. This DIC flux to the open ocean is expected to be much higher than the riverine flux in this area. The simultaneous quantification of air-sea CO2 flux and DIC export to the open ocean, which has rarely been attempted before, will significantly improve our understanding of the role that ocean margins play in the global ocean carbon cycle. In addition to the determination of overall seaward DIC flux, the team will also seek a better understanding of the relative importance of DIC fluxes carried by cross-shelf and alongshore flows by taking advantage of a recently published SAB 3-dimensional climatology model and other ongoing numerical model activities in this region. In a similar approach, seaward fluxes of Alk and dissolved organic carbon will also be estimated. Broader Impacts. The results of this project are expected to enhance our understanding and ability to predict the fate of anthropogenic CO2 in the atmosphere. This project will also promote teaching, training and learning in a number of important ways that involve graduate, undergraduate and high school students.