Collaborative Research: Photodegradation of Dissolved Organic Matter and its Contribution to Surface Water CO2 fluxes and the Carbon Cycle in a River Dominated Ocean Margin

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Ocean margins are highly dynamic systems at the land-sea-air interfaces, and they play a disproportionately large role in global carbon fluxes among these reservoirs. River dominated margins receive large quantities of terrigenous dissolved organic matter (DOM) and its chromophoric component (CDOM) that is highly photoreactive and appears to be largely remineralized to CO2 in margin surface waters. Despite the recognized importance of photochemical processes in river dominated margins, the overall significance of photochemistry in surface water CO2 fluxes remains uncertain. In this project, researchers at the University of South Carolina at Columbia and the University of Georgia will develop regional-scale estimates of photochemical and coupled photochemical-microbial carbon (including CO2 and CO) fluxes and removal of terrigenous DOM and CDOM in surface waters of the northern Gulf of Mexico margin. This ocean margin receives major contributions of terrigenous DOM (3 Tg C yr-1) and CDOM from the Mississippi River system. Specific objectives include determination of apparent quantum yields (AQY) for the photoproduction of CO2 and CO, the photochemical removal of DOC, and the coupled photochemical-microbial removal of DOC. Experimentally determined AQYs will be used in combination with field measurements, satellite imagery, and modeling to provide temporally-integrated, regional-scale assessments of photochemically-mediated carbon fluxes in the study region. The project will include improvement of remote-sensing algorithms and the development of regional-scale models for ocean margin carbon cycling. Once developed, this approach can be utilized to provide similar assessments in other river dominated ocean margins. At sea, the project will utilize a ship of opportunity and integrate with a currently funded study investigating total CO2-fluxes and biological processes in the northern Gulf of Mexico margin. This coordination of projects will provide an unprecedented opportunity for understanding the fundamental physical, biological, and photochemical processes controlling air-sea CO2 fluxes in a major river dominated margin. Broader Impacts: Measuring carbon fluxes (specifically CO2 and CO) in ocean margins and identifying the fundamental factors driving these fluxes have been identified as of great importance by the North American Carbon Program and Ocean Carbon and Climate Change programs. This project will provide regional estimates of photochemical and coupled photochemical-microbial carbon fluxes in surface waters of one of the major river dominated margins of the North American continent. This project will provide training, experience and support for a graduate student at each institution. Both principal investigators teach undergraduate and graduate classes that cover various aspects of the carbon cycle, and data collected from this project will be used as specific examples in these classes. This approach of incorporating information from active research programs into the classroom has proven to be very effective for increasing student interest in science and has encouraged undergraduate participation in research.