Significance of one and two carbon photoproducts in the photolysis of marine dissolved organic matter

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Marine dissolved organic carbon (DOC) is one of Earth’s major carbon reservoirs, but despite many years of study, the pathways and rates of DOC production and removal are poorly constrained. It is important to identify major pathways and determine rates in the oceans to better predict how DOC cycling will change in the future, and how these changes will alter the global carbon cycle. One potentially important process that affects marine DOC is photochemistry, the breakdown of organic molecules by sunlight. This project will investigate photochemical destruction of DOC. Findings from the work will be of interest to biologists, chemists, ecologists, climate scientists, and ocean-atmosphere modelers. The project will foster research and educational opportunities for one postdoctoral scholar, a graduate student, and several undergraduates. The project team will engage in public outreach and education through a project website, videoconferencing, online discussion forums, and an interactive blog in partnership with the State University of New York, College of Environmental Science and Forestry’s Louis Stokes Alliance of Minority Participation Program and the local American Chemical Society’s Project SEED for economically-disadvantaged high school students. The research plan is to re-evaluate two long-held assumptions: that dissolved inorganic carbon (i.e., carbon dioxide) is the main product produced from the photochemical breakdown of marine DOC, and that sunlight-driven chemistry is an important process in the removal of DOC from the oceans. The project will investigate three interrelated questions: (1) Are coastal-to-offshore transects in production rates of acetone, pyruvate and C1- and C2-carbon photoproducts nonlinear functions of CDOM absorption, as observed for DIC? (2) Is DIC the main carbon photoproduct produced from the photolysis of DOC in the open ocean? (3) Is the production of C1- and C2-carbon photoproducts, together with acetone and pyruvate, collectively a significant removal mechanism for DOC in the oceans on an annual basis? To address these questions, the project will combine laboratory experiments and a 19-day research cruise. The project will focus on low molecular weight carbon compounds because these are the main products produced from the photolysis of DOC, and yet no one has co-measured photochemical production rates of these compounds in seawater. Compounds to be considered include carbon monoxide, dissolved inorganic carbon, formaldehyde, acetaldehyde, acetone, glyoxal, glyoxylate, pyruvate, formate, and acetate. The team will measure photochemical production rates and determine wavelength- and temperature-dependent apparent quantum yields (AQY) for the production of these compounds. Using AQY data, they will model depth-resolved photochemical carbon fluxes using remotely sensed ocean color to determine the impact of this process in the marine DOC cycle.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.