Marine Photochemistry: Particles versus Solutes

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Photochemical transformations of organic matter have profound influences on the cycling of carbon, nitrogen, and trace gases in the ocean. Previous studies of marine photochemistry have mostly focused on dissolved organic matter (DOM) with little attention paid to particulate organic matter (POM). Preliminary tests in our and other laboratories, however, suggest that POM-based photochemical fluxes are of ecologically and environmentally significance. The overarching goal of this proposed research is to evaluate the impacts of POM photodegradation on marine cycles of carbon, nitrogen, and trace gases. Through studying five key photoproducts, dissolved organic carbon (DOC), colored DOM (CDOM), carbon monoxide (CO), dissolved inorganic carbon (DIC), and ammonia (NH3), this research program will seek to 1) quantify POM photodegradation as a sink of POC and as sources of DOC and CDOM and evaluate their seasonal and regional variability; 2) quantify POM photodegradation as sources of DIC, CO, and NH3 and evaluate their seasonal and regional variability; 3) assess the influences of particle type (terrestrial vs. marine) and environmental variables (water temperature, pH, and salinity) on these POM photoprocesses; 4) elucidate the significance of POM-based photoproduction of DIC, CO, and NH3 relative to the corresponding DOM-based photoproduction terms. Field studies will be carried out in diverse geographical regions covering estuarine, coastal, and open-ocean waters. Results from the filed surveys will be extrapolated to regional scales by establishing quantitative empirical relationships between the POM photoprocesses and environmental variables. By exploring a heretofore little explored area with potentially great biogeochemical importance, this proposed research is expected to create new research niches interrelating among chemical oceanography, marine ecology, and ocean optics. It will fill in gaps in our understanding of the roles of POM and DOM photochemistry in the cycling of carbon, nitrogen, and trace gases in marine waters and hence of their impacts on the functioning of marine ecosystems.