Oxidative marine photochemical reactions are an important step in modifying and remineralizing terrestrially-derived DOM, as shown in individual examples and indirect mechanistic evidence. Important classes of marine-derived DOM probably also enter this cycle. This project will quantify total photooxidative processes as oxygen consumption, by (1) direct O2 uptake measurements where sensitivity permits, and (2) using an indirect method sensitive enough for "blue water" and for low-reactivity coastal water studies. The results will provide much-needed quantitative evaluation of the role of photooxidation in oceanic carbon and oxygen cycles. Oxygen consumption, closely related to DOM oxidation, will be measured in coastal and estuarine waters and in organic matter concentrated by hydrophobic adsorption. Direct O2 uptake will be measured using pulsed polarographic electrodes with automated data acquisition. A sensitive new indirect technique, calibrated empirically against direct measurements, will quantify fluxes of the primary O2 -consuming species in "blue" and low-activity coastal waters. Effects of variables such as wavelength, light intensity, temperature, oxygen concentration, and prolonged photolysis on O2 consumption rates will be investigated to understand their (bio) geochemical significance and to identify the major mechanisms involved in O2 uptake/C remineralization.
