Hydrogen peroxide and superoxide photoproduction in diverse marine waters: A simple proxy for estimating direct CO2 photochemical fluxes

Abstract

The photoproduction of H2O2 and CO2 exhibits a well-defined relationship with an average CO2:H2O2 molar ratio of 6.6-±-1.8 as determined in a variety of marine waters ranging from a dark tidal creek to clear offshore stations near the Gulf Stream. Even when corrected for photobleaching, accumulation of both H2O2 and CO2 was not linear beyond 12-h of constant irradiation, with interval rates indicating that production efficiency for both products decreased with increasing photon dose. Direct measurements of O2- photoproduction, together with its dark thermal decay to H2O2, indicate that O2- may be the better proxy for photochemical dissolved organic matter oxidation to CO2. Given the very short irradiation times needed to determine O2- production rates (~2-5-min), determination of O2- photoproduction may provide robust estimates for initial CO2 photoproduction rates even in blue water, allowing greatly improved estimates for the global significance of dissolved organic carbon photooxidation.