Water collected from riverine, near coastal, and salt marsh sources in the Southeastern United States was evaluated for its ability to produce both carbon monoxide (CO) and dissolved inorganic carbon (DIC) by photochemical oxidation of natural dissolved organic carbon (DOC). Irradiation of whole water samples using simulated sunlight produced CO at rates similar to those measured previously. Production rates for DIC were more than an order of magnitude higher than those observed for CO. Based on observed DIC formation rates, photo-oxidation of DOC by sunlight should be considered a dominant removal mechanism of organic carbon from the ocean. ¿ American Geophysical Union 1995