| The photochemical oxidation of coloured or chromophoric dissolved organic matter in the ocean plays an important role in the carbon cycle. The production of dissolved inorganic carbon, DIC, represents the most rapid direct photochemical loss of dissolved organic carbon, DOC. The goal of this thesis is to make a quantitative estimate of the photochemical source of DIC in the ocean.; To calculate the rate of DIC photoproduction, efficiency (quantum yield) spectra, relationships between in situ and remotely-sensed optical properties and a model of solar spectral irradiance were required. This thesis presents the first quantum yield spectra for DIC in sea water. The magnitude of quantum yield increases with distance from shore.; Relationships between remotely-sensed reflectance and in situ attenuation of ultraviolet radiation were determined. They apply over a wide range of water types in the Bering Sea, the Mid-Atlantic Bight, and Bedford Basin, Nova Scotia from May to August. Absorption by coloured dissolved organic matter is responsible for almost all the attenuation of ultraviolet radiation in the study areas.; The monthly rate of DIC photoproduction was estimated pixel by pixel for January, April, July and October, 1998 in the Mid-Atlantic Bight from SeaWiFS ocean colour images. It increases with distance from shore. The same approach can be applied to any photoproduct with a known quantum yield. Photoproduction rates of CO, H2O2 and CS2 were estimated from SeaWiFS images and published quantum yield spectra. The ratio of DIC photoproduction to the production of CO, H2O2 and CS 2 increases from the inshore to the open ocean zone.; Global photochemical production rates of DIC, CO, H2O 2 and CS2 were also calculated. The global production rates of CO and CS2 compare well with published values. The global annual DIC photoproduction rate is approximately 1015 moles DIC year -1. This rate is higher than the annual input of terrestrial DOC to the ocean, which probably reflects the importance of the photochemical transformation of DOC formed in situ from the degradation of phytoplankton. The rate of DIC photoproduction is also comparable to the annual rate of DIC use in new production. |
