Quantum yield for the photochemical production of dissolved inorganic carbon in seawater

The direct photooxidation of coloured dissolved organic matter (CDOM) to dissolved inorganic carbon (DIC) may provide a significant sink for organic carbon in the ocean. To calculate the rate of this reaction on a global scale, it is essential to know its quantum yield, or photochemical efficiency. We have determined quantum yield spectra, OW, (moles DIC/mole photons absorbed) for 14 samples of seawater from environments ranging from a turbid, eutrophic bay to the Gulf Stream. The spectra vary among locations, but can be represented quite well by three pooled spectra for zones defined by location and salinity: inshore phi(lambda) = e(-(6.66 + 0.0285(lambda - 290))); coastal phi(lambda) = e-((6.36 + 0.0140(lambda - 290))); and ocean phi(lambda) = e(-(5.53 + 0.00914(lambda - 290))). Production efficiency increases offshore, which suggests that the most highly absorbing and quickly faded terrestrial chromophores are not those directly responsible for DIC photoproduction. (C) 2001 Elsevier Science B.V. All rights reserved.