Photochemical production of carbon disulphide in seawater

It is generally accepted that the ocean is an important source for atmospheric CS 2 , which makes a major contribution to the formation of COS in the atmosphere. The processes producing CS 2 in seawater, however, are essentially unknown. We report for the first time to our knowledge that marine photochemical reactions are identified as a significant source for oceanic CS 2 . Apparent quantum yield spectra of CS 2 production were obtained using water samples collected in the northeast Atlantic. Results indicate that it is mainly UV solar radiation (290–340 nm) which is responsible for CS 2 photoproduction. The photoproduction rate of CS 2 is positively correlated with absorbance at 350 nm, suggesting that the reactions are mediated by chromophoric dissolved organic matter (CDOM). Laboratory irradiations have confirmed that cysteine and cystine are efficient precursors of CS 2 and that OH radicals are likely to be important intermediates. Both the field survey and laboratory work point to similar mechanisms for photochemical production of CS 2 and COS in marine waters. A CS 2 production rate of 0.49 Tg yr −1 for the world oceans has been estimated using the quantum yield spectra from this work and the sea surface light field provided by Leifer [1988]. This estimate is of the same order of magnitude as the present estimate of the CS 2 flux from the ocean to the atmosphere based on surface saturation and wind speed.