Photochemical production of carbonyl sulfide in North Sea water: A process study

Abstract

Carbonyl sulfide (COS) photoproduction rates in North Sea water were determined on samples collected inshore and offshore the island of Helgoland during April 1993. A simple kinetic model including a zeroth-order photoproduction constant, surface UV light intensity, and hydrolysis removal satisfactorily describes our results. The mean COS production constants were 2.8±0.5 fmol liter−1 s−1 W−1 m2 at the inshore station and 1.2±0.3 fmol liter−1 s−1 W−1 m2 at the offshore station, corresponding to sea surface COS production rates of 0.84 nmol liter−1 d−1 and 0.38 nmol liter−1 d−1 for the inshore and offshore stations, respectively. The photoproduction constants normalized to UV absorbance at 350 nm and fluorescence intensity of humic substances were similar for the two sampling stations, indicating that the COS formation is closely related to the concentration of chromophoric dissolved organic matter (CDOM) in seawater. The COS photoproduction rates from this work and a compilation of presently available data show a remarkably high degree of correlation with CDOM absorbance. We propose that the geographical distribution of COS productivity may be extrapolated from remotely sensed CDOM optical properties.