A global, open-ocean, climatological model of marine carbonyl sulfide (OCS) with diurnal, seasonal, vertical and latitudinal resolution is presented and analyzed. The model includes the processes of photchemical production, air-sea gas exchange, vertical turbulent mixing, and hydrolysis. In accordance with observations, the model predicts the highest surface OCS concentrations during the summer in high latitudes. The model with the best guess set of parameters predicts the open ocean to be a sink of OCS (2.3 Gmol yr-1) but severely underpredicts surface OCS concentrations in most locations. When a simple temperature-dependent dark production parameterization is included, the ocean becomes a source of OCS (2.1 Gmol yr-1). In addition to dark production, the model is most sensitive to the surface concentration of colored dissolved organic matter (CDOM) and the spectral slope of CDOM absorption. ¿ 2000 American Geophysical Union