Martí Galí , Emmanuel Devred, Gonzalo Luis Pérez, David J. Kieber, Rafel Simó

Photochemical reactions initiated by ultraviolet (UV) radiation remove the climate-active gas dimethylsulfide (DMS) from the ocean’s surface layer. Here we quantified DMS photolysis using a satellite-based model that accounts for spectral irradiance attenuation in the water column, its absorption by chromophoric dissolved organic matter (CDOM), and the apparent quantum yields (AQYs) with which absorbed photons photodegrade DMS. Models with two alternative parameterizations for AQY estimate global DMS photolysis at between 17 and 20 Tg S/yr, equivalent to 13–15 Tg C/yr, of which ~73% occurs in the Southern hemisphere. This asymmetry results mostly from the high AQYs found south of 40°S, which more than counteract the prevailing low irradiance and deep mixing in that region. Simplified schemes currently used in biogeochemical models, whereby photolysis is proportional to visible radiation, likely overestimate DMS photolysis by around 150% globally. We propose relevant corrections and simple adjustments to those models.