Will marine dimethylsulfide emissions amplify or alleviate global warming? A model study

Dimethylsulfide (DMS) is the most abundant volatile sulfur compound at the sea surface and has a strong marine phytoplanktonic origin. Once outgased into the atmosphere, it contributes to the formation of sulfate aerosol particles that affect the radiative budget as precursors of cloud condensation nuclei (CCN). It has been postulated that climate may be partly modulated by variations in DMS production. We test this hypothesis in the context of anthro pogenic climate change and present here, modelled for the first time, an estimate of the radiative impact resulting from changes in DMS air-sea fluxes caused by global warming. At 2 x CO2, our model estimates a small increase (3%) in the global DMS flux to the atmosphere but with large spatial heterogeneities (from -15% to 30%). The radiative perturbation resulting from the DMS-induced change in cloud albedo is estimated to be -0.05 W.m(-2), which represents only a small negative climate feedback on global warming. However, there are large regional changes, such as a perturbation of up to -1.5 W.m(-2) in summer between 40degreesS and 50degreesS, that can impact the regional climate. In the Southern Ocean, the radiative impact resulting from changes in the DMS cycle may partly alleviate the radiative forcing resulting from anthropogenic CO2.