Potential impact of climate change on marine dimethyl sulfide emissions

Dimethyl sulfide (DMS) is a biogenic compound produced in sea-surface water and outgased to the atmosphere. Once in the atmosphere, DMS is a significant source of cloud condensation nuclei in the unpolluted marine atmosphere. It has been postulated that climate may be partly modulated by variations in DMS production through a DMS-cloud condensation nuclei-albedo feedback. We present here a modelled estimation of the response of DMS sea-water concentrations and DMS fluxes to climate change, following previous work on marine DMS modeling (Aumont et al., 2002) and on the global warming impact on marine biology (Bopp et al., 2001). An atmosphere-ocean general circulation model (GCM) was coupled to a marine biogeochemical scheme and used without flux correction to simulate climate response to increased greenhouse gases (a 1% increase per year in atmospheric CO₂ until it has doubled). The predicted global distribution of DMS at 1 × CO₂ compares reasonably well with observations; however, in the high latitudes, very elevated concentrations of DMS due to spring and summer blooms of Phaeocystis can not be reproduced. At 2 × CO₂, the model estimates a small increase of global DMS flux to the atmosphere (+2%) but with large spatial heterogeneities (from -15% to +30% for the zonal mean). Mechanisms affecting DMS fluxes are changes in (1) marine biological productivity, (2) relative abundance of phytoplankton species and (3) wind intensity. The mean DMS flux perturbation we simulate represents a small negative feedback on global warming: however, the large regional changes may significantly impact regional temperature and precipitation patterns.