The contribution of ocean-leaving DMS to the global atmospheric burdens of DMS, MSA, SO2, and NSS SO4= -: art. no. 1056

[1] The contribution of ocean-derived DMS to the atmospheric burdens of a variety of sulphur compounds (DMS, MSA, SO2, and nss SO4=) is quantified from season to season. Such quantification, especially for nss SO4= (the climate-relevant product of DMS oxidation), is essential for the quantification of the radiative forcing of climate that may be attributable to marine phytoplankton under possible future climate conditions. Three-dimensional chemical transport modeling up to the stratosphere is used as a tool in realizing this aim. Global data sets on oceanic and terrestrial sulphur sources are used as input. We find that the contribution of ocean-leaving DMS to the global annually averaged column burdens of the modeled compounds is considerable: 11.9 mumol m(-2) (98% of total global burden) for DMS; 0.95 mumol m(-2) (94% of total global burden) for MSA; 2.8 mumol m(-2) (32% of total global burden) for SO2 and 2.5 mumol m(-2) (18% of total global burden) for nss SO4=. The mean annual contribution of DMS to the climate-relevant nss SO4= column burden is greatest in the relatively pristine Southern Hemisphere, where it is estimated at 43%. This contribution is only 9% in the Northern Hemisphere, where anthropogenic sulphur sources are overwhelming. The marine algal-derived input of the other modeled sulphur compounds ( DMS, MSA, and SO2) is also greatest in the Southern Hemisphere where a lower oxidative capacity of the atmosphere, a larger sea-to-air transfer of DMS and a larger emission surface area lead to an elevation of the atmospheric DMS burden.