The contribution of ocean‐leaving DMS to the global atmospheric burdens of DMS, MSA, SO₂, and NSS SO₄⁼

Abstract

The contribution of ocean‐derived DMS to the atmospheric burdens of a variety of sulphur compounds (DMS, MSA, SO 2 , and nss SO 4 = ) is quantified from season to season. Such quantification, especially for nss SO 4 = (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 μmol m −2 (98% of total global burden) for DMS; 0.95 μmol m −2 (94% of total global burden) for MSA; 2.8 μmol m −2 (32% of total global burden) for SO 2 and 2.5 μmol m −2 (18% of total global burden) for nss SO 4 = . The mean annual contribution of DMS to the climate‐relevant nss SO 4 = 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 SO 2 ) 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.