Abstract
Abstract. The atmospheric oxidation of dimethyl-sulphide (DMS) derived from marine phytoplankton is a significant source of marine sulphate aerosol. DMS has been proposed to regulate climate via changes in cloud properties, though recent studies have shown that present-day global cloud condensation nuclei (CCN) concentrations have only a weak dependence on the total emission flux of DMS. Here, we use a global aerosol microphysics model to examine how efficiently CCN are produced when DMS emissions are changed in different marine regions. We find that global CCN production per unit mass of sulphur emitted varies by more than a factor of 20 depending on where the change in oceanic DMS emission flux is applied. The variation in CCN production efficiency depends upon where CCN production processes (DMS oxidation, SO2 oxidation, nucleation and growth) are most efficient and removal processes (deposition) least efficient. The analysis shows that the production of aerosol sulphate through aqueous-phase oxidation of SO2 limits the amount of H2SO4 available for nucleation and condensational growth and therefore suppresses CCN formation, leading to the weak response of CCN to changes in DMS emission. Our results show that past and future changes in the spatial distribution of DMS emissions (through changes in the phytoplankton population or wind speed patterns) could exert a stronger control on climate than net increases in biological productivity.
Highlights
IntroductionProcesses (DMS oxidation, SO2 oxidation, nucleation and Surface ocean DMSHcoyndcernotrlaotigonys aarne dhighly variable growth) are most efficient and removal processes (deposition) least efficient
The peak cloud condensation nuclei (CCN) response from the patch is ∼ 2 cm−3, and occurs some distance from the patch as nucleated particles are transported while growing to CCN sizes
Another peak in CCN occurs over the patch and is caused by growth of Aitken mode particles to CCN size
Summary
Processes (DMS oxidation, SO2 oxidation, nucleation and Surface ocean DMSHcoyndcernotrlaotigonys aarne dhighly variable growth) are most efficient and removal processes (deposition) least efficient. Vallina et al (2007) found exert a stronger control on climate than net increases in bio- that sea-surface DMS concentrations increased locally by up logical productivity. 20–80 % of non sea-salt sulphate near the surface over the Northern Hemisphere oceans and more than 80 % in most of the Southern Hemisphere
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