Dimethyl sulfide in the Southern Ocean: Seasonality and flux

The first flux estimate of dimethyl sulfide (DMS) from the Australian sector of the Southern Ocean (63°E to 162°E) has been calculated from seven voyages, which span spring and summer seasons from 1991 to 1995. Increases in seawater DMS and its precursor, dimethyl sulfoniopropionate (DMSP) generally occurred in Southern Ocean surface waters during the transition from spring to summer. DMS flux from the Subantarctic Zone (SAZ), Antarctic Zone (AZ), and Seasonal Ice Zone (SIZ) ranged from 1.7 to 49 μmol/m²/d with a mean value of 9.4 μmol/m²d. These flux calculations are believed to be underestimates, and do not include potential contributions from sea ice. Very high levels of DMSP in sea ice suggest that the SIZ may be a source of DMS to the atmosphere. The different types of vertical DMSP profiles found in sea ice possibly reflect the type of algal assemblage present and the age of the sea ice. Without considering contributions of DMS from sea ice, the overall Southern Ocean DMS emission estimate from this work was 139 Gmol S/yr. The emission estimate for the Antarctic region alone (AZ and SIZ) was 85 Gmol S/yr. This represents 17% of the global emission estimate, from 6% of the ocean surface area. This emission estimate is almost double that of an earlier estimate by Berresheim [1987] of 48 Gmol S/yr, and is likely to be higher when the amount released from the sea ice surrounding Antarctica is more accurately characterized.