Variation of dimethylsulfide mixing ratio over the Southern Ocean from 36°S to 70°S

Atmospheric dimethylsulfide (DMS) was measured to investigate the variation in its concentration over sea ice free oceans and sea ice regions of the Southern Ocean, using a proton transfer reaction-mass spectrometer (PTR-MS) on board the icebreaker Shirase from 1 December 2009 to 16 March 2010. In general, DMS concentrations over sea ice regions were very low compared with those over the sea ice free ocean. However, abrupt increases in DMS concentrations occurred over sea ice regions while the ship was moving and crushing the sea ice. Undoubtedly, the elevated DMS concentrations were caused by large DMS emissions from gaps in the ice made by the ship. During the period when Shirase had anchored off Syowa Station (69°00.4′S, 39°35.3′E), Antarctica, DMS concentrations were not detected. At this time, the surrounding sea of East Ongul island, on which Syowa Station is located, was completely covered with multi-year fast ice. Sea ice probably inhibits DMS emission from the ocean to the atmosphere. In addition, there was no evidence that chlorophyll a concentration in the sea water or wind speed above the sea surface affect atmospheric DMS concentrations over the sea ice free ocean regions.