Summary
ABSTRACT The first estimate of the flux of dimethylsulphide (DMS) from the Australian sector of the Southern Ocean from 63oE-162oE has been calculated from seven voyages, which span spring and summer seasons from 1991-1995. DMS flux from the Sub Antarctic Zone (SAZ), Antarctic Zone (AZ), and Seasonal Ice Zone (SIZ) ranged from 1.7- 49 mmol/m2/d with a mean value of 9.4 mmol/m2/d. The flux of DMS from the AZ and SIZ in summer of 20 and 49 mmol/m2/d was extremely high. It would appear from the flux estimates presented here that the Southern Ocean, particularly the AZ and the SIZ, are greater sources of DMS than previously thought. In spring DMS concentrations under the SIZ were generally < 1nM. However, occasionally DMS reached levels between 1 nM and 4.4 nM amongst the sea ice. These high levels in early spring may reflect DMS released from the sea ice. The highest level (338 nM) of dimethylsulphoniopropionate (DMSP), the precursor compound of DMS, occurred in ice collected from the Davis region at 64.34oS, 74.59oE, about three times the mean levels found in other cores from the same region. Using an average ratio of DMSP: DMS (7.3:1; n=70), in seawater from the Southern Ocean, the approximate concentration of DMS in melted sea ice was estimated to average 20 nM in the Davis region, and 5.5 nM in the Dumont d’Urville region. If we assume that all this DMS is released into seawater from melting sea ice, a DMS flux of 15-57 mmol/m2/d is available for air-sea transfer. Levels of DMS in air above the sea ice, in the spring of 1994 were elevated at 63oS (0.2-0.8 nmoles/m3) compared to DMS levels either side of this location. These elevated DMS levels were also close to the area where the highest concentrations of DMSP were found in the pack ice. High levels of DMS in air occurred at the AZ at 55-57oS, suggesting a source of DMS at this location, with concentrations comparable to levels of DMS detected over the sea ice.