Oceanic emission of the trace gas dimethyl sulfide (DMS) is the major source of reduced sulfur into the marine boundary layer, influencing atmospheric chemistry (von Glasow et al. 2004) and contributing to the radiative properties of oceanic clouds (Ayers et al 1991, Charlson et al. 1987, Korhonen et al 2008). DMS is an enzymatic breakdown product of dimethylsulfoniopropionate (DMSP) synthesised by phytoplankton. Both DMS and DMSP also contribute significant proportions of the carbon and sulphur flux through microbial foodwebs (Simo et al. 2004) and may play important roles as infochemicals, influencing predator prey interactions (Wolfe et al. 1997). We observed the horizonal and vertical (upper 100 m) distributions of DMS in the Amundsen Sea using a membrane inlet mass spectometer (MIMS).