INFLUENCE OF DIFFERENT WATER MASSES AND BIOLOGICAL-ACTIVITY ON DIMETHYLSULFIDE AND DIMETHYLSULPHONIOPROPIONATE IN THE SUB-ANTARCTIC ZONE OFTHE SOUTHERN-OCEAN DURING ACE-1

Measurements of salinity, temperature, phytoplankton biomass and speci ation, dissolved nitrate, dimethylsulfide (DMS) in seawater and air, a nd dimethylsulfoniopropionate (DMSP), were made in the subantarctic zo ne of the Southern Ocean from 40 degrees-54 degrees S, and 140 degrees -153 degrees E during the southern hemisphere marine First Aerosol Cha racterization Experiment (ACE 1) DMSP concentrations were highest in s ubtropical convergence zone (STCZ) waters, intermediate in subantarcti c waters, and lowest in polar waters. DMSP appeared to decrease at fro ntal regions between these major water masses. In subantarctic waters, high levels of DMSP were generally associated with an increase in din oflagellate biomass and low microzooplankton grazing rates. Lower DMSP concentrations occurred in polar waters when the diatom biomass and g razing rates were high. DMS levels measured on Southern Surveyor range d from not detectable (nd) to 5.6 nM (mean 1.7 nM), with below average levels in subantarctic waters (mean 1.25 nM), and above average level s (mean = 1.93 nM) in polar waters. Pulses of DMS occurred as Southern Surveyor traveled south into polar waters, with a large pulse (mean = 2.3 nM) highlighted as the vessel traveled back into subantarctic waf ers (46 degrees-47 degrees S, 148 degrees-151 degrees E) in early Dece mber. By using the dissolved DMSP (DMSPd) to DMS ratio as an index of the bacterial conversion of DMSPd to DMS some evidence was found that, in polar waters, increased microzooplankton (MZP) grazing in diatom d ominated waters, may lead to above average concentrations of DMS. This does not appear to be the case when the biomass was dominated by dino flagellates in subantarctic waters.