MARINE SULFUR EMISSIONS

The principal Volatile sulphur species found in seawater are dimethyl sulphide (DMS), carbonyl sulphide (COS) and carbon disulphide (CS2). O f these, DMS is the most abundant and widespread in its distribution. The predominant oceanic source of DMS is dimethylsulphoniopropionate ( DMSP), a compatible solute synthesized by phytoplankton for osmoregula tion and/or cryoprotection. Not all species have the same ability to f orm DMSP; for example, diatoms generally produce little, whereas prymn esiophytes and some dinoflagellates make significantly larger amounts. Much of the release of DMSP and DMS to the water occurs on death or t hrough predation of the plankton. Our recent held data strongly sugges t that oxidation of DMS to dimethyl sulphoxide (DMSO) is an important process in the water column, and it is clear that considerable interna l cycling in the DMSP/DMS/DMSO system occurs in the euphotic zone. A f raction of the DMS crosses the sea surface and enters the atmosphere w here it is oxidized by radicals such as OH and NO3 to form products su ch as methanesulphonate (MSA), DMSO and non-sea salt sulphate (NSSS) p articles. These particles are the main source of cloud condensation nu clei (CCN) over oceanic areas remote from land.