EFFECT OF UV-RADIATION ON DMSP CONTENT AND DMS FORMATION OF PHAEOCYSTIS-ANTARCTICA

DMSP (dimethyl sulphonium propionate) contents produced by an Antarcti c marine phytoplankton species, Phaeocystis antarctica (Prymnesiophyta ), which were incubated under light conditions with radiations of diff erent UV wavebands, were measured by gas chromatography after various exposure times. Full light (UV-B + UV-A + PAR) caused the strongest de crease in the production of DMSP in the alga. A marked depression of D MSP content was also observed with short UV-B and UV-A wavebands after 3 h. It was therefore hypothesised that DMSP production in Phaeocysti s antarctica was inhibited by UV radiation. There was a negative corre lation on change of DMSP contents under UV radiation. There was a nega tive correlation on change of DMSP contents under UV radiation with ex posure times. The conversion rate of DMSP dissolved to DMS (dimethyl s ulphide) was significantly increased with UV radiation. The possibilit y could not be excluded that a high concentration of free chemical rad icals in seawater due to UV radiation resulted in an increase of DMSP cleavage in seawater. The oxidation of DMS in seawater due to UV-B rad iation could result in a decrease of its flux to the atmosphere. The e ffect of UV radiation on DMSP production and oxidation of DMS may be a n important factor in the variability of DMSP and the global flux of D MS from ocean to atmosphere.