RESPONSE OF A NATURAL PHAEOCYSTIS POPULATION TO AMBIENT FLUCTUATIONS OF UVB RADIATION CAUSED BY ANTARCTIC OZONE DEPLETION

During the austral spring of 1990, rotation of the Antarctic polar vortex resulted in a 2-fold change in ozone concentrations (170-380 Dobson units) over regions of the marginal ice zone of the Bellingshausen Sea. The changes in ozone caused significant variations in incident and in-water UVB fluences. Phytoplankton cell densities, nutrient concentrations, DNA concentrations and stable carbon isotope ratios (delta(13)C) of particulate organic and dissolved inorganic carbon were monitored for a 5-week period during the ozone fluctuations. Phaeocystis was the dominant phytoplankton taxon and cell numbers were positively correlated to ozone and the delta(13)C of seawater Sigma CO2, and negatively correlated to nutrient concentrations. The densities of co-occurring diatoms were not related to changes in ozone, delta(13)C or nutrients. These observations suggest that Phaeocystis sp. responds very rapidly and adversely to increased UVB exposure, and that seawater delta(13)C data may be a useful tool for assessing the physiological state of high-latitude marine communities relative to increased UVB levels.