The Antarctic is currently experiencing a thirty to fifty percent springtime loss of its stratospheric ozone layer, resulting in a least a several-fold increase in UVB (280-320nm) radiation reaching the surface of the Southern Ocean. In spite of low solar elevation and persistent cloud cover, the magnitude of ultraviolet radiation fluence rates now experienced in polar regions roughly approaches that routinely measured in tropical latitudes. Perhaps more importantly, biologically damaging UVB radiation has increased in the Antarctic while both UVA (320- 400nm) and photosynthetically available radiation (PAR, 400- 700nm) have remained unchanged. This collaborative project will use recently developed improvements in atmospheric modeling and in-water UV and visible spectroradiometers to conduct a field study during austral spring 1990. The day-to-day variations in the magnitude and ratio of UVB:UVA:PAR irradiance incident on and penetrating the euphotic zone of marginal ice edge Antarctic waters will be qualified. The impact of this increase of UV radiation on abundance, composition and vitality of the phytoplankton community during the ice-edge spring bloom will be documented. During this time, strong vertical stratification restricts the phytoplankton to the upper water column, thus creating favorable conditions for increased UVB susceptibility. Special emphasis will be placed on defining biological restraints imposed by enhanced UVB radiation and altered UVB:UVA:PAR ratios on the balance of UVB photodamage to photorepair, photoprotective and photosynthetic mechanisms operating in the water column. The overall aim is an objective test of the hypothesis that phytoplankton in Antarctic waters are adversely unfluenced by ozone depletion.
