The Antarctic is now experiencing large springtime losses of stratospheric ozone, resulting in an increase in ultraviolet B (UVB, 280-320nm) radiation. The magnitude of ultraviolet radiation reaching the surface now approaches that measured in tropical latitudes. Perhaps more importantly, UVB radiation has increased in the Antarctic while both UVA (320-400nm) and photosynthetically available radiation (PAR, 400-700nm) have remained unchanged. Recent improvements in atmospheric modeling and technology in oceanographic instrumentation will be used in a six week field study during the austral spring 1990. The prime objective will be to document the impact of UV radiation on the phytoplankton community during the ice-edge spring bloom. During this time, oceanographic processes create favorable conditions for increased UVB susceptibility. Biological and bio-optical information will be used to define and quantify linkages between ozone-dependent oscillations in UV to PAR ratios and phytoplankton productivity. Special emphasis will be place on defining biological restraints imposed by enhanced UVB and altered UVB:UVA:PAR ratios on the balance of UVB photodamage to photorepair, photoprotective and photosynthetic mechanisms operating in the Southern Ocean. The overall aim is to test the hypothesis that phytoplankton in Antarctic waters are adversely influenced by ozone depletion.