Field studies show that photosynthesis by Antarctic phytoplankton is inhibited by the increased ultraviolet radiation (UVR) resulting from springtime stratospheric ozone (O3) depletion. To extend previous observations, a numerical model utilizing satellite-derived distributions of O3, clouds, sea ice, surface temperature, and phytoplankton biomass was developed to study the hemispheric-scale seasonal effects of a deep Antarctic O3 hole on primary production in the Southern Ocean. UVR-induced losses of surface phytoplankton production were substantial under all O3 conditions, mostly due to UVA. However, when integrated to the 0.1% light depth, the loss of primary production resulting from enhanced fluxes of UVB due to O3 depletion was <0.25%. The loss of primary production is minimized by the strong attenuation of UVR within the water column and by sea ice which is at its peak extent at the time of the most severe O3 depletion.