Remote sensing data from a combination of NASA sensors, that enable large-scale mapping of both surface solar ultraviolet radiation (UVR) and chlorophyll, show that biologically significant UVR increases began to occur over the Southern Ocean three years before the ozone "hole" was discovered. During October, the fraction of Southern Ocean phytoplankton biomass under ozone-depletion-enhanced UVR exceeded 10% in all years between 1982 and 1994 (except for 1988), and this fraction rose to above 30% in 1997-99. Beginning in October 1983, the most frequent occurrences of enhanced UVR over phytoplankton-rich waters occurred in the Weddell Sea and Indian Ocean sectors of the Southern Ocean. By the late 1990s the surface biomass fraction under enhanced UVR in these sectors regularly exceeded 60%. This time series of satellite retrievals suggests two reasons why more serious impacts to the base of the marine food web may not have been detected by field experiments: (1) the onset of UVR increases several years before dedicated field work began may have impacted the most sensitive organisms long before such damage could be detected, and (2) most biological field work has so far not taken place in Antarctic waters most extensively subjected to enhanced UVR.