Effect of column ozone on the variability of biologically effective UV radiation at high southern latitudes

Solar irradiance measurements from Ushuaia (Argentina) and Palmer and McMur do Stations in Antarctica covering four seasons from mid-1993 through early 1997 have been analyzed and their variations compared with column ozone ch anges, UV irradiances were weighted for biological effectiveness using a pu blished biological weighting function for dose-dependent inhibition of phot osynthesis by phytoplankton from the Weddell Sea. All calculations involved integrated daily UV doses and visible exposures (weighted UV and unweighte d visible irradiances, respectively). The results show that daily biologica lly effective total UV doses underwent large shortterm variations at all th ree sites, with day-to-day increases up to 236% at Ushuaia, 285% at Palmer and 99% at McMurdo. Parallel changes in visible exposure indicated that the total UV changes were preponderantly due to variations in cloudiness. On a 12-month basis, daily biologically effective UV doses correlated strongly with visible exposures (R greater than or equal to 0.99), Anticorrelations of total UV with ozone, on the other hand, were poor (R > -0.11), The large st daily biologically effective UV doses, and their day-to-day increases, o ccurred as part of the normal variability related to cloud cover and were s eldom associated with significant ozone depletion. UV dose/visible exposure ratios tended to reflect ozone depletion events somewhat more consistently than UV doses alone. With the Weddell Sea phytoplankton weighting function used in this study, antarctic ozone hole events were seldom readily discer nible in the biologically effective UV record. The results suggest that, wh ere the UV sensitivity of organisms was similar to that of the Weddell Sea phytoplankton, seasonal ozone depletion had no appreciable effect on annual primary productivity during the 1993-1997 period. Additional data on the g eographical and seasonal variation of biological weighting functions are de sirable for more comprehensive assessments of ozone depletion effects at hi gh southern latitudes.