A nearly continuous data set of solar ultraviolet spectral irradiance exists for Ushuaia, Argentina, latitude 54°59′ S, over the period from mid‐September 1990 to mid‐March 1991. This includes a season of prolonged depletion in column ozone over Antarctica, 10° or more in latitude poleward of Ushuaia. Cloudiness provides a major source of variance in the measurements. When this influence is removed, the irradiances at wavelengths between 300 and 310 nm are enhanced relative to clear sky calculations based on a 10‐year ozone climatology. During December the average noontime irradiance at 306.5 nm, which is a good proxy for erythemal irradiance, is 45% larger than the zonal mean climatological prediction. The largest noontime radiation levels observed at Ushuaia are equivalent to moving 20° in latitude closer to the equator at the summer solstice.

Measurements of biologically active UV radiation made by the National Science Foundation (NSF) scanning spectroradiometer (UV‐monitor) at Palmer Station, Antarctica, during the Austral springs of 1988, 1989, and 1990 are presented and compared. Column ozone abundance above Palmer Station is computed from these measurements using a multiple wavelength algorithm. Two contrasting action spectra (biological weighting functions) are used to estimate the biologically relevant dose from the spectral measurements: a standard weighting function for damage to DNA, and a new action spectrum representing the potential for photosynthesis inhibition in Antarctic phytoplankton. The former weights only UV‐B wavelengths (280–320 nm) and gives the most weight to wavelengths shorter than 300 nm, while the latter includes large contributions out to 355 nm. The latter is the result of recent Antarctic field work and is relevant in that phytoplankton constitute the base of the Antarctic food web. The modest ozone hole of 1988, in which the ozone abundance above Palmer Station never fell below 200 Dobson units (DU), brought about summerlike doses of DNA‐effective UV radiation 2 months early, but UV doses which could inhibit photosynthesis in phytoplankton did not exceed a clear‐sky “maximum normal” dose for that time of year. The severe ozone holes of 1989 and 1990, in which the ozone abundance regularly fell below 200 DU, brought about increases in UV surface irradiance weighted by either action spectrum. Ozone abundances and dose‐weighted irradiances provided by the NSF UV‐monitor are used to derive the radiation amplification factors (RAFs) for both DNA‐effective irradiance and phytoplankton‐effective irradiance. The RAF for DNA‐effective irradiance is nonlinear in ozone abundance and is in excess of the popular “two for one” rule, while the RAF for phytoplankton‐effective irradiance approximately follows a “one for one” rule.

Measurements of ultraviolet solar spectra from Palmer Station, Antarctica have defined the surface radiation environment of the region during the Austral spring of 1988. At wavelengths where absorption by ozone is negligible, 335–345 nm, the noontime irradiances show the expected gradual increase from the first day of measurements, 19 September, through 21 December. Large variations related to cloudiness are imposed on this background. At wavelengths less than 310 nm the influence of the 1988 ozone “hole” is apparent. The noontime irradiance observed in the wavelength band 295–305 nm on 19 October, two months prior to summer solstice, exceeded any value measured through 21 December.