UV pours through ozone hole.

Even as this year's ozone hole opens over Antarctica, scientists report that the region received a dramatically high dose of ultraviolet radiation in late 1990 as a result of last year's ozone hole.

During December, the beginning of the austral summer, levels of damaging ultraviolet light last year registered twice their normal value, according to John E. Frederick and Amy D. Alberts of the University of Chicago, who made their measurements at Palmer Station, a U.S. base on the Antarctic Peninsula. The radiation reaching Antarctica last summer may have been the strongest the region has experienced since the ozone layer formed about a billion years ago, the researchers assert in the October GEOPHYSICAL RESEARCH LETTERS.

Ultraviolet light from the sun can harm humans, plants and animals. In Antarctica, biologists have found such radiation damages the DNA of certain species of phytoplankton, tiny floating plants that are a critical component of the polar food web. The seasonal hole began forming in the late 1970s because of increasing concentrations of ozone-destroying chlorine pollutants in the stratosphere.

Ultraviolet radiation reached such strong levels in 1990 because the springtime ozone depletion persisted longer than it had in past years, the researchers say. Winds from the north normally invade the Antarctic stratosphere in October and November, replenishing lost ozone before the most intense sunlight reaches the southern hemisphere. Because this process was delayed, ozone remained diminished even into summer. While polar regions normally receive far less intense light than the midlatitudes, the amount of ultraviolet light reaching Palmer Station last year surpassed the peak summer levels typically seen in a city like Chicago.