Ozone hole hikes Antarctic ultraviolet.

Ozone hole hikes Antarctic ultraviolet

Detailed measurements reveal that increased amounts of harmful ultraviolet radiation reach Antarctica as a result of the yearly ozone hole, the National Science Foundation reported last week.

An initial biological study finds the extra radiation has not caused significant immediate harm to phytoplankton--tiny, free-floating plants that form the base of the marine food web. However, researchers caution that ultraviolet light streaming though the hole could change biological communities in the Antarctic over many years. The hole is a reduction in the ozone layer that normally shields Earth's surface from much of the sun's ultraviolet rays.

Taken last year between Sept. 19 and Dec. 21, the measurements show that biologically harmful ultraviolet light reached twice its normal strength at the surface in October -- early spring in Antarctica and the period of greatest ozone loss. At this time, levels of 300-nanometer ultraviolet light were typical of summer for that region, report Dan Lubin and John E. Frederick of the University of Chicago.

Their calculations show that even more radiation would have passed through the hole in 1987, when ozone amounts over Antarctica reached record lows. "Biologically effective radiation levels were a factor of four or five above what they would have been," says Frederick. These levels "were quite a bit bigger than anything down there had ever seen before."

Other researchers will use these ultraviolet records to examine how the ozone hole affects phytoplankton and other organisms, says Osmund Holm-Hansen, head of the polar research program at Scripps Institution of Oceanography in La Jolla, Calif. In work last year near Palmer Station, he found that total ultraviolet radiation -- both the normal amount and the extra light allowed by the ozone hole -- slowed photosynthesis by phytoplankton in the uppermost meter of water by 25 percent. However, damage drops off with depth. When averaged over 50 meters depth, which is the range for phytoplankton, the reduction in photosynthesis is no longer significant, he says.

Deneb Karentz of the University of California, San Francisco, another researcher who has worked at Palmer, says scientists worry the ozone hole will alter the ecology by promoting organisms that are better adapted to ultraviolet radiation.