AS the spring ozone hole over Antarctica increased in size this year, setting a new record, scientists fiercely debated whether the problem is as serious as it sounds.
``People seem to have the impression that the ozone hole represents an opening in the sky through which a laser beam of radiation is flowing ... that's just not accurate,'' says Osmund Holm-Hansen of Scripps Institution of Oceanography at the University of California-San Diego.
Dr. Holm-Hansen works at Palmer Station, Antarctica, a United States research facility that a Monitor reporting team recently visited as guests of the US National Science Foundation (NSF).
``Mankind is going to survive the ozone hole,'' says C. R. Booth, president of Biospherical Instruments Inc., a San Diego-based company that operates a network of instruments measuring solar radiation in both polar regions. This year, Mr. Booth says, ozone levels fell earlier in the season than they have in previous years.
The ozone hole's depth and size has increased since researchers at the British Halley Bay base first discovered it in the mid-1980s. In recent years, between 30 and 50 percent of springtime ozone over Antarctica has disappeared, scientists say. But this year, more than 60 percent of the ozone was destroyed over an area larger than Europe.
The World Meteorological Organization in Geneva reported earlier this month that it ``registered the lowest-ever daily total ozone values for the months of September and October [Antarctic spring].''
It also said that the ozone hole's ``enormous surface coverage of greater than 23 million square kilometers classifies this austral spring season as the greatest ozone hole ever detected.''
Vice President Al Gore Jr. describes the ozone problem in his 1992 book, ``Earth in the Balance.'' During Antarctica's brutally cold winter months, the polar vortex over the continent holds a ``frigid chemical brew - chlorine, bromine, ozone, and ice crystals - tightly in place, as if in a bowl, until the sun comes up,'' he writes. When the first springtime sun hits this combination, a frenzy of ozone destruction is touched off.
Back in 1974, F. Sherwood Rowland and Mario Molina of the University of California-Irvine postulated that the release of chlorofluorocarbons (CFCs) into the atmosphere would result in the depletion of Earth's protective ozone layer.
Ozone shields the planet from some of the more destructive wavelengths of solar radiation. In the atmosphere, CFCs break up into the powerful chlorine atoms that Mr. Gore lists in his ``frigid chemical brew.'' A single chlorine atom can tear apart as many as 100,000 molecules of ozone.
Stopping CFC output into the atmosphere became a worldwide environmental campaign that resulted in the signing of the Montreal Protocol in 1987. Industrialized nations agreed to find refrigeration and propellant substitutes to slash CFC output in half by 1999. Because of increased concern, the protocol was amended to eliminate CFC use by the year 2000. ``It is an extremely optimistic note that many nations and conflicting groups could get together, decide that a technology is harmful, and decide to modify it,'' Booth says.
Scientists reported earlier this year that the rate of increase of CFCs has slowed, though the total amount in the atmosphere is rising. The effects of excess ultraviolet light (UV) on plants, animals, and humans is only beginning to be understood.
``At our lab at the South Pole, we measure the total ozone between our station and the sun,'' says Kate McNitt of the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo. She wintered at the Amundsen-Scott South Pole Station. ``This year we measured a record low,'' she says. ``But we don't want to scare anybody.... The fact of the matter is that unless you were exposed to long hours of sunlight, it's just like being at a high altitude here in Colorado.''
Since humans are generally bundled in clothing from nose to toe while working outdoors here, researchers are not concerned. But the effect of excess UV on plants and animals living in the rich oceans around Antarctica is a hotly debated topic. UV findings of different scientists are not too far apart, Booth says. ``They diverge in their subjective evaluation of the numbers.''
``The whole definition of what is high and low ozone in the Antarctic keeps getting redefined'' as lower measurements become the norm, says Barbara Prezelin, who with Raymond Smith is studying UV effects. They are looking at phytoplankton, the tiny plants that form the base of the food chain. Shrimp-like creatures called krill graze on phytoplankton. Then seals, penguins, and whales dine on the vast shoals of krill floating near the surface; groups of up to 1 billion krill have been documented.
Researcher Langdon Quetin studies the krill population near Palmer Station. He heads a group of projects here that are part of the Long-Term Ecological Research network. It was established to assess environments such as Antarctica's, so that scientists can see how changes in populations, pollution, and climate fit into an extended time frame.
Dr. Prezelin and others are finding that phytoplankton can take various measures to protect themselves from UV. One strategy discovered recently is ``downregulation.'' ``It is a protective mechanism,'' Prezelin says. But the result is a reduction in photosynthesis. Though the plant might keep itself from being hurt by the excess UV, it is not growing at the normal rate.
In a 1990 study, Prezelin and Dr. Smith found that excess UV from the ozone hole brought a minimum 6-to-12-percent reduction in primary productivity for phytoplankton in Antarctic waters, a ``significant effect on an ecosystem no matter what theoretical model you use,'' Prezelin says.
That is, unless you use the theoretical model put together by Holm-Hansen. He runs another project assessing UV effects on phytoplankton. His model shows that while UV-induced losses are 2.8 percent, total productivity of the ecosystem is reduced by only 0.2 percent. ``That may not sell many newspapers, but it is true,'' he says.
Holm-Hansen's model is illustrated in the graphic at the left. Because the ozone hole occurs each year at a time of almost maximum ice cover for the Antarctic oceans, the net amount of damage during the summer growing season (November through March) is limited.
``This past October we had the worst UV conditions ever at Palmer Station,'' he says. ``But water is a very good UV absorber, particularly for the shortest [most damaging] wavelengths, which are absorbed very quickly.''
Excess UV for plants and animals on land poses a much more severe hazard ``than for anything living in the aquatic environment,'' Holm-Hansen says. ``Crops like corn can suffer losses in yields, growth, and dry weight.''
Given the lively debate, only one thing is certain about research in Antarctica, says Erick Chiang, manager of the polar-operations section for the National Science Foundation: ``When you go there, you always come out with more questions than when you went in.''