The ozone hole above Antarctica may not be damaging life in the ocean below after all. If Californian researchers are right, then increased ultraviolet radiation is having scarcely any effect on the growth of marine plankton, the base of the ocean's food chain.
The team, led by Kevin Arrigo of Stanford University in Palo Alto, has created computer models of phytoplankton growth over a year in the southern hemisphere before and after the ozone hole appeared in the 1980s. They included such factors as the position of the ozone hole, cloud cover, and UV-B strength, the type of ultraviolet radiation that increases as atmospheric ozone declines.
To find out what increased UV-B did to phytoplankton, the researchers compared two models: one based on data from 1992, a year with a yawning ozone hole and the other with the same parameters except for the ozone levels, which were taken from 1978, a year of "normal" conditions before the hole appeared.
Over the southern hemisphere ecosystem as a whole, they found that primary phytoplankton production decreased by only about 1 per cent in 1992, which is significantly lower than other estimates.
Arrigo's work does not discount the results of a number of studies showing that increased UV-B can stunt phytoplankton growth by 10 per cent or more in localised areas or in the laboratory (New Scientist, 8 August 1998, p 24). The difference is that his study looked at the big picture of UV-B for the whole ocean.
In previous studies, researchers scaled up measurements of plankton growth beneath the hole and elsewhere to calculate an overall effect for the whole Southern Ocean. But although they knew that factors such as cloud cover were important, they are difficult to include in such calculations.
"On a cloudy day under a deep hole, there's still not nearly as much UV flux as on a clear day with no hole," says Arrigo. Another important factor is that, at any given time, around 80 per cent of the southern hemis
Contact: Claire Bowles