ANTARCTIC researchers are bracing themselves for a record ozone hole over
the continent within the next fortnight. 鈥淭he hole has formed early and spread
over a wide area this year,鈥� says Neil Harris of the European Ozone Research
Coordinating Group, based in Cambridge. 鈥淭he latest ozone readings are very low
颈苍诲别别诲.鈥�
New records have already been set. The former British Faraday base, now run
by Ukraine, recorded by far its lowest ever August ozone level this year. And
earlier this month, the World Meteorological Organization reported a 35 per cent
loss of ozone above Tierra del Fuego in southern Argentina, a loss previously
recorded only in early October, when the hole is usually at its deepest.
Over Britain鈥檚 Halley base, the amount of ozone in the atmosphere had sunk
early this week to 130 Dobson units. Without the ozone hole it would typically
be between 350 and 400 units.
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So far, the results are following the predictions of David Hoffmann of the US
government鈥檚 National Oceanic and Atmospheric Administration (NOAA), who earlier
this month forecast a record hole. In a letter to Nature, he pointed
out that the deepest ozone holes appeared every two years.
The cycle, he said, was caused by a natural oscillation in air movements in
the southern hemisphere that brings heavy doses of ozone-destroying chemicals
south towards Antarctica every second year. Combined with the continued rise in
general levels of the destructive chemicals in the upper atmosphere, this
鈥渟hould result in a deeper ozone hole in 1996 by late September to early
October鈥�, he warned.
Some researchers are not so sure that this year will prove exceptional. 鈥淚 am
sceptical,鈥� says Jonathan Shanklin of the British Antarctic Survey. He believes
the early record lows may be associated with unusual meteorology in the region,
which has moved the vortex of very cold air in which ozone destruction takes
place.
鈥淭he vortex is offset this year towards South America,鈥� he says. This means
ozone destruction began earlier further north, over Tierra del Fuego. It doesn鈥檛
necessarily mean we will have a record hole.鈥� In any case, says Harris, 鈥渟o much
ozone is destroyed now over Antarctica each year that frankly there isn鈥檛 much
scope to lose any more.鈥�