Surprising ozone loss
Every winter, almost 10 miles above Earth, manmade compounds are destroying ozone
at a rapid rate, according to new findings released at the spring meeting of the
American Geophysical Union in May. Atmospheric scientist Darin Toohey of the University
of Colorado at Boulder and colleagues have observed the breakdown of CFCs at latitudes
higher than 50 degrees in the lowermost part of the stratosphere (upper atmosphere).
People, with a few exceptions, thought that nothing was happening at these
latitudes and these altitudes. We thought this was a region of the atmosphere
where in fact these kinds of chemical reactions would not be occurring,
Toohey says. Scientists historically have looked at higher altitudes, because
water particles, necessary ingredients for the ozone-destroying reactions, were
thought to be hard to come by at these lower altitudes.
Using an instrument he designed that collects data aboard an aircraft flying at
about 40,000 feet and aboard balloons, Toohey measured chlorine monoxide, a compound
that destroys ozone. Its one of the breakdown products of CFCs, the
one that people often call the smoking gun. If you see it, it means ozone destruction
is occurring, Toohey explains. Seeing the chlorine monoxide at these relatively
low altitudes was surprising because the region is 20 degrees warmer than the
well-known Antarctic ozone hole, located about 13 miles up. Cold temperatures
make it easier for the chemicals that are the precursors to the reactive forms
of chlorine to stick to the particles, thus initiating ozone destruction.
The connection between temperature and ozone depletion relates the research to
global climate change. When carbon dioxide increases in the atmosphere, it actually
cools the upper atmosphere. Therefore, as the atmosphere continues to change,
so too will ozone depletion, Toohey says.
Also significant is that the ozone loss is occurring in atmospheric regions that
are in greater communication with middle latitudes. The chemical
reactions that are occurring here are occurring in a leaky part of the atmosphere,
Toohey says. That means the air can readily leak to lower latitudes, having a
greater influence on the air over our heads.
The high latitude measurements Toohey and his team took cover a region from central
Canada to western Russia. Although the coverage was not global, Toohey says, we
have no reason to believe that the situation would be any different at different
longitudes, same latitudes, he explains. The stratosphere tends to be uniform
at any given latitude.
This research really begs us in the scientific community to look at lower
stratospheric ozone depletion. And, for the person on the street, it makes a strong
connection to global climate change, Toohey says.
Lisa M. Pinsker
Lake Vostok, Antarcticas
largest subglacial lake, has a small clone, scientists announced at the spring
meeting of the American Geophysical Union in Washington on May 28. While recently
scouring over ice-penetrating radar data collected in the summer of 2000 over
East Antarctica, Anahita Tikku of the Lamont-Doherty Earth Observatory at Columbia
University discovered an anomaly. Previously considered one of Antarcticas
many smaller, 2 to 3 square-kilometer subglacial lakes, Lake Concordia actually
measures at least 800 square kilometers.
Photo by Michael Studinger
While nowhere near the size of Lake Vostoks 10,000 square kilometers,
the newly identified Lake Concordia shares similar features of basal freezing.
Four thousand meters of ice cover the lake. But as the continental ice sheet
flows across the long axis of Lake Concordia, the ice sheet appears to thin
by 150 meters indicating areas of potential accretion, where the surface
of the lake has frozen to the bottom of the ice sheet. Such areas of accretion
in Lake Vostok provide scientists a means of sampling the subglacial lake without
actually penetrating through the ice to the lake water itself, an event many
fear might contaminate an otherwise untapped environment.
Scientists are currently studying the glacier ice and accreted ice at Vostok
to learn what organisms may exist within the lake water. For Michael Studinger
and Robin Bell, co-authors of the report and also from Lamont, Lake Concordia
proves a promising second to Vostok, Studinger says. The lake measures
at least 40 by 20 kilometers, but could be larger, because the radar profiles
did not cover Concordias northern shore. It is significant for us
to have another lake where we know interactions between lake water and the ice
sheet occur, he adds. A lot of ideas we developed at Vostok are
stimulated at Concordia.
But Lake Concordia may not be alone in its similarity to Lake Vostok. Also at
the meeting, Italian and French scientists presented radar evidence indicating
two additional large lakes in East Antarctica. More may still crop up in the
future. Says Studinger: There are probably a significant number of intermediate
sized lakes that we havent discovered so far.