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Field Notes 
Surprising ozone loss   Mini-Vostok


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. “It’s 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


Mini-Vostok

Lake Vostok, Antarctica’s 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 Antarctica’s 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 Vostok’s 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 Concordia’s 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 haven’t discovered so far.”

Christina Reed


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