Cracking The Ice

(2 of 3)

To describe these organisms as hardy would be an understatement. The Dry Valleys are so cold (the mean annual temperature hovers around -5ºF) that glacier-fed streams run no more than six weeks a year, and so arid that what little snow falls turns to vapor almost overnight. Scientists recently reported, however, that sequestered in the 60 ft. of ice that covers one of the largest Dry Valleys lakes, Lake Vida, are dormant but still viable bacteria that have been sealed off from the outside world for some 3,000 years.

The Dry Valleys are not just a biological laboratory; they are a climate laboratory as well. Between 1986 and 2000, scientists involved in a long-running ecological study documented a succession of cold summers that crimped the short, seasonal ice melt to such an extent that not only did lake levels fall but so did the photosynthetic activity that underpins their biology. Then, last summer, from December 2001 through January 2002, temperatures shot up and lake levels soared. For a brief time, conditions became so balmy that streams of meltwater cascaded off glaciers and ice falls, and the Onyx River flowed with enough vigor to support a series of whitewater rapids.

What does that exceptionally warm summer represent? Was it just a weird anomaly that briefly interrupted longer-term cooling? Or was the cooling trend itself a temporary glitch, as rising lake levels prior to the mid-1980s suggest? "At the moment," concedes Ohio State University geochemist Berry Lyons, "we don't even know if we're looking at changes that are just regional or if they are related to changes on a global scale."

To begin solving this puzzle, scientists working in the Dry Valleys need climate records that extend over a longer period of time, and now it appears they may finally have them. In November, the University of Illinois' Doran and his colleagues retrieved a series of sediment cores from the bottom of three lakes that march up Taylor Valley like Cyclopean footprints: Fryxell, Hoare and Bonney. These cores are layered like the pages of a history book, and the record of geochemical shifts they contain can be used to reconstruct lake levels and stream flow for past centuries. Doran thinks that the record from Lake Fryxell may extend back 15,000 years.

Icemare: Ross Ice Shelf
McMurdo Station is the sprawling complex of buildings from which the National Science Foundation (NSF) runs the U.S. Antarctic program, and right now McMurdo has a problem. Those big bergs that are hanging around the neighborhood have pinned up to 40 miles of sea ice next to shore, creating a daunting obstacle course for a nearby colony of Adelie penguins and a serious navigational hazard for people who service the station. The penguins are having trouble getting out to sea to feed — so much trouble that their numbers are in precipitous decline — and the NSF's supply ships are having trouble getting in. Earlier this month the NSF called in a second Coast Guard icebreaker to help clear the ice from McMurdo Sound.

Sooner or later the big bergs will move off and break up. What they will leave behind is a vague sense of menace. For the parent of the big bergs, the Ross Ice Shelf, is a floating extension of the West Antarctic Ice Sheet, which, for the past 10,000 years, has been slowly slipping into the sea. Should that ice sheet start a more rapid slide, it would trigger a lot more havoc than a few hulking icebergs.

Like Julius Caesar's Gaul, the ice that covers Antarctica is divided into three parts. There is the small ice of the Antarctic Peninsula. There is the big ice that covers the solid, continental block of East Antarctica to a depth, in places, of nearly three miles. And there is the middle-size ice of West Antarctica, much of which lies below sea level, so that its outermost fringes come into potentially perilous contact with seawater.

The most obvious danger lies in the melting that would occur if the temperature of Antarctica's salty, frigid waters climbed well above freezing. A greater if less obvious danger is that rising sea levels could undermine the ice sheet, triggering its collapse. Experts are concerned that if the West Antarctic Ice Sheet broke apart in this fashion, global sea levels could rise as much as 16 ft. in just a few decades.

Other factors affect the ice sheet's stability. One of the most important is the balance between the rate at which the ice sheet is growing (because of snowfall) and the rate at which it is shrinking. An ice sheet is, in essence, a viscous plateau, and under the burden of its own weight it is ever so slowly sliding downhill. Because of variations in underlying terrain, however, its slide is not uniform. In the Ross Sea sector, for example, ice is most efficiently conveyed out of the ice sheet's interior by ice streams, which spill onto the Ross Ice Shelf like frozen rivers.