Aktineq Glacier has shrunk back about a kilometer since 1948, Shilts said. Most of the other glaciers on Bylot Island, and on nearby Baffin Island, also appear to be melting away.
A glacier that shrinks over a period of decades may seem like an overt sign of a warming climate, but other contributors to glacial retreat are less obviously tied to climate change. Warmer temperatures can bring on more frequent freeze-thaw cycles that open fissures in the rock walls above a glacier, dumping debris on the glacier's surface that hastens melting by absorbing more of the sun's heat.
A more precise way of timing glacial events involves radiocarbon dating the soil in embankments near glacial moraines. Shilts and his colleagues conducted such studies on Bylot Island, and found that an undisturbed sand bank near a glacial moraine was about 6,800 years old.
"That means at the very least that the glacier that is a couple of feet away from that sand bank has not gone across that sand bank in 6,800 years," he said.
Another approach, called cosmogenic dating, indicated that the boulders just outside the 1948 moraine were even older. The technique, conducted by Shilts' former graduate student, Shirley McCuaig, dated those boulders at 55,000 years, plus or minus 5,000 years.
That finding confirmed something that another student, Rod Klassen, had suggested in his PhD thesis at Illinois, Shilts said. "And that is that the glaciers that are now on Bylot Island were as far advanced in the 1940s as they have been in the last 55,000 years. And now they are retreating."
"My interpretation of what I saw on Bylot Island is that we're in another cycle of glacial retreat," Shilts said. "Whether that cycle is primarily driven by human emissions of carbon dioxide in the atmosphere creating a warming trend, or whether it's driven by natural cycles, which relate to our orbit around the sun, sunspot
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign