The kilometers-thick ice sheets that smothered northeastern Canada and scoured the landscape there during recent ice ages left sediments intact in some locales. This surprising finding could prove a boon to climate researchers.
Most scientists have assumed that the ice sheets that form during ice ages scrape the land clean as they plow across the terrain. Indeed, most of the sot in previously ice-covered arctic areas either formed there since the most recent ice age ended, about 10,000 years ago, or was carried there by wind after the ice sheet disappeared, says Jason P. Briner, a geologist at the State University of New York at Buffalo.
In the past few years, teams of researchers have discovered a few tiny lakes on Canada's huge, northeastern Baffin Island that contain sediments deposited before the most recent ice age. At first, the scientists theorized that those sites, near the island's eastern shore and a few hundred meters above sea level, hadn't been covered by the ice sheet, says Briner. Now, however, research reported by Briner and his colleagues in the October Geology suggests that the ice sheet flowed across those lakes but somehow didn't clear away their sediments.
The team analyzed core samples from a 0.3-square kilometer lake on Baffin Island, a 10-meter-deep body of water dubbed Lake CF8 that's similar to dozens of others in the region, says Briner. In its deposited sediments, thick layers of organic-rich material alternate with thin bands of coarse sand. …