Rock Shines Naked Light on Greenland Ice

Bedrock drilled from deep under the rapidly-melting Greenland ice sheet contains evidence that the island may once have been almost totally ice-free.

Greenland, which has an icecap that holds enough water to raise global sea levels by at least seven meters, has melted almost completely in the recent geological past, according to new research.

And if it did so once, then perhaps it could be denuded again as the Arctic region warms at an alarming speed.
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But researchers from Columbia University, New York, and others report in Nature journal that the chemistry of the bedrock below Greenland’s ice suggests that it must have been exposed − for entirely natural reasons − to the atmosphere for 280,000 years in the last 1.4 million years.

Chemical signature
The researchers cannot be sure whether this chemical signature represents one big event, or whether the ice vanished many times over shorter periods.

“Unfortunately, this makes the Greenland ice sheet look highly unstable,” says Joerg Schaefer, a palaeoclimatologist at Columbia’s Lamont-Doherty Earth Observatory.  “If we lost it in periods of natural forcing, we may lose it again.”

Right now, the surface ice of Greenland has been melting at a faster rate, and glaciologists have reported dramatic increases in the flow rate of the island’s giant frozen rivers.  There is evidence, too, that both processes could accelerate.

In the last four years, as a result of global warming driven by greenhouse gas emissions from the combustion of fossil fuels, Greenland has shed an estimated trillion tons of ice, and sea levels are creeping up at three millimeters a year.

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