Greenland Ice Sheet Collapse Linked to Massive Sea Level Rise 400,00 Years Ago

About 400,000 years ago, our Earth experienced a period of warming that pushed the Greenland ice sheet far past its stability threshold, resulting in near complete deglaciation. Now, scientists have found that this warming period is lined to a sea level rise of a staggering four to six meters.

"The climate 400,000 years ago was not that much different than what we see today, or at least what is predicted for the end of the century," said Anders Carlson, one of the researchers, in a news release. "The forcing was different, but what is important is that the region crossed the threshold allowing the southern portion of the ice sheet to all but disappear. This may give us a better sense of what may happen in the future as temperatures continue rising."

Until now, scientists have been unsure of how much sea level rise could be attributed to Greenland, and how much may have resulted from the melting of the Antarctic ice sheets or other causes. That's why they examined sediment cores collected off the coast of Greenland from what is called the Eirik Drift. They sampled the chemistry of the glacial stream sediment on the island, and discovered that different parts of Greenland have unique features. During the presence of ice sheets, sediments are scraped off and deposited in the Eirik Drift.

"Each terrain has a distinct fingerprint," said Carlson. "They also have different tectonic histories and so changes between the terrains allow us to predict how old the sediments are, as well as where they game from. The sediments are only deposited when there is significant ice to erode the terrain. The absence of terrestrial deposits in the sediment suggests the absence of ice. Not only can we estimate how much ice there was, but the isotopic signature can tell us where ice was present, or from where it was missing."

In the end, the researchers found that the deglaciation in southern Greenland would have caused at least four meters, if not six meters, of global sea level rise. It's very likely that ice sheet loss went beyond the southern edges of Greenland, though not all the way to the center.

"This is the first step toward more complete knowledge of the ice history," said Carlson. "But it is an important one."

The findings are published in the journal Nature.