Ancient lake bed may reveal secrets of the Greenland ice sheet

Ancient lake bed may reveal secrets of the Greenland ice sheet. Scientists have discovered evidence of an ancient lake bed more than a mile beneath the Greenland ice sheet. The study from Columbia University’s Earth Institute is the first of its kind to ever identify this type of sub-glacial feature anywhere in the world.

Sediments from the huge ancient lake bed suggest that it formed at a time when the area was ice-free, but now it is completely frozen off and sealed. According to the scientists, the lake could be hundreds of thousands to millions of years old. It is expected to contain unique fossils and chemical traces of past climates. 

“This could be an important repository of information, in a landscape that right now is totally concealed and inaccessible,” said study lead author Guy Paxman. “We’re working to try and understand how the Greenland ice sheet has behaved in the past. It’s important if we want to understand how it will behave in future decades.” 

The Greenland ice sheet has been retreating at an increasing rate. If all of Greenland’s ice was lost, the global sea level would rise by about 24 feet. It is important for experts to gain a better understanding of how the ice sheet changed in the past in order to make more accurate predictions of how it will transform in the future. 

To map the ancient lake bed, the researchers used data collected by airborne instruments that penetrate the ice and provide images of the geologic structures below. Most of the data came from low-flying aircraft missions for NASA’s Operation IceBridge.

The Columbia team discovered that the basin was once home to a lake covering about 2,700 square miles, while some lake sediments were up to three-quarters of a mile thick. The experts also recognized about 18 stream beds that connected to the lake, which had an estimated maximum depth of 800 feet.

Paxman said there is no way to tell how old the lake bed is. The researchers believe that the Greenland ice sheet has periodically advanced and retreated over much of the last 10 million years.

The area of the lake bed could have been repeatedly covered and uncovered, said Paxman, leaving a wide range of possibilities for the lake’s history. He added that in any case, the substantial depth of the sediments in the basin suggest that they must have built up during ice-free times over hundreds of thousands or millions of years.”If we could get at those sediments, they could tell us when the ice was present or absent.”

The contents of the sediment will remain a mystery for now. Material washed out from the edges of the ice sheet have been found to contain the remains of pollen and other materials, suggesting that Greenland may have undergone warm periods during the last million years. This would have allowed plants and potentially even forests to become established.

The researchers concluded that the lake basin is an important site for future sub-ice drilling and the recovery of sediment records that may yield valuable insights into the glacial, climatological and environmental history of the region. 

The study is published in the journal Earth and Planetary Science Letters.

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By Chrissy Sexton, Earth.com Staff Writer