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The remains of a gigantic ancient lake have been discovered beneath Greenland, buried deep beneath the ice sheet in the northwest of the country and are estimated to be hundreds of thousands of years, if not millions, scientists say.
The enormous “ fossil lake bed ” is a phenomenon that scientists have never seen before in this part of the world, even though we know that the colossal Greenland ice sheet (the second largest in the world, after that of Antarctica) remains full of mysteries hidden under its icy lid as it lost mass at an alarming rate.
Last year, scientists reported the discovery of more than 50 subglacial lakes beneath the Greenland ice sheet: bodies of thawed liquid water trapped between the bedrock and the overlying ice sheet.
The new find is of a different nature: an ancient lake basin, long dry and now filled with aeons of sedimentary fill – loose rock measuring up to 1.2 kilometers (three-quarters of a mile) thick – and then covered by another 1 , 8 kilometers of ice.
(Columbia University, adapted from Paxman et al., EPSL, 2020)
Above: The lake basin (red outline), fed by ancient streams (blue).
When the lake formed long ago, however, the region would have been ice-free, the researchers say, and the basin would have supported a monumental lake with a sprawling area of about 7,100 square kilometers (2,741 square miles).
It is roughly the same size as the combined area of the US states Delaware and Rhode Island, and this huge lake would have held approximately 580 cubic kilometers (139 cubic miles) of water, being fed by a network of at least 18 ancient waterways. that once existed north of the lake bed, flowing into it along a sloping escarpment.
While there is currently no way of knowing how ancient this lake is (or whether it has filled and dried up numerous times), we may be able to find out if we could analyze the loose rock material now within the basin: a gigantic time capsule of preserved sediments that could give us some clues about the environment of Greenland more or less forever.
“This could be an important repository of information, in a landscape that is totally hidden and inaccessible right now,” says Guy Paxman, chief researcher and glacial geophysicist at Columbia University.
“If we could get to those sediments, they could tell us when ice was present or absent.”
The giant lake bed – dubbed “Camp Century Basin,” in reference to a nearby historic military research base – was identified through observations from NASA’s Operation IceBridge mission, an aerial survey of the world’s polar regions.
During flights over the Greenland ice sheet, the team mapped subglacial geomorphology beneath the ice using a range of instruments that measured radar, gravitational and magnetic data. The readings revealed the profile of the gigantic loose mass of sedimentary fill, made up of less dense and less magnetic material than the harder rock surrounding the mass.
It is possible, the team thinks, that the lake formed in warmer periods due to shifting of the bedrock due to an underlying fault line, which is now dormant. Alternatively, glacial erosions may have carved the shape of the basin over time.
Either way, the researchers believe the ancient basin may hold an important sedimentary record, and if we can somehow dig deep enough to extract and analyze it, it could indicate when the region was ice-free or covered with ice, reveal constraints of the extent of the Greenland ice sheet and provide information on past climate and environmental conditions in the region.
Whatever secret those deeply buried rocks may tell us about polar climate change in the ancient past, it could be vital information for interpreting what is happening in the world right now.
“We are working to try to understand how the Greenland ice sheet has behaved in the past,” says Paxman. “It is important if we want to understand how it will behave in the coming decades.”
The results are reported in Science letters of the earth and planets.
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