Under Greenland, the remains of a giant ancient lake were discovered deep under the ice sheet in the northwest of the mainland. Scientists say it is hundreds of thousands of years old, if not millions.
The huge 'fossil lake bottom' is a phenomenon like never seen before in this part of the world, although we know that the colossal Greenland ice sheet (the world's second largest after Antarctica) remains full of hidden secrets.
Last year, scientists reported the discovery of more than 50 subglacial lakes beneath the Greenland ice sheet: melted liquid water between bedrock and ice sheets.
The new find has a different nature: the basin of an ancient lake, long dried up and now full of eons of sedimentary deposits – loose rock up to 1.2 kilometers thick, and then covered with another 1.8 kilometers of ice.
Lake basin (red outline) fed by ancient streams (blue). (Columbia University, adapted from Paxman et al., EPSL, 2020).
However, when the lake formed, the researchers said the region would be ice-free and the basin could support a monumental lake with a surface area of about 7,100 square kilometers.
Slightly smaller than Lake Onega, this massive lake would hold about 580 cubic kilometers of water, feeding on a network of 18 ancient streams that once existed north of the lake bottom, flowing into it along a gentle slope.
While it is now impossible to know how ancient this lake is, we could figure out if we can analyze the loose material that is now inside the basin: a giant time capsule of surviving sediment that could provide some clues about Greenland's environment roughly forever ago.
“The lake could be an important repository of information in a landscape that is now completely hidden and inaccessible,” says lead researcher and geophysicist Guy Paxman of Columbia University.
“If we could get to these deposits, they could tell us when ice was present or not.”
The giant lake bed, dubbed the 'Camp Century Basin' due to the nearby historic research base, was discovered by aerial observations from NASA's Operation IceBridge mission of the world's polar regions.
During flights over the Greenland Ice Sheet, the researchers mapped subglacial geomorphology using a range of instruments that measure radar, gravity and magnetic data. The readings revealed the outlines of a giant loose mass of sedimentary fill, consisting of less dense and less magnetic material than the rock surrounding the mass.
The lake may have formed during warmer times as a result of bedrock displacement from the fault line below it, which is now inactive. Alternatively, glacial erosion could have shaped the basin over time.
In any case, researchers believe that the ancient basin may have contained an important sedimentary record, and if we can somehow go deep enough to extract and analyze it, this could indicate when the region was ice-free or covered with ice, reveal limitations. the extent of the Greenland ice sheet and will give an idea of the past climate and environmental conditions in the region.
Whatever secrets these deeply buried rocks tell us about the polar climate change in the ancient past, it can be important information for interpreting what is happening in the world right now.
“We're working to try to understand how the Greenland ice sheet has behaved in the past,” says Paxman. “This is important if we want to understand how he will behave in the next decades.”
The results are reported in the journal Earth and Planetary Science Letters.
Sources: Photo: A pond of melt water on the Greenland ice sheet. NASA / Michael Studinger.
