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A team of scientists from the Lamont-Doherty Earth Observatory at Columbia University has discovered a paleolatose basin located under the ice sheet in northwestern Greenland; Geomorphological analyzes and hydrological models indicate that the basin once housed a lake with an area of up to 7,100 km2 and a volume of up to 580 km3; it may be hundreds of thousands or millions of years old and contain unique fossil and chemical traces of past climates and life.
Paxman et al. mapped a huge ancient lake basin (outlined here in red) under the Greenland ice; the more red colors indicate higher elevations, the lower green ones; a flow system etched into the bedrock that once fed the lake is shown in blue. Image credit: Paxman et al., doi: 10.1016 / j.epsl.2020.116647.
“This could be an important repository of information, in a landscape that is totally hidden and inaccessible right now,” said Dr Guy Paxman, lead author of an article published in the journal Science letters of the earth and planets.
“We are working to try to understand how the Greenland ice sheet has behaved in the past. It is important if we want to understand how it will behave in the decades to come. “
Dr Paxman and colleagues mapped the ancient lake bed by analyzing data from airborne geophysical instruments that can read ice-penetrating signals and provide images of underlying geological structures.
Most of the data came from planes flying low over the ice sheet as part of NASA’s IceBridge operation.
The geophysical images show a network of at least 18 apparent watercourse beds carved into the adjacent bedrock in a north-sloping escarpment that must have fed the lake. The image also shows at least one apparent outlet stream to the south.
The researchers calculated that the water depth in the lake once ranged from about 50 to 250 m.
“The basin may have formed along a long-dormant fault line as the bedrock elongated and formed a low point,” they said.
“Alternatively, but less likely, earlier glaciations may have carved out the depression, leaving it to fill with water as the ice receded.”
The sediments in the basin appear to be 1.2 km thick. What they might contain is a mystery.
The washed-out material from the edges of the ice sheet has been found to contain remnants of pollen and other materials, suggesting that Greenland may have experienced warm periods during the last million years, allowing plants and possibly even forests to take hold.
But the evidence is not conclusive, in part because it is difficult to date such loose materials.
The newly discovered lake bed, by contrast, could provide an intact archive of fossils and chemical cues from a distant, hitherto unknown past.
“The basin could be an important site for future sub-ice drilling and recovery of sediment records that could provide valuable insight into the region’s glacial, climatological and environmental history,” the scientists said.
“With the top of the sediment located 1.8 km below the current ice surface, such drilling would be daunting, but not impossible.”
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Guy JG Paxman et al. A fault-bound paleo-lacustrine basin preserved under the Greenland ice sheet. Science letters of the earth and planets, published online on October 28, 2020; doi: 10.1016 / j.epsl.2020.116647
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