The mostly asymptomatic surface of the Greenland ice sheet, such as the geophysical features seen through the window of a packed P3 aircraft aimed at finding geological features below. Credit: Kirsty Tinto / Lemont-Doherty Earth Observatory
Unavailable for now, the unique site can capture the secrets of the past.
Scientists have discovered what they call a huge ancient lake bed silt sealed more than a mile under the ice of northwestern Greenland – the discovery of this type of sub-glacial feature anywhere in the world. Apparently designed at a time when the area was ice-free but is now completely frozen, the lake bed may be hundreds of thousands or millions of years old and may contain unique relics and chemical traces of past climates and life. Scientists believe the climate is important for understanding this type of data as the weather warms up in the coming years so what can a sheet of greenland ice do, and thus make the site a boring target for drilling. A paper describing the discovery is in the press in the journal Earth and Planetary Science Letters.
“This could be an important source of information, in a landscape that is currently completely hidden and inaccessible,” said Gay Paxman, a postdoctoral researcher. Columbia UniversityLemont-Doherty Earth Observatory and lead author of the report. “We are working to understand and understand how the Greenland ice sheet behaved in the past. If we are to understand how it will behave in future decades. “Ice sheets that have been melting at a dynamic pace in recent years have enough water to raise the global sea level by about 24 feet.
The researchers mapped the lake bed by analyzing data from aerial geophysical instruments that could read signals entering the ice and provide images of the geological formations below. Most of the data came from planes flying at low altitudes over a sheet of ice as part. NASAOperation Icebridge.
A newly created lake on the shores of the Greenland ice sheet, exposing the silt released by the ice. Such lake beds are becoming more common as the snow recedes. Credit: Kevin Krajic / Earth Institute
The team says the basin at one time covered a lake covering about 7,100 square kilometers (2,700 square miles), including the U.S. of Delaware and Rhode Island. About the size of the states. The silt in the basin, vaguely shaped like a meat cleaver, measuring 1.2 kilometers (three quarters of a mile). Geographic images show a network of at least 18 clear one-time flow beds in the bedrock attached to the north-facing escarpment that must have fed the lake. The image also shows at least one clear outlet stream to the south. Researchers have calculated that the depth of water in Onetime Lake ranges from about 50 meters to 250 meters (maximum 800 feet).
In recent years, scientists have discovered existing subglacial lakes in both Greenland and Antarctica, which contain liquid water in ice or between bedrock and ice. This is the first time anyone has seen a fossilized lake bed, apparently formed when there was no ice, and will later be fixed in place by covering it. There is no evidence that there is liquid water in the Greenland Basin today.
Paxman says there’s no way to tell how old the lake bed is. Researchers say it is possible that ice has periodically advanced and retreated over most of Greenland over the past 10 million years, and will probably go back 30 million years. A 2016 study led by Lam Mont-Doherty geochemist Jorge Schaefer suggested that much of Greenland’s ice has melted for one or more extended periods over the past million years, but the details are specific. This particular area would have been frequently covered and exposed, leaving many possibilities for the history of the lake, Xavier said. In any case, Paxman says, the significant depth of silt sediments in the basin indicates that they have been built during ice-free time for hundreds of thousands or millions of years.
“If we could get to that silt, he would be able to tell us if the ice was present or absent.”
Using geological tools, scientists have mapped a huge ancient lake basin (described in red here) beneath the Greenland ice, covering about 2,700 square miles. Redder colors indicate higher elevation, green less. A flow system is shown in blue in the bedrock that once fed the lake. Credit: Paxman et al., EPSL, adapted from 2020
The researchers collected a detailed picture of the lake basin and its surroundings through radar, gravity and analysis of magnetic data collected by NASA. Ice-penetrating radar provides an original topographic map of the Earth’s surface under ice. This revealed the outline of a simple, low-lying basin inhabited by high-elevation rocks. Gravity measurements show that the material in the basin is less ga ense than the surrounding hard, metaphorical stones – evidence that it is made of silt washed from the sides. Magnetic measurement (silt is less magnetic than solid rock) helps the team to map sediment.
Researchers say the basin would now have formed along the long-passive fault line, while the bedrock stretched and created a lower space. Alternatively, but with less probability, previous glaciers would have created tension, while the ice would have been filled with less water.
It is a mystery what silt can contain. The material washed from the edge of the ice sheet has been found to contain remnants of pollen and other materials, suggesting that Greenland may have spent warmer times over the last million years, which will also capture plants and forests. But the evidence is not conclusive, partly because it is difficult to date such loose material. Newly discovered lake beds, by contrast, can provide an unbroken collection of remnants and chemical signals from the hitherto unknown past.
The basin could be an important place for future recovery of sub-ice-drilling and silt records, which could gain valuable insights into the region’s glacier, meteorological and environmental history, the researchers wrote. With a peak of silt 1.8 kilometers below the current ice surface (1.1 miles), such drilling would be terrible, but not impossible. In the 1990s, researchers achieved several feet of bedrock by penetrating about 2 miles to the top of a Greenland ice sheet – at the time, the largest esto ice core ever drilled. The feat, which lasted five years, has not been repeated in Greenland since then, but a new project aimed at reaching the shallow beds in another part of northwestern Greenland is being planned for the next few years.
Reference: Earth and Planetary Science Letters.
The study was also based on the Jacqueline US Sterman and Kirsty Tinto, both at the LL Mont-Doherty Earth Observatory. The research was supported by the US National Science Foundation.
