An inaccessible, unique website can keep the past secret.
Scientists have discovered, according to them, the remains of a huge old lake bed, which was sealed under the ice of northwestern Greenland more than a kilometer away. The first discovery of such a subglacial property anywhere in the world. It is evident that it was formed when the area was free of ice but is now completely frozen. Scientists believe that such data could be used to understand what Greenland ice can do in the coming years as the climate warms, making the site a tangible target for drilling. A paper describing the application is published in the journal Earth’s science letters,
“It could be a storehouse of information in a landscape that is now completely hidden and inaccessible,” said Guy Paxman, a postdoctoral researcher. Columbia UniversityLamont-Doherty Earth Observatory գլխավոր lead author of the report. “We are trying to understand how the Greenland ice sheet has behaved in the past. That is possible if we are to understand how it will behave for decades to come. ” The ice sheet, which has been melting at an accelerating rate in recent years, contains enough water to raise global sea levels by about 24 feet.
The researchers plotted the lake bed by analyzing data from airborne geophysical instruments that could read the signals that penetrate the ice and give images of the geological structures below. Most of the data came from planes flying at low altitudes on ice as part of NASAIceBridge operation.
The team says the pool once hosted a lake that covered about 7,100 square kilometers (2,700 square miles), about the size of the US states of Delaware and Rhode Island. Sediment in the basin, which is as cloudy as fog, seems to fluctuate 1.2 kilometers (three quarters of a mile) in thickness. Geophysical images show a network of at least 18 apparent disposable flow beds carved deep into the Adjacent River into a north-facing ridge that fed the lake. The figure also shows at least one apparent outflow to the south. Researchers estimate that the depth of water in the lake once ranged from about 50 meters to 250 meters (maximum about 800 feet).
In recent years, scientists have discovered glacial lakes in both Greenland and Antarctica that contain liquid water in the ice or in the gutter. This is the first time anyone has noticed a fossil lake bed that apparently formed when there was no ice and then covered and froze on the spot. There is no evidence that the Greenland Basin contains liquid water today.
Paxman says there is no way to tell how old the lake’s bed is. Researchers say that it is possible that the ice has evolved periodically, receding over most of Greenland over the last 10 million years, and possibly going back as far as 30 million years. A 2016 study led by Lamont-Doherty geochemist er org Schaefer suggests that much of Greenland ice may have melted over a period of one or more years over the last few million years, but the details are sketchy. This special area could be covered and uncovered many times, Paxman said, leaving ample opportunity for the lake’s history. In any case, Paxman says, the considerable depth of sediments in the basin suggests that they would have accumulated without ice for hundreds of thousands or millions of years.
“If we could reach those sediments, they could tell us when the ice was there or not,” he said.
The researchers collected a detailed picture of the lake basin and its surroundings by analyzing the gravitational magnetic data collected by NASA radars. The ice penetrating radar provides the basic topographic map of the earth’s underlying ice. This revealed the outlines of a flat, low-lying basin perched at higher altitudes. Gravity measurements showed that the material in the basin was less dense than the surrounding hard, metamorphic rocks, indicating that it was composed of sediments washed from the sides. Magneticity measurements (sediments are less magnetic than solid rocks) helped the team map sediment depths.
Researchers say the pool may have formed along the line of the now dormant fault when the foundation was stretched and caused a low spot. Alternatively, but less likely, the former glaciers can carve out the depression, leaving it to fill with water after the ice has receded.
What the sediments may contain is a mystery. The ice sheet has been found to contain pollen and other residues, suggesting that Greenland may have undergone warm periods over the last million years, allowing plants, perhaps even forests, to take over. But the evidence is not convincing, in part because such loose material is difficult to date. In contrast, the newly discovered lake bed could provide an intact archive of fossil chemical signals dating back to the hitherto unknown distant past.
Therefore, the basin “could be a potential site for future ice drilling and restoration of sediment records that could provide valuable insights into glacial, climatic, and environmental history,” the researchers wrote. When the top of the sediment is 1.8 kilometers (1.1 miles) below the current ice surface, such drilling would be intimidating, but not impossible. In the 1990s, researchers penetrated the top of the Greenland ice sheet for almost two miles and restored several feet of ground. When was the deepest iceberg drilled? The operation, which lasted five years, has not been repeated in Greenland since then, but a new project is planned for the next few years to reach a surface in another part of northwestern Greenland.
Reference. Earth’s science letters,
The study was co-authored by Jacqueline Austermann and Christy Tinto, both of whom were housed at the Lamont-Dohert Earth Observatory. The study was supported by the US National Science Foundation.