Scientists have discovered an ancient lakebed buried under more than a mile of ice that may hold secrets to Greenland's past climate.
The lake formed when northwest Greenland was ice-free, sometime between hundreds of thousands or even millions of years ago. Given Greenland's rapid melt today, the lake could reveal something about the Arctic's future as the ice caps shrink.
"This could be an important repository of information, in a landscape that right now is totally concealed and inaccessible," Guy Paxman, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory, said in a statement. "We're working to try and understand how the Greenland ice sheet has behaved in the past. It's important if we want to understand how it will behave in future decades."
Buried in ice
Paxman and his colleagues discovered the lake using data from instruments that use radar to penetrate beneath the ice surface to measure topography; much of the data came from NASA's Operation IceBridge.
The lake basin sits 1.1 miles (1.8 kilometers) below the surface of the ice and stretches over 2,700 square miles (7,100 square km), the size of Rhode Island and Delaware combined. At its deepest point, the lake would have extended about 800 feet (250 meters) down.
The researchers also mapped 18 streambeds that would have flowed into the lake from the north, as well as an outlet that would have drained the lake to the south. Today, this ancient water system is nothing but sediment, and scientists don't know when it last held water. According to previous research, Greenland's ice has advanced and retreated at various points over the last million years. There may have also been ice-free stretches going back over the past 30 million years, according to the Lamont-Doherty Earth Observatory.
Past and future
The depth of the sediments in the lake suggests it is between hundreds of thousands and millions of years old, Paxman said. To get more specific than that, scientists would have to drill beneath the ice into the lake sediments to study them directly.
The lake may have been formed when an ancient fault pulled the Earth apart, creating a depression, the researchers said, or it may have been a bowl carved out by a retreating glacier.
Drilling into the lakebed might also provide clues to the future. The lakebed may contain traces of certain chemicals or fossils that could reveal more about Greenland's past climate. Scientists could then compare these past conditions with the changing conditions in the Arctic today.
There are no current plans to drill into the lakebed, but such a feat would be possible. In 2003, researchers drilled 1.9 miles (3,085 m) beneath the ice surface in Greenland. A project set to launch in 2021 called GreenDrill will aim to drill into the bedrock at several sites in northern Greenland to determine when and for how long portions of the region were ice-free in the past.
Paxman and his colleagues reported their findings online Oct. 28 online in the journal Earth and Planetary Science Letters.
Originally published on Live Science.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.
Back in the late Eocene (~34 Myr-ago, the climate was mild and the pCO2 was more than double what it is now. When the pCO2 dropped below a threshold value of about 750 ppm, the polar ice sheets began to form. This may have been when the now-buried lake was there.Reply
Cool, extinct (or extant!) life seen in the sediments will be useful data.Reply
Back in the late Eocene (~34 Myr-ago, the climate was mild and the pCO2 was more than double what it is now. When the pCO2 dropped below a threshold value of about 750 ppm, the polar ice sheets began to form. This may have been when the now-buried lake was there.
Maybe - they will disappear within 1 kyrs https://www.sciencealert.com/greenland-s-ice-sheet-will-disappear-over-the-next-1000-years-nasa-model-shows ], and the man made CO2 release that forced that result has "only" pushed the CO2 from ~ 250 ppm http://www.realclimate.org/index.php/archives/2018/10/pre-industrial-anthropogenic-co2-emissions-how-large/ ] to 410 ppm https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide ]. But of course that factor alone has a complex dynamic, since the global warming is 1,000 times faster than other observed.
Mostly, plate tectonic and so circulation regimes differed between now and then. And the casues and timing differed between the two land ice sheets (which contains the water that will increase sea levels and make more acute problems).
The Eocene is not only known for containing the warmest period during the Cenozoic, but it also marked the decline into an icehouse climate and the rapid expansion of the Antarctic ice sheet. The transition from a warming climate into a cooling climate began at around 49 million years ago. Isotopes of carbon and oxygen indicate a shift to a global cooling climate. The cause of the cooling has been attributed to a significant decrease of >2,000 ppm in atmospheric carbon dioxide concentrations.
Global cooling continued until there was a major reversal from cooling to warming indicated in the Southern Ocean at around 42–41 million years ago. Oxygen isotope analysis showed a large negative change in the proportion of heavier oxygen isotopes to lighter oxygen isotopes, which indicates an increase in global temperatures. This warming event is known as the Middle Eocene Climatic Optimum. The warming is considered to be primarily due to carbon dioxide increases, because carbon isotope signatures rule out major methane release during this short-term warming.
Cooling continued throughout the rest of the late Eocene into the Eocene-Oligocene transition. During the cooling period, benthic oxygen isotopes show the possibility of ice creation and ice increase during this later cooling. The end of the Eocene and beginning of the Oligocene is marked with the massive expansion of area of the Antarctic ice sheet that was a major step into the icehouse climate. Along with the decrease of atmospheric carbon dioxide reducing the global temperature, orbital factors in ice creation can be seen with 100,000-year and 400,000-year fluctuations in benthic oxygen isotope records. Another major contribution to the expansion of the ice sheet was the creation of the Antarctic Circumpolar Current.
The presence of ice-rafted sediments in deep-sea cores recovered from northwest Greenland, in the Fram Strait, and south of Greenland indicated the more or less continuous presence of either an ice sheet or ice sheets covering significant parts of Greenland for the last 18 million years. From about 11 million years ago to 10 million years ago, the Greenland Ice Sheet was greatly reduced in size. The Greenland Ice Sheet formed in the middle Miocene by coalescence of ice caps and glaciers. There was an intensification of glaciation during the Late Pliocene. Ice sheet formed in connection to the uplift of the West Greenland and East Greenland uplands. The Western and Eastern Greenland mountains constitute passive continental margins that were uplifted in two phases, 10 and 5 million years ago, in the Miocene epoch. Computer modelling shows that the uplift would have enabled glaciation by producing increased orographic precipitation and cooling the surface temperatures. The oldest known ice in the current ice sheet is as much as 1,000,000 years old.
Professor Larsson has collected, accumulated and itemized an abundant pile of "google" type evidence that does not negate the fact that the polar ice sheets began forming when the geological and geochemical evidence shows that the pCO2 began dropping about 34 Myr ago. The climate back then was not devastatingly hot. The marine carbonate plankton were thriving and life on land was lush. A fact?Reply
The question asked here was about when this lake formed. If Professor Larsson has another suggestion he should tell us what it is and not go off in another direction for another purpose.