Ancient Tundra Found Beneath Greenland Ice Sheet; Could Be Up To 3 Million Years Old
Greenland was actually green millions of years ago, until 80 percent of it got covered by an ice sheet. A team of scientists recently made this discovery, also concluding that the ice sheet over Greenland is much older than previously thought.
"We found organic soil that has been frozen to the bottom of the ice sheet for 2.7 million years," said University of Vermont geologist and lead author of the study Paul Bierman, in a press release. The findings, published in the journal Science, hint that the ice sheet has survived many periods of global warming, he said.
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Greenland's ice sheet is a treasure trove for climate change experts who find valuable records of the Earth's past climates in its layers of ice, which are billions of years old. As the second largest body of ice in the world, it's estimated that if the entire ice sheet were to melt, it would cause the global sea-level to rise 7.2 meters.
"The ancient soil under the Greenland ice sheet helps to unravel an important mystery surrounding climate change," said Dylan Rood, from the Scottish Universities Environmental Research Centre and the University of California, Santa Barbara, in the release. "How did big ice sheets melt and grow in response to changes in temperature?"
According to previous research, global warming through the years greatly reduced the size of the ice sheet, but the new research indicates that its center always remained stable, even during the warmest years. It is under this stable ice that the scientists found the tundra landscape locked away. Generally, glaciers scrape off everything from vegetation to soil to the top layer of bedrock, but this newly discovered tundra seems unchanged after billions of years of unpredictable climate - a marvel of nature.
"Some ice sheet models project that the Greenland Ice Sheet completely melted during previous interglacial periods. These data suggest that did not happen," said co-author Tom Neumann, a cryospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "We don't know how much of the ice sheet remained - to estimate it, we'd have to study other ice cores in Greenland that have sediment in the bottom to see if ancient soil is preserved under those sites as well."
The scientists came to this conclusion after examining 17 samples of ice mixed with sediments, also called "dirty ice." The 10,019-foot GISP2 ice core in Greenland was drilled up to the bedrock in 1993. The new study was conducted on samples recovered from the bottommost 40 feet of the glacier.
From this sediment, Bierman and a team at the University of Vermont's Cosmogenic Nuclide Laboratory extracted a rare form of the element beryllium, an isotope called beryllium-10. It is mainly formed by the impact of cosmic rays on surfaces like rock and soil. The longer soil is exposed at Earth's surface, the more beryllium-10 it accumulates. So, measuring its amount gives clues on the age of ice sheets.
The researchers expected to find in the sediment, soil from the bedrock which may have been eroded by the ice. But when the silt was measured for beryllium-10 concentrations on a particle accelerator at Lawrence Livermore National Laboratory, in Livermore, California, they found high amounts of it.
"On a global basis, we only find these sorts of beryllium concentrations in soils that have developed over hundreds of thousands to millions of years," said co-author Joseph Graly, who analyzed the beryllium data while at the University of Vermont.
The conclusion was that the soil was not always covered with ice but had been stable and exposed at the surface for somewhere between 200,000 and one million years. The theory was further confirmed when they found similar beryllium levels in a modern permafrost tundra soil on the North Slope of Alaska.
In addition, the team also measured nitrogen and carbon that could have been left by plant material in the core sample. They found measurable quantities of organic material which further corroborated the idea that the pre-glacial landscape may have been a partially forested tundra.
"Greenland really was green! However, it was millions of years ago," said Rood. "Before it was covered by the second largest body of ice on Earth, Greenland looked like the green Alaskan tundra."
These million-year-old glaciers are gradually depleting because of man-made global warming. If temperatures continue to rise, then according to Bierman it would be "far warmer than the warmest interglacials in millions of years. There is a 2.7-million-year-old soil sitting under Greenland. The ice sheet on top of it has not disappeared in the time in which humans became a species. But if we keep on our current trajectory, the ice sheet will not survive. And once you clear it off, it's really hard to put it back on."
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