The ice of glaciers preserves many things. Not only gas bubbles that open a window for science into the climate of the past, or bodies of animals and people from the Stone Age, but also plant remains that tell an exciting and intriguing story about the Greenland Ice Sheet. This is the conclusion of a study by an international team of researchers who accidentally stumbled across forgotten drilling samples from the 1960s. The sensational result of the study: Greenland’s ice sheet has largely melted away at least once for an extended period of time in the past 1 million years, probably twice.
They’re fossils, but they look like they just died yesterday.Andrew Christ, lead author, University of Vermont
The research team, led by Paul Bierman of the University of Vermont, Joerg Schaefer of Columbia University and Dorthe Dahl-Jensen of the University of Copenhagen, came to this conclusion after discovering partially perfectly preserved plant remains in sediment samples from ice cores. The samples came from cores taken from Camp Century, the former US base in Greenland’s ice sheet, about 120 kilometres from the coast. Andrew Christ from the University of Vermont and lead author of the study, had examined the remains in the sediment samples and explains: “Ice sheets typically pulverize and destroy everything in their path. But what we discovered were delicate plant structures. They’re fossils, but they look like they died yesterday. It’s a time capsule of what used to live on Greenland that we wouldn’t be able to find anywhere else.” The team’s study is featured in the latest edition of the Proceedings of the National Academy of Sciences PNAS.
The significance of the find becomes clear when one considers that the cores at the end of which the sediment samples were found came from a 1.4 kilometre thick ice sheet, in the middle of the Greenland ice sheet. The plants clearly show that this ice sheet had not been there for a long time, so that a forest community had been able to develop. “Our analyses show that they come from boreal forest—the conifer, birch and willow forests common to Canada and Alaska,” explains Professor Dorthe Dahl-Jensen. “These hardy plants and trees are tolerant of cold conditions.” To learn more about the circumstances, the researchers used different isotope analyses, i.e. different chemical forms of the same element, and were thus able to show that there could have been no ice at the site. In combination with luminescence measurements of the soil samples, radiocarbon measurements of the plants and the arrangement of the ice and dirt layers, the researchers concluded that most of Greenland must have been completely ice-free at least once in the last million years. Maybe even several times during the interglacial periods.
“This is not a twenty-generation problem, but an urgent problem in the next 50 years”Professor Paul Bierman, study leader, University of Vermont
Until now, it was assumed that the ice sheet could have been smaller during these warm periods. But the new results show how sensitively this actually mighty ice sheet reacts to warming and has melted much more than previously assumed. “Our study shows that Greenland is much more sensitive to natural climate warming than we used to think. And we already know that humanity’s out-of-control warming of the planet hugely exceeds the natural rate,,” Andrew Christ continues. Professor Paul Bierman agrees: “This is not a twenty-generation problem, but an urgent problem for the next 50 years. Professor Dahl-Jensen also sees the need to act now to prevent the ice sheet from melting to such an extent that plant communities would form again.
The story of the sediment samples themselves is also intriguing in itself. That’s because the samples were created in the 1960s at the then-secret U.S. military camp Camp Century. The camp was built into the ice sheet of Greenland and was to serve as a test for missile launching bases in the ice. Therefore, the ice sheet was examined, among other things with drill samples. In the process, the samples were unearthed and stored in a US Army freezer. On winding paths they found their way to Copenhagen, where they were simply stored until a few years ago. It was only when the institute moved to a new location that they accidentally came to light and were examined. The ice cores were among the first of their kind and helped create the first climate models of Earth’s past. The camp itself was used from 1959 to 1967 and then abandoned. It gained notoriety when it became clear that the US Army had operated a nuclear reactor there, which was subsequently removed. But the rest of the garbage was simply left in the eternal ice in the hope that it would do no harm there. But Greenland’s ice is not that eternal, as the new study just shows.
Dr Michael Wenger, PolarJournal
Link to study: Christ et al (2021) PNAS 118 (13) e2021442118; A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century; https://doi.org/10.1073/pnas.2021442118
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