Million-year-old plant fossils are a warning from the Greenland ice sheet – tech2.org

Million-year-old plant fossils are a warning from the Greenland ice sheet


icebergs float when the sun rises near Kulusuk, Greenland.

icebergs float when the sun rises near Kulusuk, Greenland.
Photo: Felipe Dana (AP)

Jars of dirt taken from a Cold War-era military prank and lost in a freezer for decades could contain crucial new information about climate change and rising sea levels. TO study published Monday in the Proceedings of the National Academy of Scientists says plant fossils found in a soil sample collected from a mile below the ice in the mid-1960s suggest that the world’s prehuman climate was at one point sufficiently warm enough to completely melt the Greenland ice sheet.

The soil the researchers inspected is a sediment sample from the bottom of an ice core, recovered by drilling through the ice sheet that covers most of Greenland. It’s quite difficult to get to the bedrock when sampling because of the incredible pressure of the ice, explained Drew Christ, lead author of the study and a postdoctoral fellow at the University of Vermont. There are only a few expeditions that have obtained sediments from the bottom of the glacier. “We have less of this [sediment] than the lunar rocks, ”said Christ.

This particular sample produced a large amount of plant matter, some of which was visible to the naked eye. “It’s like you go on a hike, and you put a bunch of twigs and things from the forest floor on the sole of your boot and see them at the end of the day,” Christ said. “It is something like that, but it has been frozen for 1 million years.”

Christ and the team behind the study used isotope analysis of various elements that helped the researchers determine the last time the samples were exposed to the sun and cosmic rays. The dating showed that the plant matter is approximately 1 million years old.

Before analyzing this particular sample, Christ said, the scientists had “circumstantial” evidence that the Greenland ice sheet had once completely melted. But the discovery of these fossils definitely suggests that Greenland was once ice-free enough to provide a home for a variety of plants. And that’s bad news for us right now. The Greenland Ice Sheet is a ticking weather bomb, and some estimates project that the sheet could raise sea level by 6.1 meters (20 feet). if it melted completely. While it is not scheduled to fully melt tomorrow, the ice sheet is now melting six times faster than in the 1980s. Changes set in motion by rising carbon dioxide will take centuries to manifest as the climate adjusts to a new equilibrium. Knowing its history is essential to understanding the future of the ice sheet.

“The Greenland ice sheet has disappeared in a climate system that had no human influence,” Christ explained. “Before humans added hundreds of parts per million of fossil fuels to the atmosphere, our climate could melt the ice sheet. In the future, as we continue to warm the planet at an uncontrollable rate, we could force the Greenland ice sheet to exceed a certain threshold and melt it and raise sea level. “

A microscopic view of twigs and moss from the soil sample.

A microscopic view of twigs and moss from the soil sample.
Picture: University of Vermont

The soil sample that Christ and his team used to reach these conclusions has its own incredible backstory, even one that was almost lost to history. The sample was originally recovered from the first Greenland ice core taken during a 1966 expedition to a military base called Camp Century. The real purpose of the expedition was a secret James Bond-style mission called Iceworm project (yes, really) to try to hide nuclear missiles under the ice near the Soviet Union (we are not making this up). The scientific part of the expedition, while valid, was created primarily to cover this Cold War prank. The Ice Worm Project eventually failed, but at least we got this fascinating ice core out of it. (However, on the downside, climate change is melting Camp Century and could cause a toxic waste spill leftover supplies and chemicals from the Cold War era).

Although the land sample is remarkable in itself, given that the Camp Century attempt was the first ice core recovered from Greenland, the researchers were more interested in what the ice itself could tell them and less in the land to come with the core.

“I was pulling out one-inch-long twigs of this material. We could see with our naked eyes, as if this was definitely plant material, ”Christ said. “Seeing this as someone who was born long after all of this happened, it’s like, how [the scientists] Didn’t you think to take a closer look? I think they had a higher priority to analyze the ice and then the soil was not analyzed. “

In what Christ describes as a “strange trick of history,” the soil was such a low-level priority for researchers that it was eventually lost when the expedition got home. The samples were stuffed into the back of an army freezer at the University of Buffalo, then moved undercover with a bunch of other material to another freezer at a research facility in Denmark in the 1990s. It was only in 2017. When JP Steffensen, one of Christ’s mentors and author of the article, was taking inventory to help that facility prepare its freezer for a move, that samples were rediscovered and could be more fully analyzed.

And while researchers in the 1960s may not have known what they got when they unearthed ancient soil, Christ is grateful that his work provided him with one of the most exciting moments of his scientific career.

“The day we found the fossils was one of those ‘eureka’ moments. I never thought those days really happened for scientists, but they did happen for me, ”he said, describing how he first saw specks of plant material as his team cleaned up sediment samples for analysis. “I was jumping in the lab. It was so exciting. “

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