Jars of dirt taken from a Cold War-era military caper and lost in a freezer for decades could hold crucial new information about climate change and sea level rise. A study published on Monday in Proceedings of the National Academy of Scientists says that plant fossils found in a sample of dirt collected from a mile beneath the ice in the mid-1960s suggest that the world’s pre-human climate was at one point warm enough to completely melt the Greenland ice sheet.
The dirt researchers inspected is a sediment sample from the bottom of an ice core, retrieved by drilling down into the ice sheet that covers the majority of Greenland. It’s pretty hard to actually reach all the way down to bedrock when taking samples due to the incredible pressure from the ice, explained Drew Christ, the study’s lead author and a postdoctoral fellow at the University of Vermont. There are only a few expeditions that have actually gotten sediment from the bottom of the glacier. “We have less of this [sediment] than moon rocks,” Christ said.
This particular sample yielded a lot of plant matter, some of which was visible to the naked eye. “It’s like if you went hiking, and got a bunch of twigs and forest floor stuff in the bottom of your boot and poured it out at the end of the day,” Christ said. “It’s kind of like that, but it’s been frozen for 1 million years.”
Christ and the team behind the study used isotope analyses of various elements that helped the researchers tease out the last time the samples were exposed to the sun and cosmic rays. The dating showed the plant matter is roughly 1 million years old.
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Before analysing this particular sample, Christ said, scientists had “circumstantial” evidence that the Greenland ice sheet had once melted away completely. But the discovery of these fossils definitively 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 climate bomb, with some estimates projecting that the sheet could raise sea levels by 6.1 metres if it fully melted. While it’s not slated to completely melt tomorrow, the ice sheet is now melting six times faster than it was in the 1980s. The changes put in motion by rising carbon dioxide will take centuries to play out as the climate adjusts to a new equilibrium. Knowing its history is crucial to understanding the ice sheet’s future.
“The Greenland ice sheet has disappeared in a climate system that didn’t have any human influence,” Christ explained. “Before humans added hundreds of parts per million of fossil fuels to the atmosphere, our climate was able to melt away the ice sheet. In the future as we continue to warm the planet at an uncontrollable rate, we could force the Greenland ice sheet past some threshold and melt it and raise sea levels.”
The dirt sample Christ and his team used to reach these conclusions has its own incredible backstory, including that it was almost lost to history. The sample was originally recovered from the first ice core of Greenland ever taken during a 1966 expedition to a military base called Camp Century. The actual purpose of the expedition was a top-secret James Bond-esque style mission called Project Iceworm (yes, really) to try and hide nuclear missiles under the ice near the Soviet Union (we’re not making this up). The scientific part of the expedition, while valid, was created mostly to give cover to this Cold War caper. Project Iceworm eventually failed, but at least we got this fascinating ice core out of this. (On the downside, though, climate change is melting out Camp Century, and could cause a toxic waste spill from leftover Cold War-era supplies and chemicals.)
Even though the dirt sample is itself remarkable, since the Camp Century attempt was the first ice core ever retrieved from Greenland, researchers were mostly interested in what the ice itself could tell them, and less invested in the dirt that came with the core.
“I was pulling out inch-long twigs out of this stuff. We could see with our bare eyes, like, this is definitely plant material,” Christ said. “Looking at this as someone who was born way after any of this went down, it’s like, how did [the scientists] not think to look more carefully? I think they had more of a priority to analyse the ice and then the soil didn’t get analysed.”
In what Christ describes as a “weird trick of history,” the soil was such a low-level priority for researchers that it eventually got lost when the expedition got home. The samples were shoved in the back of an army freezer at the University of Buffalo, then moved incognito with a bunch of other material to another freezer at a research facility in Denmark in the 1990s. It was only in 2017, as JP Steffensen, one of Christ’s mentors and an author on the paper, was doing inventory helping that facility prepare its freezer for a move, that the samples were rediscovered and able to be more fully analysed.
And even though researchers in the 1960s may not have known what they got when they dug up ancient dirt, Christ is grateful that their work provided him with one of the more exciting moments of his scientific career.
“The day that we found the fossils was one of those ‘eureka’ moments. I never thought that those days actually happen for scientists, but it did happen for me,” he said, describing how he first saw specks of plant material as his team was cleaning the sediment samples for analysis. “I was jumping around in the lab. It was so exciting.”