In 1966, scientists at Camp Century, a now deserted U.S. navy base within the Arctic, drilled deep into the Greenland ice sheet, extracting a cylinder of ice almost a mile lengthy together with 12 ft of the frozen sediment that sat beneath it.
“That was a pretty miraculous engineering feat that has been really hard to repeat,” mentioned Andrew Christ, a geoscientist who not too long ago accomplished a postdoctoral fellowship on the University of Vermont.
The pattern was the primary deep ice core that scientists had ever collected, and over the a long time that adopted, the ice turned the topic of intense scientific examine, offering vital clues in regards to the planet’s local weather historical past. The identical couldn’t be mentioned for the sediment, which was largely missed earlier than vanishing fully.
In 2017, the sediment was rediscovered in a freezer in Denmark. Now, a examine of the frozen samples is shedding new mild on Greenland’s previous and, maybe, offering an ominous warning for the long run. The findings, which were published in Science on Thursday, recommend that roughly 400,000 years in the past the Camp Century web site in northwestern Greenland was quickly ice-free. They add to accumulating proof that Greenland’s ice sheet has not been steady for the final 2.5 million years, as scientists as soon as assumed.
“The big take-home message from this is Greenland is vulnerable,” mentioned Paul Bierman, a geoscientist on the University of Vermont and an creator of the brand new examine. “The ice sheet has melted in the past, and therefore it can melt again.”
Dr. Bierman and an international team of collaborators first started finding out the sediment a number of years in the past, they usually rapidly made a stunning discovery. The prime layer of the pattern, the place they’d anticipated to discover little greater than a jumble of compressed rock, was stuffed with plant matter: twigs, leaves, tiny items of moss. The discovery, which the scientists published in 2021, urged that the world had not at all times been coated in ice.
“But the question we didn’t answer at that time was how old were these plants and the sediment from this landscape that didn’t have ice on it?” mentioned Dr. Christ, who can be an creator on the brand new evaluation. “This new examine in Science is telling us when that occurred, which was 400,000 years in the past.”
To arrive at that date, the scientists used a way often known as luminescence relationship. As minerals sit within the floor, they’re uncovered to environmental radiation and accumulate free electrons. Those electrons construct up over time, however publicity to daylight basically sweeps the electrons away, as a washer may take away the layers of dust that construct up on an merchandise of clothes over the course of a weekslong tenting journey, Dr. Christ mentioned.
By measuring the sign that the amassed electrons had been giving off, the researchers had been ready to calculate the final time that the highest layer of sediment had been uncovered to the solar — and thus, how way back the positioning had been ice-free.
(Tammy Rittenour, a geoscientist at Utah State University who led this a part of the examine, had to analyze the samples in the dead of night to keep away from “resetting” the electron clock.)
Once the scientists had estimated the approximate date of the thaw, they modeled numerous eventualities that might have resulted in an ice-free sampling web site 400,000 years in the past, calculating that the ice sheet would have to have melted sufficient to improve sea ranges by at the very least 4 and a half ft.
That “is a lot of sea-level rise,” Dr. Christ mentioned. “And that is something that we need to really consider as a worst-case scenario for future climate change.”
The temperature on the time was not a lot increased than it’s now, he famous, and the carbon dioxide ranges within the environment had been a lot decrease.
Still, many uncertainties stay about how the ice sheet will reply to continued warming, mentioned Elizabeth Thomas, a geologist on the University at Buffalo and an creator of the brand new examine. And it’s troublesome to extrapolate from that one sampling web site, which is “close to the edge of the ice sheet and is also not in a particularly sensitive part of the ice sheet,” she mentioned.
Samples from components of the ice sheet which can be identified to be much less steady could also be extra informative about what may occur because the planet warms, she mentioned.
“We have these amazing samples that were collected in the 1960s,” Dr. Thomas mentioned. “It’s so cool that we get to work on them.” Still, she added, it will be good to “go back in time and say, ‘Hey, first ice-core drilling team, can you please choose a different site?’”
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