April 20, 2024

Ancient Soil Discovered in Ice-Free Greenland’s Freezer Reveals Hints of Future Risks : ScienceAlert

A mile-thick ice sheet in Greenland disappeared about 416,000 years ago during a period of moderate natural warming, causing global sea level rise to levels that would be catastrophic for coastal regions today, a study said Thursday.

The findings overturn the long-held view that the world’s largest island has been an impregnable ice fortress for the past 2.5 million years and instead show that it will be much more vulnerable to human-induced climate change than previously thought.

“If we want to understand the future, we need to understand the past,” University of Vermont scientist Paul Bierman, who led the paper published in Sciencesaid AFP.

The research relied on an ice core extracted 4,560 feet (1,390 meters) below the surface of Northwest Greenland by scientists at Camp Century, a secret US military base that operated in the 1960s.

This 12 foot long tube of soil and rock was lost in a freezer only to be rediscovered in 2017.

Scientists were surprised to discover that there was not just sediment but leaves and moss – irrefutable evidence of an ice-free landscape, perhaps covered by an ancient forest once roamed by woolly mammoths.

Green Greenland

Although researchers have had access to the precious sample for years, Bierman said in some ways it was “providential,” because the cutting-edge techniques used so far were recent.

These include “luminescence dating”, which has allowed scientists to determine when sediments buried beneath the Earth’s surface were last exposed to light.

Camp Century sub-ice sample from the lower part of the core. (Andrew Christ/University of Vermont)

“As sediment is deposited below the surface, background radiation from the soil fills in the small holes or imperfections in minerals such as quartz or feldspar, and builds up what we call a luminescence signal over time,” co-author Drew Christ told AFP.

In a dark room, the scientists took strips inside the ice core and exposed them to blue-green or infrared light, releasing trapped electrons that form a kind of ancient clock that shows the last time they were exposed to sunlight, destroying the luminescence signal.

“And the only way to do that at Camp Century is to remove a mile of ice,” said Tammy Rittenour, co-author of the study at Utah State University. “Plus, to have plants, you have to have light.”

Comparison of ice core samples.
Camp Century sub-ice samples comparing the original core before it was cut to the core taken in 2020. (Andrew Christ/University of Vermont)

Luminescence dating provided the endpoint of the ice-free period, while another technique provided the starting point.

Within the quartz from the Camp Century core, rare forms – called isotopes – of the elements beryllium and aluminum increase when the earth is exposed to the sky and cosmic rays.

By looking at the ratio of the normal forms of these elements to the rare isotopes, the scientists could derive a window into how long the rocks were at the surface versus how long they were buried.

They found that the sediment had been exposed for less than 14,000 years, which means that this is how long the area has been ice-free.

Coastal cities at risk

The core of Camp Century was built only 800 miles from the North Pole, and the study showed that the entire region would be covered with vegetation.

This happened in a time of natural warming called an interglacial period, when temperatures were similar to today, about 1.8-2.7 degrees Fahrenheit (1-1.5C) warmer than the pre-industrial era.

The team’s modeling showed that the melting of ice at that time would have resulted in between five and twenty feet of sea level rise.

This suggests that all coastal regions around the world, which contain many global population centers, will be at risk of inundation in the coming centuries.

Joseph MacGregor, a climate scientist at NASA who was not involved in the study, noted that the interglacial period that warmed Greenland during this period lasted thousands of years, much longer than humans have so far experienced.

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But even so, “we are much higher than the amount of greenhouse gas pushing back there,” he said.

Levels of heat-trapping carbon dioxide are currently 420 parts per million (ppm) versus 280 ppm during Greenland’s ice-free period, and this will remain in the skies for thousands of years.

“We’re doing a huge experiment on the Earth’s atmosphere, and we don’t know the results of that experiment,” Bierman said. “I don’t take it as ‘Oh my god, the sky is falling,’ I take it because we have to get it together.”

© Agence France-Presse

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