Earlier this week, we reported on a story about how methane could seep and burst from under the Arctic seafloor as the Arctic ice sheet melts. Scientists used sediment core samples and radiometric dating to understand some naturally occurring warm periods in the Earth’s past. Today, scientists have done something similar to understand the dangers for Greenland’s ice sheet. And the results are not any better for us.

This story starts, though, back in the 1960s. The Cold War was quietly raging, with both sides playing terrible games to one-up the other with “my arsenal is bigger than your arsenal” and then hiding how that might be true. Under the guise of scientific research, the U.S. Army built Camp Century in Greenland. Ostensibly a site to test construction techniques under Arctic conditions, in particular sub-glacial construction. However, documents declassified in the 1990s showed that the actual intent was to house a large number of missiles aimed at the Soviet Union. That never happened for a variety of reasons, not the least of which was the lack of desire to get permission from the Danish government.

Appearances must be kept up, though, so ice core samples were taken at the site. One of those cores was 1400-meters deep and included 4.5 meters of the ground below all the ice. Then the soil was put in a freezer and basically lost for decades. Until now.

The soil samples were rediscovered in 2017, and numerous scientists around the world have taken the opportunity to study and analyze the contents. In research published this month in the Proceedings of the National Academy of Sciences, a team led by Andrew Christ present their findings. And what a find it was. The soil samples contained not sand and rock but fossilized twigs and leaves. Sometime in the past million years, Greenland’s ice sheet was gone, and Greenland really was, well, green.

The scientists involved in the research used a variety of modern techniques to understand these fossils. Carbon dating won’t work due to the relatively short half-life of radioactive carbon, so instead, isotope ratios of aluminum and beryllium were measured. These isotopes only form in quartz when the mineral is exposed to cosmic rays, and over a kilometer of ice ensures that doesn’t happen. So then we know when the minerals were exposed.

Other techniques included oxygen isotope ratio measurements, studies of luminescence, and analyzing the actual arrangement of the layers. Everything came back to the upper part of the sediment having been reburied around one million years ago. That upper sediment matches subglacial bedrock found in central Greenland, suggesting the history is similar across the ice sheet. And there were two distinct periods of warmer, ice-free, vegetated ground.

The concern here is that the processes that caused Greenland’s ice sheet to melt were purely natural and not anthropogenic as we’re currently experiencing. That means that this ice sheet isn’t as durable as we thought previously, which is pretty darn scary. The loss of the ice sheet due to climate change means all that newly liquid water enters our oceans, and that would, in turn, lead to a global sea-level rise of six meters. Pick a coastal city. Any coastal city. And it’s in trouble.

This problem is one we need to solve, as a global society, sooner rather than later. We’ll continue to update you all about any progress made as we learn of it.

More Information

EarthSky article

“A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century,” Andrew J. Christ et al., 2021 March 30, PNAS