What’s at the Bottom of Greenland’s Ice Sheet?

As the world's largest island, Greenland is home to one of the largest ice sheets after Antarctica. If its two-mile (3 kilometers) ice sheets melt completely, it would raise global sea level by 23 feet (7 meters), drowning portions of coastal regions underwater.

GreenDrill Project

There has been a growing concern to study Greenland's bedrock to understand the instability of the overlying ice in the past. Many scientists have attempted to explore the ice sheet by drilling into it to extract the environmental history preserved there. However, very few drilling projects have successfully penetrated the ice and the bedrock underneath.

To investigate one of the planet's unexplored frontiers, the National Science Foundation has funded a multi-million dollar collaborative research project called GreenDrill. It was led by researchers at the Pennsylvania State University and is scheduled to last five years.

The team worked with the US Ice Drilling Program to develop and execute an ambitious drill plan to drill through the Greenland Ice Sheet in strategically selected four locations around the top of northern Greenland. At each location, the experts collected a transect of three sections of bedrock stretching from off the ice's edge toward the interior.

To determine whether ice covered a particular location, the team looked for radioactive isotopes produced in a rock when exposed to air and cosmic rays.

What Lies Beneath

After six weeks of drilling through 557 yards (509 meters) of ice at Prudhoe Dome, NW Greenland, the researchers finally reached the bed in June 2023. The team could use the latest equipment to pull up 8 yards (7.4 meters) of frozen sediment and rock.

Preliminary analysis of the rock and sediments from beneath Greenland's thick ice suggests that, at some time in the past three million years, the material in the core was once exposed to air. It was recommended that the sediment portion contains high levels of beryllium-10, one of the key isotopes used in studying bedrock exposure.

The amount of beryllium-10 suggests almost 40,000 years of exposure to air. This exposure could have been a continuous event or multiple episodes spread over the past few million years. This means that the ice on top had melted away temporarily. The experts' calculations suggest that if the Prudhoe Dome was ice-free, then Greenland must have melted enough to contribute between 7 inches (19 centimeters) and (29 inches) 73 centimeters of global sea-level rise.

The findings are preliminary since the sediments could have been disturbed or moved around, and the measurements must be confirmed. Still, the smaller amounts of beryllium-10 in the rock beneath the sediment support the idea that it was all exposed to air.

The rock and sediment cores beneath Greenland's ice also include the bottom of the GISP2 core, which was extracted from central Greenland in 1993. It shows signs that the site was ice-free several times in the past 2.6 million years, roughly the same time suggested by the Prudhoe Dome core. Additionally, a core drilled in 1966 in northwest Greenland offers that the site was ice-free for an unknown amount of time, around 400,000 years ago.