Greenland ice completely melted 7,000 years ago and could happen again

The findings, published in Nature Geoscience, show that this elevated region in the northwest part of the ice sheet is highly sensitive to even modest warming. The melting occurred during the Holocene, the relatively stable climate period that began 11,000 years ago and continues today.

"This is a time known for climate stability, when humans first began developing farming practices and taking steps toward civilization. So for natural, mild climate change of that era to have melted Prudhoe Dome and kept it retreated for potentially thousands of years, it may only be a matter of time before it begins peeling back again from today's human-induced climate change," says Jason Briner, PhD, professor and associate chair of the Department of Earth Sciences in the UB College of Arts and Sciences, who co-led GreenDrill with Joerg Schaefer PhD, research professor at Columbia University's Lamont-Doherty Earth Observatory.

Drilling Beneath Greenland's Ice for Clues

GreenDrill is a unique effort funded by the U.S. National Science Foundation that aims to drill through Greenland's ice and collect ancient material from below. Scientists actually have fewer samples of rock and soil from beneath Greenland than from the moon, yet these materials hold critical information. Their chemical signatures reveal when the surface was last exposed to sunlight, helping pinpoint past periods when the ice sheet disappeared.

For this study, researchers examined core samples taken from 1,669 feet below the surface during a weeks-long expedition at the summit of Prudhoe Dome in 2023.

To determine when the sediment was last exposed, the team used luminescence dating. This method measures energy stored in mineral grains. When buried, these grains trap electrons from natural radiation. Once exposed to light, they release that energy as a faint glow that scientists can measure.

The strength of this signal showed that the sediment last saw daylight between 6,000 and 8,200 years ago.

Evidence of Past Warming and Future Risk

"This means Prudhoe Dome melted sometime before this period, likely during the early Holocene, when temperatures were around 3 to 5 degrees Celsius warmer than they are today. Some projections indicate we could reach those levels of warming at Prudhoe Dome by the year 2100," says the study's lead author, Caleb Walcott-George, PhD, a former UB graduate student and now assistant professor at the University of Kentucky.

These findings carry important implications for rising sea levels. By identifying weak points along the edges of the Greenland Ice Sheet, scientists can better predict where melting may begin and which coastal regions could face the greatest risk.

"Rock and sediment from below the ice sheet tell us directly which of the ice sheet's margins are the most vulnerable, which is critical for accurate local sea level predictions. This new science field delivers this information via direct observations and is a game-changer in terms of predicting ice-melt," Schaefer says.

Life and Challenges on the Ice

GreenDrill established two drilling sites on Prudhoe Dome -- one at the summit and another closer to the edge, where the ice is thinner. (This study analyzed the sample collected from the summit.)

The sites were located near Camp Century, a Cold War-era base where U.S. Army researchers once drilled into the ice while attempting to conceal nuclear missiles. Instead, they recovered sediment that later helped scientists discover the ice sheet had been much smaller around 400,000 years ago.

During the spring 2023 expedition, the team lived in a network of yellow tents connected by flagged paths. Their daily work included collecting ice fragments brought up during drilling and clearing snow from the camp, while specialized drillers worked through hundreds of feet of ice.

The mission nearly failed near the end when a fracture appeared at the summit drilling site. A last-minute switch to a drill bit typically used for rock allowed the team to complete the final 390 feet and reach the underlying material just before their equipment was scheduled to be removed.

"It was like watching a Buffalo Bills game," Briner says. "Just stressful until the final minute."

Briner praised the collaboration between scientists, drillers, and support staff who made the effort possible. Team members included Nicolás Young, PhD, associate research professor at Lamont and GreenDrill co-principal investigator; Allie Balter-Kennedy, PhD, a former postdoc at Lamont and now assistant professor at Tufts University; and Nathan Brown, PhD, assistant professor at the University of Texas at Arlington.

"This project involved more complicated logistics than any I've been involved with in my career. So many moving parts, and so much talent among the scientists, drillers and support staff," Briner says.

Walcott-George, who played a major role in setting up the camps and based his dissertation on the work, described the experience as deeply humbling.

"When all you see is ice in all directions, to think of that ice being gone in the recent geological past and again in the future is just really humbling," he says.

What Comes Next for GreenDrill

Researchers say this is only the beginning. Additional studies are planned using other samples, including one taken closer to the edge of Prudhoe Dome, which may reveal the ice cap's most vulnerable areas. The cores may also contain traces of ancient plants, offering clues about Greenland's past environment.

"We have a treasure chest in our hands now that we can pick apart and explore," Briner says.

The team hopes to continue drilling and encourage similar efforts. While earlier projects such as Camp Century and the Greenland Ice Sheet Project 2 in the 1990s collected material beneath ice cores, GreenDrill is the first to intentionally target sub-ice material when choosing drilling locations.

"GreenDrill really demonstrated that, if you can logistically pull it off, there is the technology available to drill down to the bedrock and there's an analytical toolkit to then analyze it," Briner says. "We have very reliable, numerical models that can predict the rate of melting, but we also want real, observational data points that can tell us indisputably that X amount of warming in the past led to X amount of ice being gone."