Greenland Ice Cap Vanished Just 7,000 Years Ago

Adapted from a press release from the University at Buffalo

• Sediment drilled from beneath 1,700 feet of ice was last exposed to daylight 6,000 to 8,200 years ago.
• Findings suggest this part of Greenland is highly sensitive to modest warming, with implications for future retreat.
• Sub-ice samples like these help identify where melting may start and improve local sea-level risk estimates.

The first study from GreenDrill—an ambitious project to recover rock samples buried thousands of feet beneath the Greenland Ice Sheet—finds that Greenland’s Prudhoe Dome ice cap had fully melted around 7,000 years ago, much more recently than previously thought. This research, co-led by Columbia University and the University at Buffalo, is intended to assess how sensitive Greenland’s ice is to climate change.

Published in Nature Geoscience, the findings suggest that the Prudhoe Dome, an ice dome in northwestern Greenland about 1,700 feet thick covering 965 square miles, is highly sensitive to the relatively mild temperatures of the Holocene, the interglacial period that began 11,000 years ago and continues today.

“The Holocene is a time known for climate stability, when humans first began developing farming practices and taking steps toward civilization,” says University at Buffalo’s Jason Briner, who co-leads the GreenDrill project. “If natural, mild climate change of that era 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,”

Joerg Schaefer, Lamont research professor at the Lamont-Doherty Earth Observatory, part of the Columbia Climate School, is GreenDrill’s lead principal investigator. He says the new study shows just how sensitive parts of the Greenland Ice Sheet are to a level of warming that is well within the range of what climate models project for the coming decades.

“These early GreenDrill results are first direct observations of the Greenland Ice Sheet’s response to warming,” Schaefer says.

Co-authors on the paper include Nicolás Young, Lamont associate research professor and GreenDrill’s co-principal investigator, and Allie Balter-Kennedy, a former Lamont-Doherty postdoctoral scientist now at Tufts University.

GreenDrill is a first-of-its-kind endeavor funded by the U.S. National Science Foundation to drill down into the Greenland Ice Sheet and retrieve the frozen, ancient bedrock and sediment underneath. The scientific community has less rock and sediment material from beneath Greenland’s ice than it does from the moon, yet these new samples prove to be invaluable. Chemical signatures can tell us when the material was last exposed to open sky, pinpointing when the ice sheet has melted in the past.

This first GreenDrill study analyzes core samples pulled from 1,669 feet below the surface during the team’s weeks-long encampment at the summit of Prudhoe Dome in 2023.

They used a technique called luminescence dating on the sediment. When sediment is buried, electrons become trapped inside tiny mineral grains and remain there until the sediment is exposed to light again, producing a measurable glow. The intensity of that glow revealed that the Prudhoe Dome sediment was last exposed to daylight sometime between 6,000 and 8,200 years ago.

“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,” says the study’s lead author, Caleb Walcott-George, assistant professor at the University of Kentucky. “Some projections indicate we could reach those levels of warming at Prudhoe Dome by the year 2100.”

The results also have large implications for sea level rise. Analyzing vulnerable areas along the edge of the ice sheet, such as Prudhoe Dome, helps scientists identify where melting will occur first and which coastal communities face the most immediate 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,” Schaefer says. “This emerging field delivers that information through direct observations and is a game-changer in terms of predicting ice melt.”

On the ice

GreenDrill set up two drill sites on Prudhoe Dome—one on the summit and another near the edge where the ice is much thinner. (This study analyzed the sample collected from the summit.)

These sites, where Schaefer, Briner, Walcott-George, Balter-Kennedy and their colleagues spent time in the spring of 2023, were a collection of yellow tents and pathways marked by red, black and green flags. Days consisted of collecting ice chips pushed up by drilling fluid and shoveling out the camp from windblown snow, while ice drillers from the NSF Ice Drilling Program worked on pushing through hundreds of feet of ice.

There was plenty of drama, too—a fracture in the ice at the summit site nearly doomed the project at its final stage. A last-minute solution, using a drill bit normally reserved for rocks, allowed them to finish drilling the last 390 feet of ice and sample the bed just before planes arrived to remove their equipment. Briner credits the teamwork and camaraderie of the scientists and drillers on the ice, as well as the support crew behind the scenes handling logistics.

“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 set up the camps with Lamont-Doherty’s Young, and ultimately based his dissertation on the project, called his time on the ice “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.

A promising future

The GreenDrill team says this is the first of many studies they expect to produce. The other core drilled from near the edge of Prudhoe Dome promises to give insight into the ice cap’s most vulnerable point. Traces of plants in the samples could also shed light on Greenland’s ancient environment. Briner calls it a “treasure chest” of samples that the team can now pick apart and explore.

“We have the samples, the tools and the scientists to push the limits and improve our physical understanding of the ice sheet and how it might respond to warming in the decades to come,” Schaefer says.