Greenland’s Prudhoe Dome ice cap was completely gone only 7,000 years ago, first GreenDrill study finds

(Press-News.org) BUFFALO, N.Y. — The first study from GreenDrill — a project co-led by the University at Buffalo to collect rocks and sediment buried beneath the Greenland Ice Sheet — has found that the Prudhoe Dome ice cap was completely gone approximately 7,000 years ago, much more recently than previously known.

Published today (Jan. 5) in Nature Geoscience, the findings suggest that this high point on the northwest section of the ice sheet is highly sensitive to the relatively mild temperatures of the Holocene, the interglacial 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.

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 soil material from below Greenland’s ice than it does from the moon, yet it is 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 then used a technique called luminescence dating on the sediment. When sediment is buried, electrons can become trapped inside its tiny mineral grains due to natural radiation and remain there until the sediment is exposed to light again, at which point they produce 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. 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. 

The results also have large implications for sea level rise. Analyzing vulnerable areas along the edge of the ice sheet like Prudhoe Dome can give scientists an idea of where the ice sheet will melt first and, thus, which coastal communities are at 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. This new science field delivers this information via direct observations and is a game-changer in terms of predicting ice-melt,” Schaefer says.

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.)

Their sites were not far from the Cold War-era base Camp Century, where U.S. Army scientists attempted to drill into the ice to hide nuclear missiles but instead serendipitously pulled up the sediment underneath. That sediment was stored at UB for many years and would later help scientists learn the ice sheet was much smaller approximately 400,000 years ago.

The GreenDrill sites where Briner, Schaefer and Walcott-George and colleagues all spent time in the spring of 2023 were a collection of yellow tents and pathways marked by red, black and green flags. Their 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.

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

He credits the teamwork and camaraderie of the scientists and drillers on the ice, as well as the support crew behind the scenes handling logistics. Collaborators on the project 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 took a leading role setting up the camps 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.

Project’s 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. 

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

 They also hope to possibly drill again and inspire other groups to do the same. The Camp Century team, as well as the Greenland Ice Sheet Project 2 in the 1990s, collected material below their ice cores, but GreenDrill is the first time that researchers selected drill sites based on collecting material from below the ice sheet. 

“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.”

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