Greenland’s Prudhoe Dome Was Ice-Free 7,100 Years Ago, Study Finds, Raising New Warnings on Future Melt

The wind was already howling over Prudhoe Dome when the drill finally hit rock.

For weeks in the spring of 2023, a small team of scientists and drillers lived in tents on a lonely rise of ice in northwestern Greenland, racing storms and an expanding fracture in the ice sheet itself. Their goal was not to collect more ice—polar research has done that for decades—but to punch through more than 1,600 feet of ice to the bedrock below.

On one of their last workable days, the steel bit broke through. Months later, in a darkened laboratory thousands of miles away, grains of sand from beneath that ice began to glow under a carefully controlled beam of light. The signal they gave off stunned the team.

The thick ice cap they had camped on—a dome that looks timeless and immovable—had not been there for most of the last ice age. In geologic terms, it is a recent arrival.

A dome that disappeared in a climate not much warmer than today

In a study published Jan. 5 in Nature Geoscience, researchers report that Prudhoe Dome—a roughly 500-meter-thick inland extension of the northwestern Greenland Ice Sheet—was completely ice-free about 7,100 years ago, plus or minus 1,100 years. The finding means a large, high-elevation sector of Greenland’s ice vanished during a naturally warm period in the early Holocene, when local summer temperatures were only about 3 to 5 degrees Celsius (5 to 9 degrees Fahrenheit) warmer than today.

Some climate models project similar levels of warming in that region later this century under high greenhouse gas emissions.

“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 today,” lead author Caleb Walcott-George, a glacial geologist now at the University of Kentucky, said in a statement. “Some projections indicate we could reach those levels of warming at Prudhoe Dome by the year 2100.”

Prudhoe Dome is not a coastal glacier spilling into the ocean. It is a broad inland ice cap, covering roughly 2,500 square kilometers of northwestern Greenland, thickly connected to the main ice sheet. Scientists chose it precisely because it was expected to be relatively stable. If such a site had melted away, it would signal extensive retreat of Greenland’s interior margin.

Inside GreenDrill: punching through 500 meters of ice

The work is part of GreenDrill, a five-year National Science Foundation–funded project led by researchers at the University at Buffalo and Columbia University’s Lamont-Doherty Earth Observatory, with partners including the University of Kentucky, the University of Wisconsin–Madison, the University of Copenhagen and NASA’s Goddard Space Flight Center.

Using the NSF Ice Drilling Program’s Agile Sub-Ice Geological Drill, the team bored through more than 500 meters of firn and ice at the summit of Prudhoe Dome in 2023, then recovered about three meters of sediment and more than four meters of underlying bedrock—7.4 meters of material that had not seen the open air in thousands of years.

How scientists dated the last time the bedrock saw sunlight

The key to the new age estimate lies in a technique known as luminescence dating. Mineral grains buried underground slowly accumulate trapped electrons from natural radioactivity. Sunlight effectively “zeros” that clock. When the grains are later stimulated in a laboratory, the stored energy is released as faint light, or luminescence, whose intensity reveals how long it has been since they were last exposed to the sun.

In this case, single grains of potassium feldspar from the sediment directly below the ice showed they were last sunlit about 7,100 years ago. That timing, combined with chemical measurements from the overlying ice and modeling of its flow and age, points to a complete melt-out of the ice cap’s summit around that time.

The ice core above the sediment tells a complementary story. Its isotopic signature shows only Holocene, or interglacial, ice—none from the last glacial period survives at the site. The absence of older ice suggests the dome did not simply thin; it disappeared and re-formed.

When Walcott-George first saw the luminescence ages, he was taken aback. In an interview with The Washington Post, he recalled thinking, “Oh boy.” The team had hoped to find evidence that Prudhoe Dome had been continuously covered since the last interglacial more than 100,000 years ago. Instead, the bedrock appears to have been ice-free within the last 8,200 years.

Why the early Holocene matters for future sea levels

The early Holocene, which began roughly 11,700 years ago, is often described as a relatively stable climate era that allowed agriculture and complex societies to flourish. But in parts of the Arctic, changes in Earth’s orbit and tilt produced a so-called Holocene Thermal Maximum, when summer temperatures were a few degrees warmer than 20th century averages.

“People think about the Holocene as a time known for climate stability,” said Jason Briner, a co-author of the study and a professor of geology at the University at Buffalo. “So for natural, mild climate change of that era to have melted Prudhoe Dome, it may only be a matter of time before it begins peeling back again from today’s human-induced climate change.”

The study does not claim that Prudhoe Dome will melt away by 2100. Ice sheets respond slowly; even under sustained warming, the full retreat of a sector can take centuries or longer. Instead, the authors say the new result shows that northwestern Greenland’s interior margin is more sensitive to relatively modest warming than many models have assumed.

That finding matters because Greenland is now the single largest contributor to global sea-level rise. Between 1992 and 2018, the ice sheet lost enough ice to raise sea level by around 11 millimeters, according to international assessments, and melt has accelerated since the 1990s.

If warming similar to the early Holocene were sustained again, ice losses on par with Prudhoe Dome’s past retreat could ultimately add several inches to a couple of feet to global sea level over long timescales, researchers said in interviews. One analysis cited by The Washington Post suggests that a comparable-scale retreat in northwestern Greenland alone could contribute roughly 7.5 inches to 2.4 feet.

Even small additional increases compound risks for low-lying coastal areas. Higher baseline sea levels allow storm surges to penetrate farther inland, worsen chronic “sunny day” flooding and increase saltwater intrusion into groundwater and agricultural land. Cities such as Miami, New York and Shanghai, along with many small island states and river deltas, are already grappling with the costs of upgrading defenses or relocating infrastructure.

Globally, the potential stakes are far larger. If the entire Greenland Ice Sheet were to melt—a process that would likely take many centuries to millennia—it holds enough ice to raise global mean sea level by about 7.3 meters (24 feet). The U.N. Intergovernmental Panel on Climate Change estimates that, under very high emissions scenarios, total sea-level rise from all sources by 2100 is likely to fall between roughly 0.63 and 1.01 meters, with Greenland providing a growing share.

Not a perfect analog—but a crucial calibration point

Scientists stress that the early Holocene is not a perfect blueprint for the future. Then, warming was driven by slow, predictable changes in Earth’s orbit, and Arctic summers were particularly affected. Today, the rapid rise in carbon dioxide from fossil fuel burning is producing more uniform, year-round warming worldwide.

For the ice, however, the details of the cause matter less than the temperature itself and the time over which it is applied.

“We’re trying to understand how X amount of climate change translates to X amount of ice volume change,” Briner said. “Having a concrete data point like Prudhoe Dome’s deglaciation at known temperature conditions helps us calibrate the models that project future sea-level rise.”

GreenDrill is designed to add more such data points. Over five years, the project aims to drill through northern Greenland’s ice at four key sites, each with a transect of boreholes from thick interior ice to exposed bedrock at the margin. By analyzing cosmogenic isotopes and luminescence signals in the recovered rock and sediment, the team hopes to reconstruct when different parts of the ice sheet retreated in past warm periods and which areas remained covered.

Rock and soil samples from beneath the ice are notoriously hard to obtain. The University at Buffalo notes that scientists have, so far, collected less material from beneath Greenland’s ice sheet than they have from the surface of the moon.

“Those rocks tell us directly which of the ice sheet’s margins are the most vulnerable,” said Joerg Schaefer, a co-leader of GreenDrill and a research professor at Lamont-Doherty. “That’s a game-changer in terms of predicting ice melt.”

A threshold within this century’s projected warming range

The Prudhoe Dome core is the first result from that effort. It shows that, in a climate only slightly warmer than today’s, a seemingly secure inland dome disappeared and then re-formed—and that the threshold for such a change is within the upper range of warming projected for this century.

For policymakers and the public, the study compresses geologic time into a human frame. Seven thousand years ago, when the bedrock under Prudhoe Dome last saw the sun, people were already farming in the Fertile Crescent and building some of the earliest known cities. On Greenland, however, a thick ice cap that looks eternal had yet to grow back.

Standing on that ice now, Walcott-George said, is “humbling.” The new evidence suggests that whether Prudhoe Dome and its neighbors endure is not just a matter of natural cycles, but of choices made far from Greenland’s windswept plateau—about how quickly, and how far, the world lets temperatures rise.