The Mile-Thick Ice Shelf That Held Back Three Ice Sheets

Scientists have uncovered the remains of a Mile-Thick Ice Shelf that once propped up three of the largest ice sheets in the Northern Hemisphere, and they say its sudden disappearance carries a warning for the future of Antarctica.

About twenty thousand years ago, the floating fortress of ice sat in Baffin Bay, west of Greenland, stretched 1.6 kilometers thick, and pressed against the margins of the Greenland Ice Sheet to the east, the Innuitian sheet to the north and the Laurentide sheet to the west. When it finally broke apart, it helped release land ice that pushed seas higher and helped draw the modern coastlines we live with today, according to a report on the findings published by Phys.org.

Nobody was looking for it. Researchers from the University of Florida, the University of North Carolina Wilmington, Columbia University and several partner institutions set out on a five-week research cruise across the bay hoping to collect sediment cores that would explain what destabilized the Greenland ice at the end of the last ice age. Instead, sonar mapping of the seafloor revealed unmistakable scars of an enormous shelf that had once filled the entire bay. The Mile-Thick Ice Shelf discovery came as a complete surprise to everyone on board.

"The thing that really surprised us was this evidence was over a mile deep into the ocean," said Robert Hatfield, an associate professor of geology at the University of Florida and a co-author of the study. "That is at least half a mile thicker than any previously known ice shelf in the Northern Hemisphere." The team had expected to study a collapsing ice sheet margin, he added, not to stumble on a structure on this scale.

A Floating Fortress Nobody Expected

Floating shelves work like buttresses for the far larger masses of ice sitting on land. "These ice sheets are like a Gothic cathedral," Hatfield said. "You have this big, tall cathedral of ice and these flying buttresses of floating ice shelves that support them. They help stop the ice on land from flowing into the ocean and contributing to sea level rise."

That mechanism is exactly what worries researchers watching the frozen south today. "One of the biggest concerns in Antarctica right now is how fast that ice on land will flow into the ocean when we lose that buttressing effect," Hatfield said.

Gone in Centuries, Not Millennia

Sediment cores taken from across the bay suggest the shelf, which was roughly the size of some of the most important Antarctic shelves today, vanished over a span of roughly five hundred to a thousand years. Once it was gone, the big glaciers on land sped up, flowed faster into the sea and helped lift ocean levels. "That is one of the scary takeaways we did not expect, that an ice shelf the scale of the ones in Antarctica could completely disappear in a matter of centuries," Hatfield said.

The ancient breakup was fast by geological standards and slow by human ones, which is precisely why it matters as a reference point. It shows that a shelf on the scale of today's Antarctic giants can come undone far quicker than older models assumed.

Why It Matters for Antarctica

The findings, published in the journal Nature Geoscience, give modelers fresh evidence about how shelves behaved when the planet warmed out of the last ice age. That could sharpen predictions of how quickly Antarctic glaciers might melt and raise seas in a warming world. Coastal readers have the most at stake: even a fraction of the ancient sea-level rise replayed today would redraw flood maps. The pressure is already visible in current climate data, with the UN warning that a coming El Nino could go off the charts.

There is important nuance here. The ancient collapse is not a forecast for tomorrow. The Baffin shelf took centuries to disappear, and Antarctica's geology and climate differ from the Arctic's. What the study offers is a proof of scale: shelves this big can vanish far faster than old assumptions allowed, which is why researchers want the new data folded into sea-level models.

The mile-scale discovery also lands at a moment when global climate efforts are faltering. The world already missed its climate target, with overshoot now seen as certain, and the world's nature plan recently earned a failing grade in Armenia. For a generation that will watch coastlines shift within its lifetime, the study is both a history lesson and a heads-up. The ice left clues on the seafloor about what happened the last time a giant shelf let go, and scientists are reading them as fast as they can.