In a groundbreaking discovery that links Britain’s icy past to the future of Earth’s polar regions, scientists have found the first clear evidence that massive icebergs once floated off the coast of Britain during the last ice age. The study, published in Nature Communications, reveals that colossal, flat-topped “tabular” icebergs the size of Cambridge drifted across the North Sea between 18,000 and 20,000 years ago.
This ancient drift has left behind distinctive, comb-like grooves etched into the seabed near Aberdeen, Scotland. These geological markings, preserved in sediment, were identified through seismic survey data initially gathered to locate offshore drilling platforms. The analysis was led by researchers from the British Antarctic Survey (BAS), who say the discovery not only sheds light on Britain’s glacial history, but also offers new insight into how the modern climate crisis could affect the Antarctic ice sheet.
Ancient Giants Beneath the Sea
“We’re talking about enormous flat-topped, or tabular, icebergs,” said Dr James Kirkham, lead author of the paper and a marine geophysicist at BAS. “Conservatively, they measured five to perhaps a few tens of kilometres in width – comparable to the area of a medium-sized UK city such as Cambridge or Norwich – and could be a couple of hundred metres thick.”
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These tabular icebergs would have broken off from ice shelves that once covered the British Isles during the last glacial maximum. As global temperatures began to rise, the ice sheet that once enveloped much of Britain and Ireland began retreating rapidly—by as much as 200 to 300 metres annually at its edges. The presence of broad, parallel grooves or “tramlines” in the Witch Ground basin (between Scotland and Norway) signals that these mammoth structures drifted across the seabed, their undersides scraping along the ocean floor.
While single grooves created by smaller iceberg keels have been documented before, these comb-like patterns are the first indication that tabular icebergs – the type more commonly associated today with Antarctica – once floated as far north as the North Sea.
Clues to Antarctica’s Future
Understanding how these icebergs formed, drifted, and ultimately disappeared could be key to predicting the future stability of the Antarctic ice sheet.
In Antarctica today, tabular icebergs are calved from ice shelves – the floating extensions of glaciers that act as buttresses, holding back vast quantities of inland ice. When these shelves collapse, as seen with the dramatic disintegration of Larsen B ice shelf in 2002, the glaciers behind them can surge forward unchecked, contributing to sea level rise.
According to co-author Dr Kelly Hogan, also a marine geophysicist at BAS, “We can actually document the catastrophic collapse of these ice shelves at the end of the last ice age using our data.”
The study notes a striking shift in the geological record: from multi-keel grooves left by tabular icebergs (a sign of intact ice shelves) to single, narrower grooves made by smaller icebergs after the shelves disintegrated.
This transition mirrors what was seen in the rapid breakup of Larsen B. In 2002, a series of warm Antarctic summers led to surface meltwater pooling on the shelf. The water seeped into cracks, splintering the structure into thousands of smaller icebergs in a matter of weeks. After the collapse, glaciers previously restrained by Larsen B accelerated their flow into the sea.
The North Sea: A Mirror for Modern Change?
According to Dr Rob Larter, another co-author of the paper, what happened in the North Sea millennia ago may hold the key to understanding ice shelf dynamics today.
“There’s this transition from having ice shelves and producing multi-keel icebergs, and then suddenly they’re gone,” said Larter. “The question is a chicken and egg one: Did the ice shelves just disappear because of changes already in progress, or did their disappearance trigger further retreat?”
This is a critical question for today’s climate scientists. The Antarctic and Greenland ice sheets are increasingly vulnerable to warming seas and atmospheric temperatures. Ice shelves that collapse due to such warming may accelerate ice loss inland, pushing sea levels higher at a faster rate.
The new findings suggest that similar collapses happened in the geological past, under conditions not unlike those beginning to unfold today.
Geological Record and Climate Science
The seismic data used in the study came from the Witch Ground basin, where energy companies conducted surveys to identify sites for oil and gas exploration. The researchers re-analysed this data, looking not for hydrocarbon deposits, but for geological signs of past glaciation. What they found were stunningly preserved iceberg ploughmarks, some stretching across many kilometres of seafloor.
These grooves, according to the study, were likely formed as tabular icebergs – calved from a then-retreating British-Irish ice sheet – dragged their massive undersides along the shallow seabed as they drifted toward the open ocean.
As the ice sheet melted, possibly due to warmer air and sea temperatures, the floating ice shelves fringing it would have weakened and disintegrated. The transition in seafloor markings from comb-like to single grooves appears to document the sequence of this collapse in real time.
“The seabed here is like a tape recorder,” said Dr Kirkham. “It holds the signature of a dynamic and changing climate.”
Future Implications
Although this discovery relates to events that occurred 18,000 to 20,000 years ago, the implications for today are pressing.
The British Antarctic Survey team hopes their findings will contribute to more accurate modelling of how ice shelves influence glacier stability, and how their collapse could rapidly change Earth’s coastlines. More precise dating of the seafloor sediments is planned to better understand the timing and speed of these ancient events.
The researchers emphasise that while the UK is no longer home to icebergs, the patterns left behind on the seabed offer a rare and valuable window into ice-ocean dynamics during a time of significant climate change.
“If we want to understand how Antarctica might respond to warming in the future,” said Dr Hogan, “we have to look at how these systems responded in the past.”
In the end, the deep scars carved into the North Sea floor are more than remnants of ancient ice—they’re warnings etched into stone, reminders of how quickly Earth’s great ice structures can unravel in the face of rising temperatures.
