Evidence of massive ancient icebergs found off the coast of Britain

When most people picture drifting tabular icebergs – flat-topped behemoths the size of city blocks – they imagine the frigid waters fringing Antarctica.

Yet a new study shows that, at the height of the last ice age, leviathan icebergs cruised less than 90 miles from Britain’s east coast.

Their deep underbellies ploughed into soft marine sediments, leaving parallel gouges that have been preserved for nearly 20,000 years beneath today’s North Sea seafloor.

Seafloor comb-marks tell the tale

Researchers made the discovery while analyzing seismic-reflection data collected for oil-and-gas exploration in the Witch Ground Basin, a trough between Scotland and Norway.

Scientists found comb-like furrows, hundreds of meters wide and stretching for kilometers, instead of expected fossil fuel structures. The team realized vast, flat-tipped icebergs carved these features as tides and currents pushed them southward along the sea floor.

“We’re talking about enormous flat-topped, or ‘tabular,’ icebergs,” explained lead author James Kirkham of the British Antarctic Survey (BAS).

“Conservatively, they measured five to perhaps a few tens of kilometers in width – comparable to the area of a medium-sized UK city such as Cambridge or Norwich – and could be a couple of hundred meters thick.”

Ice shelves surrounded Britain

Such colossal bergs calve today from Antarctic ice shelves, the floating extensions of land-based glaciers. If tabular icebergs roamed the ancient North Sea, ice shelves must have once bordered the British and Irish Ice Sheet.

This conclusion reshapes our picture of the region during the Last Glacial Maximum, when ice covered much of the British Isles but was beginning to retreat as the climate warmed between 20,000 and 18,000 years ago.

Ice shelves play a crucial role in stabilizing their parent ice sheets by buttressing inland glaciers. When shelves thin or break up, glacier flow tends to accelerate, raising global sea level.

The presence – and subsequent collapse – of shelves in the North Sea offers a natural experiment that may help scientists predict Antarctica’s future under today’s warming trends.

Iceberg size shifted suddenly

The seismic record captures not just the heyday of giant bergs but also their disappearance.

“Around 18,000 years ago we detect a shift in the type of iceberg plough-mark recorded in seafloor sediments, from giant tabular bergs – produced by the normal calving lifecycle of ice shelves – to much more numerous and smaller icebergs as the ice shelves disintegrated,” said co-author Kelly Hogan, a scientist at the British Antarctic Survey.

Glaciologists saw a similar event in 2002, when Antarctica’s Larsen B Ice Shelf shattered after rapid surface melting.

Glaciers once buttressed by Larsen B quickly sped up, dumping extra ice into the ocean. The Witch Ground record suggests the British and Irish Ice Sheet may have experienced a large-scale analogue. It likely retreated 200 – 300 meters per year at its edges once its shelves vanished.

What triggered the collapse?

One key question is whether ancient British ice shelf breakup triggered rapid retreat or simply mirrored already accelerating ice loss. Better dating of seafloor deposits could reveal which came first.

“If we observe a similar transition from large tabular icebergs to smaller icebergs in Antarctica today, it could indicate the continent is about to experience significant and rapid mass loss,” said BAS co-author Rob Larter.

Lessons for a warming world

Greenland and parts of West Antarctica are currently losing ice at rising rates, and many Antarctic ice shelves are thinning. Understanding how ancient shelves collapsed, and how quickly adjacent glaciers responded, can inform projections of future sea-level rise.

“Understanding how regime shifts in iceberg calving behavior affect ice shelf stability remains a challenge for numerical models. This is an important question as we consider the fate of the ice shelves that currently buttress the Antarctic Ice Sheet and hold back the bulk of its potential upstream sea-level contribution,” wrote the researchers.

The North Sea plough-marks remind researchers that ice-shelf dynamics are not unique to polar realms; they can shape mid-latitude marine basins when climate and geography align.

For now, the hidden grooves beneath North Sea sediments stand as silent testimony to a long-lost icy era. Britain’s horizon was once patrolled by icebergs the size of cities – a legacy that informs future coastal challenges.

The study is published in the journal Nature Communications.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–