Ice age relics discovered beneath the North Sea

Scientists have created spectacular maps of drowned worlds beneath the North Sea, revealing enormous channels forged during the last ice age.

“In the way that we can leave footprints in the sand, glaciers leave an imprint on the land upon which they flow,” explains James Kirkham, a geophysicist from the British Antarctic Survey (BAS) and the University of Cambridge.

Kirkham is the lead author on the new study, published in Geology, which could tell us how ice sheets respond to a warming world.

Read more: Glaciers are shrinking faster every year

For much of the last 2.5 million years, the Earth oscillated between glacial and interglacial periods, with ice sheets alternately advancing and retreating. The last frozen period peaked between 26,500 and 20,000 years ago, with much of North America, northern Europe and Asia covered in ice sheets.

While this frozen world has melted away, the ice left tell-tale marks on the landscape.

A map of the north sea showing the distribution of buried channels
A map of the North Sea showing the distribution of buried channels (tunnel valleys) that have been previously mapped using 3D seismic reflection technology. The limit of the last ice sheet to cover the UK (around 21,000 years ago) is overlain. Credit: BAS/Kirkham et al 2021

A team of scientists has mapped “tunnel valleys” forged by this ancient ice. These valleys, or channels, are the remnants of massive river systems that wound beneath ice sheets, fed by meltwater as the temperature rose and the ice disappeared.

Image of a tunnel valley within sediment
Image of a tunnel valley, shown in context of the high-resolution 3D seismic data which can be ‘sliced’ both vertically and horizontally to reveal buried landscapes. Credit: BAS/Kirkham et al 2021

Each channel is carved into the rock hundreds of metres below the sea floor of the North Sea. The team had to use 3D seismic reflection technology – similar to an MRI (magnetic resonance imaging) – to find and map the features in unprecedented detail.

“Although we have known about the huge glacial channels in the North Sea for some time, this is the first time we have imaged fine-scale landforms within them,” says Kelly Hogan, co-author of the study and a geophysicist at BAS.

“These delicate features tell us about how water moved through the channels beneath the ice and even how ice simply stagnated and melted away.”

Read more: Mapping the undersea landscape of the Great Barrier Reef

The tech used by the research team harnesses sound waves. Pulses are sent down through the water, bounce off the rock of the sea bed, and return. These signals can then generate a 3D representation of the features deep below the Earth’s surface, just like how MRI can scan structures within the body.

The resulting images are accurate to within a few metres, even for features buried under hundreds of metres of sediment.

Showing mapped landforms on left, photos of modern landforms on right
Comparison of the buried landforms (glacial footprints) with examples of modern landforms exposed at the margins of retreating glaciers in Svalbard and Iceland. Credit: BAS/Kirkham et al 2021

The exceptionally detailed maps of these ancient channels will be compared to the features left behind by modern glaciers. This will give the research team clues into how these ancient ice sheets behaved as they retreated – and therefore how modern ice sheets, like the Antarctic and Greenland ice sheets, may behave in a changing climate.

“It is very difficult to observe what goes on underneath our large ice sheets today, particularly how moving water and sediment is affecting ice flow – and we know that these are important controls on ice behaviour,” Hogan explains.

“As a result, using these ancient channels to understand how ice will respond to changing conditions in a warming climate is extremely relevant and timely.”

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