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.
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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 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.
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.”
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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.
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.”