The hidden scars left in the landscape during the ice ages of thousands to millions of years ago have now been imagined with spectacular detail.
Using a technique called seismology of reflection, a team of scientists has imagined huge gouges cut by subglacial rivers, buried hundreds of meters below the bottom of the North Sea. These features, called “tunnel valleys,” can help us understand how icy landscapes change in response to warming weather.
“The origin of these channels has not been resolved for more than a century. This discovery will help us better understand the current retreat of today’s glaciers in Antarctica and Greenland,” said British geophysicist James Kirkham. Antarctic Survey.
“In the way we can leave footprints in the sand, glaciers leave their mark on the land where they flow. Our new cutting-edge data provides us with important de-icing markers.”
(James Kirkham)
At the top: A map reveals the location of the channels buried under the North Sea with an overlay showing the boundaries of the ice sheet 21,000 years ago.
Reflection seismology, as its name suggests, is based on vibrations that propagate underground to generate a density profile to significant depths. It is a bit like how we can use earthquakes to map the density of the interior of the entire planet, but directed and at smaller scales.
In this case, clusters of aerial weapons were towed over a section of the North Sea. As these sound waves propagated from these clusters, the hydrophones picked up the reflections as they bounced off structures of different densities under the seabed.
The researchers cleaned up and analyzed the high-resolution 3D data to build a layered map of the ancient landscape.
One of the valleys of the tunnel revealed by seismic data. (James Kirkham)
Even buried under a sediment of up to 300 meters (984 feet), this equipment is capable of capturing elements as small as 4 meters. This means that the data obtained are the most detailed to date on the tunnel valleys under the North Sea.
The data revealed 19 transverse channels between 300 and 3,000 meters wide, with undulating thalwegs. Based on the morphology of these channels, the researchers interpreted them as tunnel valleys formed by melting water escaping beneath the old ice sheets.
Due to the high level of detail, these channels reveal information about how the ice sheets interacted with the channels as they formed. Since the ice sheets at the Earth’s poles are currently melting in response to a warming climate, a better understanding of this process can help us figure out what will happen to Greenland and Antarctica in the future.
“While we’ve known the huge glacial channels of the North Sea for a long time, this is the first time we’ve imagined large-scale landforms inside it,” said geophysicist Kelly Hogan of the British Antarctic Survey.
A comparison of the tunnel valleys with current glacial features. (James Kirkham)
“These delicate features tell us about how water moved through the canals (under the ice) and even how the ice just stagnated and melted. It’s very difficult to see what’s going on under our big layers. of ice currently, particularly how water and sediment move affects the flow of ice and we know that these are important controls on the behavior of ice, ”Hogan added.
“As a result, the use of these ancient channels to understand how ice will respond to changing conditions in a warming climate is extremely relevant and timely.”
Future research, according to the team, should involve surface drilling to establish better chronological constraints in the tunnel valleys, as well as collect a wide range of seismic data.
This more granular detail will allow us to better model the hydrological systems of the old ice sheets and apply this knowledge to our current situation.
The research has been published in Geology.