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The hidden scars left on the landscape during the Ice Ages thousands to millions of years ago have now been imaged in spectacular detail.
Using a technique called reflection seismology, a team of scientists photographed huge gouges carved out by subglacial rivers, buried hundreds of meters below the North Sea floor. Called “tunnel valleys,” these features can help us understand how frozen landscapes change in response to global warming.
“The origin of these channels has not been elucidated for over a century. This discovery will help us better understand the ongoing retreat of current glaciers in Antarctica and Greenland,” said geophysicist James Kirkham of the British Antarctic. Survey.
“Just as we can leave footprints in the sand, glaciers leave a footprint on the land on which they sink. Our new cutting-edge data gives us important markers of deglaciation.
(James Kirkham)
Above: A map reveals the location of the channels buried under the North Sea with an overlay showing the limits of the ice cap 21,000 years ago.
Seismology by reflection, as its name suggests, relies on vibrations propagating underground to generate a density profile to great depths. It’s a bit like how we can use earthquakes to map the density of the interior of our entire planet, but focused and on a smaller scale.
In this case, clusters of air guns were towed over part of the North Sea. As these sound waves from these clusters propagated, the hydrophones picked up the reflections as they bounced off structures of different densities under the seabed.
The researchers then cleaned and analyzed the high-resolution 3D data to create a layered map of the ancient landscape.
One of the tunnel valleys revealed by seismic data. (James Kirkham)
Even buried under up to 300 meters (984 feet) of sediment, this equipment is capable of capturing features as small as 4 meters. This means that the data obtained is the most detailed to date on the tunnel valleys under the North Sea.
The data revealed 19 transverse canals between 300 and 3000 meters wide, with undulating troughs. Based on the morphology of these channels, the researchers interpreted them as tunnel valleys formed by meltwater flowing under ancient ice caps.
Due to the high level of detail, these channels reveal information about how the ice caps interacted with the channels as they formed. Since the ice caps found at the Earth’s poles today are melting in response to global warming, a better understanding of this process can help us understand what will happen to Greenland and Antarctica in the near future. ‘to come up.
“Although we have known about the enormous glacial channels of the North Sea for some time, this is the first time that we have imagined small-scale landforms there,” said geophysicist Kelly Hogan of the British Antarctic Survey.
A comparison of the tunnel valleys with current glacial characteristics. (James Kirkham)
“These delicate features tell us how the water moved in the channels (under the ice) and even how the ice simply stagnated and melted. It is very difficult to observe what is happening under our great ice caps today. “hui, particularly how water and sediment move, affects the flow of ice and we know these are important controls over the behavior of ice,” Hogan added.
“Accordingly, using these ancient channels to understand how the ice will react to changing conditions in a warming climate is extremely relevant and timely.”
Future research, the team said, should involve shallow drilling, to place better time constraints on the tunnel valleys, as well as collecting a wider band of seismic data.
This more granular detail will allow us to better model the hydrological systems of ancient ice caps and apply this knowledge to our current situation.
The research was published in Geology.
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