Deep valleys buried beneath the seabed of the North Sea record how the ancient ice sheets that covered the UK and Europe expelled water to prevent them from sinking.
A new study published this week surprised the research team, who found that the valleys took only hundreds of years to form as they transported large amounts of meltwater away from beneath the ice and out to sea .
This new understanding of when the great ice sheets melted 20,000 years ago has implications for how glaciers may respond to climate warming today. The study is published in the journal Quaternary Science Reviews.
Tunnel valleys are huge channels, sometimes up to 150 km long, 6 km wide and 500 m deep (each several times larger than Loch Ness), which drain water from beneath the layers of melting ice There are thousands buried beneath the seabed of the North Sea that record the melting of the ice sheets that have covered the UK and western Europe over the past two million years.
Lead author James Kirkham, of the British Antarctic Survey (BAS) and the University of Cambridge, says:
“This is an exciting discovery. We know that these spectacular valleys are carved during the death of ice sheets. Using a combination of state-of-the-art subsurface imaging techniques and a computer model, we have learned that tunnel valleys can erode rapidly under ice sheets that experience extreme heat.”
The team analyzed “jaw-wrenchingly detailed” seismic images that provide a 3D scan of the Earth’s buried layers. Informed by delicate tracks discovered in the valleys, the authors carried out a series of computer modeling experiments to simulate the development of the valley and test how quickly they formed when the last sheet of ice to cover the UK it melted at the end of the most recent ice age. 20,000 years ago.
The research suggests that this process is rapid on geological time scales, with melting ice forming giant tunnel valleys over hundreds of years, expelling water that might otherwise accelerate rates of ice loss.
Drainage of water from beneath ice sheets is traditionally thought to stabilize ice flow, a process that could prevent the collapse of modern ice sheets in a warming climate. But as they inspected the detailed seismic scans, the authors began to find telltale signatures of stagnant and rapid ice movement in the valleys, complicating the picture of how these rapidly forming channels might affect the ice sheet’s future behavior .
What is certain is that the surprisingly fast speed at which these tunnels form means that scientists must begin to consider their effects in models of how today’s ice sheets will evolve in the coming decades or centuries.
There are no modern analogues for this rapid process, but these ancient valleys, now buried hundreds of meters beneath the seafloor mud of the North Sea, record a mechanism of how ice sheets respond to extreme heat that is missing from models of current ice sheets. . These models do not currently resolve fine-scale water drainage processes, although they appear to be an important control on future rates of ice loss and ultimately sea-level rise.
James Kirkham continues: “The rate at which these giant channels can form means they are an important, if currently ignored, mechanism that can help stabilize ice sheets in a warming world. As climate change continues to drive the retreat of the present-day Greenland and Antarctic ice sheets at an ever-increasing rate, our results call for renewed investigation of how tunnel valleys may help stabilize contemporary ice losses and thereby , sea level rise, if they change. under the Earth’s ice sheets in the future.”
BAS co-author and geophysicist Dr Kelly Hogan says:
“We’ve been observing these huge meltwater channels from areas covered by ice sheets for more than a century, but we didn’t really understand how they formed. Our results show, for the first time, that the mechanism most important is probably the summer melt on the surface of the ice that is directed to the bed through cracks or chimney-like ducts and then flows under the pressure of the ice layer to cut the channels. Surface melting is already very important for the Greenland ice sheet today, and this process of transporting water through the system will only increase as our climate warms. The crucial question now is whether this “Extra” meltwater flow in the channels will cause our ice sheets to flow faster, or slower, to the sea.”
The work highlights a currently overlooked process that can be rapidly activated beneath melting ice sheets. Whether these channels will act to stabilize or destabilize Earth’s contemporary ice sheets in a warming world remains an important and open question.
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