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Hidden valleys buried beneath the ocean floor in the North Sea were carved out rapidly during the “deaths” of an ancient ice sheet towards the end of the last ice age around 20,000 years ago, according to a new study. Surprising underground structures could provide clues to how modern ice sheets will react to rapid warming caused by climate changesay the researchers.
The buried structures, known as tunnel valleys, are vast underground ravines carved into the ancient sea floor by meltwater draining into channels beneath the ice sheets. The sheer weight of the rapidly melting ice sheets forced the flowing water to cut deep canyons on the sea floor. These channels have since been covered by hundreds of meters of sediment accumulation. Tunnel valleys can be up to 93 miles (150 kilometers) long, 3.7 miles (6 kilometers) wide, and 1,640 feet (500 meters) deep; researchers statement (opens in new tab).
In 2021, researchers from the British Antarctic Survey (BAS) mapped the network of tunnel valleys in the North Sea, once covered by a massive ice sheet that also covered parts of mainland Europe and the UK during the last ice age, between 126,000 with 12,000 years ago. Using 3D seismic reflection technology, which emits sound waves to detect structures beneath the sea floor, the team uncovered thousands of buried canyons, some dating back around 2 million years. These results were published in September 2021 in the journal Geology (opens in new tab).
In the new study, which was published Oct. 5 in the journal Quaternary Science Reviews (opens in new tab), the same researchers used the canyon maps, combined with computer models, to determine exactly how some of the tunnel valleys were born. The results showed that the tunnels were likely dug over a period of a few centuries, which is much faster than the team had originally predicted.
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“This is an exciting discovery. We know that these spectacular valleys are carved during the death throes of the ice sheets,” lead study author James Kirkham, a PhD candidate at BAS, said in the statement. “We’ve learned that tunnel valleys can erode quickly under ice sheets that experience extreme heat.”
Scientists have known about similar tunnel valleys for decades, but until now, the creation of these channels was shrouded in mystery.
“We’ve been observing these huge meltwater channels from areas covered by ice sheets in the past for more than a century, but we didn’t really understand how they formed,” said study co-author Kelly Hogan, a marine geophysicist at BAS. the STATEMENT.
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The tunnel valleys form when meltwater drains through vertical cracks in the ice into a river of meltwater beneath the ice sheet, which channels liquid like a vast “plumbing system,” the researchers wrote in the paper. As a result, valley formation is highly seasonal, with increased summer melting leading to more meltwater that temporarily accelerates valley growth.
Although tunnel valleys form toward the end of an ice sheet’s life, the study authors suspect that this drainage system could actually reduce the rate at which the ice melts and, in fact, may have extended its life life of the ancient North Sea ice sheet. . This hypothesis suggests that, by draining meltwater away from the ice sheets, the channels stopped the accumulation of liquid above or below the ice and thus prevented more ice from melting.
However, researchers are unsure how fast the ice sheet was melting at this stage. Some tunnel valleys showed evidence of limited ice movement, suggesting that the valleys slowed the rate of ice loss. But others showed evidence of rapid ice retreat, which could mean the valleys were actually having the opposite effect of increasing the rate of ice loss, according to the statement.
Therefore, scientists will continue to study the tunnel valleys to see if they can get to the bottom of how meltwater channels can affect ice loss rates. “The critical question now is, will this extra meltwater flow in the channels cause our ice sheets to flow faster or slower to the sea?” Hogan said.
The answer to this question could be critical to predicting precisely how modern ice sheets, such as those that exist Antarctic and Greenland, will be affected by climate change, the researchers said.
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Current models that predict the rate of ice loss in these regions don’t take tunnel valleys into account, meaning researchers are missing a vital piece of the puzzle. If new valleys begin to form tunnels or “open up” beneath modern ice sheets (assuming they haven’t already), it could drastically change how quickly the ice sheets melt, particularly since these structures only take a few hundred years to form. the researchers wrote.
“The rate at which these giant channels can form means it’s an important, but currently overlooked, mechanism,” Kirkham said.