A new study reports that hidden valleys buried beneath the ocean floor in the North Sea rapidly formed from the 'death throes' of ancient ice sheets about 200,000 years ago or near the end of the ice age.
Researchers said that the subterranean structures could give clues on how the modern ice sheet will respond to climate change. The study titled "Tunnel Valley Formation Beneath Deglaciating Mid-latitude Ice Sheets: Observations and Modelling" is published in Quaternary Science Reviews.
Mapping Hidden Valleys Buried Beneath the North Sea
The buried subterranean structures are known as tunnel valleys, which are massive underground ravines that meltwater from the ice sheets etched into the ancient seafloor. The weight of the melting slabs forced the flowing water into the canyons and into the seafloor that have been covered by hundreds of meters of sediment buildup.
The team said in a statement that the tunnel valleys can measure up to 93 miles (150 kilometers) long, about 3.7 miles (6 kilometers) wide, and 1,640 feet (500 meters) deep.
Researchers from the British Antarctic Survey (BAS) presented a map of the tunnel valleys in the North Sea in their 2021 study published in Geology. They showed that the North Sea was once covered by a massive ice sheet that also covered parts of Europe and the UK during the last ice age about 126,000 to 12,000 years ago.
They used a 3D seismic reflection technology that emits sound waves to scan for subterranean structures on the ocean floor. The team found thousands of buried canyons that date back around 2 million years.
Meanwhile, the new study by the same researchers used canyon maps with computer models to determine how these tunnel valleys formed. They discovered that these hidden valleys likely formed over a few centuries, which is faster than the team anticipated.
James Kirkham, the lead author of the study and a doctoral candidate from BAS, said in the statement that their findings show an exciting discovery on how the spectacular valleys were formed during the death throes of ice sheets. They also found that these tunnels can be eroded by ice sheets experiencing extreme warmth.
Drainage System From Ice Sheets Affect Rate of Ice Loss
Researchers wrote in the paper that tunnel valleys were created when meltwater drains through vertical cracks in the ice into a meltwater river below the ice sheet. According to Live Science, that means that the formation is highly seasonal, wherein increased summer melting results in more meltwater that accelerates that valley's growth.
The authors suspect that the drainage system could reduce the rate of ice loss although the tunnel valleys form toward the end of the life of an ice sheet. They believe that it may have prolonged the life span of the ancient ice sheet in the North Sea. This hypothesis proposes that the channels stopped liquid from pooling on top or below the ice, preventing more ice loss.
But they are uncertain about how quickly the ice sheet is melting at that stage as some tunnel valleys showed evidence of limited movements, which implies that they were slowing down the rate of ice loss. On the other hand, some evidence also suggests a rapid ice retreat that may have the opposite effect of increasing the ice loss rate.
Marine geophysicist Kelly Hogan, a co-author of the study, said that they will be continuing their research about the tunnel valleys to see if they could get to the bottom of how meltwater channels may affect the rate of ice loss.
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