‘Death pangs’ of ancient ice caps could give clues to climate change impacts: ScienceAlert
Hidden valleys buried beneath the ocean floor in the North Sea were quickly carved out during the “agony” of an ancient ice cap near the end of the last ice age around 20,000 years ago, according to a new study.
The startling underground structures could give clues as to how modern ice caps will respond to the rapid warming caused by climate changesay the researchers.
The buried structures, known as tunnel valleys, are massive underground ravines that were carved out of the ancient seabed by meltwater that flowed through channels beneath the ice sheets.
The immense weight of the rapidly melting ice sheets forced the flowing water to carve deep canyons in the seabed; these channels have since been covered by hundreds of meters of sediment accumulation.
Tunnel valleys can be up to 150 kilometers long, 6 km wide and 500 meters deep, according to a researchers statement.
In 2021, researchers from the British Antarctic Survey (BAS) mapped the tunnel valley network of the North Sea, which was once covered by a huge ice cap that also covered parts of mainland Europe and the UK during the last ice age, between 126,000 and 12,000 years ago.
Using 3D seismic reflection technology, which emits sound waves to search for structures beneath the seabed, the team discovered thousands of buried canyons, some dating back around 2 million years. These results were published in September 2021 in the journal Geology.
In the new study, which was published Oct. 5 in the journal Quaternary Science Reviewsthe same researchers used the canyon maps, combined with computer models, to determine exactly how some of the tunnel valleys came into being.
The results showed that the tunnels were probably dug in a few centuries, which is much faster than the team had originally expected.
“This is an exciting discovery. We know that these dramatic valleys are carved out during the agony of the ice caps,” lead study author James Kirkham, a PhD student at BAS, said in the statement.
“We learned that tunnel valleys can be eroded quickly under ice caps experiencing extreme heat.”
Scientists have known about similar tunnel valleys for decades, but until now the creation of these channels has been shrouded in mystery.
“We’ve observed these massive meltwater channels for more than a century from areas covered by ice caps, but we haven’t really understood how they formed,” the co-author said. study, Kelly Hogan, marine geophysicist at BAS. said in the statement.
Tunnel valleys form when meltwater flows through vertical cracks in the ice into a river of meltwater beneath the ice sheet, which channels the liquid like a huge ‘plumbing system’, according to researchers. researchers written in the diary.
As a result, valley formation is highly seasonal, with increased summer melt bringing more meltwater which temporarily accelerates valley growth.
Although tunnel valleys form towards the end of an ice sheet’s life, the study authors suspect that this drainage system may actually reduce the rate at which ice melts and, in fact, may have prolonged the lifespan of the ancient North Sea ice sheet. .
This hypothesis proposes that by draining meltwater from the ice sheets, the channels prevented liquid from accumulating above or below the ice and thus prevented more ice from melting.
However, researchers don’t know how fast the ice sheet was melting at this point. Some tunnel valleys showed signs of limited ice movement, suggesting that the valleys were slowing the rate of ice loss.
But others showed signs of rapid ice retreat, which could mean the valleys were actually having the opposite effect of increasing the rate of ice loss, the statement said.
Scientists will therefore continue to study the valleys of the tunnels to see if they can understand how meltwater channels may affect ice loss rates.
“The crucial question now is whether this additional flow of meltwater into the channels will cause our ice sheets to flow faster or slower into the sea?” hogan said.
Answering this question could be key to accurately predicting how modern ice sheets, like those of Antarctic and Greenland, will be affected by climate change, the researchers said.
Current models that predict the rate of ice loss in these regions do not account for tunnel valleys, which means researchers are missing a critical piece of the puzzle.
If new tunnel valleys begin to form, or “ignite”, under modern ice sheets (assuming they haven’t already), this could drastically change the rate at which the ice sheets melt, particularly because these structures only take a few hundred years to form, the researchers wrote.
“The rate at which these giant channels can form means they are an important, but currently overlooked mechanism,” Kirkham said. said.