The ice deep underneath Greenland seems to be slowly churning into bizarre, plume-like swirls, according to a recent paper. Understanding this strange process could help researchers better predict how Greenland’s ice is behaving while it rapidly melts into the sea.
The formations were first spotted in 2014 using radar imaging, but how they formed remained unclear.
Now, researchers suggest the answer lies in thermal convection, the same force that pushes and pulls Earth’s red-hot mantle.
“We often think of ice as a solid material, cold and rigid,” said Prof Andreas Born, from the University of Bergen, Norway. “So, the fact that we discovered that parts of the Greenland ice sheet undergo thermal convection, almost like a pot of boiling pasta, is pretty wild and fascinating.”
Convection happens when hotter parts of a material rise and cooler parts sink, in a slow, cyclical movement.
In this case, the plumes seem to have formed in the solid ice over thousands of years, caused by heat rising from deep inside Earth.
“The fact that thermal convection can occur inside an ice sheet is a bit counterintuitive,” said first author Dr Robert Law, a glaciologist at ETH Zurich, Switzerland. “But since ice is at least a million times softer than Earth’s mantle, the physics actually makes sense.”
To understand whether convection could feasibly produce the mysterious plumes, Law and his team recreated a digital version of Greenland’s ice sheet with a computer model that’s usually used to simulate convection in Earth’s mantle.
After tweaking variables – such as ice thickness, softness and movement – the model began to form rising columns of ice, swirling into shapes that resembled those in the Greenland ice sheet.
Law told BBC Science Focus that the relatively stable, low-snowfall conditions found in northern Greenland seemed to provide the perfect insulation layer to encourage these shapes to form over thousands of years.
But the study also allowed the scientists to understand more about the properties of ice that would otherwise be difficult to measure.
“It’s really challenging to gather information on ice properties, particularly those deep in the ice sheet,” explained Law.
“Approaches like this can provide really valuable information we wouldn’t gather from other sources. Our results suggest that ice is actually softer and more sensitive to stress than commonly thought – though we need further studies to be absolutely certain about this.”
That’s important because the Greenland ice sheet is huge, estimated to be more than 1.7 million square kilometres (650,000 square miles). If the entire sheet melted, it would raise sea levels by 7.4 metres (24 feet), according to estimates from the US National Snow and Ice Data Center.
Another recent study, this time led by the University of Barcelona, has shown that the ice is melting at unprecedented levels.
“The Greenland ice sheet is experiencing more frequent, larger and more intense extreme melt events than in the past,” first author Dr Josep Bonsoms, geography researcher at Barcelona, told BBC Science Focus.
“Most of the top 10 extreme melting years have occurred since 2000. As one of the largest stores of frozen water on Earth, the melting of Greenland makes a significant contribution to global sea-level rise and adds urgency to international climate action.”
Law told BBC Science Focus what his study meant for the future of Greenland and the wider climate.
“On their own, the plumes aren’t a sign that we should expect the ice sheet to decay faster than presently anticipated,” he said.
“They’re like an ancient artefact – a thicker, colder, drier and more stable ice sheet, from the last ice age. However, ice physics remains poorly understood. Every advance in physical understanding allows us to better predict the rates of ice-sheet melt and sea-level rise.”
Law added that he hoped people who came across his research would be filled with “the same awe at nature and the Greenland ice sheet,” as his team was when they conducted their research.
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