Two major Antarctic glaciers are tearing loose from their restraints, scientists say

“The loss of the glacier could trigger the broader collapse of the West Antarctic ice sheet, which contains enough ice to eventually raise seas by about 10 feet.”

WaPo: Two major Antarctic glaciers are tearing loose from their restraints, scientists say

Pine Island and Thwaites glaciers already contribute 5 percent of sea-level rise.

Enormous curved crevasses near the Pine Island Glacier shear margin. (Brooke Medley/NASA)

September 14, 2020 at 12:03 p.m. PDT

Two Antarctic glaciers that have long kept scientists awake at night are breaking free from the restraints that have hemmed them in, increasing the threat of large-scale sea-level rise.

Located along the coast of the Amundsen Sea in West Antarctica, the enormous Pine Island and Thwaites glaciers already contribute around 5 percent of global sea-level rise. The survival of Thwaites has been deemed so critical that the United States and Britain have launched a targeted multimillion-dollar research mission to the glacier. The loss of the glacier could trigger the broader collapse of the West Antarctic ice sheet, which contains enough ice to eventually raise seas by about 10 feet.

The new findings, published Monday in the Proceedings of the National Academy of Sciences, come from analysis of satellite images. They show that a naturally occurring buffer system that prevents the glaciers from flowing outward rapidly is breaking down, potentially unleashing far more ice into the sea in coming years.

The glaciers’ “s hear margins,” where their floating ice shelves encounter high levels of friction that constrain the natural flow of ice, are progressively weakening and in some cases breaking into pieces.

“The stresses that slow down the glacier, they are no longer in place, so the glacier is speeding up,” said Stef Lhermitte, a satellite expert at Delft University of Technology in the Netherlands who led the new research along with colleagues from NASA and other research institutions in France, Belgium, Austria and the Netherlands.

While many of the images have been seen before, the new analysis suggests that they are a sign of further disintegration to come.

“We already knew that these were glaciers that might matter in the future, but these images to me indicate that these ice shelves are in a very bad state,” Lhermitte said.

It’s just the latest in a flurry of bad news about the planet’s ice.

Arctic sea ice is very close to — but likely to not quite reach — a record low for this time of year. Last month, Canada lost a large portion of its last major Arctic ice shelf.

And in Greenland, the largest still-intact ice shelf in the Northern Hemisphere, sometimes known as 79 North because of its latitude (its full name is Nioghalvfjerdsfjorden), just lost a large chunk of ice, equivalent in size to roughly two Manhattan islands, according to the Geological Survey of Denmark and Greenland. Experts there blamed the fracture on a strong general warming trend and temperatures that have been “incredibly” high in the northeast of Greenland in recent years.

Ice shelves are vast floating platforms that extend across the surface of the ocean at the outer edge of marine-based glaciers. As they flow over the water, these shelves freeze onto mountainsides and islands and anchor themselves to bumps in the seafloor. In this way, the shelves provide a braking mechanism on the natural outward flow of ice.

The buttressing effect occurs in the shear margins, where faster-flowing ice meets ice that is more static and stable, often because it is moored to some part of the landscape. In these places, the ice frequently crumples and contorts, a visible indication of the powerful stresses that it is under.

The Pine Island Glacier's damaged shear margin. — The Pine Island Glacier’s damaged shear margin. (NASA Goddard Space Flight Center)

But when those stresses become too much, ice breaks. That’s what’s now happening in West Antarctica, the new research argues, suggesting that warm ocean water has thinned the ice shelves out enough from below that they became brittle.

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