Key Glaciers “Breaking Free”

September 15, 2020

Take a break from the Disastrous fires, and impending hurricanes, and relax with this news from Antarctica.

Paper and some sobering videos, ( with some kind of protection that won’t let me post them) here.

Washington Post:

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.

Crevasses on Pine Island Glacier

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’ “shear 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.

Shear margin at Pine Island Glacier

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.

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.

At the same time, and for the same reason, the glaciers themselves began to flow outward faster. The resulting forces led the shear-margin ice to break into pieces — which means that the glacier, less constrained, will now be able to add ice to the ocean even faster.

For the Pine Island Glacier, the new study finds that while the cracking and fraying at the shear margin dates to 1999, it accelerated in 2016.

Even more concerning is the Thwaites Glacier. Here, again, the breakdown of the shear margin has increased in recent years.

“This is important work,” Richard Alley, a glaciologist at Pennsylvania State University, said of the new study.

Alley noted that the processes playing out in Antarctica appear to have already reached their completion in parts of Greenland, where one of the largest glaciers, Jakobshavn, no longer has any significant ice shelf at all. When it lost that shelf around the year 2000, Jakobshavn’s rate of ice loss steeply increased.

“The new paper shows that the Amundsen Sea Embayment ice shelves have gone through most, but not all, of the Jakobshavn steps,” Alley said in an email. “[A] warming ocean thinned the ice shelves, this reduced buttressing, this let the non-floating ice move faster, contributing some to sea-level rise and also starting to break the sides of the ice shelves, but additional acceleration could occur if the rest of the steps (further fracture and ice-shelf loss) should occur.”

Multiple ice-shelf collapses have already been seen in Canada, Greenland and the warmer Antarctic Peninsula, where the onetime Larsen A and Larsen B ice shelves fractured and, today, no longer exist.

3 Responses to “Key Glaciers “Breaking Free””

  1. grindupbaker Says:

    Eric Rignot figures 6x to 7x ice discharge rate with the “restraints” gone. All Antarctica discharges 2,200 Gt / year. I don’t know how that divides up between the glaciers.

  2. grindupbaker Says:

    The paper says 11 feet, not 10 feet

  3. indy222 Says:

    How does the 6-7x rate turn into sea level rise rate?


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