Two Antarctic glaciers that have long kept scientists awake at night are breaking free from the constraints that have bottomed them out, increasing the threat of large-scale sea level rise.
Located along the shores of the Amundsen Sea in western Antarctica, the huge Pine Island and Thwaites glaciers already contribute approx. 5% of global sea level rise. Thwaite’s survival has been considered so critical that the United States and Britain have launched a multi-million dollar research mission to the glacier, the loss of which could trigger a wider collapse of the West Antarctic ice sheet, which contains enough ice to raise oceans by approx. feet.
The new findings, published Monday in the Proceedings of the National Academy of Sciences, come from the analysis of satellite images. They show that a naturally occurring buffer system that prevents glaciers from flowing outward rapidly will collapse and potentially release far more ice into the ocean in the coming years.
The so-called “displacement margins”
“The stresses that slow down the glacier are no longer in place, so the glacier is faster,” said Stef Lhermitte, a satellite expert at Delft University of Technology in the Netherlands, who led the new research with colleagues from NASA and 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 a further resolution.
“We already knew it was glaciers that might matter in the future, but these pictures to me show that these ice shelves are in a very bad state,” Lhermitte said.
It’s just the latest in a stream of bad news about the planet’s ice.
Arctic sea ice is very close to – but probably not quite reached – a record low level this year. Last month, Canada lost its last major Arctic ice shelf.
And in Greenland, the largest remaining ice shelf in the northern hemisphere, sometimes known as 79 north due to its latitude (its full name is Nioghalvfjerdsfjorden), just lost a large piece of ice the size of about two Manhattan islands, according to Denmark and Greenland geological survey. Experts who accused the breach of a strong general warming trend and temperatures that have been “incredibly hot” in northeastern Greenland in recent years.
Ice shelves are large floating platforms that extend outward over the sea surface at the outer edge of marine-based glaciers. As they float across the water, these shelves freeze on mountain sides and islands and anchor to bumps in the ocean floor. In this way, the shelves provide a braking mechanism on the natural ice that flows outwards.
The support takes place in regions called “displacement margins”, where faster liquid ice meets ice that is more static and stable, often because it is moored to a part of the landscape. In these places, the ice often curls and distorts, which is a visible indication of the heavy loads it is under.
But when these loads become too much, the ice breaks. That’s what’s happening now in western Antarctica, new research claims, suggesting that warm ocean water has thinned ice shelves off from below enough to make them crisp.
At the same time and for the same reason, the glaciers themselves began to flow outward faster. The resulting forces led to the ice of the displacement margin breaking – which means that the glacier is now able to add ice to the sea even faster.
For the Pine Island glacier, the new study finds that while cracks and fractures at the displacement margin date back to 1999, it accelerated in 2016.
“This is important work,” Richard Alley, a glaciologist at Penn State University, said of the new study.
Alley noted that the processes that are now taking place in Antarctica have apparently already been completed in parts of Greenland, where one of the largest glaciers, Jakobshavn, has no significant ice shelf at all. When it lost its shelf around the turn of the century, Jakobshavn’s speed for istab increased sharply.
79 The northern glacier still has an ice shelf, as do some of Greenland’s other northernmost glaciers, but many of these have lost significant size in recent decades.
“The new paper shows that the Amundsen Sea Embayment ice shelves have undergone most, but not all, of the Jakobshavn steps,” Alley said in an email. “[A] warming the sea thinned the ice shelves, this reduced support, this allowed the non-liquid ice to move faster, which contributed to an increase in sea level and also began to break the sides of the ice shelves, but further acceleration could occur if the rest of the steps (further break and loss of ice shelf) should occur. ”
Several ice shelf collapses have already been seen in Canada, Greenland and the warmer Antarctic Peninsula, where disposable Larsen A and Larsen B ice shelves broke and no longer exist today.
“When the ice shelves are damaged by climate change, as we saw on the Antarctic Peninsula in recent decades, their supportive effect is reduced and ice currents accelerate and raise sea levels,” said Isabella Velicogna, a glaciologist at the university. in California, Irvine, who commented on the new study. “The acceleration increases the damage, a positive feedback, which is not good news.”
If a similar process takes place in the Amundsen Sea in western Antarctica, where Pine Island and Thwaites are located, the consequences for the sea surface could be enormous.
Lhermitte presented calculations that showed that over the past six years, the western and central parts of the Pine Island ice shelf have dropped in size by about 30% from about 1,500 square kilometers in size down to nearly 1,000 square kilometers. In other words, an area the size of Los Angeles has been lost.
“This displacement margin is so damaged that we believe it presupposes this ice shelf for long-term destabilization,” Lhermitte said. “These are the first signs we see the Pine Island ice shelf disappearing. This injury is difficult to heal. ”
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