Why Did Two Antarctic Ice Shelves Fail? Scientists Say They Now Know.

The rapid collapse of two ice shelves in the Antarctic Peninsula over the past quarter-century was most likely caused by the arrival of huge plumes of warm, moist air that created extreme conditions and destabilized the ice, researchers said Thursday.

The breakup of the Larsen A Plateau in 1995 and of the Larsen B Plateau in 2002 was preceded by the landing of these plumes, called atmospheric rivers, from the Pacific Ocean. They caused extremely warm temperatures for several days that caused the surface ice to melt, leading to fractures, and reduced sea ice cover, which allowed ocean swells to bend the ice shelves and further weaken them.

“We identify atmospheric rivers as a mechanism that can create extreme conditions over the Antarctic Peninsula ice shelves and potentially lead to their destabilization,” said Jonathan Wille, a climatologist and meteorologist at the Université Grenoble Alpes in France and the lead author of a study. study describing the research in the journal Communications Earth and Environment.

While there have been no collapses on the peninsula since 2002, Dr. Wille and colleagues found that atmospheric rivers from 2000 to 2020 also caused 13 of the 21 major iceberg calving events.

dr. Wille said the larger Larsen C plate, which is still mostly intact and is Antarctica’s fourth-largest ice shelf at about 17,000 square miles, could eventually suffer the same fate as A and B.

“The only reason the melting hasn’t been significant so far is because it’s just further south compared to the others, so colder,” he said. But as the world continues to warm, atmospheric rivers are expected to intensify. “The Larsen C is now at risk from the same processes,” he said.

Kyle R. Clem, a researcher at the Victoria University of Wellington in New Zealand who was not involved in the study, said the work also showed that other parts of Antarctica that don’t warm as quickly as the peninsula may eventually be susceptible as well. since the mechanism the researchers documented relies more on warming where the atmospheric river originates.

“The amount of heat and moisture that atmospheric rivers carry is higher than without global warming,” said Dr. Clem. “So the air mass hitting Antarctica is much, much warmer. And it is these episodes of extreme events that lead to the collapse of the ice shelf.”

“You could get this anywhere in Antarctica,” he said.

Shelves are floating tongues of ice that serve to hold back most of the ice covering Antarctica to a depth of nearly 3 miles. When a shelf collapses, the flow of this land ice accelerates to the ocean, raising sea levels.

Although the Antarctic Peninsula’s ice sheet is relatively small (if it all melted, the seas would rise by less than a foot), the collapse of ice shelves elsewhere on the continent could lead to much greater sea-level rise over the centuries. .

Last month, a small ice shelf collapsed in East Antarctica, which is considered the most stable part of the continent. In the days before, an intense atmospheric river arrived in the region. It led to record high temperatures, but researchers aren’t sure yet if it played a role in the shelf disintegration.

Atmospheric rivers form when a large stationary zone of high-pressure air meets a low-pressure storm system. A narrow stream of moist air flows from the confluence of the two.

In a typical Southern Hemisphere summer, the peninsula gets one to five of these events, the researchers said. They only looked at those that contained the greatest volume of water vapor.

If a river is intense enough, it can lead to several days of melting of the ice shelf’s surface. As the meltwater flows into fissures, it refreezes, causing the cracks to get bigger and bigger. Ultimately, such repeated hydraulic fracturing, as the process is called, can cause the ice shelf to disintegrate.

The atmospheric river can also stimulate the process by melting sea ice, or if the accompanying wind pushes the sea ice away from the shelf. As a result, ocean waves can rock the ice shelf, stressing it even more.

Some large ice shelves in West Antarctica are thinning as a result of warm ocean water melting from below. Catherine Walker, a glaciologist at the Woods Hole Oceanographic Institution in Massachusetts who was not involved in the study, said that regardless of the long-term trends of warming and thinning, “this paper raises the important point that very short-term weather events can push past an ice shelf.” its tipping point.”

SOURCE – www.nytimes.com

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