Scientists solve Antarctic mystery

(ORDO NEWS) — The rapid collapse of two ice shelves on the Antarctic Peninsula over the past quarter century was most likely caused by huge plumes of warm, moisture-laden air that created extreme conditions and destabilized the ice, researchers said Thursday.

The destruction of the Larsen A shelf in 1995 and the Larsen B shelf in 2002 was preceded by the landing of these plumes, called atmospheric rivers, from the Pacific Ocean.

They created extremely warm temperatures for several days, which caused surface ice melt, which led to cracking, and shrinkage of the sea ice sheet, which allowed ocean waves to bend the ice shelves and further weaken them.

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

Although the peninsula has not had a collapse since 2002, Dr Wille and colleagues found that atmospheric rivers also triggered 13 of 21 large iceberg collapses between 2000 and 2020.

Dr. Wille said that the larger Larsen C Shelf, which is still largely intact and, covering an area of ​​about 17,000 square miles, is the fourth largest ice shelf in Antarctica, could eventually suffer the same fate as Shelves A and b.

“The only reason the melt hasn’t been significant so far is because it’s further south than other shelves and therefore colder,” he said. But as the climate continues to warm, atmospheric rivers are expected to become more intense. “Larsen C will now be threatened by the same processes,” he said.

Kyle R. Clem, a researcher at the University of Wellington Victoria in New Zealand who was not involved in the study, said the work also shows that other parts of Antarctica that are not warming as fast as the peninsula could end up being susceptible as well. because the mechanism that the researchers have documented depends more on warming at the source of the atmospheric river.

“The amount of heat and moisture carried by atmospheric rivers is higher than it would be without global warming,” Dr. Clem said. “Therefore, the air masses that hit Antarctica are much, much warmer. And it is these episodes of extreme events that lead to the destruction of the ice shelf.”

“It could happen anywhere in Antarctica,” he said.

Shelves are floating tongues of ice that serve to hold most of the ice covering Antarctica up to 3 miles deep. As the shelf collapses, the flow of this land ice into the ocean accelerates, increasing the rate of sea level rise.

Although the Antarctic Peninsula ice sheet is relatively small (if all of it melted, sea levels 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 centuries.

Last month, a small ice shelf collapsed in East Antarctica, considered the most stable part of the continent. A few days before, an intense atmospheric flow had come into the region. It led to record high temperatures, but researchers are not yet sure what role, if any, it played in the destruction of the shelf.

Atmospheric rivers occur when a large stationary zone of high pressure air meets a low pressure storm system. From the place of their confluence follows a narrow stream of moist air.

According to the researchers, during a typical summer in the southern hemisphere, one to five such events occur on the peninsula. They considered only those of them that contained the largest amount of water vapor.

If the river is intense enough, it can melt the surface of the ice shelf within days. As meltwater flows into cracks, it freezes, expanding and enlarging the cracks. Eventually, this repetitive hydraulic fracturing, as the process is called, can lead to the destruction of the ice shelf.

Scientists solve Antarctic mystery

An atmospheric river can also spur this process by melting the sea ice, or if associated winds push the sea ice away from the shelf. This allows ocean waves to rock the ice shelf, further loading it.

Some of the large ice shelves in West Antarctica are thinning as a result of melting under the action of warm ocean water.

Katherine Walker, a glaciologist at the Woods Hole Oceanographic Institution in Massachusetts who was not involved in the study, said that regardless of long-term warming and thinning trends, “this paper highlights the important point that very brief weather events can push the ice shelf to a tipping point. “.

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