The rapid collapse of two ice sheets on the Antarctic Peninsula in the last quarter of a century was most likely caused by the arrival of huge jets of warm, humid air, which created extreme conditions and destabilized the ice, researchers said Thursday.
The collapse of the Larsen A shelf in 1995 and the Larsen B shelf in 2002 were preceded by the landing of these jets, called atmospheric rivers, from the Pacific Ocean. They generate extremely warm temperatures for several days, which cause the ice surface to melt, causing fragmentation, and reduce sea ice cover, allowing 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 destabilize them,” said Jonathan Ville, a climatologist and meteorologist at the University of Grenoble Alps in France and lead author of the study. in the journal Communications Earth and Environment.
Although there have been no landslides on the peninsula since 2002, Dr. Will and his colleagues found that atmospheric rivers also caused 13 of the 21 major iceberg hotel events from 2000 to 2020.
Dr Will said the larger Larsen C shelf, which is still almost intact and about 17,000 square miles, is the fourth largest ice shelf in Antarctica, 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 than the others, so it’s colder,” he said. But as the world continues to warm, atmospheric rivers are expected to become more intense. “Now Larsen C will be at risk from the same processes,” he said.
Kyle R. Clem, a researcher at 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 are not warming as fast as the peninsula may eventually also be susceptible, as the mechanism documented by researchers is more dependent on warming where the atmospheric river originates.
“The amount of heat and moisture that atmospheric rivers carry is higher than it would be without global warming,” said Dr. Clem. “So the air mass colliding in Antarctica is much, much warmer. And it is precisely these episodes of extreme events that lead to the collapse of the ice shelf. “
“You can get that anywhere in Antarctica,” he said.
Shelves are floating ice tongues that hold back most of the ice that covers Antarctica to depths of nearly 3 miles. When the shelf collapses, the flow of this land ice to the ocean accelerates, increasing the rate of sea level rise.
While the ice cover of the Antarctic Peninsula is relatively small (if the whole melts, the seas will rise by less than a foot), the collapse of ice shelves elsewhere on the continent could lead to much higher sea levels over the centuries. .
Last month, a small ice shelf collapsed in East Antarctica, which is considered the most stable part of the continent. A few days ago, an intense atmospheric river arrived in the area. This has led to record high temperatures, but researchers are still unsure what role, if any, played in the collapse of the shelf.
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Atmospheric rivers occur when a large stationary area of high-pressure air encounters a system of low-pressure storms. A narrow stream of moist air flows from the merger of the two.
In a typical summer in the southern hemisphere, the peninsula receives one to five of these events, the researchers said. They consider only those that contain the largest volume of water vapor.
If the river is intense enough, it can lead to several days of melting on the surface of the ice shelf. As the molten water flows into the cracks, it freezes again, widening and widening the cracks. Ultimately, such repeated hydrofracture, as the process is called, can lead to the disintegration of the ice shelf.
Atmospheric rivers can also stimulate the process by melting sea ice or if associated winds push sea ice off the shelf. This allows the ocean waves to shake the ice shelf, putting extra strain on it.
Some large ice shelves in West Antarctica are thinning as a result of melting from below by warm ocean water. Catherine Walker, a glaciologist at the Woods Hole Oceanographic Institute in Massachusetts who did not participate in the study, said that despite long-term warming and thinning trends, “this paper highlights an important moment that very brief weather events can lead to an ice shelf over its critical point. “