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

The rapid collapse of two ice shelves on the Antarctic Peninsula over the past quarter-century was triggered by the emergence of warm air currents, researchers said on Thursday. pressure, humidity, creating extreme conditions and destabilizing ice.

The disintegration of the Larsen A shelf in 1995 and the Larsen B shelf in 2002 was preceded by the landing of these plumes, known as atmospheric rivers, from the Pacific Ocean. They generate extremely warm temperatures over a few days that cause the surface to melt leading to faults, and reduce sea ice cover, allowing ocean bulges to bend ice shelves and weaken them. weaker.

Jonathan Wille, a climatologist and meteorologist at the University of Grenoble Alpes in France and the lead author of a research descriptive research in the journal Earth and Environment Communications.

Although there has been no collapse on the peninsula since 2002, Dr Wille and his colleagues found that atmospheric rivers also cause 13 of the 21 major ice-forming events. from 2000 to 2020.

Dr Wille said the larger Larsen C shelf, which is mostly intact and about 17,000 square miles wide, is the fourth largest ice shelf in Antarctica, which could eventually suffer the same fate as A and B.

“The only reason the melting hasn’t been much so far is because it’s located further south than elsewhere, so it’s colder,” he said. But as the world continues to warm, atmospheric rivers are expected to become more intense. “Larsen C will now be at risk from similar processes,” he said.

Kyle R. Clem, a researcher at Victoria University, Wellington in New Zealand who was not involved in the study, said the work also shows that other areas of Antarctica are not warming as rapidly as the terminal peninsula. may also be susceptible, as the mechanism the researchers documented is more dependent on warming where the river originates in the atmosphere.

“The amount of heat and moisture transported by rivers in the atmosphere is higher than in the absence of global warming,” Dr. Clem said. “So the air mass over Antarctica is a lot warmer. And it is these waves of extreme events that lead to the collapse of the ice shelf.”

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

Racks are floating blades of ice that keep much of the ice that covers Antarctica at depths of up to nearly 3 miles. When a shelf collapses, the flow of ice from the land to the ocean accelerates, accelerating sea level rise.

While the ice on the Antarctic Peninsula is relatively small (if it all melted, sea levels would rise less than a foot) the collapse of ice shelves elsewhere on the continent could lead to sea levels much higher over the centuries.

Last month, a small ice shelf collapsed in East Antarctica, is considered the most stable part of the continent. In the previous days, a river with high atmospheric intensity reached the area. It led to record-high temperatures, but researchers are still uncertain what role it played, if any, in shelf decay.

Atmospheric rivers occur when a large stationary region of high-pressure air encounters a low-pressure storm system. A narrow stream of moist air flows out from the confluence of two moist air streams.

During a typical summer in the Southern Hemisphere, the peninsula has between one and five of these events, the researchers say. They only considered those that contained the highest amount of water vapor.

If a river is intense enough, it can lead to the surface of the ice shelf melting within days. As melt water enters the crevices, it coagulates, widens and widens the cracks. Ultimately, this process, known as repeated hydrolysis, can cause the ice shelf to disintegrate.

The atmospheric river could also accelerate the process by melting sea ice, or if its associated winds push sea ice off the shelf. That allows ocean waves to shake the ice shelf, putting additional stress on it.

Several large ice shelves in West Antarctica are thinning due to melting from below by warm ocean water. Catherine Walker, an glaciologist at the Woods Hole Oceanographic Institution in Massachusetts, who was not involved in the study, said that regardless of long-term trends in warming and thinning, “this paper makes the important point that Very brief weather events can spur an ice shelf past its tipping point. “