Super colossal holes in the Antarctic ice demystified by scientists


It's a strange thing. When the Antarctic winter died below zero, when the world's oceans were frozen, scientists observed large holes the size of South Carolina or larger openings in the pack ice.

The rare and disconcerting phenomena occurred recently in winter 2016 and 2017, although considerably larger holes opened up in the 1970s. Now scientists understand why such large holes, called polynyas (in Russian, "holes in ice "), are formed.

A large number of environmental factors must come together at the same time for large ice voids to open. The research, published Monday in the journal Nature, used observations taken on large floats in the distant ocean, NASA satellites and even sensors attached to elephant seal heads to show how the ocean under the ice was mixing like a bartender shaking a cocktail. In the end, this mixture transports relatively hot water to the surface.

"The water is hot enough to melt the ice," said Ethan Campbell, lead author of the study and PhD student at the University of Washington. student in physical oceanography.

It condemns large expanses of ice. And there is growing evidence that these warming episodes could start more often.

It is not a gradual event. The gaping holes are formed quickly, without notice. "Suddenly, a hole appears in the floating ice," said Ted Scambos, an Antarctic expert and senior scientist at the Earth Science and Observation Center in the state of Colorado. The ice is a few meters thick, added Scambos, who played no role in the study.

The polynya of September 25, 2017.

The polynya of September 25, 2017.

Image: NASA Worldview / NASA Blue Marble

There is of course another massive component of the great polynyas that can not be ignored, said Scambos. Her name is Maud Rise and it is a huge underwater mountain located near these holes. "You can think of this as a Mount Everest under the ocean," said Campbell, pointing out that the shape and topography of the high mount amplify the movement of warm waters toward the surface.

But Campbell noted: "[Maud Rise] There are some every day, but we do not see polynyas every year. To explain the polynyas, we had to go to the ocean. "

"Suddenly, a hole appears in the floating ice"

The key ingredient is violent storms (previous research had suggested). And during the winter, the ocean that surrounds Antarctica, called the Southern Ocean, is an infernal place. "It's characterized by storms every day, with winds of almost hurricane force," noted Campbell. Gnarled winds shake the ice, disrupting the water below, and blow directly through cracks, hollows and gaps in the sea ice, he explained. This can force an extremely cold layer of water near the surface to mix, allowing warmer, saltier water to mix – and melt the ice.

An elephant seal equipped with a monitoring equipment of the ocean.

An elephant seal equipped with a monitoring equipment of the ocean.

Image: Dan Costa / University of California at Santa Cruz

It is crucial to note that in some years, winds swirling around Antarctica are narrowing around the large ice-covered continent, which means that exceptionally strong gusts can permeate the sea ice and impose an exceptional upheaval of the waters below, giving rise to massive polynyas.

The amount of heat produced by this warmer water is deep.

"We have this huge and incredible heat release," said Alek Petty, a polar sea ice scientist at NASA's Goddard Space Flight Center, who played no role in the research. The amount of heat released by these gaping holes equals the total amount of heat typically lost from the Southern Ocean throughout the winter, Petty added. This burning heat of exposed heat is then absorbed into the atmosphere, where it can have a global effect on the weather, even influencing the places where it rains (for years) in the tropics.

Scientists like Petty are therefore more closely observing polynyas. These are not just giant and intriguing curiosities in a remote part of the world.

"These are fundamental elements of the climate system," said Petty.

And, as the climate changes, polynyas can become more common. "We could start seeing these things more often," said Campbell of the University of Washington. Due to the general climate disruption on the planet, atmospheric scientists expect the winds around Antarctica to strengthen – which could well mean more polynyas.

The growing polynya in September 2017.

The growing polynya in September 2017.

Image: University of Washington

In addition, the same heat increase that allows these large polynyas to form could also be found on the increasingly vulnerable Antarctic ice shelves – which are the extremities of the giant glaciers that float above the ice. 'ocean. Warmer waters are already damaging these ice masses, which act as plugs preventing the Antarctic leaves from sinking unhindered into the ocean.

But with more polynyas, there could be a new source of heat amplifying the modern threat weighing on the largest ice storage on the planet.

"This is a future area of ​​research," said Petty, noting that NASA plans to study the phenomenon. "Is it going to be another source of heat and melt?"

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