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A study released last week by the American Geophysical Union documents a chaotic, low-frequency buzz on the Ross Ice Shelf, a platform the size of France that floats off the coast of Canada. 39, West Antarctica.
The locations are caused by the wind that hits the snow dunes, and it's kind of a strange song. But, say the researchers, it is also a harbinger of one of the nightmare scenarios in the science of climate change: the disintegration of the largest ice shelf in the Antarctic and the subsequent slide of glaciers in the ocean.
The song slows down when the snow begins to melt in the upper layers of the pack ice. It's already happened.
The ice has been shaking for centuries: a discordant song whose worms told the story of cold winds and changing snow dunes vibrating through Antarctica.
Accelerated thousands of times in the frequency range of human hearing, it seemed like the sound of ice had been toned down to sound like a hissing whistle that lasted two weeks among the hottest never recorded on the polar continent. A song that warned of melting snow.
If scientists fear climatologists – if, during a particularly hot month of this century, the Ross Ice Cap, 500 km long, collapses like a crumbling border wall, thus allowing the Inland Antarctic glaciers cross it from spilling into the sea – we could see little of the calamity beginning.
When a small ice floe collapsed across western Antarctica in January 2002, we were blind.
"Scientists monitoring the daily satellite imagery of the Antarctic Peninsula have observed with astonishment almost all of the Larsen B ice floe cracked and collapsed in a little over a month," NASA wrote in its memorial dedicated to this event. 10,000 year old ice platform.
"It's collapsed between images of a satellite," said the Washington Post's Julius Chaput, a geophysicist at Colorado State University. "One photo was there, the next one was not there."
But the pack ice was sick well before his spectacular death. As Chaput explains, the first stages of disintegration are insidious and largely invisible to satellites.
Repeated heat waves melt and refreeze the snow carpet at the top of the pack ice. With each new frost, the snow becomes harder. Eventually, it becomes so hard that puddles of water form on the surface of the snow and sink down, digging tunnels in the snow to reach the ice below.
The ice weakens as a rotting boat hull under the onslaught of melt water. It crackles. The scale of the damage is obvious for the satellites towards the end, when the whole plateau – ice, snow and everything – breaks up and dissolves in the ocean in a few days.
This is an understatement, to put it mildly, for the end of the world as we know it.
But as Chaput and his team have demonstrated in an article published by the American Geophysical Union last week, an injured pack ice will be singing about his problems long before we show them.
The discovery was "a complete accident," said Chaput. Nobody expected the ice to sing.
Several years ago, another team of researchers installed dozens of seismic stations on the Ross Ice Shelf. Like many climatologists, they feared that if the French-style floating ice platform collapsed as was the case with Larsen B in 2002, the titanic glaciers behind it would be free to flee the Antarctic continent, increasing thus the level of the ocean of several feet.
"For the moment, Ross's ice shelf seems to be stable," said Chaput. "But that could change extremely quickly and without notice."
The seismic stations were designed to measure what the Earth's crust and mantle do under ice – massive earthquake-scale vibrations.
But while he was reviewing the data set from late 2014 to 2017, Chaput noticed something in the sine waves: a subtle song, vibrating through the upper layers of the snow.
"You had these tones, these incredibly defined, persistent and defined tones at each station," he said. "They would change all the time, with changes in air temperature, storms and winds."
Even the movement of a snow dune could change the frequencies, said Chaput. It was as if all the snow bed had been dug as an old phonograph record, humming with the rustling of the atmosphere.
The notes hovered around 5 hertz, about four times less than the human ear can detect. But Chaput could easily speed them up enough to hear – compress rhythms of several days into minutes or seconds.
That's how he could hear what happened in early 2016 – when a particularly hot summer arrived in Antarctica and the phonograph jumped.
Chaput did not discover the great event of the cast of January 2016. As Chris Mooney wrote in the Washington Post, this disrupted the scientists who had learned it at the time .
The two-week melting has left nothing as obvious as a lake on the surface of the Ross ice floe. On the contrary, it turned a wet, sodden Texas-sized snowpack as the air temperature reached freezing point. Scientists first detected it through the presence of vapor clouds over the pack ice, Mooney wrote, before using microwave satellites to confirm the damage. .
But when in the music of the snow, melting was impossible to miss.
At the seismic stations on the other side of the pack ice, the vibrations of the voice are silent. Notes stretched in a long drone in some places, like a tornado siren. For Chaput, it sounded like a two-week whine.
"It does not seem very happy to me," he said.
The music of the ice, he explained, comes from the wind that passes over the snow dunes and sends vibrations through trillions of ice crystals compressed in the snow bed – called "firn". "The snow contains 80% air, with flaky links between crystals," Chaput said. "As they weaken, the movement speed of a wave decreases, so the tones go down. It goes down and becomes quieter."
All this could simply mean that Chaput found a depressing soundtrack for melting an ice cap. But as described in his article, music also has potential as a measurement tool – something like a sonogram for the health of snow and ice in times of future warming, which he expects a lot .
It does not mean that we will like what we hear.
The old rumbling of the pack ice Ross returned shortly after the end of the heat wave at the end of January when the snow was covered with snow and the crystals reshaped their links. But on many listening stations, the sound is no longer the same. The grass now has something like a rasp.
"You can see the physical impact," Chaput said. "When it cools again, the nicotine heals partially and bounces in some ways, but not entirely."
He does not know if the Ross Ice Shelf will regain its original structure and voice, or whether it has been permanently damaged, because the Larsen B ice shelf had to be l & # 39; to be long before breaking.
For the moment, even imperfectly, he continues to sing.
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