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Research published Last week, the American Geophysical Union documented a chaotic, low-frequency buzz on the Ross Ice Shelf, a French-size platform floating off the coast of West Antarctica.
The wind hits the snow dunes, it's a strange song. But according to the researchers, it is also a harbinger of one of the nightmarish scenarios of the science of climate change: the disintegration of the largest Antarctic ice sheet and the consequent sliding of glaciers into the ocean.
As you can read in the article below, the song slows down when the snow begins to melt in the upper layers of the pack ice.
As you can hear in the researcher's audio files, this has 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.
It was not music as we think. Days or months may elapse between each change of tone, composed of notes so low and so slow that they are inaudible to the human ear. But if you could stay 1000 years on Ross's big ice shelf and feel every thrill that went through it – if you were the snow itself – then you'd know the chorus.
In January 2016, the song became flat.
Accelerated thousands of times in the frequency range of the human audience, it seems that the sound of the ice is fading into a tone, a moaning whistle that has lasted two weeks among the hottest ever recorded on the polar continent . A song that warned of melting snow.
Listening
If scientists fear climatologists – if, during a particularly hot month of this century, the Ross Ice Cap dies out like a crumbling border wall, allowing the Antarctic interior glaciers to flow along the see little of the beginning of the calamity.
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. "A photo, it was there. The next was not the case. "
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. Finally, it becomes so hard that puddles form on the surface of the snow and flow downhill, digging tunnels in the snow to reach the ice below.
The ice is weakening like a decaying ship's hull under the onslaught of meltwater. 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.
[Scientists are slowly unlocking the secrets of the Earth’s mysterious hum]
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 climate scientists, they feared that if France-sized floating ice sheets collapsed – as Larsen B did in 2002 – the titanic glaciers behind would be free to escape the Antarctic continent. and to raise the level of the oceans by several feet.
"For now, the pack ice Ross seems stable," Chaput said. "But that could change extremely quickly and without warning."
The seismic stations were designed to measure what the Earth's crust and mantle are doing under the 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.
[Scientists stunned by Antarctic rainfall and a melt area bigger than Texas]
Chaput did not discover the great event of the cast of January 2016. As Chris Mooney wrote in the Washington Post, it bothered the scientists who had learned it at that 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 the crystals," Chaput said. "As they weaken, the speed of movement of a wave decreases and the tones go down." He sinks 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," said Chaput, who plans to continue his studies on the Arctic as a faculty member at the University of Texas at El Paso. "When it cools again, the nicotine heals partially and bounces in some ways, but not entirely."
He does not know if the Ross Ice Plate will regain its original structure and voice, or if it has been permanently damaged, because the Larsen B ice sheet had to be long before it broke. .
For the moment, even imperfectly, he continues to sing.
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