A recent expedition to Antarctica revealed a puzzling discovery about the Ross Ice Shelf — the frozen continent’s largest floating slab of ice and the biggest ice shelf in the entire world.
As it turns out, the enormous Antarctic ice shelf — a plate of glacial ice about the size of Texas drifting over the Southern Ocean — is making a strange noise, “singing” into the wind as powerful gusts sweep across its surface.
According to the American Geophysical Union (AGU), the eerie “song” is actually a slow seismic hum produced by the ice shelf’s thick cover of snow as it vibrates under the merciless whipping of the wind.
This insulating “snow jacked” is known as firn and protects the ice below from warming temperatures. Made up of a dense layer of snow several meters deep, the firn takes on the full wrath of the wind above and is, therefore, under constant movement.
As a result, it gives off an incessant set of low-frequency tones — a somber tune that changes pitch as the wind blows across the massive snow dunes on top, remodeling the frozen landscape.
“It’s kind of like you’re blowing a flute, constantly, on the ice shelf,” says geophysicist and mathematician Julien Chaput from Colorado State University, lead author of a new study announcing the discovery.
His team spent more than two years studying the Ross Ice Shelf between late 2014 and early 2017. The scientists stumbled upon its secret “song” after burying 34 extremely sensitive seismic sensors across its surface and listening in on what goes on inside the snow blanket covering the Antarctic ice shelf.
“We discovered that the shelf nearly continuously ‘sings’ at frequencies of five or more cycles per second, excited by local and regional winds blowing across its snow dune‐like topography,” the authors wrote in their paper, published yesterday in the journal Geophysical Research Letters.
Although the “hum” of the Antarctic ice shelf is too low in frequency to be heard by human ears, Chaput managed to make it audible by speeding up the firn’s vibrations about 1,200 times.
Here’s what the “song” of the Ross Ice Shelf sounds like, as recorded in 2015.
“The scientists liken it to ‘singing’, but to our ears the creepy dirge of Antarctic ice shelf vibrations sounds more like the sinister score of a horror movie,” notes Science Alert.
Meanwhile, glaciologist Douglas MacAyeal of the University of Chicago, who wasn’t involved in the study, offers a different analogy to describe the ice shelf’s “song.”
“If this vibration were audible, it would be analogous to the buzz produced by thousands of cicada bugs,” MacAyeal writes in an accompanying commentary, published alongside the study.
While the “song” of the ice shelf can certainly make a lasting impression, it may also provide scientists with a way of monitoring the Antarctic ice from afar.
This is because the seismic hum coming from underneath the snow alters its pitch each time the firn undergoes a significant change. As Chaput explains, powerful storms that unleash strong winds across the surface of the ice shelf reshape the snow dunes on top, causing the firn to vibrate in a different way.
The same thing happens whenever the insulating jacket of snow starts melting, as his team observed during a warm spell in January 2016. Both types of events were found to affect the pitch of the “song,” changing the speed of seismic waves as they traveled through the firn.
“Either you change the velocity of the snow by heating or cooling it, or you change where you blow on the flute, by adding or destroying dunes,” remarked Chaput.
By tuning in to the “song” of the ice shelf, researchers could have an open line to what happens under the snowy surface and be alerted to the potential cracking and melting of Antarctic ice.
“The response of the ice shelf tells us that we can track extremely sensitive details about it,” said Chaput.
“Basically, what we have on our hands is a tool to monitor the environment, really. And its impact on the ice shelf.”