Wind on the snow dunes of the Ross Ice Shelf causes a near-constant hum that is as beautiful as it is haunting.
We usually think of the landscape as being relatively quiet. Sure, trees and creatures may create a cacophony of nature sounds, but the land itself generally plays the role of the strong and silent type.
In Antartica? Not so much. No, there the snow dunes conspire with the wind to produce a near-constant set of seismic tones that are hauntingly beautiful. It's as if they are alive.
The phenomenon was captured on Antarctica’s Ross Ice Shelf when scientists were studying the physical properties of the shelf, a plate of glacial ice the size of Texas that floats atop the Southern Ocean. The shelf is fed from the inside the continent and buttresses other ice sheets, helping to keep it all in place.
The researchers sunk 34 super sensitive seismic sensors into the shelf's snowy dunes in an effort to monitor vibrations and study its structure and movements. The sensors recorded date from late 2014 to early 2017.
"When the researchers started analyzing seismic data on the Ross Ice Shelf, they noticed something odd: Its fur coat was almost constantly vibrating," explains the American Geophysical Union (AGU).
The "fur coat" they refer to is comprised of thick blankets of snow topped with tremendous snow dunes, all acting like a coat to keep the ice below insulated, preventing it from heating up and melting.
"When they looked closer at the data, they discovered winds whipping across the massive snow dunes caused the ice sheet’s snow covering to rumble, like the pounding of a colossal drum," writes AGU.
When weather conditions changed the snow layer's surface, the pitch of this seismic hum changed as well.
“It’s kind of like you’re blowing a flute, constantly, on the ice shelf,” said Julien Chaput, a geophysicist and mathematician at Colorado State University in Fort Collins and lead author of the study.
Chaput explains that much in the way a musician can alter the pitch of a flute's note by changing which holes are blocked and how fast the air flows, so does weather change the frequency of the vibrations by altering the dunes' topography.
“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,” he says. “And that’s essentially the two forcing effects we can observe.”
The amazing thing is that beyond their beauty, the songs of the snow dunes could actually prove to be valuable to researchers.
Stable ice shelves prevent ice from flowing faster from land to sea ... which can raise sea levels. As ice shelves across Antarctica have been feeling the effects of increasing air and water temperatures, they have been thinning and even breaking or retreating.
Now the researchers think that setting up "seismic stations" could help them to continuously monitor the conditions on ice shelves in near real-time. In an accompanying editorial comment to the study, University of Chicago glaciologist Douglas MacAyeal, writes that studying the vibrations of an ice shelf’s insulating snow jacket could give scientists a sense of how it is responding to changing climate conditions. A changing hum could offer clues about conditions of melt ponds or cracks in the ice.
As Chaput adds, it could act as an ear to the ground, so to speak, in tracking both the ice shelf itself and the environment at large as well.
“The response of the ice shelf tells us that we can track extremely sensitive details about it,” Chaput said. “Basically, what we have on our hands is a tool to monitor the environment, really. And its impact on the ice shelf.”
The research was published in the AGU journal, Geophysical Research Letters.