Antarctic ice shelf ''sings'' as winds whip across its surface

Washington

Winds blowing across snow dunes on Antarctica's Ross Ice Shelf cause the massive ice slab's surface to vibrate, producing a near-constant set of seismic "tones" which  could be used to monitor changes in the ice from afar, according to a study.

The Ross Ice Shelf is Antarctica's largest ice shelf, a Texas-sized plate of glacial ice fed from the icy continent's interior that floats atop the Southern Ocean, said researchers at Colorado State University in the US.

The ice shelf buttresses adjacent ice sheets on Antarctica's mainland, impeding ice flow from land into water, like a cork in a bottle, according to the study published in the journal Geophysical Research Letters.

 When the researchers started analysing seismic data on the Ross Ice Shelf, they noticed something odd: Its fur coat was almost constantly vibrating.

 "It's kind of like you are blowing a flute, constantly, on the ice shelf," said Julien Chaput, a geophysicist at Colorado State University.

 To better understand the physical properties of the Ross Ice Shelf, researchers buried 34 extremely sensitive seismic sensors under its snowy surface.

 The sensors allowed the researchers to monitor the ice shelf's vibrations and study its structure and movements for over two years, from late 2014 to early 2017.

 Ice shelves are covered in thick blankets of snow—often several metres deep—that are topped with massive snow dunes, like sand dunes in a desert.

 This snow layer acts like a fur coat for the underlying ice, insulating the ice below from heating and even melting when temperatures rise.

Researchers discovered winds whipping across the massive snow dunes caused the ice sheet's snow covering to rumble, like the pounding of a colossal drum.

They also noticed the pitch of this seismic hum changed when weather conditions altered the snow layer's surface.

The researchers found the ice vibrated at different frequencies when strong storms rearranged the snow dunes or when the air temperatures at the surface went up or down, which changed how fast seismic waves travelled through the snow.

Just like musicians can change the pitch of a note on a flute by altering which holes air flows through or how fast it flows, weather conditions on the ice shelf can change the frequency of its vibration by altering its dune-like topography, according to Chaput.

The hum is too low in frequency to be audible to human ears, but the new findings suggest scientists could use seismic stations to continuously monitor the conditions on ice shelves in near real-time. PTI