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Study co-author Rick Aster on a set-up tour of the Ross ice shelf equipped with a broadband seismometer. These sensitive sensors were buried at depths of two meters (6 feet) to record the microscopic scale seismic movements of the pack ice in three dimensions over a two year period. Credit: Rick Aster.
Winds blowing over the snow dunes on the Antarctic ice shelf in Ross are thrilling the surface of the massive ice slab, producing an almost constant set of seismic "tones" that scientists could potentially use to monitor changes of the ice shelf by far, according to new research.
The Ross ice floe is the largest ice floe in the Antarctic, a plate of glacial ice the size of Texas, fed by the interior of the icy continent that floats over the Southern Ocean. The pack ice reinforces adjacent ice sheets on the Antarctic continent, preventing ice from flowing from the ground into the water, like a cork in a bottle.
When ice trays collapse, ice can move more quickly from the land to the sea, which can raise sea levels. Antarctica have been thinning and, in some cases, have broken or retreated due to rising ocean and air temperatures. Previous observations have shown that Antarctic ice floes can collapse sharply and without obvious warning signs, which occurred during the abrupt collapse of the Larsen B ice shelf on the Antarctic Peninsula in 2002.
To better understand the physical properties of Ross ice floes, the researchers buried 34 extremely sensitive seismic sensors under its snow-covered surface. The sensors allowed the researchers to monitor the pack ice vibrations and study its structure and movements for more than two years, from late 2014 to early 2017.
The ice floes are covered with a thick layer of snow, sometimes reaching several meters deep, topped with huge snow-covered dunes, like sand dunes in a desert. This layer of snow acts as a fur coat for the underlying ice, isolating the ice from the heat and melting even as the temperature increases.
When the researchers began analyzing the seismic data on Ross's ice shelf, they noticed a strange phenomenon: his fur coat vibrated almost constantly.
Looking more closely at the data, they realized that winds blowing over the huge snow dunes caused the roar of the ice sheet, like the sound of a colossal drum. Listen to the "song" of the ice cap here.
They also noted that the height of this seismic buzz was changed as weather changed the surface of the snow cover. They discovered that the ice vibrated at different frequencies when strong storms rearranged the snow dunes or that the temperature of the air at the surface rose or fell, which changed the speed at which the seismic waves propagated in the sea. snow.
"It's a bit like you're constantly blowing on the pack ice," said Julien Chaput, a geophysicist and mathematician at Colorado State University in Fort Collins and senior author of the new study published today in the Letters of geophysical research, a journal of the American Geophysical Union.
Just as musicians can change the pitch of a note on a flute by changing the holes in which the air is flowing or how fast, the weather on the ice can change the frequency of its vibrations by altering its dune topography, according to Chaput.
"Either you change the speed of the snow by heating it or cooling it, or you change the place where you blow into the flute, adding or destroying dunes," he said. "And these are essentially the two forcing effects that we can observe."
The buzz is too low to be heard by human ears, but new findings suggest that scientists could use seismic stations to continuously monitor conditions on ice platforms in near real time. According to Douglas MacAyeal, a glaciologist at the University of Chicago who did not participate in the new study, commented on the vibrations of the insulating snow jacket of an ice floe, scientists might have an idea of how it reacts. to climate change. the results also published today in Letters of geophysical research.
Modifications to seismic snoring on ice could indicate whether melt ponds or ice cracks are forming that may indicate if the ice is likely to break.
"The reaction of the pack ice tells us that we can follow extremely sensitive details about it," Chaput said. "Basically, what we have in our hands is a tool to monitor the environment, really, and its impact on the pack ice."
Explore further:
Tracing the Antarctic Ice Age
More information:
J. Chaput et al., Enforced changes to the environment near the Ross ice floe surface observed with ambient seismic noise, Letters of geophysical research (2018). DOI: 10.1029 / 2018GL079665
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