"Nov.
27, 2013 — Scientists
have recorded and identified one of the most prominent sounds of a warming
planet: the sizzle of glacier ice as it melts into the sea. The noise, caused
by trapped air bubbles squirting out of the disappearing ice, could provide clues
to the rate of glacier melt and help researchers better monitor the
fast-changing polar environments."
Erin Pettit, a
geophysicist and researcher at the University of Alaska, would constantly hear
popping and cracking sound when she would kayak in the northern waters.
Underwater microphones that she had set up also picked up the sounds. She
believed it to be the melting of ice but couldn’t confirm her theory. So she
received help from Kevin Lee and Preston Wilson who are acoustic experts from
the University of Texas. She sent them a chunk of glacier, which they mounted
in a tank of chilled water. They recorded the audio and vide of the ice melting
and matched the sounds of the recording to the escape of bubbles from the ice.
Lee said that the bubbles make sound when they are being released by
oscillating at a frequency between 1 – 3 kilohertz. He said that the smaller
the bubble the higher the pitch would be.
Scientists have
known for decades that bubbles form in glaciers when snow crystals trap air and
then get squashed down under the weight of more snow. As more snow accumulates
and compacts, it turns into ice and that air bubbles are pressurized. The
bubbles form by even distribution within the ice. This is a way that can
measure the rate of ice melting.
“Pettit and Lee
say they could imagine using hydrophone recordings in glacial fjords to monitor
relative changes in glacier melting in response to one-time weather events,
seasonal changes, and long-term climate trends.” Sound travels a long distance underwater;
therefore they are able to place microphones far underneath unstable sheets of
ice to record sound. The audio recordings would complement other methods of
measuring the rate of ice melting.
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