The sizzling of glacier ice as it melts into the sea is one of the most prominent sounds of a warming planet, researchers found.
The noise, caused by trapped air bubbles escaping from the sinking ice, was picked up by underwater microphones geophysicist Erin Petit, a researcher at the University of Alaska, set up off the Alaskan coast.
In a statement, Petit said she often heard popping and crackling sounds while kayaking in the northern waters, but the noise recorded underwater was at a much louder volume than above water.
"If you were underneath the water in a complete downpour, with the rain pounding the water, that's one of the loudest natural ocean sounds out there," Petit said. "In glacial fjords we record that level of sound almost continually."
Petit suspected the noise was coming from the melting glaciers, but she couldn't confirm that hypothesis without a more controlled experiment.
According to a press release, Petit enlisted the help of Kevin Lee and Preston Wilson, acoustics experts from the University of Texas. Pettit sent the Texas researchers chunks of glacier, which they mounted in a tank of chilled water. Lee and Wilson recorded video and audio of the ice as it melted and were able to match sounds on the recording to the escape of bubbles from the ice.
"Most of the sound comes from the bubbles oscillating when they're ejected," Lee said. "A bubble when it is released from a nozzle or any orifice will naturally oscillate at a frequency that's inversely proportional to the radius of the bubble."
By this, Lee means the smaller the bubble the higher the pitch. The researchers recorded sounds in the 1 - 3 kilohertz range, which is right in the middle of the frequencies humans hear
According to the researchers, the noise, caused by trapped air bubbles squirting out of the disappearing ice, could provide clues to the rate of glacier melt and help better monitor the fast-changing polar environments.
