The popping, crackling noises, caused by trapped air bubbles squirting out of disappearing ice, could provide clues to the rate of glacier melt and help researchers better monitor fast-changing polar environments, University of Alaska researchers reported Thursday.
Geophysicist Erin Pettit said she often hears such sounds when kayaking in frigid northern waters, and when she set up microphones underwater the sounds came through even louder.
"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," she said. "In glacial fjords we record that level of sound almost continually."
To confirm the glacial source of the sound, chunks of glacier ice were placed in a tank of chilled water, and video and audio recordings were able to match sounds captured to the escape of bubbles from the ice.
"Most of the sound comes from the bubbles oscillating when they're ejected," said Kevin Lee, an acoustics experts from the University of Texas who helped conduct the lab experiment.
"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," he said, meaning the smaller the bubble, the higher the pitch.
The bubble sounds recorded were right in the middle of the frequencies humans can hear, the researchers said.
Using hydrophone recordings of sounds in glacial fjords might help monitor relative changes in glacier melting in response to one-time weather events, seasonal changes, and long-term climate trends, they said.
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