Popping Air Bubbles Create Loudest Underwater World on Earth

The sound of bubbles escaping from melting ice is so loud that scientists report the glacial fjords where the melting occurs are one of the loudest natural marine environments on Earth.

University of Alaska geophysicist Erin Pettit said the cracking, popping sound of air bubbles escaping melting ice can be heard heard from the surface by kayakers, but that below the surface the noise is much louder. Pettit said the noise is among the loudest sounds in the ocean.

"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."

The noise could also give researchers clues to better monitor for changing environmental conditions in the polar climate.

Because Pettit could not confirm her suspicions that the noise was indeed coming from the bubbles of trapped air escaping from melting ice, she teamed up with Kevin Lee and Preston Wilson, acoustics experts from the University of Texas. The acoustics experts mounted a chunk of glacier ice in a tank of cold water and recorded video and audio of the melting process. When the lab recordings were compared against ice melting noises recorded in the field, the sounds matched.

"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," he said, meaning the smaller the bubble, the higher the pitch.

While the phenomenon of noisy ice melting has been on the record for years, this latest research pointed to the uniformity in which the air bubbles are released from the ice, which is important if researchers want to use sound intensity of air bubbles escaping from ice as a measure for the melt rate.

The researchers envision using the sound intensity to monitor relative change in glacier ice in response to one-time weather events.

Petitt, Lee and Wilson will present their research at the upcoming 16th meeting of the Acoustical Society of America.