Glaciers Sizzle as They Melt Offering a Scientists New Way to Track the Process

Global warming is something you can hear, says geophysicist Erin Pettit of the University of Alaska.

Pettit often heard the crackling of glacier ice melting into the sea while she was out kayaking. She was also able to successfully pick up the sounds by underwater microphones she set up off the Alaskan coast.

"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."

In order to prove the noise came from melting ice, Pettit teamed up with Kevin Lee and Preston Wilson, acoustic experts from the University of Texas.

Pettit sent the duo chucks of glacier they then mounted in a tank of chilled water. In recording video and audio of the ice as it melted, the researchers were able to match the sounds to those of bubbles escaping from 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."

This means the smaller the bubble, the higher the pitch. Together the scientists recorded noises that ranged from 1-3 kilohertz, right in the middle of the frequencies the human ear can detect.

Bubbles form in glaciers when snow crystals trap pockets of air that are then slowly squashed under the weight of more snow. The snow then becomes ice as it is compacted and the air bubbles become pressurized. Because bubbles form in a regular pattern, they are evenly distributed throughout the ice, making them an effective tool in measuring ice melt, according to the researchers.

Because sound travels long distances underwater, noise measurements would allow scientists to detect rates of melting far from the unstable ice sheets.

According to the team of researchers, for these and other reasons, audio recordings would offer a beneficial complement to other measurements of ice melt, including salinity readings and time-lapse photography.