10 May 2018

Sounds of melting glaciers could reveal how fast they shrink

Posted by Lauren Lipuma

By Lauren Lipuma

Scientists could potentially use the racket made by melting glaciers to estimate how fast they are disappearing, according to a new study of audio recordings captured in the waters of an Arctic fjord.

As glaciers melt, air bubbles trapped in the ice make popping or crackling sounds when they meet seawater, the same way ice cubes sizzle when placed in a warm drink.

New underwater recordings taken from Hornsund fjord in Svalbard, Norway, show melting icebergs make more noise the faster they melt. The recordings also distinguish melting sounds from grounded glaciers and floating icebergs.

The results suggest scientists could potentially use acoustics to track how fast Arctic glaciers are melting, according to a new study detailing the findings in Geophysical Research Letters, a journal of the American Geophysical Union.

Scientists typically measure glacier retreat by analyzing satellite data, but acoustic recordings would allow scientists to better understand what’s happening where the ice meets ocean water, an area difficult to observe with satellites.

Estimating glacier melt would help scientists better understand the effects of sea level rise, according to the researchers. The Arctic is warming at an unprecedented pace, and the melting of Arctic ice contributes to global sea level rise, which is currently about 3.4 millimeters (one-eighth of an inch) per year, according to NOAA.

“There is great possibility to use noise produced by bubbles trapped in glacier ice to study changing climate associated with iceberg melt and glacier melt,” said Oskar Glowacki, a geophysicist at Scripps Institution of Oceanography at the University of California San Diego and lead author of the new study.

“These tiny air bubbles are singing songs, and these songs are the songs of the changing climate.”

Listening for sounds of change

Pockets of air between snowflakes get trapped and compressed over time as layers of snow build up and condense into ice to form glaciers. Icebergs break off glaciers where the ice meets the sea.

Acoustic recordings made near drifting icebergs in the early 1970s showed ice “sizzles” when it melts, as the air bubbles trapped in the ice explode into seawater. Research published in 2015 showed melting glaciers are the loudest places in the ocean and scientists could potentially use this noise to study the melting ice.  

In the new study, Glowacki and colleagues from Scripps and the Polish Academy of Sciences in Warsaw placed microphones that can record underwater in Hornsund fjord during the summers of 2013, 2015 and 2016. They wanted to capture sounds of melting glaciers within the fjord to see if they could use the noise as a proxy for how fast the glaciers were melting. They also wanted to see if they could distinguish between sounds made by melting icebergs and those made by the glaciers themselves.

The researchers found the hiss of melting icebergs is slightly different than the sound of melting glaciers. Recordings of the glaciers revealed the explosions of bubbles into seawater were continuous, like rain hitting the surface of a lake.

This recording captures 30 seconds of underwater sound produced by the melting of Hans Glacier in Hornsund fjord, pictured here. Credit: Oskar Glowacki.

But with melting icebergs, the noises were more discrete: The researchers could hear individual bubbles bursting in the water when the icebergs were close to the microphones. Glowacki suspects this is because icebergs are much smaller than the glaciers they broke off of and therefore have fewer air bubbles overall.

This recording captures thirty seconds of underwater sound produced by an iceberg in close proximity to the underwater microphone. Credit: Oskar Glowacki.

The study’s authors also found the iceberg sounds changed depending on where the iceberg was in relation to the microphones, meaning researchers could use the recordings to track the movements of individual icebergs over time.

The researchers also quantified the sound energy released by melting icebergs and found they crackle louder when they melt faster.  

“In locations where we expect higher melt rates, we hear more intense noise, which is the first sign that maybe in the future it will be possible to use the noise to estimate the melt rate,” Glowacki said.

Taken together, the findings suggest scientists could use acoustics to estimate how fast Arctic glaciers are melting, according to the authors. The next step will be to correlate the sound levels to rates of glacier retreat, Glowacki said.

— Lauren Lipuma is AGU’s public information specialist and science writer. Follow her on twitter at @Tenacious_She.