Editor’s note: Call to Earth is a CNN initiative in partnership with Rolex. Michel Andre is a laureate of the Rolex Awards.
Click, crack, pop: the sound of a glacier. Large bodies of tightly packed ice may look like immobile masses, but they flow and break, grow and shrink, and these processes are anything but silent.
In fact, glacial ice is known as carbonated. Cubes of it have long been used on cruise ships in Alaska, added to scotch or gin and tonic, because the ice makes a unique hiss as it slowly releases the high-pressure air that has been trapped there for hundreds, sometimes thousands of years .
But the sounds made by glaciers can be used for more than just new ice cubes. with Many glaciers around the world are shrinking Because of the climate crisis, scientists are looking to analyze these noises to predict exactly how fast the ice is melting and what that might mean for sea level rise.
“Glaciers are undergoing rapid retreat as the atmosphere and ocean warm,” says Grant Dean, a research oceanographer at the Scripps Institution of Oceanography in San Diego, California. “If we want to (predict) sea-level rise … we need a way to monitor these glacial systems, and underwater sounding can be an important and interesting way to do that.”
Dean, who has worked in the field of underwater sound for more than two decades, explains that there are two main processes by which glaciers retreat, both of which produce different noises. There’s a “bright, energetic sound of bubbles exploding in the water as the ice melts,” he says, which he compares to fireworks or sizzling bacon. There’s also the “deep, eerie rumble” of a calving event, when a block of ice breaks off the end of a glacier, which he says sounds like sustained thunder.
Both events occur at the boundary where the ice meets the ocean, normally a very dangerous area for humans. This is one of the reasons that acoustics that can be observed from afar are so valuable.
Using underwater sounding to predict ice melt is still a relatively new field. In 2008, the eminent oceanographer Wolfgang Berger co-authored an article in the scientific journal Nature Geoscience who proposes the use of hydroacoustics (sound in water) to monitor the Greenland ice sheets. This inspired Dean – who was already listening to the crashing waves of the ocean to understand how gases are carried from the sea into the air – to turn his ears to the glaciers.
“As the ocean rises, it will affect much of our civilization. We need to be able to predict the stability of these ice sheets so we can plan well and live well as our environment changes,” he says.
Using underwater microphones to record the sound of calving events on Hans Glacier, in Svalbard, northern Norway, along with time-lapse photography, Dean and Oskar Glowacki of the Polish Academy of Sciences demonstrated that the amount of ice loss can be estimated from the noise made when an iceberg breaks into the ocean. Their findings were published in Cryosphere Journal in 2020
Air bubbles can also reveal vital information. “If we can count how many bubbles come out of the ice per unit time, we can tell how much ice has melted,” says Dean. This could be the key to understanding how much ice will melt in the future.
It’s simple in idea, but far from simple in practice. The volume of the air bubbles changes depending on how they’re released, Dean says, and it’s possible that noise levels vary between glaciers due to geology and local conditions.
But Dean’s research, focusing primarily on Svalbard, showed that the intensity of sound generated by air bubbles increases as water temperature increases, showing that sound volume can be an indicator of ice melting. “With each expedition, we get closer to the actual answer, where we can turn those signals into the numbers we need,” he says.
Several different and some much more developed methods for studying glaciers now exist, including seismology, satellite photography, underwater sonar, and ice-penetrating radar. But Dean insists that acoustics can complement these methods and offer some advantages.
Hydrophones (underwater microphones) can be deployed in glacial fjords and monitored remotely for long periods of time, he says, and unlike satellite observations, which don’t work during the six months of the year when it’s dark at the North and South Poles, acoustic technology works all year round and is cheaper than other methods.
Listening to glaciers doesn’t just show us how they’re melting—it can also teach us more about the marine ecosystem. Glaciologist Erin Pettit used acoustic technology to determine this glacial fjords are some of the noisiest places in the ocean thanks to the constant hiss of air bubbles released as the ice melts, and this noise can provide refuge for marine mammals.
Pettit and her team of researchers watched the seals swim to glacial bays in Alaska and Antarctica, presumably to protect themselves from predatory whales that don’t like loud noises.
“The ecosystem changes as the soundscape changes,” she says, adding that if the volume is increased or decreased, there will be a ripple effect. “If the glacier rises out of the fjord and there’s less ice in the water itself, the sound will slowly decrease … then it’s no longer noisy and it’s no longer a safe place for the seals.” In this way, acoustic measurements could offer insight into the decline of seal populations in these areas.
Pettit notes that the field of acoustics is still in its infancy, and to measure long-term changes in glaciers, scientists will need to collect more robust data. But she believes the technology holds great promise.
“Sound doesn’t give us all the answers – but it provides a relatively cheap, easy-to-deploy means of capturing the whole fjord and glacier environment,” she says. If the hydrophones were deployed over a long period of time, they could help scientists understand the glacier’s “normal” noise levels and detect unusual sounds that could indicate instability, she added.
Dean’s goal is to follow in the footsteps of the late Wolfgang Berger and establish long-term acoustic monitoring stations in Greenland to help track the stability of its ice sheet, which could increase sea level by 25 feet if completely melted.
“I want recording systems running from south to north around the Greenland ice sheets,” he says. “The first task is to make sure we can understand the sounds. If we can prove that we can do that, then we can argue that we should be continuously listening to these glaciers.”
“The future of the oceans depends on us (humans),” he adds. “We have to start listening to what they are telling us.