Scientists listen to glaciers to discover the secrets of the oceans

Editor’s note: Call to Earth is a CNN initiative in partnership with Rolex. Michel Andre It is a Rolex Award winner.



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Snap, bang, bang: the sound of a glacier. Large bodies of densely packed ice may look like static blocks, but they flow, crack, grow and contract, and these processes are anything but silent.

In fact, glaciers are notorious for being invasive. Cubes of it have long been used on Alaskan cruise ships, added to Scotch or gin and tonic, as the ice emits a unique hiss when it slowly releases the intensely pressured air that’s been held there for hundreds and sometimes thousands of years.

But the sounds of glaciers can be used for more than just fresh ice cubes. with Many glaciers around the world are shrinking Because of the climate crisis, scientists are looking to analyze this noise to predict exactly how fast the ice will melt and what it might mean for sea level rise.

“Glaciers are retreating rapidly as the atmosphere and oceans warm up,” 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 ice systems and underwater sound could 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, and both make distinct noises. There is “the bright, vibrant sound of bubbles exploding in the water as the ice melts,” he says, which he compares to fireworks or sizzling bacon. And there’s the “ominously deep bang” of the birth event, when a lump of ice breaks off the end of a glacier, which he says sounds like extended thunder.

Both events occur at the boundary where the ice meets the ocean, usually a very dangerous area for humans. This is one reason why acoustics, which can be monitored from afar, are so valuable.

The use of underwater sound to predict ice melt is still a relatively new field. In 2008, distinguished oceanographer Wolfgang Berger co-authored an article in the scientific journal natural earth sciences which proposed the use of hydroacoustics (sound in water) to monitor the Greenland ice sheets. This inspired Dean—who was already listening to the breaking ocean waves to understand how gases move from sea to air—to turn his ears to the glaciers.

“As the ocean rises, it will affect a lot of our civilization. We need to be able to predict the stability of these ice sheets so we can plan well and live well with our environment changes,” he says.

Using underwater microphones to record the sound of calf birth events at Hans Glacier, in Svalbard, northern Norway, along with time-lapse photography, Deane and Oskar Glowacki of the Polish Academy of Sciences show that the amount of ice loss can be estimated from the noise generated when an iceberg hits by the ocean. Their findings were published in Cryosphere Magazine in the year 2020.

Air bubbles can also reveal vital information. “If we can count the number of bubbles coming out of the ice in any given unit of time, we can tell how much ice has melted,” Dean says. This may be key to understanding how much ice will melt in the future.

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It’s a simple idea, but far from simple in practice. Dean says the size of the air bubbles changes depending on how they are released, and there is a possibility that noise levels may vary between glaciers due to geology and local conditions.

but religion Research, focusing mostly on Svalbard, showed that the intensity of the sound produced by air bubbles increases with increasing water temperature, indicating that volume can be an indicator of ice melt. “On each expedition, we get closer to the actual answer as we can convert those signals into the numbers we need,” he says.

A close-up of an iceberg shows its high density of air bubbles.

Several different methods, some of them more sophisticated, actually exist for studying glaciers, including seismology, satellite imaging, underwater sonar and ice-penetrating radar. But Dean insists that acoustics can complement these methods and offer some advantages.

Hydromics (underwater microphones) can be deployed in ice straits and monitored remotely over long periods of time, he says, and unlike satellite observations, which don’t work for six months out of the year when it’s dark at the North and South poles, the acoustic technology It operates all year round and is cheaper than other methods.

Listening to glaciers not only shows us how they are melting – it can also teach us more about the marine ecosystem. Glaciologist Irene Pettit used acoustic technology to determine this icy fjords Are some of the loudest places in the ocean thanks to the constant hissing of air bubbles emitted as the ice melts, and these noises can provide a haven for marine mammals.

Pettit and her team of researchers have observed how seals swim to glacier bays in Alaska and Antarctica, possibly to protect themselves from predatory whales that don’t like loud noises.

“The ecosystem changes as the audio landscape changes,” she says, adding that if the volume goes up or down, there will be a ripple effect. “If the glacier withdraws from the fjord and there is a little ice in the water itself, the sound will slowly decrease… then it is no longer noisy and it is no longer a safe place for the seals.” In this way, acoustic measurements can provide insight into the decline in seal populations in these areas.

Icebergs born from the end of the Lo Conte Glacier, Alaska.

Pettit notes that the field of acoustics is still in its early days, and to measure long-term change in glaciers, scientists will need to gather more sound data. But she believes the technology holds great promise.

“Audio doesn’t give us all the answers — but it does provide a relatively low-cost, easy-to-use way to capture the fjord and the entire icy environment,” she says. She adds that if hydrophones are deployed over a long period, they could help scientists understand the “normal” noise levels of glaciers, and detect abnormal sounds that may indicate instability.

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Deane’s goal is to follow in the footsteps of the late Wolfgang Berger and set up long-term acoustic monitoring stations in Greenland to help track the stability of the ice sheet, which could be rising. Sea level by 25 feet If it will completely dissolve.

“I want logging systems that run from south to north around the Greenland glaciers,” he says. “The first task is to make sure that we can understand the sounds. If we can prove that we can do that, then we can prove that we must constantly listen to these glaciers.”

“The future of the oceans depends on us[humans],” he adds. “We need to start listening to what they tell us.”

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