Scientists listen to glaciers to discover the secrets of the oceans

Scientists listen to glaciers to discover the secrets of the oceans
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Editor’s Note: Call to Earth is a CNN initiative in partnership with Rolex. Michel André Rolex Award Winner.


It’s crunchy, it’s crunchy, it’s the sound of a glacier. Large densely packed ice floes may look like inert masses, but they flow and break and they get bigger and smaller, and these processes are anything but silent.

In fact, glacial ice is notoriously gassy. Its cubes have long been used on cruise ships in Alaska, added to a Scotch or a gin and tonic because the ice emits a unique hiss as it slowly releases the high-pressure air that has been trapped there for hundreds and sometimes thousands of years. years.

But the sounds glaciers make can be used for more than just new ice cubes. With Many glaciers around the world are shrinking Due to the climate crisis, scientists are trying to analyze these sounds to predict exactly how fast the ice is melting and what this might mean for sea level rise.

“Glaciers are shrinking rapidly as the atmosphere and ocean warms,” ​​says Grant Deane, a research associate 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 sound can be an important and interesting way to do that.”

Deane, who has worked in the field of underwater sound for over two decades, explains that there are two main processes by which glaciers retreat, both of which make a distinctive sound. There’s the “bright, energetic sound of bubbles popping into the water as the ice melts,” which he compares to fireworks or sizzling bacon. And when a block of ice breaks off from the end of a glacier, there’s the “deep, ominous rumble” of a calving event that he says sounds like a long thunder.

Both events take place on the border where the ice meets the ocean, often in a very dangerous area for humans. This is one reason why remote-monitored acoustics are so valuable.

Using 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. Nature Geology He proposed using hydroacoustics (sound in water) to monitor Greenland’s ice sheets. This inspired Deane, who was already listening to the breaking waves of the ocean to understand how gases move from sea to air, to turn his ears to glaciers.

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

Deane and Oskar Glowacki of the Polish Academy of Sciences showed that, in conjunction with time-lapse photography, the amount of ice loss can be estimated from the noise produced by using underwater microphones to record the sound of calving events at Hans Glacier in Svalbard, northern Norway. when an iceberg hits the ocean. Their findings were published in the journal. cryosphere diary in 2020.

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

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Simple in idea, but far from simple in practice. Deane says the volume of air bubbles varies depending on how they are released, and that noise levels are likely to vary between glaciers due to geology and local conditions.

But Deane’s Researchshowed that the intensity of the sound produced by air bubbles increases as the water temperature increases, and that the volume may be an indicator of melting ice. “With each discovery, we get closer to the real answer, where we can convert these signals into the numbers we need,” he says.

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

Several different and some much more advanced methods already exist for studying glaciers, such as seismology, satellite photography, underwater sonar and ice-penetrating radar. But Deane insists that acoustics can complement these methods and offer some advantages.

Hydrophones (underwater microphones) can be deployed in glacial fjords and monitored remotely over long timescales, he says, and unlike satellite observations that don’t work six months out of the year when it’s dark at the north and south poles, acoustic technology works all year round and is less expensive than other methods.

Listening to glaciers not only shows us how they melt, but can teach us more about the marine ecosystem. Glaciologist Erin Pettit used acoustic technology to determine this. glacial fjords They are some of the loudest places in the ocean, thanks to the constant hiss of air bubbles released as the ice melts, and this sound can provide shelter for marine mammals.

Pettit and his research team observed how seals swim to glacial bays in Alaska and Antarctica, possibly to protect themselves from predatory whales who don’t like loud noises.

“As the soundscape changes, so does the ecosystem,” he says, adding that if the sound level goes up or down there will be a ripple effect. “If the glacier comes out of the fjord and there is less ice in the water itself, the sound will gradually decrease…then it will no longer be noisy and it will not be a safe place for seals.” In this way, acoustic measurements can give an idea about the reduction of seal populations in these regions.

Icebergs breaking off the end of Le Conte Glacier in Alaska.

Pettit notes that the acoustic field is still in its early days, and scientists need to collect more robust data to measure long-term changes in glaciers. But he believes the technology shows great promise.

“Sound doesn’t give us all the answers – but it does provide a relatively low-cost, easy-to-deploy tool for capturing the entire fjord and glacial environment,” he says. If hydrophones were deployed over an extended period of time, they could help scientists understand the “normal” noise levels of a glacier and detect abnormal sounds that could indicate instability, he adds.

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Deane’s goal is to set up long-term acoustic monitoring stations to follow in Wolfgang Berger’s footsteps and help monitor ice sheet stability in Greenland. 25 feet sea level if it melted completely.

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

“The future of the oceans depends on us (people),” he adds. “We need to start listening to what they’re telling us.”

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