How the mournful songs of icebergs reverberate around the world

Icebergs produce some of the loudest natural noises in the oceans. Can we learn anything about their birth, life and death by listening in?

From the surface, the ice shelves of Antarctica are vast, white deserts – almost featureless save for a few ruts and crevices. Occasionally, cracks as long as a small country can widen and a piece breaks off, forming huge icebergs that drift out into the Southern Ocean.

Hemmed in by the sea ice that forms around the continent, and caught in vast traffic jams of fellow floating ice, the progress of these giant frozen slabs is slow. For months at a time, they barely move. Stand on one of these tabletop-shaped ice giants and only the occasional creak betrays their movement. But underwater, another story unfolds – the icebergs are singing.

When played at frequencies audible to human ears, it could easily be mistaken for whale song. But in fact, the noise is produced by the grinding and scraping of the craggy underside of these icebergs on the seafloor and as they rub against each other. The resulting song can be detected thousands of miles away in the far-off waters of the Indian Ocean.

"An iceberg plate works as a tuning fork," says Alexander Gavrilov, a professor at the Centre for Marine Science and Technology at Curtin University in Australia. "The song frequencies depend on iceberg's dimensions."

It is a haunting lament to the final, inevitable fate of all icebergs. As they drift into warmer waters, they begin to collapse and the sounds they produce change from a song to a raucous clanging.

Meanwhile, in the Arctic Ocean, icebergs create a different, but almost as deafening, noise as they calve off Greenland's enormous tongues of glacier ice and break apart.

Now, at both ends of the planet, scientists are tuning into the music of icebergs in the hope of gaining new insights into the birth and death of icebergs, and how climate change is altering these processes.

"These are really powerful noises," says Vera Schlindwein, a professor of polar and marine seismology at the University of Bremen in Germany and a researcher with the Alfred Wegener Institute's Helmholtz Centre for Polar and Marine Research. "When they were first discovered, research on iceberg sounds was mainly just out of curiosity."

With modern satellite imagery and the ability to set up seismic and acoustic monitoring systems close to the source of the sounds, that is now changing, says Schlindwein.

In the Antarctic, the effects of climate change are a complicated picture. Some parts of the continent are warming far faster than others, while in some areas the extent and thickness of the ice shelves that stretch out over the ocean, along with the amount of seasonal sea ice, has been increasing. One signal that has emerged in recent years is extreme variability in conditions around the frozen continent. And this has a corresponding effect on the icebergs Antarctica gives birth to.

The amount of noise produced by icebergs waxes and wanes on many different timescales. The tides generate movement on a daily basis that causes neighbouring icebergs to rub against each other or grind the seafloor, the frequency of the noise they produce changing with the speed of that grinding. There are seasonal signals too – the amount of noise generated by icebergs in the Southern Ocean goes up and down as Antarctica moves from summer to winter. As giant icebergs collapse in the warmer temperatures, enormous blocks crash into the ocean, generating a cacophony of deep booming sounds and "bloops" that radiate out across the ocean.

Variation over longer timeframes, however, is much more mixed. One study in the South Atlantic, for example, found that as total iceberg volume decreased between 2004 and 2012, so did the low-frequency noise levels produced by melting icebergs. Others, however, have struggled to see any trends in long-term acoustic recordings. Gavrilov recently did some preliminary analysis of a set of hydroacoustic recordings from between 2002 and 2022, obtained by three listening stations in the Indian Ocean that are used to monitor for nuclear explosions under the Comprehensive Nuclear Test Ban Treaty. There wasn't any obvious interannual trend, although he cautions a more thorough analysis is needed and the results haven't been published in a peer-reviewed journal or made public yet.

The harmonic songs of Antarctic icebergs are particularly difficult to associate with individual events, says Schlindwein. When the strange wailing they produce was first detected in 2002 in recordings taken by hydroacoustic sensors in Polynesia, scientists were able to attribute them to a large iceberg that calved off Antarctica's enormous Ross Ice Shelf. There had been hopes that it might be possible to use these songs as a way of monitoring the break-up of ice around the continent remotely, but as more researchers analysed such recordings, it became apparent that the songs were a near constant noise emanating from the south of our planet.

"It doesn't work for the continuous songs at a distance as you don't know the beginning of the signal," says Schlindwein. "But sometimes icebergs run really powerfully into the ground and make a short earthquake. If you can pick that up on a seismic array and see an iceberg turning in satellite images, you can be say, 'OK, this iceberg has been in ground contact'," she says.

To really understand what is going on you need to get your seismic arrays and hydrophones as close as possible to the icebergs themselves. "It's all a question of logistics," says Schlindwein. "Go to the iceberg, bring your seismometers, leave them out, pick them up again in the next survey."

That is expensive and time-consuming work. Scientists at the Ukrainian Antarctic research base Vernadsky Station have installed seismic and infrasound detectors to monitor the ice cap and glaciers of the Antarctic Peninsula. Although the 2022 escalation of the war in Ukraine has waylaid their research, the equipment is allowing them to monitor avalanches and iceberg calving remotely, says Alex Liashchuk, a geophysicist working at the State Space Agency of Ukraine, who was one of those leading the project.

"The data is sent to Ukraine, and the staff at the Antarctic station maintain the equipment," he says.

In the Arctic, however, it is a different story. Here the icebergs don't sing as they don't reach the kind of sizes needed for this, but the underwater booms as glacier ice calves off into fjords, the roar as they tumble through the water and clangs as the icebergs break apart offer a window into the effects of climate change. Scientists have also detected the underwater crackle of bubbles being released from the melting glacier ice in fjords.

Researchers at the Scripps Institution of Oceanography in La Jolla, California, have found they can estimate levels of ice loss from Arctic glaciers from the underwater noise produced. Such techniques are proving to be particularly useful during winter, when sea ice makes accessing such areas difficult. Scientists working around Svalbard in Norway, for example, found underwater noise associated with melting could help to identify abnormal spikes in sea temperatures. These events are often related to sudden intrusions of warm water due to extreme cyclone events – sometimes called weather bombs – and may play an important role in the loss of Arctic.

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Some researchers are now hoping to use acoustic arrays deployed in the Arctic to help them monitor rates of iceberg calving from glaciers over longer timescales to help them spot changes that are occurring annually as the climate warms.

Schlindwein herself is planning a project next summer where she will install seismometers in front the Nioghalvfjerdsbrae glacier in Greenland. "There's a lot of local seismicity there," she says. "It may be related to the contact of icebergs with the ground or crashing against something."

But the noise produced by icebergs isn't just of interest to climate researchers. It could also be affecting the marine wildlife around the poles.

The sounds produced by calving icebergs in Greenland, for example, are the loudest natural source of noise in the Arctic. One recording of an iceberg breaking off the Bowdoin Glacier in Greenland in July 2019 produced a "detonation-like" sound that lasted for around 30 minutes and was equivalent to an explosion of 0.1-7.6 tonnes TNT. The event, produced noise in frequencies that also happen to be within the same frequency range as that used by the enigmatic horned Arctic sea mammal, narwhals.

"The loudest noise is usually associated with iceberg capsize, which occurs after calving at glacial fronts," says Evgeny Podolskiy, an associate professor at the Arctic Research Center of Hokkaido University in Japan. "Calved icebergs are gravitationally unstable. After rupturing off, the iceberg rotates, may even pop-up above the level of the calving front, hit the newly formed ice cliff, and disintegrate further into smaller and smaller chunks."

There are more than 200 glaciers that spill ice into the ocean around Greenland, so together they contribute a significant amount of noise to the marine environment, says Podolskiy.

Podolskiy and his colleagues have suggested that the noise produced by calving icebergs could pose a risk to the hearing of narwhals and other sea mammals.

"The animals can be very close to such events and that the corresponding sound exposure may lead to direct mechanical damage to their hearing," says Podolskiy. But during their observations of narwhals during calving events, the creatures don't seem to adjust their calls to compensate for the background noise.

In the Southern Ocean, however, iceberg noise may be having a direct effect on the calls produced by the largest animals on the planet. Scientists have found that the songs of blue whales have been getting deeper in pitch over the past several decades. They also get louder at certain times of the year. This, the researchers from University of Brest, France, suggest, could be because the whales are compensating for changes in the noise produced by icebergs as the climate changes as the harmonic songs produced by giant icebergs occur at similar frequencies to the calls of blue whales and other whales in the Southern Ocean.

But without long-term data tying changes in iceberg behaviour around Antarctica to changes in noise, it is hard to be completely sure what effect climate change may be having, warns Schlindwein.

And if predictions for how rising ocean temperatures will alter the polar regions come to pass, there could be some dramatic changes ahead. The icebergs could stop singing altogether.

Research suggests that rising ocean temperatures are increasing the level of melting at the bottom of the vast ice sheets that project out over the sea from the continental landmass of Antarctica. This is thinning the ice shelves – which can be up to 600m (1,980ft) thick – in many places, leaving them more fragile and vulnerable to calving events. But it could also mean the icebergs themselves will fragment into smaller pieces, meaning fewer of the really vast tabular icebergs that can travel far out over the Southern Ocean, creating unique ecosystems around them as they melt.

Thinner ice sheets will also mean they are less likely to scrape along the seafloor when icebergs do break off. Less sea ice would also mean icebergs would be freer to drift around. But the noise of smaller icebergs breaking apart could also increase, says Schlindwein.

"I really wouldn't want to predict what would happen," says Schlindwein.

But if the iceberg songs were to disappear, it would be one more natural wonder lost to the world.

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