Record-setting record

A three-year recording of whales and ice.

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If you listened to the Southern Ocean year-round, you would hear mainly whales quacking and ice grinding, according to a study of marine sounds published in Royal Society Open Science.

Researchers left recording devices underwater off the coast of Antarctica for three years, creating the first year-long baseline measure of maritime sounds in an ocean largely free of human activity. The closest major shipping lane was 4000 kilometres away.

Aside from water, wind and ice, the dominant sounds collected were from three species of whale and the leopard seal. The whale calls were constant—the combined sound energy of a pod creates a continuous chorus—with different species dominating the soundscape at different times of the year.

The Antarctic blue whale and fin whale were loudest in autumn, while in winter, the Antarctic minke whale took over. The study also discovered Antarctic minke whale song follows a 24-hour rhythm, which is connected to the nightly movement of the whales’ food source, krill, to the surface of the ocean.

As sea ice spread in winter, the number of sounds diminished, partly due to the marine mammals’ migration and partly due to the frozen surface: without open water, there’s no grinding and smashing of ice, and no sounds of wind.

Marine technologist Sebastian Menze says the Southern Ocean is important because it is largely undisturbed. It can be compared with altered marine habitats around the world, or used as a reference point in future when all oceans contain human interference and noise pollution.

Sea wookiees

Sweeps, quacks, bumps and moans form the vocabulary of marine mammals, says Sebastian Menze, author of the study.

“The Antarctic minke whale sounds were in fact called ‘bio-duck’ sounds before the whales could be identified as the source,” he says. “Blue and fin whale calls are often termed ‘sweeps’ or ‘bumps’, whereas leopard seal sounds are sometimes referred to as ‘moans’. I rather think that leopard seals sound a bit like wookiees.”

The sea also had its own song: the scratching and grinding of ice floes rubbing and crashing against each other, says Menze. “Sometimes, the ice is even ‘singing’, when ice floes are squeezed together by a more constant force such as tides or wind.”