Researchers have finally identified the source of a mysterious sound coming from the deepest ocean trench. The strange sound, described as a “biotwang” sound, sounds like a sci-fi spaceship, and is actually a whale call from a Bryde’s whale (Balaenoptera edeni). Researchers say the whales may use the calls to find each other like a giant game of Marco Polo.
Scientists first detected these unusual sounds in 2014 while using underwater gliders to conduct acoustic surveys in Mariana Trench — the world’s deepest ocean trench, which stretches more than 1,500 miles (2,400 kilometers) south of Japan and has maximum depth 35,876 feet (10,935 meters).
The biotwang sound can be broken down into two distinct parts: first, a low, rumbling sound that echoes through the depths; and second, a high-pitched metallic ringing that researchers have likened to the sound made by spaceships in Star Trek and Star Wars.
The sounds initially baffled scientists. But in 2016, researchers revealed that the biotwang most likely a call from a large baleen whalelike blue whale (Praying mantis) or humpback whale (Megaptera novaeangliae). However, the sound did not match any known whale calls.
In a new study published Wednesday (Sept. 18) in the journal Frontiers in Marine ScienceResearchers have finally been able to prove that Bryde’s whales are making the sounds, thanks in part to a new artificial intelligence (AI) tool that sifted through more than 200,000 hours of audio recordings containing a variety of ocean sounds.
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Researchers strongly suspected that Bryde’s whales were behind the biotwang sound when they spotted 10 cetaceans swimming near the Mariana Islands and recorded nine of them making the distinctive sound.
“Once, it’s a fluke. Twice it’s a fluke. Nine times, it’s a Bryde’s whale,” said the study’s lead author. Ann Allenan oceanographer at the National Oceanic and Atmospheric Administration’s (NOAA) Pacific Islands Fisheries Science Center, told Scientific American.
But to prove conclusively that it was Bryde’s whales making the sounds, the team matched the occurrence of the sounds to the species’ migration patterns, which meant sifting through years of audio recordings taken by monitoring stations across the Mariana Islands and beyond.
They speed up that process by using AI to turn biological sounds into images, known as spectrograms, that can be easily distinguished from other sounds by machine learning algorithms.
The study also found that biotwang could only be heard in the northwest Pacific, even though Bryde’s whales range over a much wider area, suggesting that only certain whale populations make the sound.
The data also showed an increase in biotwang sounds in 2016, when sea temperatures rose due to El Niño event causing an increase in the number of Bryde’s whales visiting the area.
It’s still unclear why these calls sound so strange but researchers have a hunch as to why they are being made.
“It’s possible they use biotwang as a contact call, a kind of ‘Marco Polo’ of the ocean,” Allen said. told Popular Science“But we need more information before we can be sure.”
