Mysterious ‘Mechanical-Sounding’ Noise Near the Mariana Trench May Now Have an Explanation

In 2014, researchers conducting an acoustic survey near the Mariana Trench recorded an eerie underwater noise that rather resembles the shrieking mechanical Leviathan from Disney’s Atlantis: The Lost Empire. Though researchers thought it sounded more like Star Trek spaceships paired with a groan, they suspected the “mechanical-sounding” noises to be a baleen whale call.

“Your average person would not think that it was made by an animal—they would think it was some ship or the [U.S.] Navy,” Ann Allen, a research oceanographer at the National Oceanic and Atmospheric Administration (NOAA), tells New Scientist’s Jeremy Hsu.

Now, Allen and a cross-disciplinary team of experts have used artificial intelligence to track this noise—which they termed “biotwang”—across hundreds of thousands of hours of marine acoustic recordings. The results of their work were published in the journal Frontiers in Marine Science on September 17.

ORCAA_Lab · BioTwangExample

Researchers solved the biotwang mystery during a month-long visual and acoustic survey for marine mammals in 2018. Teams spotted ten groups of Bryde’s whales off the Mariana Islands, and when observing nine of those groups, they also recorded the strange sound, per a statement from NOAA.

“Once, it’s a coincidence,” Allen tells Scientific American’s Melissa Hobson. “Twice is happenstance. Nine times, it’s definitely a Bryde’s whale.”

Bryde’s whales—pronounced broodus whales—are secretive members of the baleen whale family that favor temperate waters across the Atlantic, Indian and Pacific oceans. They are one of the least understood whale species, because their constant movement makes them difficult to spot. According to NOAA, scientists don’t even have enough information to estimate the species’ population trends. That might start to change, however, now that researchers know they emit biotwangs.

“It’s important any time you can discover a new call type for any species of animal that occurs most of the time out of sight of people, because it allows you to use passive acoustic monitoring to detect their presence,” Caroline B. Casey, a marine research scientist at the University of California, Santa Cruz, who was not involved with the study, tells New Scientist.

NOAA has long-term passive acoustic recorders in 13 remote locations of the North Pacific’s seafloor, which have captured more than 500 terabytes of data since 2005. Using these, the team decided to retroactively track the biotwangs—which they interpreted as signals for the presence of Bryde’s whales—to better understand the species. However, the sheer volume of data they would have to sort through—almost 200,000 hours of audio—posed a significant challenge.

“It’s so much data that it’s simply impossible to analyze [manually],” Olaf Meynecke, a research fellow at the Coastal and Marine Research Center at Griffith University in Australia who wasn’t involved in the study, tells Scientific American.

Cue artificial intelligence. The scientists partnered with Google to turn the recordings into visual representations called spectrograms, then trained a machine learning model to categorize the vocalizations based on their frequencies.

“With the help of A.I. and machine learning, we were able to identify where and when biotwangs were recorded in past acoustic data,” per NOAA’s statement. “Thanks to A.I. we were able to do it in a matter of hours, rather than years.”

The A.I. identified consistent biotwangs occurring seasonally in the western North Pacific. The seasonal aspect is consistent with Bryde’s whale migration patterns, thus providing further proof that the mammal is indeed the source of the mysterious sound. The geographic location, on the other hand, suggests biotwangs might not originate from all Bryde’s whales, but just a specific population in that region.

These details can help scientists study the distribution of that population moving forward, which could reveal how climate change is impacting their behaviors. Scientists think Bryde’s whales might have to travel longer distances to find food amid shifting ocean currents, so understanding this impact could support conservation efforts.

One puzzle that A.I. hasn’t been able to solve, however, is the reason for the biotwang.

“It’s possible that they use the biotwang as a contact call, a sort of ‘Marco Polo’ of the ocean,” Allen tells Popular Science’s Laura Baisas. “But we need more information before we can say for sure.”

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.