Mariana Trench ‘Metallic Sound’ Solved: What Biotwang Is

Deep underwater in the Mariana Trench, passive acoustic sensors captured a bizarre, metallic pinging sound that stumped marine biologists for a decade. Dubbed the “Biotwang,” this 3.5-second vocalization ranged from a deep bass moan to a futuristic ray-gun ringing tone. Today, advanced acoustic mapping and artificial intelligence have finally identified the mystery singer hiding in the open ocean.

The 2014 discovery

Back in 2014, researchers from Oregon State University and the National Oceanic and Atmospheric Administration (NOAA) deployed autonomous underwater gliders in the Mariana Trench Marine National Monument east of Guam. They expected to record routine ocean noise like distant ship propellers, underwater quakes, and weather passing overhead.

The remote depths of the Mariana Trench. Source: Geographical Magazine

Instead, the hydrophones picked up something that sounded straight out of a classic sci-fi movie.

The audio clip lasted roughly 3.5 seconds. It started with a low, rumbling groan and finished with a high-pitched, metallic “twang.” Nothing in the scientific archives matched it. Oceanographers verified that the signal wasn’t coming from human ships, military sonar, or seismic shifts. It was clearly biological, but what creature could make a sound so complex?

38 Hz to 8,000 Hz

What made the Biotwang so fascinating to sound engineers and biologists was its extreme frequency range. The sound broke down into five distinct parts, blending deep bass with sweeping high notes:

• The Low-Frequency Foundation: The call starts with a deep, chest-thumping moan around 38 Hertz (Hz).
• The High-Frequency Sweep: It rapidly ramps up through mid-tones, eventually hitting frequencies as high as 8,000 Hz (8 kHz).
• The Duration: The entire sequence plays out in about 3.5 seconds.

Why does that range matter? Human hearing spans from 20 Hz to 20,000 Hz. In a single breath, this mystery creature was spanning nearly our entire everyday auditory spectrum, moving from a sub-woofer growl to a metallic whistle.

The minke whale ‘Star Wars’ connection

When scientists first tried to pinpoint the culprit in 2016, they looked at known marine vocalizations. Their closest clue came from Australia’s Great Barrier Reef.

Dwarf minke whales in that region make a famous noise known as the “Star Wars” call. That call also features a strange, synthetic-sounding twang. Because the acoustic structure matched so closely, researchers initially theorized that a species of minke whale was responsible for the Mariana Trench sound.

Yet, a huge puzzle remained. Minke whale vocalizations are almost exclusively mating calls, meaning they only happen during specific breeding seasons. The Biotwang, however, was picked up year-round — during autumn, winter, and spring alike. If it was a mating call, why were they singing out of season?

2024 breakthrough: nine sightings and google Ai

The cold case finally cracked open when a research team led by NOAA scientist Dr. Ann Allen published groundbreaking findings in Frontiers in Marine Science.

The visual smoking gun

During a marine mammal survey around the Mariana Islands, field researchers spotted ten separate groups of Bryde’s whales (Balaenoptera edeni). Crucially, as they watched nine of those groups swim past, hydrophones in the water recorded the exact Biotwang sound in real time.

As Dr. Allen noted, hearing it once might be luck, but recording it nine times alongside visual confirmation proved the source beyond a doubt.

Sorting 200,000 hours of audio with Ai

Confirming the species was only half the battle. Researchers wanted to know where these whales traveled and why the sound was so unique to the area.

NOAA had collected over 500 Terabytes of acoustic recordings across 13 locations in the Pacific since 2005 — equal to nearly 23 years of continuous listening. Manually reviewing that mountain of audio would have taken decades. NOAA partnered with Google AI to train a machine-learning model capable of spotting the Biotwang’s signature frequency shape.

In a matter of hours, the AI mapped every instance of the call across the Pacific.

Why do bryde’s whales make the Biotwang?

Now that we know who is singing, what are they actually saying?

Bryde’s whales are medium-sized baleen whales found in warm, tropical waters across the globe. Unlike humpback whales, which stick to predictable migration routes between polar feeding grounds and tropical breeding lagoons, Bryde’s whales wander widely.

Scientists believe the Biotwang serves as an oceanic contact call — a long-distance game of “Marco Polo.”

1. Maintaining Group Cohesion: In the vast open ocean where visibility is nearly zero, high-frequency twangs travel across vast distances, helping pods stay organized.
2. Navigation and Spacing: Synchronized calls allow traveling whales to keep ideal spacing without bumping into each other or drifting too far apart.
3. Regional Identification: Because Biotwangs were almost exclusively detected in the Mariana Archipelago and near Wake Island, scientists suspect this specific call belongs to a distinct regional population of North Pacific Bryde’s whales.

What once sounded like alien technology hiding seven miles down turned out to be the complex social voice of one of the ocean’s most elusive giants.