10-year Mystery of ‘Alien’ Sounds from Deepest Ocean Trench Solved

Ten years ago scientists detected odd and mysterious noises coming from inside the planet’s deepest ocean trench, the Mariana Trench. The sounds were identified as “biotwangs” and were comprised of deep moaning or grumbling noises followed by a series of high-pitched metallic-sounding pings. Despite the almost mechanical nature of the sound, scientists were certain that it must be the call of some species of animal (most likely a large whale). That theory has now been confirmed.

With the help of an artificial intelligence identification system developed by Google, experts affiliated with the United States government’s National Oceanic and Atmospheric Administration (NOAA) have discovered that the strange sounds were made by Bryde’s whales. This species of baleen whale is seldom spotted in the wild, but these gigantic creatures (they can grow to up to 55 feet or 17 meters long) possess the ability to swim to extreme depths.

Artificial Intelligence Reveals the Secret Lives of Bryde’s Whales

The odd biotwangs were recorded in 2014 by scientists using underwater vehicles to complete an acoustic survey of the Mariana Trench, which can be found in the northwestern Pacific Ocean running diagonally of the coast of Japan. This huge underwater landform covers more than 1,500 miles (2,400 kilometers) of seafloor, reaching a maximum depth of 6.8 miles (10.9 kilometers).

SRTM bathymetry map shows the depth of the Mariana trench region, off the coast of Japan and Insonesia. (astrobob/CC BY-SA 4.0)

In an article published in Frontiers in Marine Science, the researchers involved in this new study explain how they used the AI system to sort through more than 200,000 hours of undersea audio recordings, looking specifically for whale sounds. These recordings were made by NOAA hydrophones mounted in the region surrounding the Mariana Islands, which are located above the massive trench that shares their name.

The AI system was trained to detect the distinctive signals of eight species of whale, including Bryde’s whales, whose sounds had been recorded while they were swimming near the Mariana Islands a few years ago.

Scientists already knew there was a strong similarity between the sounds heard coming from the Mariana Trench and the calls emitted by the Bryde’s whales spotted near the adjacent islands. And in a 2016 study they’d detected certain markers in the 2014 recordings that proved they must have come from some type of baleen whale.  But this wasn’t enough to conclusively prove a link. More evidence was needed, and this is what the undersea NOAA recordings provided.

Given the voluminous nature of the recordings collected by NOAA, it would have been impossible for humans to sort through them looking for specific sounds linked to one animal species. But the high-powered AI system created by Google was able to track the migratory movements of Bryde’s whales across the region, separating out its distinctive calls and connecting them to the underwater locations where they were recorded as they swam by. It did this using a unique process that converted the biotwangs and related sounds into images known as spectrograms, which a machine learning algorithm was then able to differentiate from other recorded noises.

Throughout their travels one group of Bryde’s whales in particular continued to emit the biotwang sounds that could now be identified as the same ones detected in the Mariana Trench in 2014. With so many matches sorted out of recordings, the source of the mysterious trench sounds could no longer be debated, despite its highly extraordinary qualities.

Bryde’s whale breaching the ocean surface off the coast of Brazil. (Zejulio/CC BY-SA 4.0)

“Your average person would not think that it was made by an animal – they would think it was some ship or the [US] Navy,” study lead author Ann Allen from the National Oceanic and Atmospheric Administration (NOAA) said in an interview with New Scientist. 

Intriguingly, these distinctive whale calls were not found in recordings that covered Bryde’s whale migration paths in other parts of the Pacific. It was only the Bryde’s whales living in the vicinity of the Mariana Trench that were recorded making these sounds, as they completed their migrations across that underwater region of the globe.

This means the strange biotwang belongs to what is essentially a local dialect, highlighting the intelligence and creativity of this elusive baleen whale species.

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

Whale Migrations May Be Threatened by Climate Change

One surprising finding of the new research is that there was a sudden increase in the frequency of the biotwang noises in 2016. At this time there was a rise in ocean temperatures in the northwest Pacific caused by an El Niño event, which led to increased migration of Bryde’s whales into the area.

The Mariana Trench is located in a part of the ocean where a moving boundary separates warm water from cool water, and Bryde’s whale migrations seem to be tied to the movements of that boundary (warmer waters means an increase in the population of plankton and other creatures these huge whales consume). The boundary actually has a name, which is the transition zone chlorophyll front.

“As climate change advances, we expect more frequent and more extreme El Niño and La Niña events, and we expect this transition zone chlorophyll front to go further north and be more variable,” Allen said.

“This means that the whales may have to travel further and work a lot harder to find their food, which can impact the health of the population.”

It is intriguing to speculate whether the whales themselves will recognize that underwater conditions are changing as climate change progresses. They obviously wouldn’t know what was responsible for the changes, but given their great intelligence it seems possible that they understand that something significant was going on.

Top image: Deep sea fish, the type imagined to be found in the Mariana Trench.  Source: superjoseph/Adobe Stock

By Nathan Falde