Mystery behind strange noises coming from world's deepest trench finally solved

Scientists believe they may have finally solved the long-running mystery of a strange sound emanating from one of earth's least explored places.

Mariana Trench, in the western Pacific Ocean, remains a place of intrigue among researchers given how hard it is to reach and explore.

So when it was first reported that odd noises were coming from within the 37,000ft deep oceanic trench in 2014, experts knew working out the source of them would be a challenge.

With little definitive evidence to go on, some suggested the usual sounds, known among researchers as "biotwangs", were evidence of an alien species hiding from humanity in the depths.

Listening to them it's easy to understand why, with the five-part sounds beginning with a deep, low frequency moan before "twanging" upwards to as high as 8,000 hertz.

Even scientists compared the 2.5 to 3.5-second vibrations to the sounds made by futuristic spacecraft in Star Wars and Star Trek.

But now, ten years on, experts at the National Oceanic and Atmospheric Administration (NOAA) have used modern tools to work out what they believe is behind it.

Two years after the first report, experts from Oregon State University (OSU) put forward the idea that it could be a new kind of baleen whale call, as the creatures are known to make low moaning sounds.

Researchers have now reanalysed the sounds using modern tools, with their study suggesting OSU were on the right track.

However, the report published in the journal Frontiers in Marine Science suggests that Bryde's whales may be the trench's mystery singers, rather than Baleens, MailOnline reports.

Dr Ann Allen, who led the team, said: "It was assumed to be produced by a baleen whale, but without visual verification it was impossible to assign a species.

"Using a combination of visual and acoustic survey data collected in the Mariana Archipelago, we determined that Biotwangs are produced by Bryde's whales."

The researchers spotted ten Bryde's whales, which are found in oceans including the Atlantic, Indian and Pacific, swimming in the area, and were able to record nine making the unmistable noises.

In order to prove the whales had made the sounds, the scientists used artificial intelligence trained to recognise them.

"We used a combination of manual and machine learning annotation methods to detect Biotwangs in our extensive historical passive acoustic monitoring datasets collected across the central and western North Pacific," the team wrote in the report.

"We identified a consistent seasonal presence of Biotwangs in the Mariana Archipelago and to the east at Wake Island, with occasional occurrence as far away as the Northwestern Hawaiian Islands and near the equator (Howland Island)."

What's not clear is why the sound is so unique, and why the creatures make them. Dr Allen told popular science that biotwangs may be "a contact call, a sort of 'Marco Polo' of the ocean," but added that "we need more information before we can say for sure".