The Mariana Trench is one of the most mysterious places on Earth.
The trench, nearly seven miles (36,201 feet) deep, lies at the bottom of the Pacific Ocean and is so difficult to reach that only a handful of people have ventured there.
It’s no surprise then that unusual sounds coming from the Mariana Trench sparked fears of an alien invasion when they were first recorded in 2014.
The noises, which lasted between 2.5 and 3.5 seconds, were dubbed “biotwangs” although their origin was unknown.
Ten years later, scientists at the National Oceanic and Atmospheric Administration (NOAA) have reanalyzed the sounds and believe they have finally revealed the truth.
The Mariana Trench (artist’s impression) is one of the most mysterious places on Earth.
The disturbing noises were first recorded in 2014 by underwater gliders being used to conduct acoustic surveys of the trench.
Lasting between 2.5 and 3.5 seconds, the five-part sounds include deep moans at frequencies as low as 38 hertz and a metallic finale that reaches up to 8,000 hertz.
At first, investigators were baffled by the noises.
However, in 2016, a team at Oregon State University (OSU) suggested they could be a new type of baleen whale call never heard before.
At the time, Sharon Nieukirk, a senior faculty research assistant in marine bioacoustics at Oregon State University, said: “It’s very distinctive, with all these crazy parts.
‘The low-frequency moan is typical of baleen whales, and it’s that kind of metallic sound that makes it really unique.
‘We didn’t find many new baleen whale songs.’
Now, scientists have reanalyzed the noises using a combination of data from visual and acoustic surveys, and their findings suggest the OSU team wasn’t far off the mark.
The Mariana Trench, nearly seven miles (36,201 feet) deep, lies at the bottom of the Pacific Ocean and is so elusive that only a handful of people have ventured there.
The eerie noises were first recorded in 2014 by underwater gliders used to conduct acoustic surveys of the trench. The sounds, which last between 2.5 and 3.5 seconds, include deep groans at frequencies as low as 38 hertz and a metallic finale reaching 8,000 hertz.
Rather than being produced by baleen whales, the new study suggests that Bryde’s whales are responsible.
In their study, published in Frontiers in marine scienceThe team, led by Dr Ann Allen, explained: ‘It was assumed to have been 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.’
Bryde’s whales can be found worldwide in warm and temperate oceans, including the Atlantic, Indian and Pacific.
Bryde’s whales can be found worldwide in warm and temperate oceans, including the Atlantic, Indian and Pacific.
The Mariana Trench, nearly seven miles (36,201 feet) deep, lies at the bottom of the Pacific Ocean and is so elusive that only a handful of people have ventured there.
Researchers spotted 10 whales swimming in the area and even recorded nine of them making characteristic noises.
However, to prove that these whales were indeed the source, the team turned to artificial intelligence.
“We used a combination of manual and machine learning annotation methods to detect Biotwangs in our extensive historical passive acoustic monitoring datasets collected in the central and western North Pacific,” they explained in the study.
‘We identified a consistent seasonal presence of Biotwangs in the Mariana Archipelago and east to Wake Island, with occasional occurrence as far away as the northwestern Hawaiian Islands and near the equator (Howland Island).’
The team still doesn’t know why the whales’ calls are so unusual, or why they occur in the first place.
However, speaking with Popular scienceDr Allen suggested: “It’s possible they use the biotwang as a contact call, a sort of ‘Marco Polo’ of the ocean.
“But we need more information before we can say for sure.”