When film director James Cameron visited the deepest known point on Earth in 2012, he did not see a great deal. But if he had taken some underwater microphones with him he might have heard a lot.
For the first time, scientists have obtained audio recordings from 7 miles (11km) below sea level in Challenger Deep, the deepest part of the Mariana Trench, south-west of Guam. They reveal a soundscape rich with the rumble of earthquakes, the deep moans of whales – and the mechanical whirr of ships.
The recordings were made by researchers from the National Oceanic and Atmospheric Administration, Oregon State University and the US Coast Guard as part of an effort to measure the amount of sound pollution in the Pacific Ocean.
You can listen to some of the recordings below.
“Noise in the ocean has been increasing in the last few decades because of a growth in container shipping,” says Robert Dziak, the NOAA oceanographer who led the project. “Many researchers are now recognising that this can have an effect on marine ecosystems.”
The sound travelled very efficiently and cleanly downwards
Exactly how much of an effect, though, is unclear – partly because we do not know how bad the sound pollution is. “There are sensors out there to monitor the problem, but not as many as you might think,” says Dziak.
Placing an underwater microphone called a hydrophone into Challenger Deep has allowed Dziak to create a baseline that tells us how bad the problem is today. Then, by returning to the site in the years ahead, the researchers will be able to work out how much worse the problem is becoming.
This first set of recordings was made over a three-week period in July 2015.
At the moment, shipping makes only a modest contribution to the Challenger Deep soundscape, but the fact that shipping noises can be heard at all so far below the surface is a surprise. “The sound travelled very efficiently and cleanly downwards,” says Dziak.
This means that any increase in Pacific container shipping traffic could make a real difference to future recordings.
It is not just Challenger Deep that could become noisier in future. As the Arctic warms we can expect new shipping channels to appear there, which will make the Arctic Ocean a much noisier place for marine life. “It’s important to get baseline measures there now,” says Dziak.