It’s not silent at the bottom of ocean.
For three weeks, researchers from Oregon State University dropped a titanium-encased hydrophone at the bottom of the Mariana Trench in the Pacific, at a depth of 36,000 feet, deeper than Mount Everest is tall.
Instead of the peace and calm they expected, they heard a kaleidoscope of strange, haunting sounds, from whale calls to earthquake rumbles and typhoons.
“You would think that the deepest part of the ocean would be one of the quietest places on Earth,” Robert Dziak, chief scientist on the project, said in a statement. “”Yet there really is almost constant noise from both natural and man-made sources.”
The researchers were also able to identify sounds produced by passing cargo ships, including the noise generated by the ship propeller.
The project wasn’t just a scientific inquiry, but an engineering challenge. The pressure an object faces increases as you go further down in sea-level, and at the bottom of the Mariana Trench, it rises to over 16,000 pounds per square inch (PSI), compared to 14.7 PSI for a person on the ground.
“We had never put a hydrophone deeper than a mile or so below the surface, so putting an instrument down some seven miles into the ocean was daunting,” said Haru Matsumoto, an Oregon State engineer.
It took more than six hours for the hydrophone to free-fall into the bottom of the Mariana Trench, and it recorded for 23 days. Instead of pulling it up, a ship sent acoustic signals to the hydrophone, triggering floats that lifted it back up to the surface.
“It is akin to sending a deep-space probe to the outer solar system,” Robert Dziak, chief scientist of the project, said. “We’re sending out a deep-ocean probe to the unknown reaches of inner space.”