For the first time scientists have recorded the deepest part of the world's oceans, revealing the singular sounds of whales and earthquakes.
Imagine what it would be like 36,000 feet below the surface of ocean. Dark, of course, and quiet, right? That’s what researchers expected when they dropped a titanium-encased hydrophone recorder to the bottom of the 7-mile deep trough known as Challenger Deep in the Mariana Trench near Micronesia. But these first-ever recordings of the deepest part of the world's oceans revealed not a vast silence, but instead, a surprising cacophony of sounds.
"You would think that the deepest part of the ocean would be one of the quietest places on Earth," said Robert Dziak, a National Oceanic and Atmospheric Administration (NOAA) research oceanographer and chief scientist on the project. "Yet there really is almost constant noise from both natural and man-made sources. The ambient sound field at Challenger Deep is dominated by the sound of earthquakes, both near and far was well as the distinct moans of baleen whales and the overwhelming clamor of a category 4 typhoon that just happened to pass overhead.”
The team of researchers from the NOAA, Oregon State University and the U.S. Coast Guard deployed the recording equipment for three weeks in an effort to create a baseline for ambient noise in the deepest part of the Pacific. With the increase of manmade noise in the oceans, scientists needed data to compare future readings with to determine if noise levels are getting worse.
At seven miles deep – deeper than Mount Everest is tall; in fact, Mount Everest could fit inside and its top would still be a mile below the surface – the pressure at the bottom of the appropriately named Challenger Deep is staggering. Designing equipment sturdy enough to stand up to the pressure of 16,000 PSI was challenging.
"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 ocean engineer. "We had to drop the hydrophone mooring down through the water column at no more than about five meters per second. Structures don't like rapid change and we were afraid we would crack the ceramic housing outside the hydrophone."
After recovering the equipment the team spent several months analyzing the sounds and determining which ones are natural and which are human-sourced.
"We recorded a loud magnitude 5.0 earthquake that took place at a depth of about 10 kilometers (or more than six miles) in the nearby ocean crust," Dziak said. "Since our hydrophone was at 11 kilometers, it actually was below the earthquake, which is really an unusual experience. The sound of the typhoon was also dramatic, although the cacophony from big storms tends to be spread out and elevates the overall noise for a period of days."
They also heard the plaintive moans of whales and even surface noises from the ocean, like the sounds of waves and wind rippling over the top. The sounds are subtle, but beautiful, and haunting for their glimpse into the mysterious depths so far below. Have a listen:
Above: Example of odontocete (toothed whale or dolphin) and baleen whale calls.
Above: Sound of the propellor of a passing ship.
Above: Example of baleen whale call, it most closely resembles a Bryde’s whale call.
Above: A baleen whale vocalizing just before, and during, the magnitude 5 earthquake that occurred near Challenger Deep on July 16, 2015.