Nature

The First Audio Recordings from the Bottom of Mariana Trench Are Hauntingly Beautiful

March 8, 2016 | Joanne Kennell

View of the surface from deep below the ocean
Photo credit: pixabay.com

The deep ocean is a surprisingly noisy place.

The first audio recordings taken from the deepest point on Earth’s surface — the bottom of the Mariana Trench — have been released.  Most of us would expect it to be very quiet so deep under the ocean, however the audio recordings paint a different picture.

It turns out that a place that receives no light, lying a minimum of 10.9 kilometers (6.7 miles) below the crushing weight of the Pacific Ocean, is full of deep rumbles, moans, and squeals, as well as sounds heard that originate all the way from the surface of the ocean.  The sounds are a little haunting, but they are also quite beautiful.

“Light does not propagate underwater very far,” research oceanographer and chief project scientist Bob Dziak of the National Oceanic and Atmospheric Administration (NOAA) told Gizmodo.  “But sound waves travel long distances through the Earth’s oceans. Acoustics is really the best way to get a good picture of deep ocean environments.”

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The deepest known valley within the Mariana Trench is known as Challenger Deep, near Micronesia, and for three weeks, a titanium-encased hydrophone recorded the noise from the ocean floor at a depth of more than 36,000 feet (7 miles).

Researchers from NOAA, Oregon State University, and the U.S. Coast Guard were all surprised by how much they actually heard.

“You would think that the deepest part of the ocean would be one of the quietest places on Earth,” said Dziak in a press release.  “Yet there is almost constant noise. The ambient sound field is dominated by the sound of earthquakes, both near and far, as well as distinct moans of baleen whales, and the clamor of a category 4 typhoon that just happened to pass overhead.”

Listen to the audio recording of a toothed-whale or dolphin:

AUDIO: A NOAA hydrophone anchored on the seabed captures the call of a toothed whale or dolphin.

This is a sound of a distant baleen whale:

AUDIO: The hydrophone picks up distant sound from a baleen whale that may be a Bryde's whale.

This one is by far my favourite.  It is the sound of a 5.0 magnitude earthquake in the ocean’s crust near Guam:

AUDIO: The hydrophone picks up a 5.0 magnitude earthquake in the ocean crust near Guam.

Since Challenger Deep is close to Guam, a region known for container shipping with China and the Philippines, the hydrophone also picked up the sound from ship propellers:

AUDIO: Steady, rhythmic noise from a ship propeller miles away comes in loud and strong.

Getting the recordings was definitely not an easy task considering Challenger Deep is deep enough to hold Mount Everest.

“The pressure at that depth is incredible,” said Haru Matsumoto, an Oregon State ocean engineer who worked with NOAA engineer Chris Meinig to adapt the hydrophone.  “We had to drop the hydrophone mooring down through the water column at no more than five meters per second to be sure the hydrophone, which is made of ceramic, would survive the rapid pressure change.”

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While atmospheric pressure in the average home is 14.7 pounds per square inch (PSI), it is more than 16,000 PSI at the bottom of the Mariana Trench.  In other words, it will crush most materials, including a human body!

Joe Haxel, a co-investigator on the project, will lead a planned return to Challenger Deep in early 2017, where the researchers will deploy the hydrophone for a longer period of time and also attach a deep-ocean camera.

We know very little about what life is like deep in the ocean and the Mariana Trench is no exception — it is a very mysterious place.  But, at least now we know what it sounds like and hopefully we will soon know what it looks like!

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