For what may be the first time, scientists have eavesdropped¹ on the deepest part of the world's oceans and instead of finding a sea of silence, they discovered a cacophony² of sounds both natural and caused by humans. For three weeks, a titanium-encased hydrophone recorded ambient noise from the ocean floor at a depth of more than 36,000 feet in a trough known as Challenger Deep in the fabled³ Mariana Trench⁴ near Micronesia. The team of researchers from the National Oceanic and Atmospheric⁵ Administration, Oregon State University and the U.S. Coast Guard expected to hear little. They were surprised.

 

"You would think that the deepest part of the ocean would be one of the quietest places on Earth," said Robert Dziak, a 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 baleen⁶ whales and the overwhelming clamor of a category 4 typhoon that just happened to pass overhead.

 

"There was also a lot of noise from ship traffic, identifiable by the clear sound pattern the ship propellers⁷ make when they pass by," added Dziak, who has a courtesy appointment in Oregon State's College of Earth, Ocean, and Atmospheric Sciences. "Guam is very close to Challenger Deep and is a regional hub for container shipping⁸ with China and The Philippines."

 

The project, which was funded by the NOAA Office of Ocean Exploration and Research, was designed to establish a baseline for ambient noise in the deepest part of the Pacific Ocean. Anthropogenic, or human-caused noise has increased steadily⁹ over the past several decades and getting these first recordings¹⁰ will allow scientists in the future to determine if the noise levels are growing.

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