- A hydrophone, or underwater microphone, spent almost a month in the deepest part of the ocean and recorded some surprising sounds. .
Scientists expected seven miles under the ocean’s surface to be very quiet.
But
a team of researchers from the National Oceanic Atmospheric
Administration (NOAA), the US Coast Guard, and Oregon State University
(OSU) dropped an underwater microphone 36,200 feet to the bottom of the
Challenger Deep, the deepest part of the ocean, and were surprised by their findings.
“You
would think that the deepest part of the ocean would be one of the
quietest places on Earth,” Robert Dziak, a NOAA research oceanographer
and chief scientist on the project, tells Oregon State University. “Yet
there really is almost constant noise from both natural and man-made sources … Sound doesn’t get as weak as you think it does even that far from the source.”
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The Challenger Deep depression is at the southern end of
the underwater Mariana Trench, southwest of Guam. Compared to the
average ocean depth of 2.3 miles, little is known about the Challenger’s
mysterious setting seven miles beneath the ocean surface. Even if Mount
Everest, Earth’s tallest mountain at about 5.5 miles above sea level,
were relocated to the bottom of the Challenger Deep, more than a mile of
water would still cover its peak.
But within 23 days, the device's storage was filled with
noise. So if the bottom of the world is pretty much empty, why is it so
loud?
“There was a huge amount of energy, high winds, big waves, that made the whole basin noisy,”
Dziak tells the Seattle Times. While the hydrophone was underwater, it
picked up sounds from a category 4 typhoon overhead and earthquake
rumbles below.
Local whales don’t swim more than a mile below the
ocean’s surface, but the calls of baleen and toothed whales also
carried down to the bottom of the trench.
But the prevalence of human noise may have been the most surprising.
“The project clearly shows that man-made noise is present even in some of the most remote corners of the planet,”
explains the Seattle Times. “The nearby island of Guam is on a major
transoceanic route, so vessel traffic was a near constant source of
noise in the environment, the researchers found.” With transocean
traffic increasing, underwater noise pollution is becoming more and more
prevalent – and the Challenger Deep proves to be no exception.
“Underwater
sounds are a particularly important area of study, as scientists have
learned in recent years that too much man-made noise in the ocean – from
ship traffic, oil and gas exploration, scientific research, and
military sonar – can have harmful effects on its inhabitants,” The Christian Science Monitor’s Lonnie Shekhtman explained last week.
The
team of scientists are now planning for another venture in 2017, when a
camera will hopefully accompany the hydrophone. But getting to the
deepest part of the world isn’t easy.
“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,” Haru Matsumoto, an Oregon State ocean engineer who helped develop the hydrophone, tells OSU.
The
pressure is hard for us to imagine, says Matsumoto. At 16,000 pounds
per square inch, the pressure at the bottom of Mariana Trench is about
1,088 times that which humans experience on a day-to-day basis.
“We
had to drop the hydrophone mooring down through the water column at no
more than about five meters per second,” says Matsumoto, which took more
than six hours. The team of researchers feared a fast drop would break
the hydrophone. “It is akin to sending a deep-space probe to the outer
solar system. We’re sending out a deep-ocean probe to the unknown reaches of inner space.”
Why is the deepest part of the ocean so noisy?
![Why is the deepest part of the ocean so noisy?]()
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