海角大神

Why is the deepest part of the ocean so noisy?

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鈥檚 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, , and were surprised by their findings.聽

鈥淵ou would think that the deepest part of the ocean would be one of the quietest places on Earth,鈥� Robert Dziak, a NOAA research oceanographer and chief scientist on the project, tells Oregon State University. 鈥淵et there really is almost constant noise from 聽鈥� Sound doesn鈥檛 get as weak as you think it does even that far from the source.鈥澛�

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鈥檚 mysterious setting seven miles beneath the ocean surface. Even if Mount Everest, Earth鈥檚 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.聽聽

Previous studies have suggested that . Apart from foot-long shrimp-like crustaceans, sea cucumbers and giant amoebas, the area's lack of light and intense pressure makes the area desolate.

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?聽

鈥淭here was a huge amount of energy, high winds, big waves, ,鈥� Dziak tells the Seattle Times. While the hydrophone was underwater, it picked up sounds from a category 4 typhoon overhead and earthquake rumbles below.聽

Local whales don鈥檛 swim more than a mile below the ocean鈥檚 surface, but the calls of baleen and toothed whales also carried down to the bottom of the trench.聽

But the prevalence of human noise may have been the most surprising.聽

鈥淭he project clearly shows that man-made noise is present even in some of ,鈥� explains the Seattle Times. 鈥淭he 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.鈥� With transocean traffic increasing, underwater noise pollution is becoming more and more prevalent 鈥� and the Challenger Deep proves to be no exception.聽

鈥淯nderwater sounds are a particularly important area of study, as scientists have learned in recent years that too much man-made noise in the ocean 鈥� from ship traffic, oil and gas exploration, scientific research, and military sonar 鈥� can have harmful effects on its inhabitants,鈥� 海角大神鈥檚 Lonnie Shekhtman explained last week.聽

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鈥檛 easy.

鈥淲e had never put a hydrophone deeper than a mile or so below the surface, so putting an instrument down some seven miles ,鈥� Haru Matsumoto, an Oregon State ocean engineer who helped develop the hydrophone, tells OSU.聽

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.聽

鈥淲e had to drop the hydrophone mooring down through the water column at no more than about five meters per second,鈥� says Matsumoto, which took more than six hours. The team of researchers feared a fast drop would break the hydrophone. 鈥淚t is akin to sending a deep-space probe to the outer solar system. We鈥檙e sending out a deep-ocean probe to .鈥�