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Ocean Hum Traced to Daily Fish Migration

Source: NPR/Christopher Joyce - February 23, 2016 in Science/Tech

Ocean Hum Traced to Daily Fish Migration
Photo; Josh More/Flickr (CC BY-NC-ND 2.0)

You might expect the middle of the Pacific Ocean to be a pretty quiet place, especially a thousand feet down. But it turns out that huge parts of the ocean are humming.

Scientists have puzzled over the source of the sound for several years. Now, a marine biologist reporting Monday at a meeting of ocean scientists in New Orleans says she thinks her team may have figured it out.

The discovery started with hydrophones. Marine scientists listen to the deep ocean by dropping these underwater microphones over the side of ships, or by putting them on buoys. Usually they hear what sounds like male humpback whales calling to each other at mating time, or the clicking signals of dolphins and other marine mammals.

But a few years ago, those hydrophones picked up something weird out in the Pacific. The puzzling sound was faint, but continuous at certain times of day — just a few decibels above the background level — and definitely different from the normal sound of the ocean. It was 300 hertz and above — high for the call of a whale, and too continuous to be the signals of other marine mammals.

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