For years, many people have claimed hearing strange humming noises while traveling in the middle of the ocean. While there have been attempts to find out where these low-frequency sounds are coming from, no one has been able to pinpoint their exact source.

Marine biologist Simone Baumann-Pickering from the University of California, San Diego says that she and her team may have finally cracked the mystery of these deep-sea hums.

During Monday's summit of ocean scientists organized by the American Geophysical Union, Baumann-Pickering and her colleagues said that the humming noise that people typically hear are likely made by large groups of marine animals, such as small fish, squid and crustaceans, which tend to hide during the day and hunt for food at night.

Using hydrophones set in the Pacific Ocean, the researchers listened in to the noises made by these sea creatures. They heard a strange sound that was faint yet continuous throughout the day.

After examining the noise closely, Baumann-Pickering and her team discovered that it had qualities that were different from other noises often heard from the sea. It had a frequency of about 300 hertz, which was too high to be a call from a whale. It was also too continuous to be considered a signal from other aquatic mammals.

Baumann-Pickering compared the nature of the strange sound to the buzzing or humming noise people typically hear when they ride an airplane.

She said that the deep-sea sound tends to start right after sunset and continues for about a couple of hours. It stops for a while only to sound off again at dawn.

The researchers found that the occurrence of the humming noise coincides with the rise and fall of fish migration every day.

This involves sea creatures that exist in an area of the ocean known as the mesopelagic zone, which is located somewhere around 660 feet below the water's surface and reaches a depth of about 3,300 feet.

Baumann-Pickering and her team believe that these fish create such noises as a form of active communication in order to tell the rest of the group that they need to move and hunt for food.

The researchers also speculate that the strange sounds are likely the fish releasing gas similar to how humans fart. This gas is produced by the fish's swim bladder, which is responsible for helping them control their buoyancy.

Photo: Samuel Chow | Flickr 

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