The “Bloop” in the Ocean

Spectrogram of an unidentified deep ocean sound, referred to as "Bloop." The bloop sound was repeatedly recorded during the summer of 1997 on the Equatorial Pacific Ocean autonomous hydrophone array. The sound rises rapidly in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 km. It yields a general location near 50oS; 100oW (far off the west coast of southern South America). The origin of the sound is unknown. A recording of the bloop sound can be heard, sped up 16 times, at: http://oceanexplorer.noaa.gov/explorations/sound01/sound01.html

June 30, 2002 Woods Hole, Massachusetts - The June 13, 2002 issue of New Scientist featured an article by reporter John von Radowitz in London about an underwater sound deep in the ocean recorded in 1997 by NOAA scientists that remains unidentified. The "Bloop" was detected and recorded from an array of underwater hydrophones (microphones) originally set up by the U. S. Navy in the 1960s to track Soviet submarines. The listening technology is distributed in a deep ocean level known as the "sound layer" which marine animals such as whales and human technology such as submarines use for long-range communication.

The SOund SUrveillance System, or SOSUS, consists of bottom-mounted hydrophone arrays connected by undersea communication cables to facilities on shore. Illustration courtesy Naval Research Laboratory.

The "Bloop" was detected by hydrophones up to 4,800 kilometers apart (2,983 miles). That is a long distance for a single sound to be heard. Thus, speculation began about what the "Bloop" might be. The New Scientist article stated that the great distance it covered "meant it had to be much louder than any recognized animal noise, including that produced by the largest whales."

Recently, NOAA scientist Chris Fox who originally recorded the "Bloop," sent one recording to Dr. Phil Lobel, a marine biologist at the Woods Hole Laboratory in Massachusetts and a Professor of Marine Biology at Boston University. Dr. Lobel studies underwater sounds made by fish and other marine animals. I asked him what he thought the Bloop could be.

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