The Bloop is the name given to an ultra-low frequency and extremely powerful underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. The source of the sound remains unknown.
The sound, traced to somewhere around 50° S 100° W (a remote point in the south Pacific Ocean west of the southern tip of South America), was detected several times by the Equatorial Pacific Ocean autonomous hydrophone array, which uses U.S. Navy equipment originally designed to detect Soviet submarines.
According to the NOAA description, it “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.” The NOAA’s Dr. Christopher Fox does not believe its origin is man-made, such as a submarine or bomb, or familiar geological events such as volcanoes or earthquakes. While the audio profile of the Bloop does resemble that of a living creature, the source is a mystery both because it is different from known sounds and because it was several times louder than the loudest known animal, the blue whale. Five other significant unexplained sounds have been named by NOAA: Julia, Train, Slow Down, Whistle, and Upsweep.
Dr. Christopher Fox of the NOAA speculated that the Bloop may be ice calving in Antarctica. A year later journalist David Wolman paraphrased Dr. Fox who suggested it was likely animal in origin.