5 Most Mysterious Underwater Sound Ever Recorded


5 Most Mysterious Underwater Sounds Ever Recorded

The Ocean is a pretty scary place and over the years many mysterious sounds have been recorded from deep down that to this day have no solid explanation. Here are five of those that are not only creepy and eerie but could also be a glimpse of the incredible undiscovered creatures of the deep sea.

The Bloop, Upsweep, the Train, Julia and Slow down natural event or undiscovered sea monsters?

The Bloop

In the summer of 1997, the US National Oceanic and Atmospheric Administration picked up a sound from deep beneath the Pacific. The sound seemed to come from an animal far larger than any we’ve ever seen. This was the Bloop. The Bloop is one of about a half-dozen unexplained sounds that the NOAA’s Acoustic Monitoring Project has picked up in its more than twenty years listening to the noises of the Pacific. While some of these sounds seem to have relatively obvious explanations, a few really are baffling, and they represent one of science’s great unanswered mysteries. Let’s now take a closer listen to the Bloop and five other strange underwater sounds.


Upsweep is an unidentified sound detected on the American National Oceanic and Atmospheric Administration’s equatorial autonomous hydrophone arrays. This sound was present when the Pacific Marine Environmental Laboratory began recording its sound surveillance system SOSUS in August, 1991. It consists of a long train of narrow-band upsweeping sounds of several seconds in duration each. The source level is high enough to be recorded throughout the Pacific. The sound appears to be seasonal, generally reaching peaks in spring and autumn, but it is unclear whether this is due to changes in the source or seasonal changes in the propagation environment. The source can be roughly located at 54°S 140°WCoordinates: 54°S 140°W, near the location of inferred volcanic seismicity, but the origin of the sound is unresolved. The overall source level has been declining since 1991 but the sounds can still be detected on NOAA’s equatorial autonomous hydrophone arrays.

The Train

The Train is the name given to an unidentified sound recorded on March 5, 1997 on the Equatorial Pacific Ocean autonomous hydrophone array. The sound rises to a quasi-steady frequency. According to the NOAA, the origin of the sound is most likely generated by a very large iceberg grounded in the Ross Sea, near Cape Adare.


Julia is a sound recorded on March 1, 1999 by the U.S. National Oceanic and Atmospheric Administration (NOAA). NOAA said the source of the sound was most likely a large iceberg that had run aground off Antarctica. It was sufficiently loud to be heard over the entireEquatorial Pacific Ocean autonomous hydrophone array. The unidentified sound lasted for about 15 seconds. Due to the uncertainty of the arrival azimuth, the point of origin could be between Bransfield Straits and Cape Adare.

Slow Down

Slow Down is a sound recorded on May 19, 1997, in the Equatorial Pacific Ocean by theU.S. National Oceanic and Atmospheric Administration. The source of the sound was most likely a large iceberg as it became grounded. The name was given because the sound slowly decreases in frequency over about 7 minutes. It was recorded using an autonomous hydrophone array. The sound has been picked up several times each year since 1997. One of the hypotheses on the origin of the sound is moving ice in Antarctica. Sound spectrograms of vibrations caused by friction closely resemble the spectrogram of the Slow Down. This suggests the source of the sound could have been caused by the friction between a large ice sheet moving over land.