I read an interesting article yesterday about two mysterious signals picked up by hydrophones, acoustic listening devices that were placed by NOAA (the National Oceanic and Atmospheric Administration) in the ocean. Hydrophones were originally developed as part of a program by the U.S. Navy as part of the SOSUS (Sound Surveillance System) used to track Soviet submarines during the Cold War.. The hydrophones were attached to telecommunication cables so that the sounds picked up could be heard "real time" on land. They were effective but very expensive.
After the Cold War ended in 1991, this technology was turned over to civilians. Portable hydrophones were developed that were self contained, cheaper, and could be dropped anywhere in the ocean. However, data obtained was not real time, and could not be retrieved until the devices were picked up by a ship.
NOAA's VENTS program, which examines underwater hydrothermal venting systems, makes use of these devices. The Acoustic Monitoring Program, which has monitored ocean noises since 1991, picked up the sounds discussed here.
The first of these sounds, known as "The Bloop", was heard several times during the summer of 1997. It has not been heard since. Its origin is uncertain, but the frequency of the sound is consistent with one made by a large animal. The problem is that there is no known whale or other sea creature large enough to have made this sound. It was heard from sensors 3000 miles apart.
Here are two sound files of "The Bloop"
Another sound picked up by the Acoustic Monitoring Program is known as "The Slow Down" sound. It was recorded on May,19, 1997 Lasting for seven minutes, and heard over a range of 2,000 miles, It was never heard again
The "Slow Down" file:
Two articles on "The Bloop":
Some more ocean sounds from NOAA: