The Mysterious Bloop

Mystery of Bloop: Underwater Sound Detected in 1997 from Non-Tectonic Cryoseism

• Bloop was an ultra-low-frequency, high amplitude underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997.
• The sound was originally speculated to have originated from a marine animal but was later described by NOAA as being consistent with noises generated via non-tectonic cryoseisms originating from glacial movements such as ice calving, or through seabed gouging by ice.
• The sound's source was roughly triangulated to 50°S 100°W, a remote point in the south Pacific Ocean west of the southern tip of South America.
• The sound was detected by the Equatorial Pacific Ocean autonomous hydrophone array, a system of hydrophones primarily used to monitor undersea seismicity, ice noise, and marine mammal population and migration.
• The sound "rose" 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 (3,000 mi).
• The NOAA Vents Program has attributed the sound to that of a large cryoseism (also known as an ice quake).
• Numerous ice quakes share similar spectrograms with Bloop, as well as the amplitude necessary to detect them despite ranges exceeding 5000 km.
• In ice calving, variations result from a sound source's own motion.
• Two processes known as rubbing and ridging are responsible for acoustical emissions similar to those from ice calving.
• The source was a mystery because it would be "far more powerful than the calls made by any animal on Earth."
• Over the last decade consensus has supported the argument that the noise is produced by ice fracturing processes.
• Bloop remains one of the most mysterious sounds ever recorded in the ocean.