Bloop was an ultra-low-frequency, high amplitude underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. By 2012, earlier speculation that the sound originated from a marine animal was replaced by NOAA’s description of the sound 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°WCoordinates: 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. This is a stand-alone system designed and built by NOAA’s Pacific Marine Environmental Laboratory (PMEL) to augment NOAA’s use of the U.S. Navy Sound Surveillance System (SOSUS), which was equipment originally designed to detect Soviet submarines.
According to the NOAA description, 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 spot them despite ranges exceeding 5000 km. This was found during the tracking of iceberg A53a as it disintegrated near South Georgia Island in early 2008. The iceberg(s) involved in generating the sound were most likely between Bransfield Straits and the Ross Sea; or possibly at Cape Adare, a well-known source of cryogenic signals. Sounds generated by ice quakes are easily determined through the use of hydrophones since sea water, an excellent sound channel, allows the ambient sounds generated through ice activities to travel great distances.