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 Coordinates: , 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.:284 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.:255–256
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).
Ice quake origin
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.:5
In ice calving, variations result from a sound source's own motion.:55 As oceanographer Yunbo Xie explains, the alteration of waveforms from a detected sound "can also be caused by so-called angular frequency dependent radiation patterns associated with antisymmetric mode motion of the ice cover.":59
Rubbing and ridging events within an ice floe
Two processes known as rubbing and ridging are responsible for acoustical emissions similar to those from ice calving. Rubbing involves two or more areas of compacted glacial ice floes which are being forced together, inducing shear deformation at its edges and triggering horizontally-polarized shear waves, i. e. SH waves.:137 Ridging occurs when that ice bends or slides at the ridges.:121 According to Xie, both events will produce sound in the failure sequence (breakup) of an ice floe:
"A wave equation resulting from shear deformation will be defined in an ice floe with the rubbing effect coupled to the floe through its boundary with the adjacent ice,":137 while "ridging deformation(s) revealed by this event indicate that the failure process is associated with a crushing process that seals air or vacuous gaps between ice floes. The acoustical signals emitted by this failure process are similar to those emitted from a collapsing air bubble in a fluid.":121
NOAA's Christopher Fox, interviewed by David Wolman for an article in New Scientist, did not believe its origin was man-made, such as a submarine or bomb, nor a familiar geological event such as a volcano or an earthquake. Fox stated that while the audio profile of Bloop does resemble that of a living creature, the source was a mystery because it would be "far more powerful than the calls made by any animal on Earth." Wolman states in the article that Fox initially speculated Bloop to be ice calving in Antarctica, but later came to believe the sound to be like that of an animal in origin:
Fox's hunch is that the sound nicknamed Bloop is the most likely to come from some sort of animal, because its signature is a rapid variation in frequency similar to that of sounds known to be made by marine beasts. There's one crucial difference, however: in 1997 Bloop was detected by sensors up to 4,800 km (3,000 mi) apart. That means it must be far louder than any whale noise, or any other animal noise for that matter. Is it even remotely possible that some creature bigger than any whale is lurking in the ocean depths? Or, perhaps more likely, something that is much more efficient at making sound?:174–175— David Wolman
According to author Philip Hayward, Wolman's speculations "amplified Fox's 'hunch' and — through the use of the word 'likely' — opened the door for subsequent speculation as to what such an 'efficient' noise-making entity might be. Over the last decade consensus has, in fact, supported the argument that the noise is produced by ice fracturing processes.":175
- The Bloop was one of the phenomena investigated in the second episode of the first season of Weird or What? on Discovery Canada.
- A 2012 American made-for-TV thriller produced for Animal Planet and Discovery Channel in the form of a documentary titled Mermaids: The Body Found used the bloop sound as evidence for the existence of mermaids or an unknown species in the oceans. NOAA posted a refutation on their web site.
- The children's television animation The Deep Season 1 Episode 23 finds that the sound comes from a form of sentient coral.
- "The Big Bloop" plays an important role in Jean-Marie Blas de Roblès's novel Island of Point Nemo.
- The comic book Atomic Robo had Robo investigate the source of the Bloop for the NOAA in a deep sea submersible. 
- "Acoustics Monitoring Program – Icequakes (Bloop)". NOAA Pacific Marine Environmental Laboratory. National Oceanic and Atmospheric Administration / United States Department of Commerce. Archived from the original on February 25, 2020. Retrieved August 28, 2017.
- David Wolman (2002-06-15). "Calls from the deep". New Scientist. Archived from the original on 2013-01-06. Retrieved 2012-01-16.
- Steadman, Ian (November 29, 2012). "The Bloop Mystery Has Been Solved: It Was Never A Giant Sea Monster". WIRED UK. Conde Nast Publications.
- US Department of Commerce, National Oceanic and Atmospheric Administration (June 25, 2018). "What is the Bloop?". oceanservice.noaa.gov. Archived from the original on 7 May 2019.
- Di Mento, John Mark (December 2006). "Environmental Challenges to Post-Cold War Naval Operations: The Browning of the Blue Water Battlespace". Beyond the Water's Edge: United States National Security & the Ocean Environment (Ph.D. thesis). Medford, MA: Fletcher School of Law and Diplomacy, Tufts University. Document No. 3262885ProQuest 304741876 – via ProQuest Dissertations Publishing.
- Xie, Yunbo (1991). An Acoustical Study of the Properties and Behaviour of Sea Ice (Ph.D. thesis). Vancouver, B.C.: University of British Columbia. Document No. NN69775 – via ProQuest Dissertations Publishing.
- Pettit, Erin C. (2012). "Passive Underwater Acoustic Evolution of a Calving Event". Annals of Glaciology. 53 (60): 113–122. Bibcode:2012AnGla..53..113P. doi:10.3189/2012aog60a137.
- "CNN.com – Tuning in to a deep sea monster – June 13, 2002". CNN. 13 June 2002.
- "Scientists tune in to sounds of the sea". CNN. 2001-09-07. Retrieved 2012-01-16.
- Hayward, Philip (2017). Making a Splash: Mermaids (and Mer-Men) in 20th and 21st Century Audiovisual Media. Indiana University Press. ISBN 9780861969258. OCLC 1020857723.
- Zabarenko, Deborah (6 July 2012). "This just in: Mermaids are NOT real, U.S. agency says". Reuters. Washington. Retrieved 27 May 2014.
- "Bloop". HiveWorks. Retrieved 2020-07-24.