View source for Bloop

{{short description|Underwater sound detected in 1997 from a non-tectonic cryoseism (ice quake)}}
{{Use mdy dates|date=July 2023}}
{{other uses|Bloop (disambiguation)}}
[[File:Bloop.jpg|250px|thumb|right|A [[spectrogram]] of Bloop]]
'''Bloop''' was an ultra-low-frequency, high amplitude underwater sound detected by the U.S. [[National Oceanic and Atmospheric Administration]] (NOAA) in 1997.<ref name=pmel/> By 2012, earlier speculation that the sound originated from a marine animal<ref name="David Wolman">{{cite web |url= http://www.science.org.au/nova/newscientist/102ns_001.htm |title= Calls from the deep |work= New Scientist |author= David Wolman |date= June 15, 2002 |access-date= January 16, 2012 |archive-url=https://web.archive.org/web/20130106141048/http://www.science.org.au/nova/newscientist/102ns_001.htm |archive-date=January 6, 2013}}</ref> was replaced by NOAA's description of the sound as being consistent with noises generated via [[plate tectonics|non-tectonic]] [[cryoseism]]s originating from [[glacial motion|glacial movements]] such as [[ice calving]], or through [[seabed gouging by ice]].<ref name=pmel>{{cite web|title=Acoustics Monitoring Program – Icequakes (Bloop)|url=https://www.pmel.noaa.gov/acoustics/sounds/bloop.html|website=NOAA Pacific Marine Environmental Laboratory|publisher=[[National Oceanic and Atmospheric Administration]] / [[United States Department of Commerce]]|access-date=August 28, 2017|archive-url=https://web.archive.org/web/20200225041855/https://www.pmel.noaa.gov/acoustics/sounds/bloop.html|archive-date=February 25, 2020|url-status=dead}}</ref><ref>{{cite magazine|last1=Steadman|first1=Ian|title=The Bloop Mystery Has Been Solved: It Was Never A Giant Sea Monster|url=https://www.wired.co.uk/article/bloop-mystery-not-solved-sort-of|magazine=WIRED UK|publisher=Conde Nast Publications|date=November 29, 2012}}</ref><ref name=noaa>{{cite web |last1=US Department of Commerce |first1=National Oceanic and Atmospheric Administration |title=What is the Bloop? |url=https://oceanservice.noaa.gov/facts/bloop.html |website=oceanservice.noaa.gov |archive-url=https://web.archive.org/web/20190507010030/https://oceanservice.noaa.gov/facts/bloop.html |archive-date=May 7, 2019 |language=EN-US |date=June 25, 2018}}</ref>

== Sound profile ==
The sound's source was roughly triangulated to {{Coord|50|S|100|W|dim:5000000|display=inline, title}}, 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]],<ref name=pmel/> a system of [[hydrophone]]s primarily used to monitor undersea seismicity, ice noise, and marine mammal population and migration.<ref name=sosus/>{{rp|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 [[United States Navy|U.S. Navy]] Sound Surveillance System ([[SOSUS]]), which was equipment originally designed to detect [[Soviet Union|Soviet]] [[submarine]]s.<ref name=sosus>{{cite thesis|last1=Di Mento|first1=John Mark|chapter=Environmental Challenges to Post-Cold War Naval Operations: The Browning of the Blue Water Battlespace|title=Beyond the Water's Edge: United States National Security & the Ocean Environment|publisher=[[Fletcher School of Law and Diplomacy]], [[Tufts University]]|date=December 2006|degree=Ph.D.|location=Medford, MA|id=Document No. 3262885 {{ProQuest|304741876}}}}</ref>{{rp|255–256}}
{{Listen
 |filename     = Bloop real.ogg
 |title        = Bloop
 |description  = Bloop at 16x the original speed, from the [[NOAA]] website.
}} 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 {{convert|5000|km|miles|sigfig=1|abbr=on}}.

==Ice quake origin==
The NOAA Vents Program has attributed the sound to that of a large [[cryoseism]] (also known as an ice quake).<ref name=noaa/> Numerous ice quakes share similar spectrograms with Bloop, as well as the amplitude necessary to detect them despite ranges exceeding {{convert|5000|km|miles|sigfig=1|abbr=on}}. 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 Strait]] and the [[Ross Sea]]; or possibly at [[Cape Adare]], a well-known source of cryogenic signals.<ref name=pmel/> Sounds generated by ice quakes are easily determined through the use of hydrophones since seawater, an excellent sound channel, allows the ambient sounds generated through ice activities to travel great distances.<ref name=xie/>{{rp|5}}

===Ice calving===
In [[ice calving]], variations result from a sound source's motion.<ref name=xie>{{cite thesis|last1=Xie|first1=Yunbo|title=An Acoustical Study of the Properties and Behaviour of Sea Ice|degree=Ph.D.|publisher=[[University of British Columbia]]|location=Vancouver, B.C.|id=Document No. NN69775|date=1991|doi=10.14288/1.0053256 |url=https://open.library.ubc.ca/cIRcle/collections/ubctheses/831/items/1.0053256}}{{open access}}</ref>{{rp|55}} Icequakes, caused by the fracturing and movement of large ice masses, can produce powerful low-frequency sounds that propagate over vast distances in water. This mechanism could explain the Bloop's wide detection range and distinct acoustic signature.<ref>{{Cite journal |last1=MacAyeal |first1=D. R. |last2=Okal |first2=E. A. |last3=Aster |first3=R. C. |last4=Bassis |first4=J. N. |date=September 2008 |title=Seismic and hydroacoustic tremor generated by colliding icebergs |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2008JF001005 |journal=Journal of Geophysical Research: Earth Surface |language=en |volume=113 |issue=F3 |doi=10.1029/2008JF001005 |bibcode=2008JGRF..113.3011M |issn=0148-0227}}</ref> As oceanographer Yunbo Xie explains, the alteration of [[waveforms]] from a detected sound "can also be caused by so-called [[angular spectrum method|angular frequency]] dependent radiation patterns associated with [[lamb waves|antisymmetric mode motion]] of the ice cover."<ref name=xie/>{{rp|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]].<ref>{{cite journal|last1=Pettit|first1=Erin C.|title=Passive Underwater Acoustic Evolution of a Calving Event|journal=Annals of Glaciology|date=2012|volume=53|issue=60|pages=113–122|doi=10.3189/2012aog60a137|bibcode=2012AnGla..53..113P|doi-access=free}}</ref> Rubbing involves two or more areas of compacted glacial [[ice stream|ice floes]] which are being forced together, inducing shear deformation at its edges and triggering horizontally-polarized shear waves, i. e. ''[[S-waves|SH waves]]''.<ref name=xie/>{{rp|137}} Ridging occurs when that ice bends or slides at the ridges.<ref name=xie/>{{rp|121}} According to Xie, both events will produce sound in the failure sequence (breakup) of an [[ice stream|ice floe]]:
{{quote|"A wave equation resulting from shear deformation will be defined in an [[ice stream|ice floe]] with the rubbing effect coupled to the floe through its boundary with the adjacent ice,"<ref name=xie/>{{rp|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."<ref name=xie/>{{rp|121}}}}

==Animal origin==
NOAA's Christopher Fox, in an interview with CNN in 2001, stated that he believed Bloop to be [[ice calving]] in [[Antarctica]].<ref>{{cite web |url=http://edition.cnn.com/2001/TECH/science/09/07/listening.ocean/index.html |publisher= CNN |title= Scientists tune in to sounds of the sea |date=September 7, 2001 |access-date= January 16, 2012}}</ref> In 2002, Fox was interviewed by David Wolman for an article in ''[[New Scientist]]'', where he stated that he did not believe its origin was man-made, such as a submarine or bomb. Fox also stated that while the audio profile of Bloop does resemble that of a living creature, <ref name="David Wolman" /> the source was a mystery because it would be "far more powerful than the calls made by any animal on Earth."<ref>{{cite news|title= Tuning in to a deep sea monster |url=http://edition.cnn.com/2002/WORLD/sailing/06/13/bloop.tech/index.html|work=CNN.com|date=June 13, 2002}}</ref> Wolman reported in his article the following:

{{quotation|Fox's hunch is that the sound nicknamed Bloop is the most likely (out of the other recorded unidentified sounds) 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 {{convert|4800|km|miles|sigfig=2|abbr=on}} 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?<ref name=hayward/>{{rp|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 supported the argument that the noise is produced by ice fracturing processes."<ref name=hayward>{{cite book|last1=Hayward|first1=Philip|title=Making a Splash: Mermaids (and Mer-Men) in 20th and 21st Century Audiovisual Media|date=2017|publisher=Indiana University Press |isbn=9780861969258|oclc=1020857723|language=en}}</ref>{{rp|175}}

==See also==
* [[List of unexplained sounds#NOAA (formerly unidentified)|List of formerly unidentified sounds]]
* [[Upsweep]]

== References ==
{{reflist|30em}}

== External links ==
{{subject bar|auto=y|d=y|Earth sciences|Water}}
* [https://web.archive.org/web/20200225041855/https://www.pmel.noaa.gov/acoustics/sounds/bloop.html NOAA's PMEL Acoustics Program on Icequakes (Bloop)]
* {{Skeptoid | id=4177 | number= 177| title= The Bloop| date= October 27, 2009| quote= | access-date=}}
* {{cite podcast|title=Science Solved It: A Call From the Deep|website=Vice|host=Kayleigh Rogers|url=https://play.acast.com/s/sciencesolvedit/1---a-call-from-the-deep|time=13:45|date=April 25, 2017|publisher=Motherboard}}

[[Category:1997 in science]]
[[Category:Pacific Ocean]]
[[Category:Snow or ice weather phenomena]]
[[Category:Oceanography]]
[[Category:Unidentified sounds]]