# The Bloop and NOAA's unexplained ocean sounds > In the 1990s NOAA hydrophones in the Pacific recorded several loud, low-frequency sounds that the scientists could not at first identify and gave… Source: https://mysteriesdept.com/mysteries/noaa-ocean-sounds Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) Updated: 2026-10-27T17:47:54+00:00 --- **MYS** 0D9C766T24XP·Mystery · signal # The Bloop and NOAA's unexplained ocean sounds **0** [Follow][Ask a question](https://mysteriesdept.com/questions/key-questions?mystery=noaa-ocean-sounds) The Bloop and NOAA's unexplained ocean sounds ![Possible locations of the Bloop, an ultra-low frequency and extremely powerful underwater sound detected by the U.S.](https://mysteriesdept.com/media/folio/noaa-ocean-sounds-lead) Nojhan · CC BY-SA 3.0 Recorded by NOAA PMEL hydrophones: US Navy SOSUS from 1991 and the eastern equatorial Pacific autonomous array from May 1996⁠[[2]] Bloop Summer 1997; broadband; heard at over 5,000 km; attributed to icequakes⁠[[3]] Upsweep Since at least August 1991; seasonal; near 54°S 140°W; origin unresolved⁠[[11]] Train 4 March 1997; 32–35 Hz; attributed to an iceberg grounded near Cape Adare⁠[[7]] Slow Down 1997 (file dated day 139); attributed to an iceberg grounding⁠[[8]] Whistle 7 July 1997, one hydrophone at 8°N 110°W; resembles an erupting arc volcano⁠[[10]] Julia 1 March 1999, 21:05 GMT; attributed to an iceberg running aground off Antarctica⁠[[9]] Raw data Not publicly released; only sped-up example clips and spectrograms are online⁠[[15]] Status Partly explained Questions 0 of 5 answered People [**Christopher G. Fox** PMEL acoustic monitoring scientist; first author of the array design paper](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/people/FIG0D9C77XG4YV0/christopher-g-fox)[**Phil Lobel** Boston University marine biologist quoted on a biological source](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/people/FIG0D9C78MY4D9G/phil-lobel)[**Haruyoshi Matsumoto** PMEL acoustics engineer; co-author of the array design paper](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/people/FIG0D9C785A13XH/haruyoshi-matsumoto)[**Robert P. Dziak** PMEL acoustics scientist; led the iceberg A53a study](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/people/FIG0D9C78D43FWX/robert-p-dziak) Catalog key**MYS** 0D9C766T24XP The deep ocean carries low-frequency sound for thousands of kilometres through the SOFAR channel, a layer where temperature and pressure trap sound waves. From 1991 NOAA's Pacific Marine Environmental Laboratory (PMEL) used the US Navy's SOSUS hydrophones to listen for undersea earthquakes and eruptions, and from May 1996 it ran its own array of autonomous hydrophone moorings in the eastern equatorial Pacific for the same purpose⁠[[1]]⁠[[2]]. Among the earthquakes, whales and ships, the analysts heard a handful of loud signals they could not place and gave them names. The best known is the Bloop, a broadband sound recorded in the summer of 1997 and heard on sensors more than 5,000 km apart⁠[[3]]. In 2002 a New Scientist report, relayed by CNN, said it bore the hallmarks of an animal but was louder than any known creature, and the idea of an unknown giant animal took hold in popular culture⁠[[4]]. NOAA's own scientists had already suspected ice: in 2001 Christopher Fox of PMEL's acoustic monitoring project said it might be ice calving because "it always comes from the south"⁠[[5]]. PMEL now describes the Bloop as consistent with icequakes from large icebergs cracking, based on the similarity of its spectrogram to icequakes recorded in the Scotia Sea and on its arrival direction⁠[[3]]; NOAA's Ocean Service dates the identification to 2005⁠[[6]]. The other named sounds have been assigned in the same way. Train, Slow Down and Julia are attributed to icebergs grounding on the seafloor; Whistle to an erupting volcano too distant to locate; Upsweep, the oldest and most persistent, remains unresolved on PMEL's own page⁠[[7]]⁠[[8]]⁠[[9]]⁠[[10]]⁠[[11]]. The case is a good test of how far a spectrogram and a bearing can carry an attribution. The explanations are plausible and fit a body of peer-reviewed work showing that Antarctic ice is one of the loudest natural sources in the southern oceans⁠[[12]]⁠[[13]]⁠[[14]]. But no paper has published the original 1990s recordings, their arrival times or their azimuths, so the specific attributions cannot be checked by anyone outside NOAA. Of the 5 questions on this site, 0 are answered. The most likely answer to “What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s?”, not yet confirmed: all of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions…. ### Key questionsset by the editors [**What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s?** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas)Most likely: all of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… [**What produces the Upsweep?** ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CSR0G1Y/what-produces-the-upsweep)No answer ahead yet [All 5 questions ](https://mysteriesdept.com/questions/key-questions?mystery=noaa-ocean-sounds) ## What happened 0:00 / 0:29 ![Spectrogram of The Upsweep recording](https://mysteriesdept.com/files/v/9f52a7e0de2e73945c7b35883c5828c2dbd525acc97bb44e91adc1ff6bdcdb06/spec) 0:00Spectrogram, 0 to 1.3 kHz0:29 The Upsweep recordingNOAA Pacific Marine Environmental Laboratory, 1991. Public domain[Artifact ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7TF8459E/the-upsweep-recording) PMEL began recording the Navy's SOSUS arrays in August 1991 and was using them to locate undersea eruptions by 1993⁠[[11]]⁠[[1]]. In May 1996 it deployed its own array of autonomous hydrophones in the eastern equatorial Pacific, moored in the SOFAR channel to monitor the East Pacific Rise between 20°N and 20°S and the Galápagos Ridge; the array recorded continuously and was recovered and redeployed at intervals⁠[[2]]. Upsweep was already present when SOSUS recording began in 1991: long trains of narrowband sounds rising in pitch over several seconds each, loud enough to be heard across the Pacific, peaking in spring and autumn⁠[[11]]. In 1997 the equatorial array recorded Train on 4 March, a quasi-steady tone at 32 to 35 Hz⁠[[7]]; Slow Down, a sound that descends in frequency over about seven minutes, in a file numbered for day 139 of 1997 (19 May)⁠[[8]]; Whistle on 7 July, an undulating single tone on the hydrophone at 8°N 110°W⁠[[10]]; and the Bloop, during the summer⁠[[3]]. Julia followed on 1 March 1999 at 21:05 GMT⁠[[9]]. **Map of the world** [Open the full map](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/map) [+][−] 1 **Eastern equatorial Pacific autonomous hydrophone array** Hydrophone array (moorings between about 8°N and 8°S near 95°W–110°W) A region 2 **NOAA autonomous hydrophone at 8°N 110°W** Hydrophone mooring Within 10 km 3 **Upsweep source region, about 54°S 140°W** Open ocean (approximate location) A region 4 **Bransfield Strait, Antarctic Peninsula** Strait A region 5 **Bloop source region, between Bransfield Strait and the Ross Sea** Antarctic coast (approximate location) A region 6 **South Georgia, Scotia Sea** Island A region 7 **Cape Adare, Ross Sea** Cape Within 10 km A regionNatural Earth ### Timeline **Timeline** Squeezed where little happened. Each mark is a published claim, by how it stands:AcceptedMost likelyStill possibleDisputedRuled out ## The accounts There are no witnesses beyond the analysts and their recordings. The public record is a set of short PMEL web pages, one per sound, each with a spectrogram and an audio clip sped up 10 to 20 times so that infrasound becomes audible⁠[[3]]⁠[[11]]⁠[[7]]⁠[[9]]⁠[[10]]⁠[[8]]. The pages are undated and have been revised. The Slow Down clip is still labelled "Equatorial Pacific unknown source" on the program's index page while the cryogenic page calls it an iceberg grounding⁠[[15]]⁠[[8]]. Press accounts filled the gap. In June 2002 CNN, summarising New Scientist, described the Bloop as possibly a giant animal, quoted the marine biologist Phil Lobel doubting a squid but favouring a biological source, and quoted Fox that most of the named sounds had been explained, with Upsweep tracked to an undersea volcano⁠[[4]]. The same report said the Bloop was heard on Navy SOSUS sensors 3,000 miles apart; NOAA's Ocean Service says hydrophones more than 3,219 km apart across the Pacific; neither names the instruments precisely⁠[[4]]⁠[[6]]. NOAA's Ocean Service lists the theories that circulated: military exercises, ship engines, fishing-boat winches, giant squid, whales and unknown animals⁠[[6]]. ## What was recorded What survives in public is about a dozen sped-up audio files and spectrogram images, released as public information that may be freely redistributed with credit⁠[[16]]. The Bloop clip is 16 times real speed; Upsweep 20 times; Whistle 16 times and band-passed between 8 and 20 Hz⁠[[3]]⁠[[11]]⁠[[10]]. The raw multi-hydrophone recordings, the arrival-time picks and the azimuth estimates behind each attribution have not been published; no 1990s equatorial array data were found in NOAA's public passive acoustic archive⁠[[17]]. 0:00 / 0:10 ![Spectrogram of The Bloop recording](https://mysteriesdept.com/files/v/ecc057a98dfcb0e2a35affc54e906d9a0ee8870bc9592c8fffce873bad5b374f/spec) 0:00Spectrogram, 0 to 1 kHz0:10 The Bloop recordingNOAA Pacific Marine Environmental Laboratory, 1997. Public domain[Artifact ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7SQT2DSN/the-bloop-recording) Two things about the sounds are stated with numbers. The Bloop was detected at ranges over 5,000 km and its bearing pointed between Bransfield Strait and the Ross Sea, or to Cape Adare⁠[[3]]. Upsweep was located roughly at 54°S 140°W and has declined in level since 1991⁠[[11]]. Whistle, heard on one hydrophone, cannot be located at all, because a fix needs at least three⁠[[10]]. ## The explanations Ice is the explanation NOAA gives for four of the six. The supporting work is strong on the general point. Hydrophones moored in the Scotia Sea recorded iceberg A53a, about 55 by 25 km, producing harmonic tremor as it scraped the seabed and short broadband icequakes as it broke up near South Georgia on 2 February 2008⁠[[18]]. The breakup of icebergs C19a and B15a from late 2007 raised noise levels at mid to equatorial latitudes for about a year and a half, and seasonal noise cycles across the southern oceans track iceberg drift⁠[[12]]. Ice tremor off Wilkes Land reaches estimated source levels near 245 dB⁠[[13]], and Ross Sea icebergs were recorded as far away as French Polynesia in the same years⁠[[14]]⁠[[19]]. PMEL's case for the Bloop is that its spectrogram resembles the Scotia Sea icequakes and its bearing points at Antarctic coasts known for ice sounds⁠[[3]]. For Train and Julia the case is a steady or descending tone from the direction of the Ross Sea or the Antarctic Peninsula, which matches a berg dragging or settling on the seabed⁠[[7]]⁠[[9]]. 0:00 / 0:38 ![Spectrogram of The Train recording](https://mysteriesdept.com/files/v/7188fdded59d35a14bf2e7dfb3fdadbd4f1a88e306e64c09bd3751ab70c6b5d0/spec) 0:00Spectrogram, 0 to 1 kHz0:38 The Train recordingNOAA Pacific Marine Environmental Laboratory, 1997. Public domain[Artifact ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7V6P7CWX/the-train-recording) 0:00 / 0:10 ![Spectrogram of The Julia recording](https://mysteriesdept.com/files/v/beb0713191647eaa67a6c1ad1a401a5866af99372714e7b2eccdbbdd44497440/spec) 0:00Spectrogram, 0 to 1 kHz0:10 The Julia recordingNOAA Pacific Marine Environmental Laboratory, 1999. Public domain[Artifact ](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7XD02YJ0/the-julia-recording) A biological source was the reading the press preferred for the Bloop. Its basis was the sound's rising frequency, which reminded biologists of animal calls, and its loudness, which no known animal approaches; it rests on no recording of any animal and no NOAA scientist has proposed it⁠[[4]]⁠[[5]]. A human source (exercises, engines, winches) was suggested but fits poorly with a source to the far south at ranges over 5,000 km⁠[[6]]⁠[[3]]. Upsweep has two readings. PMEL notes that its rough location lies near inferred volcanic seismicity but calls the origin unresolved; in 2002 Fox was reported as saying it had been tracked to an undersea volcano⁠[[11]]⁠[[4]]. Its seasonality could reflect the source or seasonal changes in how sound travels⁠[[11]]; seasonal ice noise is now documented across the southern oceans, which makes an ice component worth testing⁠[[12]]. ### Published claims **Published claims and their status** | Year | Who | Claimed | Status | Reason | |---|---|---|---|---| | 1995 | Christopher Fox and colleagues (NOAA PMEL)⁠[1] | The Navy's SOSUS hydrophone arrays can detect and locate a seafloor volcanic episode, as they did on the Juan de Fuca Ridge in 1993. | Accepted | The method became routine and led to the autonomous arrays that recorded the 1990s sounds⁠[2]. | | 2001 | Christopher Fox (NOAA PMEL)⁠[5] | The Bloop may be related to ice calving, since it always comes from the south. | Still possible | The southern, Antarctic source held, but PMEL later attributed the sound to icequakes in cracking icebergs rather than calving from a shelf⁠[3]. | | 2002 | Phil Lobel, reported by New Scientist and CNN⁠[4] | The Bloop's profile resembles a sound made by a living thing, though probably not a squid. | Disputed | Icequakes recorded near Antarctica later matched its spectrogram, and NOAA now identifies the sound as an icequake⁠[3]⁠[6]. | | 2002 | Christopher Fox (NOAA PMEL), reported by CNN⁠[4] | The Upsweep has been tracked to an undersea volcano in the South Pacific. | Still possible | PMEL still calls its origin unresolved; the source lies near inferred volcanic seismicity, and an ice origin is also proposed⁠[11]⁠[12]. | | 2002 | Jacques Talandier, Olivier Hyvernaud, Emile Okal and Pierre-Franck Piserchia⁠[14] | Large icebergs in the Ross Sea make hydroacoustic signals that seismic stations in French Polynesia record thousands of kilometres away. | Accepted | Replicated for other bergs in the Indian and Pacific oceans and in the Scotia Sea⁠[19]⁠[18]. | | 2005 | Emily Chapp, DelWayne Bohnenstiehl and Maya Tolstoy⁠[13] | Drifting icebergs off Wilkes Land produce low-frequency tremor with source levels up to about 245 dB. | Accepted | Consistent with later iceberg recordings that show ice is loud enough to be heard across ocean basins⁠[12]. | | 2005 | NOAA PMEL acoustics researchers⁠[6] | The Bloop was an icequake, made by a large iceberg cracking and fracturing off Antarctica. | Accepted | The 2008 recordings of iceberg A53a breaking up gave icequakes with similar spectrograms, heard at over 5,000 km⁠[3]⁠[18]. | | 2006 | Jacques Talandier, Olivier Hyvernaud, Dominique Reymond and Emile Okal⁠[19] | Icebergs both grounded and drifting produce distinctive hydroacoustic signals recorded at long range in the southern oceans. | Accepted | Matches PMEL's attribution of Train and Julia to grounding icebergs, though those identifications rest on azimuth alone⁠[7]⁠[9]. | | 2013 | Robert Dziak and colleagues⁠[18] | Iceberg A53a gave off harmonic tremor while scraping shoals and short broadband icequakes as it broke up near South Georgia in 2008. | Accepted | The first iceberg followed acoustically from drift to breakup, and the reference for identifying the Bloop⁠[3]. | | 2014 | Haruyoshi Matsumoto and colleagues⁠[12] | Antarctic icebergs are a major source of ocean noise across the Southern Hemisphere, and seasonal noise cycles follow their drift and breakup. | Accepted | Shown with archived records of the breakup of bergs C19a and B15a; whether it also explains the Upsweep's seasonality has not been tested directly⁠[12]. | ## What would settle it Release of the original multi-hydrophone records, with arrival times, for each named sound. With those, the bearings can be recomputed and compared with iceberg positions on the same dates from the scatterometer iceberg database, which covers 1997 through ERS and NSCAT and 1999 through ERS and QuikSCAT⁠[[20]]⁠[[21]]. A classifier trained on modern labelled recordings of icequakes, groundings, tremor and eruptions could then score each 1990s sound against each class⁠[[17]]⁠[[18]]. For Upsweep, a multi-year record from hydrophones south of 40°S would show whether the source is fixed (a vent) or moves with the ice. ## Questions 0 of 5 questions are answered. **Key questions** [All 5](https://mysteriesdept.com/questions/key-questions?mystery=noaa-ocean-sounds) **0** [What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas) 0 of 3 sub-questions answered·0 Most likely: all of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions… **0** [What produces the Upsweep?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CSR0G1Y/what-produces-the-upsweep) 0 of 0 sub-questions answered·0 Open: 4 answers, none ahead ## Evidence 29 findings [What made the loud unidentified sounds recorded by NOAA's Pacific hydrophones in the 1990s?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CA41BJB/what-made-the-loud-unidentified-sounds-recorded-by-noaas)10 findings [All of them are natural geophysical or cryogenic sounds (icequakes, grounding icebergs, volcanic eruptions…](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7DH635Z3/all-of-them-are-natural-geophysical-or-cryogenic-sounds)Most likely +[Antarctic icebergs are a major natural sound source heard at mid and equatorial latitudes, with seasonal cycles tied to iceberg drift.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7DS01TAX/antarctic-icebergs-are-a-major-natural-sound-source-heard-at)Established +[Ice tremor reaches estimated source levels near 245 dB re 1 µPa at 1 m and travels thousands of kilometres.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7E0T3FGG/ice-tremor-reaches-estimated-source-levels-near-245-db-re-1)Established +[Ross Sea icebergs were recorded as far away as French Polynesia around the same years.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7E8M6XH4/ross-sea-icebergs-were-recorded-as-far-away-as-french)Established +[NOAA assigns four of the six sounds to ice and one to a volcano; Upsweep remains unresolved.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7EGE4BDY/noaa-assigns-four-of-the-six-sounds-to-ice-and-one-to-a)Supported −[The original records and bearings have not been published, so the individual attributions cannot be checked independently.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7ER81E4N/the-original-records-and-bearings-have-not-been-published-so)Established [At least one of the sounds, most often the Bloop, was made by a large animal, known or unknown.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7F024MPX/at-least-one-of-the-sounds-most-often-the-bloop-was-made-by)Disputed +[The Bloop's rising frequency reminded biologists of animal calls.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7F7W7KDX/the-bloops-rising-frequency-reminded-biologists-of-animal)Speculative −[The Bloop was far louder than any known animal; Lobel doubted cephalopods could make such a sound.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7FFP2MW8/the-bloop-was-far-louder-than-any-known-animal-lobel-doubted)Supported −[Its spectrogram resembles icequakes recorded in the Scotia Sea.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7FQG2BND/its-spectrogram-resembles-icequakes-recorded-in-the-scotia)Supported [At least one of the sounds came from human activity (military exercises, ships, winches or other machinery).](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7FZA5QEB/at-least-one-of-the-sounds-came-from-human-activity-military)Disputed −[The Bloop's bearing points between Bransfield Strait and the Ross Sea, far from shipping lanes.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7G745WX2/the-bloops-bearing-points-between-bransfield-strait-and-the)Supported −[PMEL catalogues ship and airgun sounds separately and does not class any named sound among them.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7GEY33RQ/pmel-catalogues-ship-and-airgun-sounds-separately-and-does)Suggestive [Was the Bloop an icequake, and from which iceberg?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CHY4R4M/was-the-bloop-an-icequake-and-from-which-iceberg)7 findings [The Bloop was one or more icequakes from a large iceberg cracking somewhere between Bransfield Strait and the…](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7GYJ6Y2Y/the-bloop-was-one-or-more-icequakes-from-a-large-iceberg)Most likely +[Its spectrogram resembles icequakes recorded in the Scotia Sea from iceberg A53a.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7H6C7H9S/its-spectrogram-resembles-icequakes-recorded-in-the-scotia)Supported +[Icequakes from iceberg breakup are broadband and recorded at long range.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7HE66NAJ/icequakes-from-iceberg-breakup-are-broadband-and-recorded-at)Established +[Fox suspected ice calving by 2001 because the sound always came from the south.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7HP00FDJ/fox-suspected-ice-calving-by-2001-because-the-sound-always)Suggestive −[The bearing, spectrum comparison and source iceberg are not published in any peer-reviewed paper.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7HXT47N9/the-bearing-spectrum-comparison-and-source-iceberg-are-not)Established [The Bloop was an ice sound of another kind, such as calving from an ice shelf or a collision between bergs,…](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7J5M4BVS/the-bloop-was-an-ice-sound-of-another-kind-such-as-calving)Still possible +[NOAA's Ocean Service describes it as an iceberg breaking away from an Antarctic glacier.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7JDE0412/noaas-ocean-service-describes-it-as-an-iceberg-breaking-away)Suggestive +[PMEL's comparison sounds include calving and iceberg harmonic tremor as well as icequakes.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7JN83CD8/pmels-comparison-sounds-include-calving-and-iceberg-harmonic)Suggestive [The Bloop was not made by ice.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7JX21WY2/the-bloop-was-not-made-by-ice)Disputed +[It was described in 2002 as unidentified and possibly biological.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7K4W7QG0/it-was-described-in-2002-as-unidentified-and-possibly)Speculative [What produces the Upsweep?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7CSR0G1Y/what-produces-the-upsweep)7 findings [Upsweep is produced by an undersea volcanic or hydrothermal source near 54°S 140°W.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7KMG1Y78/upsweep-is-produced-by-an-undersea-volcanic-or-hydrothermal)Still possible +[The rough location lies near inferred volcanic seismicity.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7KWA5SQR/the-rough-location-lies-near-inferred-volcanic-seismicity)Suggestive +[In 2002 Fox was reported as saying Upsweep had been tracked to an undersea volcano.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7M444VZN/in-2002-fox-was-reported-as-saying-upsweep-had-been-tracked)Suggestive −[PMEL states that the origin is unresolved.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7MBY03JQ/pmel-states-that-the-origin-is-unresolved)Established [Upsweep is an ice sound, its seasonality driven by the annual cycle of iceberg drift and breakup.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7MKR0P6H/upsweep-is-an-ice-sound-its-seasonality-driven-by-the-annual)Still possible +[Seasonal noise cycles across the southern oceans track iceberg drift and breakup.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7MVJ04XV/seasonal-noise-cycles-across-the-southern-oceans-track)Supported +[Upsweep peaks in spring and autumn, which may reflect either the source or seasonal propagation.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7N3C1XRY/upsweep-peaks-in-spring-and-autumn-which-may-reflect-either)Speculative −[Upsweep is narrowband and regular, unlike broadband icequakes.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7NB60VFT/upsweep-is-narrowband-and-regular-unlike-broadband-icequakes)Suggestive [The source is steady and the seasonality is an artefact of seasonal changes in how sound travels from it.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7NK03Z2B/the-source-is-steady-and-the-seasonality-is-an-artefact-of)Still possible +[PMEL names seasonal propagation as one possible cause of the seasonality.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7NTT0TJ2/pmel-names-seasonal-propagation-as-one-possible-cause-of-the)Speculative [Were Train, Slow Down and Julia made by icebergs grounding on the seafloor?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7D1J3NMQ/were-train-slow-down-and-julia-made-by-icebergs-grounding-on)3 findings [All three were produced by large icebergs settling on or dragging across the seafloor.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7PAE07W8/all-three-were-produced-by-large-icebergs-settling-on-or)Most likely +[Iceberg A53a produced harmonic tremor while scraping shoals, recorded on nearby hydrophones.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7PJ80V8E/iceberg-a53a-produced-harmonic-tremor-while-scraping-shoals)Established +[Grounded and drifting bergs produce long-range hydroacoustic signals catalogued in the southern Indian and Pacific oceans.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7PT23NWW/grounded-and-drifting-bergs-produce-long-range-hydroacoustic)Established −[Julia's bearing is uncertain enough to span Bransfield Strait to Cape Adare.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7Q1W6D71/julias-bearing-is-uncertain-enough-to-span-bransfield-strait)Established [Where did Whistle come from?](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/questions/QST0D9C7D9C6V99/where-did-whistle-come-from)2 findings [Whistle was an eruption signal from a distant submarine arc volcano.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/answers/ANS0D9C7QSA2QCN/whistle-was-an-eruption-signal-from-a-distant-submarine-arc)Most likely +[Its undulating single-frequency shape resembles signals from erupting arc volcanoes such as West Mata.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7R1440VV/its-undulating-single-frequency-shape-resembles-signals-from)Suggestive −[Recorded on a single hydrophone, so no location is possible from the array alone.](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/evidence/EVD0D9C7R8Y1JPS/recorded-on-a-single-hydrophone-so-no-location-is-possible)Established ## Artifacts The films, photos, papers and objects this mystery rests on, each with its own key and its distance from the original. **Artifacts** [See all 21](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts) Photo1 step from object [The Bloop recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7SQT2DSN/the-bloop-recording) Nojhan · CC BY-SA 3.0 Audio2 steps from object [The Upsweep recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7TF8459E/the-upsweep-recording) NOAA Pacific Marine Environmental Laboratory · Public domain (US government work) Audio2 steps from object [The Train recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7V6P7CWX/the-train-recording) NOAA Pacific Marine Environmental Laboratory · Public domain (US government work) Audio2 steps from object [The Slow Down recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7VY40FKX/the-slow-down-recording) NOAA Pacific Marine Environmental Laboratory · Public domain (US government work) Audio2 steps from object [The Whistle recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7WNJ4DNE/the-whistle-recording) NOAA Pacific Marine Environmental Laboratory · Public domain (US government work) Audio2 steps from object [The Julia recording](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7XD02YJ0/the-julia-recording) NOAA Pacific Marine Environmental Laboratory · Public domain (US government work) Document2 steps from object [Hydrophone recordings of iceberg A53a breaking up near South Georgia](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts/ART0D9C7YC87EPS/hydrophone-recordings-of-iceberg-a53a-breaking-up-near-south) Dziak et al. · publisher [See all 21 artifacts](https://mysteriesdept.com/mysteries/noaa-ocean-sounds/artifacts) ## See also [ **UVB-76, "the Buzzer"** A Russian shortwave station on 4625 kHz sending a repeating buzz since at least 1982. ](https://mysteriesdept.com/mysteries/uvb-76-buzzer) [ **Fast radio bursts and the origin of the one-off bursts** Millisecond flashes of radio waves from other galaxies, first reported in 2007. ](https://mysteriesdept.com/mysteries/fast-radio-bursts) [ **Tabby's star (KIC 8462852)** A star in Cygnus that dimmed by up to 20 per cent at irregular times in Kepler data. ](https://mysteriesdept.com/mysteries/tabbys-star) [ **Wow! signal** A 72-second radio signal recorded by Ohio State's Big Ear telescope in August 1977. ](https://mysteriesdept.com/mysteries/wow-signal) ## References 1. 1.[Fox, C., Radford, W., Dziak, R. et al. 1995. Acoustic detection of a seafloor spreading episode on the Juan de Fuca Ridge using military hydrophone arrays. Geophysical Research Letters 22(2): 131–134.](https://mysteriesdept.com/sources/SRC0D9C739272G6/acoustic-detection-of-a-seafloor-spreading-episode-on-the)[doi](https://doi.org/10.1029/94GL02059)cited 2 times here**SRC** 0D9C739272G6 1. 2.[Fox, C., Matsumoto, H., Lau, T. 2001. Monitoring Pacific Ocean seismicity from an autonomous hydrophone array. Journal of Geophysical Research: Solid Earth 106(B3): 4183–4206.](https://mysteriesdept.com/sources/SRC0D9C73182V9E/monitoring-pacific-ocean-seismicity-from-an-autonomous)[doi](https://doi.org/10.1029/2000JB900404)cited 5 times here**SRC** 0D9C73182V9E 1. 3.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustics Monitoring Program: Icequakes (Bloop). NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C70TY0F01/acoustics-monitoring-program-icequakes-bloop)cited 13 times here**SRC** 0D9C70TY0F01 1. 4.[CNN 2002. Tuning in to a deep sea monster. CNN.com, 13 June 2002.](https://mysteriesdept.com/sources/SRC0D9C75Q645CK/tuning-in-to-a-deep-sea-monster)cited 9 times here**SRC** 0D9C75Q645CK 1. 5.[CNN 2001. Scientists tune in to sounds of the sea. CNN.com, 7 September 2001.](https://mysteriesdept.com/sources/SRC0D9C75FC7Z2D/scientists-tune-in-to-sounds-of-the-sea)cited 3 times here**SRC** 0D9C75FC7Z2D 1. 6.[NOAA National Ocean Service n.d.. What is the bloop?. NOAA Ocean Facts (oceanservice.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C72SE163B/what-is-the-bloop)cited 5 times here**SRC** 0D9C72SE163B 1. 7.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustics Monitoring Program: Iceberg Grounding (Train). NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C71JC5TEP/acoustics-monitoring-program-iceberg-grounding-train)cited 7 times here**SRC** 0D9C71JC5TEP 1. 8.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Cryogenic (Ice) sounds. NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C72202TZM/cryogenic-ice-sounds)cited 10 times here**SRC** 0D9C72202TZM 1. 9.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustics Monitoring Program: Iceberg Grounding on Seafloor (Julia). NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C71AJ57W0/acoustics-monitoring-program-iceberg-grounding-on-seafloor)cited 7 times here**SRC** 0D9C71AJ57W0 1. 10.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustics Monitoring Program: Submarine Volcanic Eruption (Whistle). NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C71T62YG9/acoustics-monitoring-program-submarine-volcanic-eruption)cited 9 times here**SRC** 0D9C71T62YG9 1. 11.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustics Monitoring Program: Upsweep. NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C712R2AJY/acoustics-monitoring-program-upsweep)cited 15 times here**SRC** 0D9C712R2AJY 1. 12.[Matsumoto, H., Bohnenstiehl, D., Tournadre, J. et al. 2014. Antarctic icebergs: A significant natural ocean sound source in the Southern Hemisphere. Geochemistry, Geophysics, Geosystems 15(8): 3448–3458.](https://mysteriesdept.com/sources/SRC0D9C73RP5QGT/antarctic-icebergs-a-significant-natural-ocean-sound-source)[doi](https://doi.org/10.1002/2014GC005454)cited 5 times here**SRC** 0D9C73RP5QGT 1. 13.[Chapp, E., Bohnenstiehl, D., Tolstoy, M. 2005. Sound-channel observations of ice-generated tremor in the Indian Ocean. Geochemistry, Geophysics, Geosystems 6(6).](https://mysteriesdept.com/sources/SRC0D9C740G37ZY/sound-channel-observations-of-ice-generated-tremor-in-the)[doi](https://doi.org/10.1029/2004GC000889)cited 2 times here**SRC** 0D9C740G37ZY 1. 14.[Talandier, J., Hyvernaud, O., Okal, E. et al. 2002. Long-range detection of hydroacoustic signals from large icebergs in the Ross Sea, Antarctica. Earth and Planetary Science Letters 203(1): 519–534.](https://mysteriesdept.com/sources/SRC0D9C748A3W90/long-range-detection-of-hydroacoustic-signals-from-large)[doi](https://doi.org/10.1016/S0012-821X(02)00867-1)cited 2 times here**SRC** 0D9C748A3W90 1. 15.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. Acoustic Monitoring Program: Sounds (examples). NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C729T1MG7/acoustic-monitoring-program-sounds-examples)cited 3 times here**SRC** 0D9C729T1MG7 1. 16.[NOAA Pacific Marine Environmental Laboratory, A. n.d.. NOAA PMEL Acoustics Program: Multimedia and credits. NOAA PMEL Acoustics Program (pmel.noaa.gov).](https://mysteriesdept.com/sources/SRC0D9C72HM17HH/noaa-pmel-acoustics-program-multimedia-and-credits)cited 2 times here**SRC** 0D9C72HM17HH 1. 17.[NOAA National Centers for Environmental Information n.d.. Passive Acoustic Data. NOAA NCEI.](https://mysteriesdept.com/sources/SRC0D9C757J6A7Q/passive-acoustic-data)cited 2 times here**SRC** 0D9C757J6A7Q 1. 18.[Dziak, R., Fowler, M., Matsumoto, H. et al. 2013. Life and Death Sounds of Iceberg A53a. Oceanography 26(2).](https://mysteriesdept.com/sources/SRC0D9C73GW1MV0/life-and-death-sounds-of-iceberg-a53a)[doi](https://doi.org/10.5670/oceanog.2013.20)cited 8 times here**SRC** 0D9C73GW1MV0 1. 19.[Talandier, J., Hyvernaud, O., Reymond, D. et al. 2006. Hydroacoustic signals generated by parked and drifting icebergs in the Southern Indian and Pacific Oceans. Geophysical Journal International 165(3): 817–834.](https://mysteriesdept.com/sources/SRC0D9C74G44MTQ/hydroacoustic-signals-generated-by-parked-and-drifting)[doi](https://doi.org/10.1111/j.1365-246X.2006.02911.x)cited 3 times here**SRC** 0D9C74G44MTQ 1. 20.[Budge, J., Long, D. 2018. A Comprehensive Database for Antarctic Iceberg Tracking Using Scatterometer Data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 11(2): 434–442.](https://mysteriesdept.com/sources/SRC0D9C74QY45DF/a-comprehensive-database-for-antarctic-iceberg-tracking)[doi](https://doi.org/10.1109/JSTARS.2017.2784186)cited 1 time here**SRC** 0D9C74QY45DF 1. 21.[Budge, J., Vorwaller, S., Cribs, K. et al. n.d.. The Antarctic Iceberg Tracking Database (1978 & 1992–present). Brigham Young University, Microwave Earth Remote Sensing Laboratory (scp.byu.edu).](https://mysteriesdept.com/sources/SRC0D9C74ZR5AEZ/the-antarctic-iceberg-tracking-database-1978-1992present)cited 2 times here**SRC** 0D9C74ZR5AEZ Last edited 27 Oct 2026