The Julia Sound (1999): The Mysterious Underwater Signal Explained
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What Was the Julia Sound?
Julia was an underwater acoustic event recorded by NOAA on March 1, 1999.
It was not captured by a normal microphone or a camera.
Instead, it was detected by an autonomous hydrophone array.
A hydrophone is essentially an underwater acoustic sensor designed to detect sounds and pressure variations traveling through the ocean.
NOAA's Pacific Marine Environmental Laboratory operated networks of these instruments to monitor underwater acoustic activity over enormous distances.
The hydrophones were especially useful for detecting very low-frequency sounds that could travel through the ocean for thousands of kilometers.
NOAA's own records identify the Julia recording as originating from the eastern equatorial Pacific autonomous hydrophone array. (PMEL)
The important point is that the hydrophone array was located in the Pacific, while NOAA's analysis placed the likely source much farther south, near Antarctica.
This is one reason the event became interesting.
Something happening in the Antarctic region had produced an acoustic signal capable of reaching instruments far away in the Pacific.
When Was Julia Recorded?
The official NOAA record gives the date as:
March 1, 1999
NOAA's database gives the origin time as 1999 Julian Day 60 at approximately 21:05 GMT. (PMEL)
The recording therefore belongs to 1999, not 1997.
This distinction is important because several famous NOAA underwater sounds from the late 1990s are frequently mixed together online.
For example:
- Julia — March 1, 1999
- Slow Down — May 19, 1997
- Bloop — 1997
- Train — March 4, 1997
All of these are different acoustic events.
NOAA's records specifically identify Slow Down as a May 19, 1997 sound associated with a large iceberg becoming grounded near the Antarctic Peninsula. (PMEL)
The famous Bloop was also recorded in 1997 and was later associated with ice-related activity. (National Ocean Service)
Where Was the Julia Sound Recorded?
This is another part of the story that is frequently misunderstood.
Julia was detected by a hydrophone array in the eastern equatorial Pacific, but that does not mean the source was located there.
NOAA used the arrival directions of the acoustic signal to estimate where it came from.
Because the arrival azimuth was uncertain, NOAA could not pinpoint the source to one exact coordinate.
Instead, the agency gave a broad possible origin region between:
- Bransfield Strait
- Cape Adare
Both are associated with Antarctic waters and regions where large icebergs can interact with the seafloor. (PMEL)
So the basic chain was:
Antarctic region → underwater acoustic wave → Pacific Ocean → NOAA hydrophone array
That enormous distance is one of the most fascinating aspects of the event.
How Could a Sound Travel So Far?
Sound behaves very differently underwater than it does in the atmosphere.
The ocean contains layers where temperature, pressure and salinity influence the way sound propagates.
Low-frequency acoustic energy can travel extremely long distances through the ocean under the right conditions.
NOAA's hydrophone systems were specifically designed to take advantage of these properties.
The instruments were not simply listening for sounds occurring immediately around them. They were capable of detecting acoustic signals generated thousands of kilometers away. NOAA's deployment information describes autonomous hydrophones suspended hundreds to thousands of meters in the water column and positioned to take advantage of the ocean sound channel. (PMEL)
This is why a gigantic event involving an Antarctic iceberg could potentially be detected by instruments far away in the Pacific.
What Did Julia Actually Sound Like?
The original signal was at frequencies far below the range that humans normally hear comfortably.
NOAA therefore provides a version of the recording that has been sped up 16 times so people can listen to it. (PMEL)
That distinction is extremely important.
The famous audio clip circulating online is therefore not the original sound at its original playback speed.
It is an accelerated representation of the recording.
The commonly available Wikimedia Commons version is about ten seconds long and explicitly identifies the source as NOAA's 1999 recording, sped up 16 times. (Wikimedia Commons)
When played at this accelerated speed, Julia can sound strange and somewhat vocal-like.
Some listeners hear something resembling:
- a distant moan
- a cry
- a low vocal sound
- an animal-like call
- a strange underwater voice
But what something resembles to the human ear is not evidence of what produced it.
A spectrogram and the physical characteristics of the signal are much more useful for determining its source.
Why Was It Called “Julia”?
The recording became known by the nickname “Julia.”
The name is now widely associated with the NOAA recording.
However, the important scientific fact is not the nickname itself. The NOAA record identifies the event as an iceberg grounding on the seafloor and refers to the signal as the sound formerly known as “Julia.” (PMEL)
There is no need to attach a fictional story to the name.
The First Mystery
At the time the signal was encountered, scientists did not immediately have a simple visual explanation for what had produced it.
The hydrophones had detected an unusual acoustic event.
There was no underwater camera showing an iceberg at the source.
There was no photograph of a creature producing the sound.
There was no physical object recovered from the ocean.
Instead, scientists had acoustic information.
That meant the investigation had to work backward from the sound itself.
Researchers could examine:
- frequency
- duration
- arrival direction
- signal structure
- intensity
- similarity to previously recorded natural sounds
- geographic location
- known sources of low-frequency ocean noise
This is how the original mystery gradually became an environmental and geological problem rather than simply a question of identifying a strange creature.
NOAA's Iceberg Explanation
NOAA's current explanation is that Julia was most likely caused by a large iceberg grounding on the seafloor off Antarctica. (PMEL)
An iceberg is not simply a floating block of ice.
Large Antarctic icebergs can have enormous underwater portions extending far below the visible surface.
When the underwater part of a large iceberg reaches the seabed, several physical processes can occur.
The iceberg can:
- make contact with the seafloor
- scrape across sediment and rock
- become temporarily stuck
- vibrate against the seabed
- shift as ocean currents push against it
- generate acoustic energy as the contact changes
These processes can produce extremely powerful low-frequency sounds.
The important point is that an iceberg does not need to “explode” or break apart to make a significant underwater acoustic signal.
A huge mass of ice interacting with the ocean floor can act as a giant natural source of vibration.
Why an Iceberg Can Produce Such a Powerful Sound
The scale of Antarctic icebergs is difficult to appreciate.
A large iceberg can contain enormous amounts of ice beneath the surface.
If that mass contacts the seabed, the interaction can involve tremendous forces.
Scientists studying Antarctic underwater sound have documented icequakes, iceberg grounding, iceberg tremor and other cryogenic signals.
Research in the Antarctic Peninsula region has shown that iceberg grounding and rapid disintegration can release substantial acoustic energy into the ocean. (PubMed Central (PMC))
NOAA's own cryogenic acoustic records contain multiple examples of sounds generated by ice.
The agency has documented:
- iceberg cracking
- iceberg calving
- iceberg grounding
- harmonic tremor
- icequakes
- other forms of ice-generated acoustic activity
(PMEL)
This makes the Julia explanation physically plausible rather than simply a guess based on the sound's appearance.
The Importance of “Slow Down”
One of the strongest pieces of context comes from another NOAA recording called “Slow Down.”
Slow Down was recorded on May 19, 1997, two years before Julia.
NOAA located its source near 62°S, 60°W, in the region around the Antarctic Peninsula.
The sound gradually decreased in frequency for approximately seven minutes.
NOAA interpreted this as an iceberg becoming grounded and slowing down as it came into contact with the seafloor.
The signal was detected at ranges approaching 5,000 kilometers by multiple sensors. (PMEL)
This is important because it demonstrates that Antarctic ice can produce powerful long-distance acoustic signals.
Julia therefore does not exist in isolation.
There are other independently recorded examples of large ice interacting with the Antarctic environment and generating unusual underwater sounds.
The Bloop Connection
Julia is also frequently discussed alongside another famous sound: the Bloop.
The Bloop was recorded in 1997 and became famous because of its extraordinary acoustic strength.
For years, the sound was sometimes discussed as a possible unknown biological signal.
NOAA later concluded that the characteristics were consistent with icequakes generated by large icebergs cracking and fracturing. (National Ocean Service)
This does not mean Julia and Bloop were literally the same event.
They were separate recordings.
The significance is that scientists eventually found that large Antarctic ice can create acoustic signatures that initially sound very unusual when removed from their physical context.
What Did Scientists Actually Know About the Source?
There are several levels of certainty here.
What is directly established
Julia was a genuine underwater acoustic recording.
It was recorded on March 1, 1999.
It was detected by NOAA's eastern equatorial Pacific autonomous hydrophone array.
The signal was sufficiently strong to be detected across the array.
NOAA analyzed the direction of arrival and placed the possible source region in Antarctic waters between the Bransfield Strait and Cape Adare.
NOAA identifies a large iceberg grounding as the most likely source. (PMEL)
What is not known with complete precision
Scientists did not identify the individual iceberg responsible.
The exact point of origin was not determined because of uncertainty in the arrival azimuth.
There was no photograph of the specific iceberg producing Julia.
There was no underwater camera recording the event.
Therefore, it would be inaccurate to say that scientists directly watched the iceberg make the sound.
The appropriate wording is “most likely source”, which is also the wording used by NOAA.
The Giant Sea Creature Theory
One of the most popular ideas surrounding Julia is that the sound might have come from an enormous unknown marine animal.
This theory became popular because the accelerated recording sounds somewhat biological to some listeners.
The ocean is also genuinely difficult to explore, particularly the deep ocean.
That combination makes the idea attractive.
However, there is a major problem.
There is no independent biological evidence connecting Julia to an unknown animal.
There is no confirmed:
- body
- DNA sample
- photograph
- visual observation
- sonar observation of a corresponding animal
- repeated biological call pattern
- feeding behavior associated with the sound
- migration pattern connected with the recording
The sound itself therefore cannot establish the existence of a giant unknown creature.
The animal theory remains speculation rather than a competing scientific explanation supported by evidence.
Could Julia Have Been a Whale?
Whales are an important source of underwater sound and should not be completely ignored when discussing unusual acoustic recordings.
Large whales can produce very powerful low-frequency calls that travel great distances.
However, NOAA's own classification of Julia points toward an iceberg grounding, not a whale. (PMEL)
There is also a broader scientific record showing that Antarctic acoustic environments contain both biological sounds and cryogenic sounds.
Researchers studying the Antarctic Peninsula have documented whale vocalizations alongside ice-generated signals. (PubMed Central (PMC))
So the existence of whales in the same acoustic environment does not by itself make a whale the source of Julia.
Could It Have Been an Underwater Volcano?
Underwater volcanic activity can generate powerful acoustic signals.
Earthquakes, volcanic eruptions and other geological processes are routinely detected using hydrophones.
This makes volcanic activity a reasonable category to consider when an underwater sound initially has no obvious explanation.
However, NOAA's Julia page does not identify an underwater volcano as the most likely source.
Instead, the agency identifies an Antarctic iceberg grounding. (PMEL)
The geographic source region and similarity to other cryogenic signals support the ice explanation.
Could It Have Been a Giant Unknown Machine?
Another category of internet speculation suggests that mysterious ocean sounds could originate from unknown human technology.
There is no credible evidence connecting Julia to a secret underwater machine.
The recording is publicly available through NOAA-related material, and the agency's explanation is based on natural acoustic processes.
There is also no documented physical object associated with Julia that would support such a theory.
For that reason, the “secret machine” explanation should be treated as internet speculation rather than a documented possibility.
The Alien Theory
Because Julia was unusual, distant and initially difficult for casual listeners to interpret, some online discussions have connected it with extraterrestrial activity.
There is no scientific evidence supporting that interpretation.
The recording does not contain a confirmed artificial message.
There is no demonstrated mathematical structure proving intentional communication.
There is no associated object.
There is no independent observation linking the sound to extraterrestrial activity.
The fact that a sound is unusual does not automatically make it artificial.
NOAA's explanation is a terrestrial physical process involving Antarctic ice. (PMEL)
Why Did People Find the Sound So Creepy?
Much of Julia's reputation comes from the way the accelerated recording sounds.
Humans are very good at recognizing familiar patterns.
When an unfamiliar acoustic signal contains structures resembling a human voice or animal call, our brains naturally try to interpret it as something familiar.
This phenomenon can make an otherwise ordinary physical signal seem much more mysterious.
The acceleration also matters.
The version commonly heard online has been sped up by 16 times. (Wikimedia Commons)
That means listeners are not experiencing the sound exactly as the original recording existed in the ocean.
They are hearing a transformed version designed to move the very low-frequency information into a range that humans can hear.
That does not make the recording fake.
It simply means that the online listening experience is a scientific representation of the original signal.
The Spectrogram
One of the most useful pieces of evidence connected with Julia is its spectrogram.
A spectrogram displays how the frequency content of a sound changes over time.
Instead of asking only:
“What does this sound resemble?”
scientists can ask:
“What physical process produces this particular acoustic structure?”
The NOAA Julia record includes a spectrogram of the signal. A public-domain copy of the NOAA spectrogram is also available through Wikimedia Commons. (Wikimedia Commons)
Spectrograms are particularly valuable because different physical sources can leave different patterns in acoustic data.
Ice cracking, iceberg grounding, volcanic activity, earthquakes, ships and biological calls can all produce different acoustic signatures.
The Julia signal became much easier to understand when it was considered alongside other known cryogenic sounds.
Why the Antarctic Location Matters
The possible source region between the Bransfield Strait and Cape Adare is important.
Antarctica contains enormous quantities of floating ice.
Large icebergs can remain in the ocean for long periods while being pushed by currents, wind and tides.
Eventually, an iceberg can encounter shallow seabed or other underwater obstacles.
The underwater part of the iceberg can then become grounded.
This creates a natural environment in which extremely large masses of ice can interact with the seafloor.
NOAA's acoustic records contain multiple examples of these processes. (PMEL)
How the Investigation Changed the Mystery
The Julia story is interesting because the mystery did not necessarily end with someone finding an object.
Instead, the explanation developed from acoustic evidence.
The basic investigation can be understood like this:
An unusual sound is detected.
↓
Hydrophones determine that it is a real acoustic event.
↓
Arrival information provides a broad source direction.
↓
The direction points toward Antarctic waters.
↓
Scientists compare the signal with known Antarctic cryogenic sounds.
↓
Large iceberg grounding becomes the most likely explanation.
This is an important example of how an apparently unexplained event can become less mysterious as more environmental information is considered.
Was Julia Ever Completely Solved?
There is an important distinction between explained and identified with absolute certainty.
NOAA considers a large iceberg grounding the most likely source.
That is a strong scientific attribution.
However, NOAA did not identify the exact iceberg or observe the specific event directly.
Therefore, the scientifically responsible description is:
Julia is a real NOAA-recorded underwater sound whose most likely source is a large Antarctic iceberg grounding on the seafloor.
It is not accurate to say:
“Scientists proved exactly which iceberg made Julia.”
They did not.
That remaining uncertainty is genuine.
What People Thought About Julia
When Julia became known outside scientific circles, several interpretations appeared.
Some people believed it might have been:
- an enormous unknown sea creature
- a giant whale
- an unknown geological event
- an underwater volcanic phenomenon
- an unidentified mechanical object
- an extraterrestrial signal
The creature interpretation became particularly popular because of the vocal quality of the sped-up recording.
However, these ideas are not equally supported.
The available scientific evidence strongly favors the iceberg explanation, while the biological, extraterrestrial and technological interpretations lack independent evidence.
The “Sea Monster” Theory
The sea-monster interpretation is one of the most entertaining versions of the story, but it should remain clearly separated from the scientific record.
The theory generally depends on three observations:
The sound was powerful.
It was detected over a huge distance.
The sound seemed strange.
When sped up, it could sound vaguely biological.
The deep ocean remains poorly observed.
Large areas of the deep sea have not been directly explored in detail.
Those facts are all reasonable.
But they do not establish that a monster produced the sound.
A scientific hypothesis requires evidence that distinguishes it from competing explanations.
Julia does not have such evidence for an unknown animal.
Could an Unknown Animal Really Make a Sound Like Julia?
In principle, an unknown animal could produce an acoustic signal that scientists initially failed to recognize.
The deep ocean contains organisms that are still being studied, and marine animals use sound in many different ways.
But “possible” is not the same as “supported.”
For the Julia creature hypothesis to become convincing, researchers would need additional evidence such as repeated recordings with matching characteristics, a biological source observed in the same location, or physical evidence connecting an organism to the signal.
None of that has been established for Julia.
Therefore, the unknown-animal theory remains an interesting possibility in popular culture, but not the leading scientific explanation.
The Connection With Iceberg Acoustics
One of the strongest reasons the iceberg explanation is taken seriously is that scientists have recorded many other sounds generated by ice.
NOAA's cryogenic sound archive includes examples of:
Iceberg calving
Large sections of ice breaking away.
Icequakes
Acoustic signals associated with cracking and fracturing of large ice masses.
Iceberg harmonic tremor
Vibrations produced when an iceberg interacts with the seafloor or another iceberg.
Iceberg grounding
Acoustic energy generated when a large iceberg makes contact with the ocean floor. (PMEL)
Researchers have also studied Antarctic underwater sound environments and found that iceberg grounding and ice-related activity can be major contributors to the acoustic environment. (PubMed Central (PMC))
The Exact Distance Problem
It is tempting to describe Julia as having traveled a precisely known number of kilometers.
That would be misleading.
The exact source location was uncertain because NOAA could not determine the arrival azimuth perfectly.
What can be said confidently is that the signal was detected across the eastern equatorial Pacific hydrophone array while its most likely source was placed in Antarctic waters. (PMEL)
This demonstrates an enormous propagation distance without pretending that there is a perfectly measured source-to-sensor distance for Julia itself.
For comparison, NOAA's Slow Down recording was detected at a range approaching 5,000 kilometers, demonstrating how effectively certain Antarctic low-frequency sounds can propagate through the ocean. (PMEL)
Why the Mariana Trench Version Is Incorrect
A number of online mystery articles and videos associate Julia with the Mariana Trench.
There is no reliable NOAA evidence supporting that claim.
NOAA's own Julia record states that the signal was recorded on the eastern equatorial Pacific hydrophone array and that its possible source was between the Bransfield Strait and Cape Adare near Antarctica. (PMEL)
NOAA does operate hydrophones and other equipment in the Mariana region, but those are separate observations.
For example, NOAA's multimedia archive includes material concerning recovery of a hydrophone from the Challenger Deep area of the Mariana Trench in 2015. That is unrelated to the 1999 Julia recording. (PMEL)
Therefore, the correct article title should be about Julia (1999) rather than “Julia Sound in the Mariana Trench.”
Why the 1997 Date Is Also Incorrect
The 1997 date likely comes from the fact that several famous underwater sounds were recorded during the same period.
One of them was Slow Down, recorded May 19, 1997.
NOAA says Slow Down was most likely produced when a large iceberg became grounded near the Antarctic Peninsula. (PMEL)
Another famous event was Bloop, recorded in 1997 and later associated with ice-related activity. (National Ocean Service)
There was also Train, recorded March 4, 1997, which NOAA associated with a large iceberg grounded near Cape Adare. (PMEL)
These separate events are sometimes combined in online lists of “mysterious ocean sounds.”
Julia, however, belongs to 1999.
Is the Julia Recording Real?
Yes.
This is one part of the mystery that is not in serious doubt.
NOAA maintains the original acoustic information and provides a WAV version of the signal.
The public-domain Wikimedia Commons copy also identifies NOAA as the source and gives the recording date as March 1, 1999. (PMEL)
So Julia is not an invented internet sound.
The mystery concerns its source and interpretation, not whether the recording itself exists.
Is There a Real Photograph of Julia?
No authentic photograph of “Julia” itself exists because Julia was an acoustic recording, not a visually observed creature or object.
There is a real NOAA spectrogram showing the acoustic signal.
There are also real NOAA photographs, diagrams and videos concerning hydrophones and iceberg-generated sounds.
But an image showing a giant underwater creature with the label “Julia” should not be presented as a photograph of the actual source.
The source itself was never photographed.
What Remains Unresolved?
Even with NOAA's explanation, several questions remain.
Which exact iceberg produced the sound?
The specific iceberg was not identified.
Exactly where did the event occur?
NOAA narrowed the region but noted uncertainty in the arrival azimuth. (PMEL)
What exact physical interaction produced the recorded waveform?
The general explanation is iceberg grounding, but the precise combination of scraping, vibration, movement and contact responsible for the signal is not directly observed.
What did the iceberg look like?
There is no confirmed photograph of the specific iceberg responsible.
Was the event purely grounding?
It is safest to say NOAA's leading interpretation involves a large iceberg running aground. The exact physical details of that particular event were not directly witnessed.
These uncertainties are legitimate scientific limitations.
They do not require a supernatural explanation.
The Scientific Explanation in Simple Terms
The easiest way to understand Julia is to imagine an enormous floating mountain of ice.
Its underwater portion extends far below the surface.
Eventually, the iceberg encounters the seafloor.
Instead of simply stopping, its enormous mass interacts with the seabed.
The ice may scrape, vibrate, stick and shift.
Those movements generate acoustic energy.
The ocean then carries some of that low-frequency energy over a very large distance.
A NOAA hydrophone array detects the signal.
Scientists analyze its characteristics and direction.
The resulting evidence points toward Antarctica and a large iceberg grounding.
That is essentially the Julia mystery.
The fascinating part is not necessarily that something unknown made the sound.
It is that a massive natural event involving ice could make a sound powerful enough to be detected thousands of kilometers away.
Julia and the Mystery of the Deep Ocean
Julia became famous because it appeared to represent one of the things people find most fascinating about the deep ocean: we cannot easily see what is happening there.
On land, an unusual noise can often be investigated by simply looking around.
Underwater, particularly thousands of meters away from the source, that becomes much harder.
Researchers may have only:
- acoustic recordings
- timing information
- direction-of-arrival data
- frequency measurements
- spectrograms
- environmental data
The Julia case demonstrates how ocean scientists can reconstruct events without directly seeing them.
What Makes Julia Interesting Today?
Julia is still worth studying as an example of how sound behaves in the ocean.
The event connects several fascinating scientific subjects:
- deep-ocean acoustics
- hydrophone technology
- Antarctic ice
- iceberg grounding
- underwater sound propagation
- environmental monitoring
- cryogenic acoustics
- oceanography
- scientific classification of unusual signals
It also demonstrates how an unexplained observation can initially generate speculation and later receive a natural explanation.
Julia Compared With the Popular Internet Version
The distinction between these claims is important if the case is being presented as a factual mystery rather than an internet legend.
What the Evidence Actually Supports
The strongest evidence supports the following sequence:
A real acoustic signal was recorded.
The signal was detected by NOAA's autonomous hydrophone array.
The recording occurred on March 1, 1999.
The source direction pointed toward Antarctic waters.
The exact origin was uncertain, but NOAA narrowed it to a region between the Bransfield Strait and Cape Adare.
Large Antarctic icebergs are known to generate powerful underwater sounds when they fracture, ground or interact with the seafloor.
NOAA therefore considers a large iceberg grounding the most likely source of Julia. (PMEL)
That is the evidence-based version of the story.
What the Julia Sound Was Probably Not
There is currently no evidence that Julia was:
- a sea monster
- a prehistoric creature
- an extraterrestrial signal
- a secret underwater machine
- an unknown submarine
- a giant whale
- a supernatural phenomenon
Some of these ideas appear in popular discussions, but they are not supported by the evidence available for the recording.
The absence of an immediately obvious explanation is not evidence for an extraordinary explanation.
Why the Story Became an Internet Mystery
Julia appeared at the perfect intersection of several things that naturally attract public curiosity.
It was:
- genuinely recorded
- extremely unusual
- difficult to visualize
- associated with the deep ocean
- far from ordinary human activity
- low-frequency
- difficult for people to interpret by listening
- capable of sounding strangely vocal after acceleration
Once the recording was shared online, it became easy to separate the sound from its scientific context.
A listener could hear the accelerated audio without knowing:
- where it was recorded
- how hydrophones work
- what the spectrogram showed
- where NOAA placed the source
- how iceberg acoustics work
- that similar sounds had been recorded from Antarctic ice
That created room for more imaginative explanations.
The Real Mystery Behind Julia
The most interesting mystery may actually be different from the one presented in many internet videos.
The question is not:
“Was Julia a monster?”
There is no evidence supporting that conclusion.
The more scientifically interesting question is:
“How can a massive physical event involving an Antarctic iceberg generate an acoustic signal that travels across an enormous portion of the ocean and initially sounds so unusual to human listeners?”
That question has a real scientific basis.
It connects Julia with the broader study of the underwater soundscape and the enormous amount of information carried through the ocean by acoustic waves.
Where You Can Hear the Real Recording and See the Real Evidence
For your website, I would recommend linking primarily to these sources rather than mystery blogs or websites presenting fictional sea-monster claims.
NOAA Pacific Marine Environmental Laboratory — Julia recording
NOAA PMEL: Iceberg Grounding on Seafloor (Julia)
This is the most important source. It contains NOAA's description of the recording, the probable Antarctic source region, the spectrogram and the downloadable WAV recording. (PMEL)
Wikimedia Commons — Julia spectrogram
Julia spectrogram — Wikimedia Commons
This page provides a copy of the NOAA spectrogram and identifies the material as originating from NOAA. The image is marked as public domain because it originates from U.S. government/NOAA work. (Wikimedia Commons)
Wikimedia Commons — Julia audio
Julia sound recording — Wikimedia Commons
This provides the commonly accessible audio version and clearly states that the recording has been sped up 16 times. (Wikimedia Commons)
NOAA PMEL — Cryogenic Ice Sounds
NOAA PMEL: Cryogenic Ice Sounds
This is especially useful because it provides examples of iceberg calving, iceberg harmonic tremor, Bloop and Slow Down, helping readers understand why ice can generate unusual underwater sounds. (PMEL)
NOAA PMEL — Slow Down
NOAA PMEL: Slow Down underwater sound
This is useful for comparison because Slow Down was recorded in 1997 and NOAA associates it with an Antarctic iceberg becoming grounded on the seafloor. (PMEL)
NOAA PMEL — Bloop
This is another useful comparison showing how a famous “mysterious” ocean sound was later connected with Antarctic icequakes. (PMEL)
NOAA Ocean Exploration — Slow Down
NOAA Ocean Exploration: Slow Down
This provides modern NOAA Ocean Exploration material explaining the Antarctic iceberg-grounding interpretation and includes downloadable media. (NOAA Ocean Exploration)
Conclusion
The Julia Sound remains one of the more fascinating examples of how strange the underwater world can sound.
But its real story is different from the popular sea-monster version.
On March 1, 1999, NOAA's autonomous hydrophone array recorded an unusual low-frequency acoustic signal in the eastern equatorial Pacific. Scientists used the signal's characteristics and direction of arrival to associate its source with a broad region of Antarctic waters between the Bransfield Strait and Cape Adare. (PMEL)
The exact iceberg was never identified, and the precise physical circumstances of the event cannot be reconstructed with complete certainty.
However, NOAA's leading explanation is a large iceberg grounding on the seafloor.
That explanation is supported by the wider scientific record. Antarctic ice is capable of producing powerful underwater acoustic signals when icebergs fracture, ground, scrape against the seabed or interact with other ice. Similar signals have been recorded repeatedly. (PMEL)
The recording itself is completely real.
The mystery lies in the fact that scientists could hear an enormous natural event occurring thousands of kilometers away without ever seeing the event directly.
And perhaps that is what makes Julia more interesting than the monster stories.
It was not necessarily a sound from an unknown creature.
It was a reminder that the ocean can carry the sound of enormous natural events across distances that are almost impossible to imagine.
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In 1999, NOAA recorded a strange low-frequency underwater sound known as Julia. The signal was detected across an enormous area of the Pacific and initially attracted speculation about unknown creatures and other extraordinary explanations. NOAA later determined that a large Antarctic iceberg grounding on the seafloor was the most likely source.
Popular Internet ClaimWhat the Evidence ShowsJulia was recorded in 1997NOAA records it on March 1, 1999Julia came from the Mariana TrenchNOAA places the possible source near AntarcticaScientists recorded a giant sea creatureNo biological source has been demonstratedThe sound is evidence of a sea monsterNOAA's most likely explanation is an iceberg groundingThe audio is exactly what the ocean sounded like to humansThe commonly shared recording is sped up 16 timesScientists know the exact sourceNOAA gives a probable region, not a precisely identified icebergJulia was never explainedNOAA identifies a large Antarctic iceberg grounding as the most likely source