The Hydrophones
The United States Navy built a global network of underwater microphones during the Cold War. The system was called SOSUS, which stands for Sound Surveillance System, which is the kind of name that sounds like it should be classified and probably was for a long time. The purpose was to detect Soviet submarines. The hydrophones were planted at depth across the world's oceans, listening.
When the Cold War ended, NOAA, the National Oceanic and Atmospheric Administration, inherited access to some of these hydrophones for scientific purposes. Scientists used them to track whale calls, map underwater earthquakes, and listen to the various sounds the ocean makes when it thinks no one is listening. The ocean makes a lot of sounds. Most of them have been catalogued and explained.
Most of them.
The Sound
On May 19, 1997, NOAA's autonomous hydrophone array picked up a sound in the South Pacific Ocean. The sound lasted approximately one minute. It rose in frequency, which is the technical description. What it sounded like, to human ears, was something between a low, bending horn call and the kind of noise that makes the hair on your arms stand up without being able to explain why.
NOAA scientists named it the Bloop. They named it after its acoustic signature: the sound of something going "bloop" in a register that carries five thousand kilometers through open ocean. The naming committee for acoustic anomalies appears to operate under the same philosophy as the editorial board that invented Bigfoot: functional, unpretentious, deeply committed to the obvious.
The Bloop was the loudest biological sound ever recorded, at the time of its detection. Louder than a blue whale. Louder than anything known to produce sound in the ocean. It was detected by hydrophones more than three thousand miles apart. The source was estimated to be somewhere in the South Pacific, near the coordinates 50 degrees south, 100 degrees west, which is in the part of the ocean that is not near anything except more ocean.
The Internet Gets Involved
The Bloop was recorded in 1997. The internet discovered it sometime in the early 2000s, which is roughly when the internet developed the organizational capacity to become obsessed with things. What happened next was predictable and entirely human.
The Bloop was louder than any known animal. Therefore, some argued, it must be an unknown animal. Therefore it must be very large. Therefore it must be enormous. Therefore it must be something like the creature described in H.P. Lovecraft's 1928 story "The Call of Cthulhu," a cosmic horror sleeping in the sunken city of R'lyeh. Coordinates: approximately 47 degrees south, 126 degrees west. Which is, it was pointed out, not far from where the Bloop was detected.
This is not rigorous scientific reasoning. This is connecting two data points with a line and then putting a tentacled elder god on the line. But the internet is not a rigorous scientific institution, and Cthulhu is a much better story than "icequake," which is where this was always going. The Bloop became one of the first viral mysteries of the early web era, which is a kind of legacy even if the mystery didn't survive close examination.
The Icequake
In 2005, scientists at NOAA began comparing the Bloop's acoustic signature to other sounds in their database. They found a match. The Bloop's profile was consistent with "icequakes," the sounds produced when large icebergs fracture, calve, or grind against the seafloor. Antarctica was, at the time of the Bloop, producing large quantities of these sounds. Ice breaks in ways that produce exactly the kind of rising, frequency-varying signal that the Bloop exhibited.
By 2012, NOAA scientists had formally attributed the Bloop to this cause. The official position is that the Bloop was the sound of a large iceberg fracturing somewhere in the Antarctic region and the sound traveling through the ocean in the efficient way that low-frequency sounds do. Five thousand kilometers. One minute. One icequake. Case closed.
The ocean makes these sounds regularly. The icequake explanation is well-supported, acoustically consistent, and physically plausible. It is also, and this must be acknowledged, significantly less interesting than a giant tentacled creature shifting in its ancient, sunken city. The ratio of "correct but boring" to "wrong but compelling" in science is not always fair.
The Deep Ocean and What's in It
The Bloop's fame was always partly borrowed from the ocean itself. The deep ocean is one of the least explored environments on Earth. We have more detailed maps of the surface of Mars than of the ocean floor. The hadal zone, below six thousand meters, is largely unexplored. New species are found there with routine regularity: fish that produce their own light, crustaceans that live under pressures that would collapse a submarine, creatures that have never seen sunlight and do not require it.
The giant squid, Architeuthis dux, was considered mythological for most of recorded history. It was the Kraken. It was a sailor's hallucination. The first live giant squid was not photographed until 2004. It can reach forty-three feet. It exists. It was real the whole time.
The colossal squid, Mesonychoteuthis hamiltoni, is even larger and even less documented. It lives in Antarctic waters. It was first described scientifically in 1925. A full adult specimen wasn't caught and properly examined until 2007. The ocean does produce enormous things, delivers them to us slowly, and seems to enjoy the pause.
Still Listening
NOAA's hydrophone network is still active. It records continuously. Scientists monitor it for earthquakes, nuclear tests, whale migrations, and sounds that don't fit the catalogue. New acoustic anomalies are detected periodically, assigned technical designations, analyzed, and eventually explained. The ocean is not as mysterious as 1997 suggested, which is not the same as saying the ocean is not mysterious.
The Bloop's coordinates are somewhere in the South Pacific, far from any shipping lane or research station, in water several thousand meters deep. Nothing lives in the shallow sense at that depth. The pressure is approximately five hundred times surface pressure. Whatever does live there has made significant architectural compromises.
The Bloop was an icequake. The analysis is solid. The science is good. And the ocean at five thousand meters depth, at the moment a large iceberg cracked somewhere in the Antarctic darkness and sent a one-minute sound traveling north through water that no light has ever touched, was still a place nobody would want to be. Not because of Cthulhu. Because the ocean at that depth, in that darkness, making that sound, is already more than enough.
Field Notes
- The Bloop was detected on May 19, 1997 by NOAA's autonomous hydrophone array in the South Pacific Ocean. The sound was loud enough to be detected by sensors more than 5,000 kilometers apart.
- NOAA scientists formally attributed the Bloop to cryoseismic events, specifically the sounds produced by large icebergs fracturing, by 2012. The acoustic signature matched known icequake profiles.
- NOAA's hydrophone network was originally built as the U.S. Navy's SOSUS (Sound Surveillance System) during the Cold War to detect Soviet submarines.
- The first confirmed photograph of a live giant squid (Architeuthis dux) in its natural habitat was taken in 2004 by Japanese researchers Tsunemi Kubodera and Kyoichi Mori.
- The deepest known point in the ocean, Challenger Deep in the Mariana Trench, reaches approximately 10,935 meters (35,876 feet). Pressure at this depth is about 1,086 times atmospheric pressure at sea level.
Dig Deeper
Want the facts behind the folklore? Explore the real science behind the Bloop, NOAA's hydrophone network, and what actually makes noise at the bottom of the ocean.
Learn more about the Bloop