It was one of the loudest sounds ever recorded–though as low-frequency “infrasound” it was undetectable by human ears. It traveled almost 3,000 miles through the ocean. It provoked controversy and argument, and the “explanations” for it ranged from sea monsters to flying saucers. But eventually, “The Bloop” was identified.
A digital spectrogram of “The Bloop”
Listen to The Bloop (WAV file). Speeded up 16 times faster to make it audible.
In the 1960’s, during the Cold War, the US Navy installed a top-secret network of underwater microphones, called “hydrophones”, to listen for and track the movements of Soviet nuclear submarines. The system was called the Sound Surveillance System, or SOSUS. For decades, its very existence was a closely-guarded military secret.
When the Soviet Union collapsed in 1991 and the Cold War ended, the SOSUS system was made available to oceanographers and used for research, under the direction of the National Oceanic and Atmospheric Administration (NOAA). Since sound waves travel much further underwater than they do in air, oceanographers could use the SOSUS microphones to listen for anything from whale calls to undersea earthquakes.
Then in June 1997, the SOSUS hydrophones picked up an odd sound. About a minute long and consisting of ultra-low frequency “infrasound” undetectable by human ears, the sound rose rapidly in frequency, then stopped. What particularly puzzled the researchers was its intensity: the location of the sound’s origin was triangulated using a number of different hydrophones, and traced to a rough location near 50 degrees south latitude and 100 degree west longitude, off the west coast of South America near the Antarctic. This meant that the sound had been detected by SOSUS at ranges of over 3,000 miles. It was one of the loudest underwater sounds ever recorded. Over the next few weeks, similar sounds were also recorded by another system of research microphones called the Equatorial Pacific Ocean Autonomous Hydrophone Array, in the Indian Ocean. Then the sounds stopped and were not heard again. The odd noises became known as “The Bloop”.
The speculation began. Some people thought they could detect variations in the frequency that were characteristic of biological sounds, and concluded that The Bloop had been made by an animal. But the sound was several times louder than the loudest animal known–the Blue Whale–and therefore if The Bloop really came from a biological source, it had to be a truly immense animal (or it had a very efficient method of producing underwater sounds). Some serious researchers concluded that the sound had been made by a Giant Squid or perhaps a Giant Octopus: but the largest-known Giant Squid was about 60 feet long, and this one had to be very much larger than that. Some not-so-serious researchers declared that it came from an unknown sea monster, perhaps a surviving relic from the time of the dinosaurs. And some of the lunatic fringe spoke of flying saucers and space aliens, perhaps with secret underwater bases on the Antarctic sea floor. (Some folks–perhaps serious, perhaps not–pointed out that the location of The Bloop’s origin was not very far from that given in the HP Lovecraft science fiction novels for the location of the alien underwater city of R’lyeh, where “dead Cthulhu waits dreaming”. Coincidence…..?)
The serious scientists quickly ruled out several possibilities: the sound profile did not match that of a submarine or a ship, or of an underwater explosion. It was similar to an underwater earthquake or volcanic tremor, but it didn’t match those either. What it most resembled were the patterns made by polar ice sheets breaking into pieces, and this was the most-favored hypothesis for The Bloop.
Then, between 2005 and 2010, NOAA did a ship-borne acoustical survey of the Antarctic area near South America, near where The Bloop had originated, and found that the area was constantly bombarded with the sounds of ice sheets breaking. “The broad spectrum sounds recorded in the summer of 1997,” NOAA concluded, “are consistent with icequakes generated by large icebergs as they crack and fracture. NOAA hydrophones deployed in the Scotia Sea detected numerous icequakes with spectrograms very similar to ‘Bloop’. The icequakes were used to acoustically track iceberg A53a as it disintegrated near South Georgia Island in early 2008. Icequakes are of sufficient amplitude to be detected on multiple sensors at a range of over 5000 km. Based on the arrival azimuth, the iceberg(s) generating ‘Bloop’ most likely were between Bransfield Straits and the Ross Sea, or possibly at Cape Adare, a well know source of cryogenic signals.” The mystery had been solved. The Bloop was the sound of an extraordinarily large “icequake” that cracked an iceberg which had calved off of the Antarctic ice sheet and floated off.
The Bloop was not the only unidentified sound picked up by SOSUS. Over the years, odd sounds were recorded that were given names like Julia, Upsweep, Slowdown, Train, and Whistle. Most seem to be icequakes, or the sound of icebergs dragging across the sea floor. Some are from underwater volcanoes. A few are still not identified.
Nevertheless, The Bloop remains a popular fixture on various “paranormal” and “cryptozoology” websites. One reason why the “unknown sea monster” hypothesis remains so popular is that all of the sound files of The Bloop available on the Internet (including the one provided at the top of this post) have been speeded up to make them audible, and the speeded-up version sounds a lot like an animal sound. But the actual Bloop was subsonic infrasound and was 16 times slower in frequency, and would have been more like a low rumble, like faraway thunder, than an animal sound. The evidence is pretty conclusive that The Bloop was not an animal, but the sound of an unusually loud icequake.
But even though The Bloop was not the Antarctic’s Loch Ness Monster or the Call of Cthulhu, it was important anyway. Recorded way back in 1997, it demonstrates clearly that the breakup of the Antarctic ice sheets caused by global temperature rise as a result of climate change, was already beginning almost 20 years ago.