The sound's source was roughly triangulated to 50°S 100°W (a remote point in the south Pacific Ocean west of the southern tip of South America), and the sound was detected several times by the Equatorial Pacific Ocean autonomous hydrophone array. This system was developed as an autonomous array of hydrophones that could be deployed in any oceanographic region to monitor specific phenomena. It is primarily used to monitor undersea seismicity, ice noise, and marine mammal population and migration. This is a stand-alone system designed and built by NOAA's Pacific Marine Environmental Laboratory (PMEL) to augment NOAA's use of theU.S. Navy Sound Surveillance System (SOSUS), which was equipment originally designed to detect Soviet submarines.
According to the NOAA description, it "rises rapidly in frequency over about one minute and was of sufficient amplitude to be heard on multiple sensors, at a range of over 5,000 km." The NOAA's Dr. Christopher Fox did not believe its origin was man-made, such as a submarine or bomb, nor familiar geological events such as volcanoes or earthquakes. While the audio profile of Bloop does resemble that of a living creature, the source was a mystery both because it was different from known sounds and because it was several times louder than the loudest recorded animal, the blue whale. A number of other significant sounds have been named by NOAA: Julia, Train, Slow Down, Whistle and Upsweep.
Dr. Christopher Fox of the NOAA initially speculated that Bloop may be ice calving in Antarctica. A year later journalist David Wolman paraphrased Dr. Fox's updated opinion that it was probably animal in origin:
Fox's hunch is that the sound nicknamed Bloop is the most likely 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 4800 kilometres 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?
— David Wolman
The NOAA Vents Program has since then attributed the sound to that of a large icequake. Numerous icequakes share similar spectrograms with Bloop, as well as the amplitude necessary to spot them despite ranges exceeding 5000 km. This was found during the tracking of iceberg A53a as it disintegrated near South Georgia island in early 2008. If this is indeed the origin of Bloop, the iceberg(s) involved in generating the sound were most likely between Bransfield Straits and the Ross Sea; or possibly at Cape Adare, a well-known source of cryogenic signals.
In 1997, the Bloop was heard on hydrophones across the Pacific. It was a loud, ultra-low frequency sound that was heard at listening stations underwater over 5,000 km apart, and one of many mysterious noises picked up by the National Oceanic and Atmospheric Administration (NOAA). Several articles in the years that followed popularised one suggestion that the Bloop might have been the sound of an unknown animal due to the "organic" nature of the noise, a theory that elevated the Bloop to the level of a great unsolved mystery.
However, the NOAA is pretty sure that it wasn't an animal, but the sound of a relatively common event -- the cracking of an ice shelf as it breaks up from Antarctica.Several people have linked to the NOAA's website over the past week excitedly claiming that the mystery of the Bloop has been "solved", but as the information on the NOAA website was undated and without a source, Wired.co.uk spoke to NOAA and Oregon State University seismologist Robert Dziak by email to check it out. He confirmed that the Bloop really was just an icequake -- and it turns out that's kind of what they always thought it was. The theory of a giant animal making noises loud enough to be heard across the Pacific was more fantasy than science.
Dziak explained to us the NOAA's findings, and confirmed that "the frequency and time-duration characteristics of the Bloop signal are consistent, and essentially identical, to icequake signals we have recorded off Antarctica". He explained: "We began an acoustic survey of the Bransfield Strait and Drake Passage in 2005 which lasted until 2010. It was in analysis of this recent acoustic data that it became clear that the sounds of ice breaking up and cracking is a dominant source of natural sound in the southern ocean. Each year there are tens of thousands of what we call 'icequakes' created by the cracking and melting of sea ice and ice calving off glaciers into the ocean, and these signals are very similar in character to the Bloop."
That makes it "extremely unlikely" that the sound is animal in origin, but he also pointed out that the hypothesis that the Bloop was caused by an animal wasn't ever really a serious one. He said: "What has led to a lot of the misperception of the animal origin sound of the Bloop is how the sound is played back. Typically, it is played at 16 times normal speed, which makes it sounds like an animal vocalization of some sort. However, when the sound is played in real-time it has more of a 'quake' sound to it, similar to thunder." You can hear a recording of the Bloop in the video accompanying this story.
There aren't even that many mysterious sounds picked up by the NOAA's hydrophones, according to Dziak: "Nearly all sounds can be attributed to major sound categories; geophysical (submarine volcanoes or earthquakes), weather (storms, waves, wind), anthropogenic (ships, airguns), ice (sea ice, iceberg groundings), and animals (cetaceans, fish)." Anything else is usually just some kind of electronic interference with the signal.
It's easy to see why the Bloop was such a compelling mystery. The deep oceans are still mostly unexplored by humans (more than 95 percent, according to the NOAA), and only a few weeks ago an entirely new species of whalewashed up on a beach in New Zealand. It was only in 2004 that the first video footage was recorded of a giant squid in the wild. To paraphrase Donald Rumsfeld, we know there's a lot we don't know about the deep ocean.
Fans of horror fiction were also delighted to note that the location pinpointed as the source of the Bloop was located a mere 1,760km from the location of the sunken city of R'yleh, where (according to HP Lovecraft) the mythical beast Cthulhu is imprisoned. Cthulhu would certainly fit the bill of a giant sea creature capable of emitting a sound that could travel for thousands of kilometres through the ocean, but unfortunately science has, once again, ruined the fun. Alas. This page was written by Bob the Builder.