During the Cold War, the US Navy created a vast network of underwater microphones (called hydrophones) to keep tabs on Soviet submarines. Called SOSUS (for SOund SUrveillance System), the hydrophones were first installed in the “GIUK gap” – the stretch of ocean between Greenland, Iceland, and the United Kingdom, an area where Soviet subs were known to operate. By the 1960s, the Navy had expanded SOSUS to include most of the Atlantic Ocean, as well as many parts of the Pacific. In 1961, the system tracked the USS George Washington during her entire run between the United States and the United Kingdom. By early 1962, the system was capable of tracking the Soviet’s diesel submarines. And later that year, a SOSUS tracking station in the Bahamas played an important role in the Cuban Missile Crisis by keeping the Navy informed about Soviet submarine maneuvers around the Caribbean.
When the Soviet Union collapsed in the early 1990s, the Navy suddenly had little use for the system. Additionally, better technology had led to the development of smaller, easier to use hydrophones that could be easily deployed in a theatre of war as necessary. Many listening stations were abandoned, and several others were condensed. Although the Navy still listens to the hydrophones, most of the day-to-day operation of SOSUS has been turned over to the U.S. National Oceanic and Atmospheric Administration, who use it to listen for underwater earthquakes and volcanic activity, for monitoring whale migration patterns, and other scientific interests.
And, during the summer of 1997, those scientists suddenly became very interested. That’s because SOSUS recorded a sound that remains a mystery to this day. Something off the southwest coast of South America, at approximately 50° S 100° W, made a sound… a sound that defies explanation.
The sound is of a very low frequency, in the range that some animals use to communicate. But here’s the thing – the sound was picked up at two different hydrophones stationed some 3000 miles (5000km) apart! This automatically rules out almost any man-made source of the noise, as a sinking ship breaking up on the ocean floor or a shifting undersea cable can’t possibly make a noise that loud. It’s possible for whale calls to travel that far through certain “thermal layers” in the ocean, but those conditions didn’t apply in this case. In short, many scientists are convinced that the only possible source of the sound is an as-yet unidentified animal. The only thing is, that animal would have to be “several times” the size of a blue whale to make a sound that loud. And an animal just three times the size of a blue whale would be truly enormous – around 300 feet long and 570 tons in weight!
Is such an animal out there? For now, we simply just don’t know.
Listen to “The Bloop” (sped up 16 times to make it audible):
[audio:bloop.mp3]
Read more about The Bloop at this NOAA page, this page at CNN.com, or this page at Wikipedia.