The US submarine detection system recorded a pulsating signal at a depth of 8 kilometers, in the Pacific Ocean, where there are no nearby islands. Starting to check the data with the archives to identify the source, the military found that such signals had already been in the past, and the first was recorded 54 years ago.
The stored information in archival documents indicates several cases of receiving anomalous signals from great depths. But none of them could be explained.
In 1977, a radio operator on a ship in the middle of the Atlantic Ocean received a strange signal from a depth of 8 kilometers.
It follows from the documents that the military carried out studies of the ocean floor in the area after receiving acoustic anomalies, but the results of these studies were not published.
In 1991, the US Navy discovered two unknown acoustic signals, named Upsweep and Whistle, which originated from great depths. Upsweep is an unidentified sound detected on the American National Oceanic and Atmospheric Administration’s equatorial autonomous hydrophone arrays.
This sound was present when the Pacific Marine Environmental Laboratory began recording its sound surveillance system SOSUS in August, 1991. It consists of a long train of narrow-band upsweeping sounds of several seconds in duration each. The source level is high enough to be recorded throughout the Pacific.
The Upsweep signal has been seen in the spring and fall for several years, and their point of origin has been located somewhere in the Pacific Ocean.
After 6 years, in 1997, the US National Oceanic Administration received and recorded an underwater signal sent from a point located near Antarctica. It was not possible to decipher and trace Bloop, as this signal was called.
Although Bloops are some of the loudest sounds of any type ever recorded in Earth’s oceans, their origin remains unknown. The Bloop sound was placed as occurring several times off the southern coast of South America and was audible 5,000 kilometers away.
Although the sound has similarities to those vocalized by living organisms, not even a blue whale is large enough to croon this loud. The sounds point to the intriguing hypothesis that even larger life forms lurk in the unexplored darkness of Earth’s deep oceans.
A less imagination-inspiring possibility, however, is that the sounds resulted from some sort of iceberg calving. No further Bloops have been heard since 1997, although other loud and unexplained sounds have been recorded.
So far, the main version is the seismic activity of lithospheric plates. The truth doesn’t add up – the sounds did not match any of the earthquakes in the region.