What Made the Mysterious Bloop Sound in Point Nemo? (3 photos)
In the South Pacific Ocean, there's an area called Point Nemo, which represents the Oceanic Pole of Inaccessibility—the point furthest from any landmass. 
Spectrogram showing the acoustic pattern of the mysterious Bloop sound
The existence of Point Nemo was discovered in 1992 by Croatian-Canadian surveyor and engineer Hrvoje Lukatela, who used computer modeling. He chose the name of the region, referencing Captain Nemo, the Jules Verne hero who became disillusioned with humanity and retreated to the ocean depths.
If you were at Point Nemo, you would be a staggering 2,689 kilometers from the nearest land. This means that the astronauts aboard the International Space Station (ISS), flying above at an altitude of about 400 kilometers, would be the closest people to you.
Spacecraft Graveyard
The extreme isolation and virtually no maritime traffic made Point Nemo an ideal place for the "burial" of spacecraft. Since 1971, cargo spacecraft, spent satellites, and rocket stages have been dumped in this region, and after the precise coordinates were calculated in 1992, it was officially designated a "space graveyard." In total, more than 300 objects rest on the seabed.
The most famous object "buried" at Point Nemo is the Soviet orbital station Mir, which was sunk in 2001 after nearly 15 years of operation. The International Space Station (ISS), which is nearing the end of its operational life, will likely find its final resting place at Point Nemo in 2031. 
The Mysterious "Bloop"
In the summer of 1997, this silent place suddenly "spoke." Hydrophones* from the US National Oceanic and Atmospheric Administration (NOAA) detected a strange, ultra-low-frequency sound of incredible power. The signal was so loud that it was picked up by sensors located 4,800 kilometers apart.
*Hydrophones are sensitive microphones used to detect and record sound and ultrasound in aquatic environments.
The sound, codenamed "Bloop," immediately attracted the attention of scientists. Some researchers, including NOAA oceanographer Chris Fox, initially suggested a biological origin for the signal:
"There's a lot of noise down there," Fox told CNN. "Whales, dolphins, fish."
However, the weakness of this explanation was the fact that no known marine animal is capable of producing sounds of such intensity. This gave rise to a multitude of fantastical hypotheses, from giant squid to unknown deep-sea monsters.
The Mystery Solved
The truth turned out to be less romantic, but no less impressive. The same Chris Fox, having analyzed all the available data, soon put forward a hypothesis that was subsequently confirmed:
"I think it might be related to ice subsidence," Fox said. "It [ice] always comes from the south. We suspect it's ice off the coast of Antarctica, and in this case, it's pretty damn loud." 
Further research confirmed that the source of the Bloop was a breaking-up Antarctic iceberg. Remarkably, NOAA had previously recorded similar sounds and even used them to track iceberg A53A.
"The broad-spectrum sounds recorded in the summer of 1997 are consistent with icequakes generated by large icebergs as they crack and break apart," NOAA commented. "The amplitude of the icequakes is sufficient to be detected by multiple sensors over a distance of more than 5,000 kilometers. Based on the arrival azimuth, the iceberg that caused the Bloop was likely located between Bransfield Strait and the Ross Sea, or possibly at Cape Adare, a well-known source of such signals."
