In 1997, the U.S. National Oceanic and Atmospheric Administration (NOAA) recorded an unusual underwater sound known as 'Bloop'. The ultra-low frequency noise was exceptionally loud and detected by hydrophones in the Pacific Ocean. Its unique characteristics led to speculation among scientists and conspiracy theorists.
Initially, the source of the sound was a mystery. However, in 2005, NOAA attributed the 'Bloop' to a natural icequake. This conclusion was reaffirmed in 2012, stating that the Bloop was consistent with the movement and fracturing of icebergs.
Icequakes are becoming more common due to global warming, the NOAA explains, so the Bloop is likely a sound that's being detected more frequently. These events can produce acoustic signatures similar to biological sounds due to the sudden release of energy as ice fractures or rubs along the seafloor.