The Bloop — The Loudest Ocean Sound Ever Detected

In 1997, underwater hydrophones operated by NOAA detected an extraordinarily powerful, ultra-low-frequency sound in the Pacific Ocean. Nicknamed “The Bloop,” it was recorded by sensors thousands of kilometers apart, immediately raising questions about what could generate such an enormous underwater signal. Its unusual character inspired theories ranging from secret military activity and geological events to an unknown gigantic sea creature. For years, the source remained uncertain, and the mystery became one of the most famous legends associated with the unexplored depths of the ocean. Eventually, NOAA scientists compared the Bloop with other sounds recorded near Antarctica and found striking similarities to icequakes caused by huge icebergs cracking, fracturing, or breaking away from glaciers. NOAA now identifies the Bloop as a cryogenic event rather than the call of an unknown animal. The Bloop may therefore have a scientific explanation, but its story remains a powerful reminder of how little humans once understood—and still understand—about the immense soundscape of the deep ocean.