In the summer of 1997, NOAA's underwater microphone network — a Cold War-era array of hydrophones originally built to track Soviet submarines and later repurposed to monitor earthquakes and whale migrations — picked up something strange off the coast of southern Chile. The sound lasted about a minute, rose in frequency as it went, and was loud enough to register on sensors nearly 5,000 kilometers apart. NOAA scientist Christopher Fox noted that the audio profile resembled a living creature, but added that whatever made it would have to be far more powerful than any animal on Earth.
The sound — which NOAA nicknamed "the Bloop" — was recorded exactly once and never appeared again. For years, it circulated as one of the ocean's genuinely unsolved mysteries, partly because the location was near the coordinates H.P. Lovecraft had assigned to the sunken city of R'lyeh, home of Cthulhu, a detail that didn't help keep the speculation grounded.
Icequakes turned out to be the answer — more mundane than a giant squid, but stranger than anyone expected. In 2012, NOAA researchers matched the Bloop's acoustic signature to the sounds produced by massive Antarctic icebergs as they fracture and grind against the seabed. The frequency rise, duration, and amplitude all lined up with ice cracking at scale. A similar sound from iceberg A53a near South Georgia Island in 2008 helped confirm the pattern. The likely source of the original Bloop was somewhere between the Bransfield Strait and the Ross Sea.
The Cold War hydrophone array keeps running and picking up sounds that researchers can't immediately explain. The ocean generates a lot of noise.
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