In the 1990s, deep beneath the Pacific, a Cold War-era hydrophone network built to track enemy submarines began picking up something strange.
Louder than any known animal. Deeper than any ship. Stranger than anything scientists had heard before.

They called them the Bloop. Julia. Upsweep. Slow Down.
Each one a bizarre sound echoing from the deep — some lasting seconds, others hours — recorded on NOAA’s massive undersea listening arrays.

Were they icebergs? Volcanoes? Whales?
Or something still unexplained, echoing through a part of the ocean no one has ever seen?

In this episode, we dive into the most mysterious underwater recordings ever captured: the chilling NOAA signals that once sparked fears of sea monsters… and still puzzle scientists today.

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