The Bloop: The Ocean’s Loudest Mystery Sound (1997)

ARCHIVE FILE · Event year: 1997. This happened in 1997 and is not breaking news. It’s part of the Redacted Weekly evergreen archive.

In 1997, U.S. government underwater microphones in the Pacific recorded a sound so loud and so low it was picked up on several sensors more than 5,000 km (3,000 miles) apart. It rose in frequency over about a minute. Researchers called it “Bloop.” For years, the internet was sure it was something enormous and alive.

CASE FILE · RW-ARC-UNX-003
Subject: Ultra-low-frequency, high-amplitude underwater sound
When: 1997
Where: Roughly triangulated to 50°S 100°W, in the remote South Pacific west of the southern tip of South America
Detected by: NOAA’s Equatorial Pacific Ocean autonomous hydrophone array
Evidence: Hydrophone recordings; spectrogram
Status: Attributed by NOAA to an icequake
Monster: Not required

What was recorded

NOAA’s Pacific Marine Environmental Laboratory runs a stand-alone hydrophone array in the equatorial Pacific, designed to listen for undersea earthquakes, ice noise and marine mammals. In 1997, it picked up the sound later called the Bloop. It was roughly triangulated to a remote point near 50°S 100°W.

The monster phase

Early speculation suggested a marine animal. The remote location, the huge detection range, and the years it went without a firm explanation made it a favorite of sea-monster fans online.

How a scientist’s “hunch” became a sea monster

The Bloop’s reputation as a monster started with real scientists. In a 2001 CNN interview, NOAA’s Christopher Fox said he thought the Bloop was probably ice calving in Antarctica. But in 2002, speaking to journalist David Wolman for New Scientist, Fox said the sound didn’t look man-made (it wasn’t a submarine or a bomb) and that its profile resembled a living creature’s. The trouble, he said, was that it would be “far more powerful than the calls made by any animal on Earth.”

Wolman’s article described Fox’s “hunch” that the Bloop was the most animal-like of the unidentified sounds NOAA had recorded, since its frequency changed rapidly the way known marine-animal calls do. It also noted the problem: the sensors that picked it up were up to 4,800 km (3,000 miles) apart, so whatever made it was much louder than any whale.

Author Philip Hayward later argued that the article “amplified Fox’s ‘hunch’ and, through the use of the word ‘likely’, opened the door for subsequent speculation.” Online, that opening turned into years of speculation about an undiscovered giant animal.