The Mysterious Deep Sea Sound
In 1997, the U.S. National Oceanic and Atmospheric Administration (NOAA) detected an unusual and powerful underwater sound in the deep Pacific Ocean. This acoustic signature, dubbed “The Bloop,” quickly captured public and scientific attention due to its unique characteristics. The sound stood apart from typical ocean noises, sparking widespread speculation about its origin and becoming one of the ocean’s great acoustic mysteries.
The Bloop was recorded by an autonomous hydrophone array, a system of underwater microphones operated by NOAA’s Pacific Marine Environmental Laboratory (PMEL). These hydrophones were strategically placed across the Equatorial Pacific. The sound’s source was triangulated to a remote area of the South Pacific, around 50°S 100°W, west of the southern tip of South America.
Analysis revealed the Bloop was an ultra-low frequency, high-amplitude sound that “rose” rapidly in frequency over approximately one minute. Its immense intensity allowed it to be detected by multiple sensors spread over 5,000 kilometers (about 3,000 miles) apart. The sustained pattern and volume of the Bloop presented an acoustic puzzle, unlike any previously identified ocean sound.
Initial Interpretations of the Bloop
The unusual nature of the Bloop immediately puzzled researchers, prompting various hypotheses about its source. Scientists considered geological activity or man-made sources, but its acoustic profile did not align with known patterns from earthquakes, volcanoes, or underwater explosions.
The sound’s immense volume and ultra-low frequency led many to consider a biological origin. These characteristics were consistent with vocalizations from exceptionally large marine animals. Speculation arose that the Bloop could be the call of an undiscovered, massive leviathan dwelling in the ocean’s depths.
If biological, the animal responsible would need to be significantly larger than a blue whale, the largest known animal on Earth. Estimates suggested a creature producing such a powerful, far-reaching sound would need to be more than twice the size of a blue whale, potentially over 75 meters long. This prospect fueled public fascination and scientific curiosity.
The True Source Revealed
The mystery of the Bloop persisted for years, but subsequent research and ongoing acoustic monitoring by NOAA scientists ultimately provided a definitive explanation. By comparing the Bloop’s unique signature with a vast library of recorded ocean sounds, scientists identified a striking match: large “icequakes.”
An icequake is the sound generated by the cracking and fracturing of massive ice formations, such as large icebergs or glaciers. These events, common in the Antarctic region, release tremendous amounts of energy. The resulting sounds are ultra-low frequency and powerful enough to travel thousands of kilometers through the ocean, mirroring the Bloop’s impressive range.
The acoustic characteristics of icequakes—their loudness, low frequency, duration, and irregular yet sustained patterns—perfectly aligned with the Bloop’s profile. This scientific resolution confirmed that the Bloop was not a living creature, but a natural phenomenon of ice masses breaking apart. The “size” of the Bloop reflected the immense scale of ice calving events in polar regions.