What Is The Bloop Sound and What Caused It?

The Bloop is a mysterious ultra-low frequency sound recorded by NOAA in 1997 that was so powerful it was detected across 5,000 kilometers of ocean. After 15 years of investigation, scientists determined it was likely caused by Antarctic ice fracturing and breaking apart, though the sound’s immense scale initially baffled researchers.

The Discovery That Shook Ocean Science

On May 19, 1997, deep-sea microphones operated by the National Oceanic and Atmospheric Administration (NOAA) detected something unprecedented. The sound originated from coordinates 50°S 100°W in the remote South Pacific and lasted just over a minute. When researchers sped up the ultra-low frequency recording to make it audible to human ears, it produced an eerie, almost biological sound—like something enormous taking a slow, labored breath.

The sheer power required to generate a sound detectable across such vast distances suggested a source many times larger than a blue whale, the largest known animal on Earth. This discovery sent shockwaves through the marine biology and oceanography communities.

The Hunt for Explanations

Scientists initially struggled to categorize the Bloop because it didn’t match known acoustic signatures. Underwater earthquakes, volcanic eruptions, and collapsing ice shelves all produce distinctive sound profiles that researchers had cataloged over decades of deep-ocean monitoring. The Bloop’s unique frequency sweep, duration, and rise pattern fit none of these established categories.

The sound’s apparently biological characteristics led some researchers to speculate about unknown deep-sea megafauna. However, the volume required would necessitate a creature far larger than any animal that has ever existed on Earth, making this explanation highly improbable from a biological standpoint.

The Antarctic Ice Connection

The mystery began unraveling in 2005 when NOAA researcher Christopher Fox proposed that the Bloop might be linked to Antarctic ice activity. His initial hypothesis suggested that massive ice fracturing events—called icequakes—could produce sounds matching the Bloop’s characteristics.

This theory gained substantial credibility in 2012 when NOAA scientist Robert Dziak published comprehensive research using a decade of additional acoustic data. Dziak’s team demonstrated that the Bloop’s sound signature closely matched Antarctic icequake events, where enormous ice masses fracture and calve into the ocean under tremendous geological stress.

Other Mysterious Ocean Sounds

The Bloop wasn’t an isolated incident. NOAA’s classified hydrophone network, originally designed to track Soviet submarines during the Cold War, has recorded numerous unexplained sounds:

The Slowdown (1991): A seven-minute descending frequency signal that sounded like something massive running out of air. This sound has never been satisfactorily explained and hasn’t been recorded since.

The Upsweep (1991-present): A seasonal series of narrow-band sounds that intensifies during spring and autumn. While linked to underwater volcanic activity in the South Pacific, scientists cannot explain why it follows such a precise seasonal pattern.

Julia (1999): A sound so powerful it was detected across the entire Pacific hydrophone network. Its vaguely voice-like quality led to its feminine designation, though researchers believe it originated from a large Antarctic iceberg running aground.

The Deeper Mystery

While the Bloop’s explanation satisfied most scientists, it highlighted a more unsettling reality: we’ve explored less than 20% of our oceans. The deep sea remains largely acoustically invisible, containing thousands of undiscovered species adapted to crushing pressures and eternal darkness.

Recent discoveries have revealed phenomena like the Deep Scattering Layer—a massive daily migration of sea life so dense that World War II sonar operators initially mistook it for a false ocean floor. The “bio-duck” sound, recorded by submarines for 50 years, was only identified as Antarctic minke whale calls in 2014.

Sound Transmission in the Deep

Ocean acoustics operate differently than sound on land. The deep ocean’s SOFAR (Sound Fixing and Ranging) channel can trap certain frequencies, allowing sounds to travel thousands of miles without significant energy loss. This means some recordings might be acoustic “memories”—echoes of events that occurred years earlier on the opposite side of the planet.

This discovery adds another layer of complexity to interpreting deep-ocean sounds and suggests that our understanding of marine acoustics may be fundamentally incomplete.