It was loud. Ridiculously loud. In the summer of 1997, a series of underwater microphones scattered across the Pacific Ocean picked up a noise that didn't make any sense. This wasn't the rhythmic clicking of a sperm whale or the low-frequency groan of a blue whale. This was a massive, ultra-low-frequency "bloop" that lasted about a minute and was powerful enough to be detected by sensors nearly 3,000 miles apart.
Scientists at the National Oceanic and Atmospheric Administration (NOAA) were baffled. The bloop sound immediately birthed a thousand conspiracy theories. People started talking about Cthulhu, giant squids, and undiscovered prehistoric monsters lurking in the deep. Honestly, who can blame them? The ocean is a terrifyingly dark place, and we’ve only explored about five percent of it. If something made a noise that loud, it had to be big.
Really big.
What Was the Bloop Sound, Exactly?
The noise was first captured by the Sound Surveillance System (SOSUS). This was a network originally designed by the U.S. Navy during the Cold War to track Soviet submarines. By the late 90s, NOAA was using it to monitor volcanic activity and whale migrations.
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The sound had a unique "frequency rise" profile. It started low and then accelerated upward, which is why it earned the nickname "the bloop." It sounded organic. To the untrained ear—and even to some experts at the time—it resembled the vocalization of a living creature. But there was a massive problem with the "giant monster" theory. Sound travels incredibly well underwater, but to be picked up 5,000 kilometers away, the source would have to be significantly larger than a blue whale. We’re talking about a creature that would defy the laws of biology and physics.
Christopher Fox, a researcher at NOAA at the time, was one of the first to go on the record about it. He told CNN and New Scientist that he didn't think it was man-made, like a submarine or a bomb. That left two options: something biological or something geological. For years, the biological theory won the internet. People pointed to the location—roughly 50° S 100° W. This happens to be somewhat close to the fictional sunken city of R'lyeh from H.P. Lovecraft’s stories. This coincidence fueled the fire.
Breaking the Mystery: Icequakes and Moving Glaciers
For over a decade, the bloop sound remained a staple of "unexplained mystery" forums. But as technology improved, NOAA started deploying more sensors closer to Antarctica. They began hearing things. Similar things.
By 2005, and certainly by 2012, the scientific consensus had shifted away from krakens and toward ice. Specifically, "icequakes." When massive icebergs crack and fracture, or when they scrape along the ocean floor, they create tremendous amounts of low-frequency energy. This isn't just a small pop; it's a structural failure of millions of tons of ice.
Robert Dziak, a NOAA seismologist, eventually confirmed that the spectral characteristics of the bloop matched icequakes recorded in the Southern Ocean. It turns out that as global temperatures fluctuate, the Antarctic ice sheet is constantly groaning under its own weight. Large icebergs, like A-38, have been known to produce these exact sounds when they break away from the Ross Ice Shelf.
It’s less exciting than a sea monster. I get it. We want the mystery. We want there to be something "other" down there. But the reality of a continent literally cracking apart and sending sound waves across an entire ocean is actually pretty metal when you think about it.
Why We Keep Obsessing Over Underwater Noises
The bloop isn't the only weird sound the Navy has found. There was "Julia," "Train," and "Slow Down." Most of these have also been attributed to ice or seafloor tectonic activity. Yet, the bloop sound remains the most famous.
Why? Because it occupies that weird space between science and folklore. Even though NOAA has "solved" it, the sound remains a cultural touchstone. It represents our fear of the unknown depths. The ocean is basically an alien planet right here on Earth. The pressure at the bottom of the Mariana Trench is over 1,000 atmospheres. That's like having an elephant stand on your thumb. In an environment that hostile, our minds naturally fill the silence with monsters.
Technical Reality vs. Internet Fiction
If you listen to the recording of the bloop today, you're usually hearing it sped up. In its original form, it's so low you can barely hear it without high-end headphones. By speeding it up by 16 times, researchers made it audible to the human ear, which also made it sound much more "chirp-like" and animalistic.
- Original duration: About 1 minute.
- Sensor range: Over 3,000 miles (4,800 km).
- Source location: Near the Antarctic Circle in the South Pacific.
- Final verdict: Ice calving (non-biological).
There is zero evidence of a biological origin. None. If a creature were large enough to make that sound, it would need to eat a caloric load that would collapse the local ecosystem. It would have to surface for air (if it were a mammal) or leave behind some kind of physical trace that our satellite imagery or sonar would have picked up by now.
What We Can Learn From the Bloop
The story of the bloop sound is actually a success story for maritime acoustics. It showed us that our sensors were sensitive enough to hear the "pulse" of the planet. It also taught us about the impact of climate change on the Antarctic ice shelf long before we had the visual data we have now.
Every time we hear something weird in the water, it’s an opportunity to learn about the Earth's crust or the movement of the poles. We’ve since identified sounds from underwater volcanoes and even the sound of the 2011 Tohoku earthquake traveling through the water column.
How to Explore Deep Sea Mysteries Yourself
If you're fascinated by these types of phenomena, don't stop at 20-year-old YouTube videos. The field of hydroacoustics is exploding right now. You can actually access real-time or archived data from various oceanic observatories.
First, check out the NOAA Vents Program archives. They have a repository of "unidentified" sounds that were later identified, providing a great look at the "detective work" involved in oceanography. You can see the spectrograms—the visual representations of sound—and compare the bloop to known whale songs.
Second, look into the Ocean Networks Canada (ONC) data. They run massive underwater observatories that live-stream data. Sometimes you can hear real-time recordings of the deep sea. It’s mostly static and the occasional boat engine, but when a biological or geological event happens, it’s incredible.
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Lastly, stop falling for the "Cthulhu" clickbait. The real science of the bloop sound—the fact that we can hear a piece of ice the size of a city snapping off a continent from half a world away—is far more impressive than a fake monster story. Understanding how sound moves through the "SOFAR channel" (a layer in the ocean that acts as a waveguide for sound) explains how these noises travel so far without losing energy. It’s a literal acoustic highway.
The mystery is "solved," but the ocean remains largely unheard. There are plenty of other sounds out there waiting for a name.
Actionable Next Steps
- Visit the PMEL (Pacific Marine Environmental Laboratory) website to listen to the original, non-sped-up files of the bloop to understand the true scale of the frequency.
- Search for "Spectrograms of Antarctic Icequakes" on Google Scholar to see the visual proof that links the bloop to glacial movements.
- Follow the Ocean Exploration Trust (Nautilus Live) on social media; they frequently record high-quality audio and video of deep-sea phenomena that are currently being discovered.
- Download a spectrogram app on your phone and whistle or clap near it. Seeing how sound is visualized helps you understand why scientists were able to match the "shape" of the bloop to the "shape" of cracking ice.