The ocean is terrifyingly loud. You probably think of the deep sea as a silent, crushing void where nothing happens, but it’s actually a cacophony of groans, pops, and literal screams that can travel thousands of miles through the water column. Back in 1997, researchers with the National Oceanic and Atmospheric Administration (NOAA) picked up something that shouldn't have existed. They called it a call from the depths, or more famously, "The Bloop." It wasn't just a random sound. It was an ultra-low frequency, high-amplitude sound detected by hydrophones across the Pacific Ocean, stretching over 5,000 kilometers. For years, people were convinced it was a monster. They were wrong, but the reality is actually more concerning for our planet.
Sound travels differently underwater. Because water is denser than air, sound waves move about four and a half times faster and can stay intact for incredible distances. When the SOSUS (Sound Surveillance System) array—originally a Cold War tool for tracking Soviet subs—picked up the Bloop, scientists were baffled. It had an organic quality. It rose in frequency like a living creature’s voice. If it was an animal, it would have to be several times larger than a Blue Whale. Think about that. A Blue Whale is already the largest animal to ever live on Earth. Something bigger? That’s where the "Cthulhu" theories started.
Why a Call from the Depths Still Haunts Marine Biology
The mystery of a call from the depths isn't just about one weird noise from the nineties. It’s about the fact that we have only explored about five percent of the ocean floor. We’re basically flying blind. Dr. Christopher Fox, who was the chief scientist on the project at NOAA's Pacific Marine Environmental Laboratory, initially speculated that the sound might be biological. This fueled decades of internet creepypasta and "found footage" hoaxes. People wanted it to be a Megalodon. They wanted it to be a Kraken.
But science usually has a colder, more industrial explanation. By 2012, after years of data collection near Antarctica, NOAA released a formal explanation. The Bloop wasn't a beast. It was an "icequake." Specifically, it was the sound of a massive iceberg cracking and shearing away from an Antarctic glacier. When these ice giants break, they release a massive amount of energy. The acoustic profile of a "calving" iceberg matches the Bloop perfectly. It’s a relief it wasn't a sea monster, right? Not exactly.
The Problem with Modern Ocean Noise
If these sounds are getting more frequent, it’s because the poles are falling apart. We are hearing the literal breaking of the world. While the Bloop was a natural (albeit dramatic) event, the ocean is now filled with "technophony"—human-made noise. Shipping lanes, sonar, and seismic airguns used for oil exploration have turned the deep into a construction site.
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This matters because marine life depends on the acoustic environment. Whales don't use GPS; they use song. Imagine trying to have a conversation with your best friend while someone is running a chainsaw next to your ear. That’s what a modern a call from the depths often sounds like to a Beaked Whale. Research by specialists like Dr. Christopher Clark at Cornell University has shown that the "acoustic space" for right whales has shrunk by up to 90% in some areas. They can't hear each other. They can't find mates. They can't find food.
Other Unexplained Deep Sea Sounds
The Bloop gets all the press, but it wasn't the only weird thing the hydrophones caught. Have you heard of "Julia"? Recorded in 1999, it sounded like a ghostly cooing. Then there was "Slow Down," a sound that lasted about seven minutes and gradually decreased in frequency.
- The Upsweep: This one is creepy because it’s seasonal. It’s a long train of narrow-band upsweeping sounds. It was first detected in 1991 and reaches its peak in spring and autumn. Scientists think it’s related to undersea volcanism, but the exact source remains elusive because it’s so widespread.
- Train: This sounds exactly like a distant locomotive. It’s a steady hum that scientists eventually attributed to icebergs grounding themselves on the ocean floor, dragging across the mud like a giant finger on a chalkboard.
- Whistle: Captured in 1997, this one was only picked up by one hydrophone. That’s rare. It means the source was localized, but we still don't know what it was.
Honestly, the ocean is just a giant echo chamber. Sometimes a sound can hit a layer of water with a specific temperature and salinity—the SOFAR channel—and travel halfway around the world without losing its strength. It’s like a natural fiber-optic cable for noise. You could be in California hearing a glacier crumble in the Ross Sea and think it’s a monster right under your boat.
Is there anything actually living down there?
We keep finding things that shouldn't exist. In 2021, researchers found life on a boulder 3,000 feet under the ice in Antarctica. They didn't expect anything to be there. No light, no obvious food source, just sponges and unidentified stalks. When we talk about a call from the depths, we have to acknowledge that our "facts" about what can live in the deep are constantly being rewritten.
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Take the Giant Squid (Architeuthis dux). For centuries, it was a myth. Sailors told stories of the Kraken, and scientists laughed. Then, we started finding carcasses. Then, in 2004, Japanese researchers finally got the first photos of a live one. We only just got high-definition video of them in their natural habitat recently. If a 40-foot squid can stay hidden for that long, what else is moving around in the Hadal zone? Probably not a city-sized monster, but certainly species that would look like aliens to us.
How to Track Ocean Noises Yourself
You don't need a PhD to be interested in this. NOAA actually maintains an archive of these sounds. You can listen to the original Bloop recordings online. It’s a bit underwhelming at first because the recordings are usually sped up. In real-time, the Bloop was so deep you could barely hear it; you’d feel it in your chest more than your ears.
- Visit the PMEL website: The Pacific Marine Environmental Laboratory has a "Gallery of Acoustic Events." It’s the official repository for every weird noise caught by the SOSUS arrays.
- Support Acoustic Ecology: Organizations like the Ocean Conservation Research (OCR) work to reduce human noise pollution. They study how "industrial" calls from the depths affect dolphin and whale communication.
- Check out the MBARI YouTube channel: The Monterey Bay Aquarium Research Institute posts incredible footage of deep-sea life that often accompanies these acoustic studies.
What We Get Wrong About Sea Monsters
The biggest misconception is that the deep ocean is a "lost world" of prehistoric survivors. It’s not. Evolution doesn't stop. The creatures down there are highly specialized, not "old." They have evolved to handle pressures that would turn a human into a pancake. When people hear a call from the depths and hope for a dinosaur, they're missing the point. The real monsters are the changes we're seeing in the environment.
The Bloop was a warning. It was the sound of the Antarctic ice shelf reacting to a warming planet. It’s a bit of a letdown if you wanted a Kraken, but it’s a much more urgent reality. We should be paying more attention to what the planet is trying to tell us through these acoustic anomalies.
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Actionable Steps for Deep Sea Enthusiasts
If you're fascinated by the mystery of ocean acoustics, there's more to do than just read about it. The field of "Citizen Science" is growing.
First, get involved with projects like "Whale FM" or similar crowdsourced data programs. These allow volunteers to help categorize whale calls and distinguish them from background noise. Scientists have more data than they have people to process it. You could literally be the person who identifies a new acoustic signature.
Second, reduce your personal impact on ocean health. Most people don't realize that global shipping is the primary source of low-frequency noise in the ocean. Supporting local economies and reducing reliance on international shipping for every minor purchase actually helps quiet the "acoustic smog" that drowns out the real calls from the deep.
Lastly, keep a skeptical but open mind. In the world of oceanography, today’s "ghost story" is often tomorrow’s peer-reviewed paper. We are currently living through a golden age of deep-sea discovery. With new autonomous underwater vehicles (AUVs) and better sensor arrays, we are finally starting to see—and hear—the parts of our planet that have been dark for billions of years. Stay curious. The next weird sound might not be an iceberg. It might be something we haven't even named yet.