The ocean is wide, vast, and terrifying. But for the last 40 years, researchers around the world have been recording audio from hydrophones to try to understand it better. And we’ve learned a lot. But a surprising number of sounds have been recorded that defy explanation. Here are some of the most mysterious.


Scattered about the oceans of the world, you might find this:

This is a hydrophone. Microphones designed to pick up sound underwater. The National Oceanic and Atmospheric Administration has hundreds of these deployed throughout the oceans of the world.

Think of it like a deep sea surveillance system.

Just in case those blue whales start getting any crazy ideas.

And most of the time, that’s all they hear. Whale calls, dolphins, passing ships. Seismic activity in some places.

But not always. There have, in fact, been numerous sounds recorded in the oceans around the world that defy explanation. Including one in 1997 that was the loudest underwater sound ever recorded.

A sound that, for a while anyway, stupefied scientists around the world and led to an array of questions about… What exactly was down there?

If you didn’t already know, 97 percent of the world’s water is found in the ocean. Because of that, it has a massive impact on the world’s weather, temperature, and food supply. 

But it remains a mystery. In fact, more than 80 percent of it has never been explored, mapped, or even seen by humans. 

While we currently know about 226,000 ocean species, there well may be up to more than 90 percent of the ocean’s species we still don’t know about yet. 

Some scientists suggest that there could be between a few hundred thousand to a few million more to be discovered. 

And there are a lot of species that we thought went extinct but then found out that nope… They’re still out there.  

For example, there’s the famous coelacanth, a fish that was thought to have gone extinct 65 million years ago. 

But then one was caught off the South African coast in 1938, and scientists around the world went, “Whaaaaa?” That’s what scientists do.

And then there’s the symbiotic relationship between two marine lifeforms that were thought to be extinct for 273 million years. 

Scientists published a paper in 2021 stating that they found non-skeletal corals growing from the stalks of marine animals called crinoids, or sea lilies. 

They discovered these on the Pacific Ocean’s floor off the coast of Japan. 

And then there’s everybody’s favorite oversized cephalopod, the giant squid.

For years, the only reason we knew it existed was because from time to time a giant carcass would wash up on a beach, but scientists had never actually seen one in the ocean.

That changed in 2012 when a group of scientists from Japan’s National Science Museum filmed a giant squid in its natural habitat for the first time. 

Although they almost caught one in 2006 when researchers suspended bait under a ship off the coast of Japan to try and hook one. And one managed to get the bait, but did it without getting hooked. Because cephalopods are crazy smart.

I talked about cephalopods on this channel once actually, in one of the greatest scripts of the 21st century, written by one of the world’s most thought-provoking scriptwriters, playwrights, and raconteurs– Oh, this is Jason’s script isn’t it? Jason got me. He got me. Little scamp.

Anyway, the ocean is big and mysterious, which is why NOAA built that hydrophone array I was talking about at the beginning.

A little bit about how hydrophones work, in case you’re wondering, most are based on the piezoelectricity of certain ceramics that create tiny electrical currents when faced with pressure changes. 

After submerging them in the ocean, ceramic hydrophones produce small-voltage signals over a wide frequency range when they’re exposed to underwater sounds coming from any direction.

When we amplify and record the signals, sea sounds can be measured precisely. 

And when we deploy several hydrophones in an array, we can triangulate sounds by when they hit each hydrophone to figure out what direction they came from and how far away.  

The U.S. Navy used sonobuoys for decades to record the sounds of enemy submarines, usually deployed from an aircraft or a ship. 

They’ve also been used in the past to record marine mammal calls and listen for earthquake activity. 

But their short lifespan keeps them from being a long-term monitoring solution for recording ocean sounds. 

So anyway, this is one of the best ways we have to monitor what’s going on in this vast expanse of ocean because sound waves travel a lot further in water than they do in air, so there’s a lot we can discern from the sounds we record.

And over time, researchers have accumulated a vast library of sounds so what might sound like a bunch of noise to us is pretty recognizable to them.

So when they record something that doesn’t fit any of their models… it’s something they pay attention to.

Which brings us to “The Bloop.” 

Researchers were listening for underwater volcanic activity in the southern Pacific Ocean in 1997 when they recorded an extremely loud, powerful, and strange sound. 

With hydrophones placed more than 3,219 kilometers apart across the Pacific, they were able to record the sound several times. 

Scientists at NOAA’s Pacific Marine Environment Lab wanted to discover where the sound came from. But the problem is, it was so loud, they didn’t even know where to start.

Like I was just saying, normally a sound can be triangulated by a handful of hydrophones, but as the director of the acoustics program at NOAA told Vice in 2017, “It’s unusual when a sound is recorded on all of the sensors we have deployed. If it’s a ship, or a whale, when it makes a sound in the ocean, it isn’t big enough to be recorded all the way across the Pacific. But this sound was recorded on many hydrophones so it stood out in our mind as being something unique.”

With nothing else to go on, researchers decided to just call it The Bloop. And here’s why.

I’ve gotta say, you can’t deny its bloopiness.

When word got out about this mysterious sound it of course led to mountains of speculation.

One theory was that it might be underwater military exercises, but none were reported to be going on that day.

Of course it wouldn’t be reported if it were a secret military exercise, or if it were a test of some secret military technology. Huh?

Some people suggested it could be a giant squid, but squids and cephalopods don’t really make sounds.

Unless it’s some kind of undiscovered species of squids… Huh!?

Or maybe it’s Cthulhu! Seriously, some people think it might actually be Cthulhu.

For those less literate in the audience, Cthulhu is a fictional creature imagined by H.P. Lovecraft in his story The Call of Cthulhu, which, to be fair, the sound was recorded about 1,500 kilometers from where the creature first emerged in Lovecraft’s story. So, that is kinda weird.

Other theories about what was making the sound include a huge chemical reaction on the seafloor, an interaction of powerful ocean currents, and mermaids screaming.

Let’s call that one a maybe.

And of course you’ve got the alien theories, advanced underwater species a la The Abyss, an Atlantean civilization, basically any movie that involves the ocean has been used to explain it.

But maybe the idea that has gained the most interest is the idea of some kind of giant undiscovered ocean creature.

And people have put a LOT of thought into this, even speculating on biologies based on the sound and how it would make that kind of vocalization.

Some designs show it as being a gargantuan creature several times larger than a blue whale, some speculate that it’s more regular whale size but has some super-efficient mechanism by which to create sound, like the Pistol Shrimp, which is only a couple inches long but can create sound loud enough to stun prey.

The bloop’s frontal part of the body is large and similar in shape to a shark but its behind tail part gets thinner like that of a stingray. it’s limbs seem to be not fins but rather large webbed tubes which propel it through the water with massive strides. the front of its face is an odd nose-like bulb which increases the frequency of its powerful song that can nearly cause human heads to explode on contact. the creature’s top half actually moves differently from its back half, the front moves like a whale and its back moves like that of a Saltwater crocodile.”

And look, again, the ocean is huge and mostly undiscovered, thinking this came from a giant sea creature isn’t that farfetched. 

For example, the call of a blue whale can reach up to 180 decibels. That’s as loud as a jet plane.

They can also make calls at 14 Hertz, a frequency below our hearing ability. 

Those low-frequency sounds travel further with less distortion, transmission loss, and scattering. That means blue whales can communicate with each other over thousands of kilometers. 

But there’s a twist in the unsolved mystery of the Bloop. And that twist is… it’s actually been solved, we know what it is.

Over the years, NOAA has deployed hydrophone arrays closer and closer to Antarctica to study the sounds of seafloor earthquakes and volcanoes. 

And then in 2005, that’s where they finally discovered “The Bloop’s” source. 

It was the sound of an ice quake, which is an iceberg cracking and breaking away from an Antarctic glacier. 

Kind of anti-climatic, if you think about it, or maybe frightening if you’re concerned about climate change. 

I mean, this isn’t reeeeealy about climate change, though climate change is causing glaciers to crack and break apart more often.

So ice quakes are actually called cryoseisms. Which might be my favorite word.

And the way they work is, water in the ground often freezes quickly, making it expand. When it expands too much, it breaks up the soil surrounding it, creating cracks in the ground.

So, when temperatures drop at night, the top layer of slush freezes too quickly. The water underneath the slush requires more time to freeze. 

Once it freezes, it expands, which causes the slush to crack, causing an ice quake.

But “The Bloop” isn’t the only mysterious sea sound. There are several unexplained sounds found in the ocean that we still don’t know what is making them. 

Like, there’s “The Upsweep.” It consists of a long train of sounds that sweep repeatedly upwards, creating a howl from low to high frequencies. 

NOAA first detected it in the Pacific Ocean in 1991. 

Weird thing is that it changes throughout the year, peaking in the spring and fall. 

But scientists aren’t sure if this is because there are changes in the source or in the environment the sound travels through.

One possible explanation for the sound is undersea volcanoes. Maybe the sound comes from hot lava pouring out into the cold ocean water. 

And while it’s still detectable, its noise level has been slowly declining since its discovery. 

“The Whistle” is another sound that may have come from volcanic activity. 

Recorded just once in the Pacific Ocean in 1997, researchers haven’t been able to pinpoint the source. You need three microphones for that, and only one microphone picked up this sound.

In 1999, NOAA recorded the “Julia” sound. It was so loud that the entire Equatorial Pacific Ocean autonomous hydrophone array heard it. The sound lasted just under three minutes. 

Its most likely source was a large iceberg that ran aground off Antarctica, with its point of origin somewhere between Bransfield Straits and Cape Adare.

Another sound that could’ve come from an iceberg running aground is the “Slow Down.” 

First recorded in 1997, the sound decreased in frequency over seven minutes. 

While an iceberg running aground is one hypothesis, another is that it’s the sound of ice moving over land in Antarctica.

And then there’s “The Train” that was recorded in 1997 on the eastern equatorial Pacific autonomous hydrophone array. 

It was a steady sound of about 32 to 35 Hertz, and it’s most likely a large iceberg grounding itself in the Ross Sea near Cape Adare. 

Finally, I wanted to talk about another sound that we know its origin, but that doesn’t make it any less mysterious. Or sad.

It’s the 52 Hertz Whale, also known as the world’s loneliest whale. 

Researchers at the Woods Hole Oceanographic Institution heard the whale’s sound in 1989. It was unusual because it came in at 52 Hertz, which is really high for a whale species. 

The institution wrote in a report in 2000 that

“This sound source has been the only one with this call structure in the entire listening area. We have been tracking this call since 1992 and have not identified the whale species.”

They think it could be a hybrid whale. 

And there could be good news. It may not be as lonely as we think. Whales in different areas have different dialects, so its sound may be recognized by other blue whales. 

Christopher Clark, director of the Bioacoustics Research Program at Cornell, told Smithsonian Magazine in 2015 that

“The animal’s singing with a lot of the same features of a typical blue whale song. Blue whales, fin whales and humpback whales: all these whales can hear this guy, they’re not deaf. He’s just odd.”

What’s not odd is our unique ability to turn toward wild theories when something is mysterious. 

Someone doesn’t like the sunlight. Must be a vampire. 

Hear a weird sound in your attic? Must be a stranger living up there that you didn’t know about.

Can only see a straight line on the horizon. The world must be flat. 

Top Gun: Maverick got nominated for a best picture Academy Award. Scientologists must be tallying the votes.  

Mysteries are fun. They’re exciting. They engage both sides of our brains. But they can often be a bit of a letdown when they’re solved. 

That’s because the solution is often the simplest answer. 

Like, a lot of people wanted to believe “The Bloop” was a mythical sea creature created by a horror writer’s imagination. 

But it’s that imagination part that frankly, I think is pretty cool.

Look, I’ve made no secret on this channel that I’m not into conspiracy theories and I tend to hit the woo-woo alarm on cryptozoology and that kind of thing, but I love the creativity that people show in trying to figure out how creatures like this might exist.

It’s an exercise in speculative biology, like how we imagine what aliens might look like or how they might live on other worlds.

Like I’ll shout out my friend Andy Weir, the way he conceptualized the Rocky character in Project Hail Mary, we talked about it on my podcast – shameless plug – but it just blows my mind the level of thinking he put into that stuff. It’s really cool.

And with a suspected 80-90 percent of the ocean species still to be discovered, especially when you consider what we’ve already found at the depths of the ocean, which are just mind-blowing, there’s a lot of room for that kind of thinking to be applied to the Bloop or any of these other sounds. And that’s fun to me.

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