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10 Incredibly Unsettling Things We Still Don’t Know about the Ocean

by Selme Angulo
fact checked by Darci Heikkinen

We know quite a bit about the natural world, and we learn more and more every year. Scientists trek all over the globe to learn about animal behavior, ecosystems, weather tendencies, climate issues, migration patterns, and more. Their collective knowledge grows with each passing year thanks to the painstaking observations of wildlife biologists and other researchers keen on answering all the questions we have about the earth. Of course, we here in the general public get a few of those all-important facts to trickle down to us thanks to fascinating documentaries like Planet Earth and Blue Planet.

But there is one major part of the world where we still don’t know very much: the deepest, darkest depths of the world’s biggest oceans. The furthest deep trenches and bottoms and valleys in the largest oceans on earth still remain a major mystery to scientists. It’s near-impossible to send people down to the furthest depths—and especially for any length of time to make sustained observations—and the robotic, remote-controlled transports we do send only give us a partial picture. In turn, the puzzle of the ocean’s depths is far from complete.

That’s where this list comes in. Today, we’ll take a look at ten fascinating and outright creepy facts about the deepest parts of the world’s oceans. These are ten tidbits we don’t quite know yet (or ten things we know partially but are desperately trying to learn more about). The creepy, unsettling factor of the unknown makes these mysteries all the more fascinating!

Related: 10 Creepy and Gruesome-Looking Sea Creatures

10 Deep Sea Bigfoot?

Why Do Deep Sea Creatures Evolve Into Giants?

We’re sorry to tell you this, Bigfoot fans, but he doesn’t exist. We know. That’s a shock to your system. But the fact is that even in thick, dense forests, we would have come across a real-life Bigfoot (and not some suspiciously grainy video “footage” of him) by now. And even if we didn’t find Bigfoot himself, we would have found his bones—conclusive evidence that there were Bigfoot creatures living and dying in the woods. We don’t have those bones, and we don’t have that evidence, and it’s time to put that all to rest. Hate to be a buzzkill!

However, there is one place where there may yet be a Bigfoot-like species—or even several. The deepest reaches of the ocean are considered anything below 656 feet (200 meters) in depth by scientists, and the biodiversity in that region of the dark deep is nearly completely unknown.

The size of the ocean’s deep is unbelievably massive; it makes up about 85% of the earth’s living space. And while the hunt for food down there is vicious and sustenance is far more scarce than near the water’s surface, the sheer amount of ground (er, water) to track means there is an unreal amount of biodiversity to which we are clueless.

Some scientists believe that there are as many as ten million species of animals living in the deep sea. That biodiversity would make the deepest oceans as rich and various as the most dense tropical rainforests—and much more massive in size and scope, too.

Amazingly, of those ten million species, the vast majority have never been seen and certainly never been cataloged. Thus, is there an underwater version of Bigfoot lurking quietly down there? Are there several different species that might fit that bill? Scientists continue to explore the watery depths, so who knows what thy’ll eventually discover.[1]

9 The Bio-Duck

What’s Making this Mysterious Bio-Duck Quack?

Way back in 1960, submarine personnel in a vessel far off the coast of Western Australia noticed and recorded a sound being made deep in the waters of the Southern Ocean. The sound was a bizarre cadence and completely unknown as to its origin. Those who listened to the recording thought it sounded like a bit of deep sea quacking, almost like a duck.

So the name was coined: The sound was to be called the “Bio-Duck.” The problem is that nobody knew anything else at all about the sound, where it came from, or who (or what) was making it. And for the next five decades, that mystery continued. The so-called “Bio-Duck” was one of the most persistent mysteries of the deep sea.

And then, a breakthrough! Sort of. In 2014, scientists finally figured out what was making the sound. According to them, Antarctic minke whales are responsible for the “Bio-Duck” call. But beyond that, scientists still don’t know why the sound is being made or who it is meant for.

It is most often detected during austral winter in the Southern Ocean far off Australia, and interestingly, the sound is very often heard in waters closer to the surface. Then, the minke whales immediately dive deep down into the dark waters below, and everything else from there is completely unknown. Why are they doing it? Is it a mating call? Or a call to feed? Or something else entirely? We may never know.[2]

8 Life’s Origin?

The Lost City and the Origin of Life | Weird Places

Life as we know it on Earth began roughly four billion years ago. But where those first very simple cells coalesced and sparked what we now have today is still a mystery. Experts believe it may have happened way down deep in the furthest reaches of the oceans, though. See, in 2017, a group of paleontologists found a bunch of microscopic tubes and filaments that were made of an iron-rich material called hematite. These tubes were lodged in rocks that had formed between 3.77 billion and 4.28 billion years ago.

The rocks themselves are already known to be a lasting feature of the earth’s primeval ocean crust. Basically, most of the sea floor gets dragged back into the earth’s mantle and then recycled out into a new crust in a slow and endless process. Well, these rock fragments didn’t get dragged down. And because these tiny microscopic tubes were still trackable inside, it gave scientists a breakthrough—maybe.

Back in the 1990s, a NASA chemist was the first person to put forth a theory that life on Earth began in the rocky pores inside the chimneys of hydrothermal vents within the oceans. The conditions would have had to have been just right for life to start there. The temperature of the fluids rushing through these vents couldn’t have been too high. The fluids themselves would have needed to be of a high-enough alkaline consistency in order to properly generate energy to produce those first living cells.

Most ocean vents are incredibly hot and very strongly acidic—so those are out. But there is a set of vents in an extremely rare formation deep in the Atlantic Ocean called “The Lost City” where these conditions were just right to produce microscopic tubes exactly like the ones found in 2017. To that end, even though they can’t ever truly know, some scientists believe they have found the link back to the source of all life on Earth.[3]

7 Where’s All the Plastic?

Why 99% of ocean plastic pollution is “missing”

We know that quite a bit of plastic pollution is being dumped into the ocean, either directly by people littering en masse or indirectly as it washes down from rivers and streams. But once it gets there… where does it go? That question might sound simple, but amazingly, it’s not.

Sure, there are things like the Great Pacific Garbage Patch that effectively hoovers up quite a bit of the plastic that is being dumped into the ocean at greater and greater rates. But there are still veritable tons of plastic going into the oceans every year that simply cannot be accounted for by environmental scientists. Where is it? And how did it seemingly just disappear?

Oceanographers are still desperately trying to understand where all the ocean plastic that gets dumped winds up. Is some eaten or consumed by animals? Does some descend deep into the sea and wind up in nooks and crannies way far from prying eyes on the seafloor? Cynically, oceanographers have taken to calling this the question of “dark plastic.” And they simply don’t have an answer for it.

“Ninety-nine percent of all the plastic is missing,” oceanographer Erik van Sebille informed the world in a Vox podcast recently. “We have dark plastic. Like the astronomers have dark matter and dark energy, we oceanographers… don’t have an idea where most of the plastic in our ocean is. We’ve lost it.” Well, that’s creepy![4]

6 Thriving on Plastic?

The Creatures That Thrive in the Pacific Garbage Patch

Speaking of plastic in the oceans, there is one other major question about what is being dumped there: How is life surviving—and even thriving—on the plastic trash that is accumulating out at sea? Way back in 2018, two scientists who were studying debris collected as part of the Great Pacific Garbage Patch began to find something very unexpected.

In the debris they were collecting from the garbage mass way out in the middle of the Pacific Ocean, they found very tiny marine animals, including crabs and anemones. These small animals usually lived on beaches and along the coasts. But somehow, they were migrating all the way out to the Great Pacific Garbage Patch, thousands of miles from any coastline. And not only that, but they were multiplying quickly and thriving within the GPGP.

Normally, the open ocean is a very hostile environment for small marine animals like crabs and anemones. That’s why they seek out the relative shelter of the coastline, where they can use sand and rocks and all that comes with it as something of a natural defense. Now, they may be doing the same with plastic in the world’s ocean garbage dump. But how they even got all the way out there in the first place is a total mystery. Did they latch onto plastic back when it first rushed into the ocean from a river or stream and then hang on for months or years before getting to the GPGP?

And even more confusing than that: how do they seem to be thriving amid all the non-biodegradable trash? Contents that would supremely hamper most life don’t appear to be affecting these tiny marine animals at all. It’s as if they have created an entirely new ecosystem out of something so unnatural. The only problem is that scientists have absolutely no idea how they did it.[5]

5 What Makes Up a Rogue Wave?

How Dangerous Can Ocean Waves Get? Wave Comparison

Rogue waves have long been reported by sailors all across the world. For centuries and centuries, sailors have sworn that this was a thing. The ocean would be at a certain height, and all the waves would be predictable enough right around the choppiness of the water, and then suddenly, out of nowhere and without any warning, BOOM!

A rogue wave would shoot up from the sea and crest much, much higher than the other waves around it. In many cases, rogue waves like that would topple sailors off ships and send them to their deaths in the sea. In the worst cases, and with the most extreme rogue waves, they would capsize entire boats and leave entire crews to disappear and sink down to the ocean’s depths.

But science was skeptical of these centuries of sailor statements, to say the least. For nearly as long as rogue waves were reported, scientists were unable to find objective proof that they even existed. They figured that sailors had been making up the random heights of these so-called rogue waves or perhaps misremembering them during the stress of dealing with a choppy sea.

That all changed on January 1, 1995, though. On that day, the most famous freak wave that has ever existed was detected at the Draupner Gas Platform in Europe’s North Sea. The wave was a shocking 25.6 meters high (or nearly 90 feet), which was surprising because most waves in the area at the time were estimated to be less than half of that. So it truly did come out of nowhere.

But here’s where things get creepy: Science has now shown that rogue waves do, in fact, exist. All those thousands of reports from sailors that go back centuries would appear to be true. There really are unpredictable, unexplainable rogue waves out there. And unfortunately for science, even now, nearly 30 years after Draupner, we still can’t explain these waves.

Even though oceanographers know they are real, they still haven’t been able to figure out what makes a wave go rogue. The hope is that experts will one day learn that with the express purpose of figuring out a way to tip off ships of their potential. But that hasn’t happened yet, and it may never happen.[6]

4 Octopus Pals?

My Octopus Teacher Hug

Back in 2020, the documentary My Octopus Teacher was released. It followed the story of a man named Craig Foster and how he spent a year bonding with a wild octopus in the Great African Seaforest. The documentary was a huge hit, landing on Netflix and being streamed by tons of people.

It also won Academy Awards for its incredible story, cinematography, and artistic focus on Foster’s unlikely and apparently very strong relationship with a wild octopus. Through it all, it asked a very big question: Can humans and wild animals legitimately ever be friends? And with octopuses specifically, are they smart enough and sensitive enough to bond with a human being that enters their habitat?

While My Octopus Teacher argued that it is, in fact, possible, the jury on the question of friendship is still very much out as far as scientists are concerned. Oceanographers and marine biologists know quite well how intelligent octopuses are. And there’s no doubt that they can recognize humans whom they come to know and even trust.

But the question remains. Just how deep does that relationship go? How tightly can a wild octopus truly bond with a person who swims down into their habitat? We may never know the answer to that question. But if we somehow did ever learn more about it, that could open up a whole lot more information about the psychological and emotional lives of other wild animals in the deep sea and elsewhere.[7]

3 What’s in the Twilight Zone?

Mysteries of the Twilight Zone | Worlds of the Deep

The deeper you go in the ocean, the less sunlight gets through the water. When you go down a few hundred meters, you start getting into water where it becomes more and more difficult to see. About 656 feet (200 meters) beneath the surface, there is a specific area called the “mesopelagic” zone. More commonly, and more colloquially, this region is known as “the twilight zone.”

There, sunlight fades nearly completely out of view, and the further down you go at that point pushes you into complete ocean darkness. As the sunlight fades, then, so too does our knowledge and understanding of what goes on down there. And while 200 meters may not seem like a very long distance compared to how deep some of the world’s oceans are, our scientific expertise pretty much peters out at that point.

We’re not kidding about that, either. Take it from Woods Hole Oceanographic Institution expert Andone Lavery. “It’s almost easier to define it by what we don’t know than what we do know,” he said on a recent Vox podcast. “It’s remote. It’s deep. It’s dark. It’s elusive. It’s temperamental.” It’s tough and costly to get cameras and things like that down that far in the ocean.

And shining lights to be able to see anything that’s floating around pretty much instantly alters the environment and how the fish there interact with each other and the light that now occupies some of their ecosystem. Thus, it’s incredibly difficult to get any kind of reliable data or observational notes on what happens in this twilight zone. As far as we know, it’s all pretty much a mystery—still to this day![8]

2 Got GPS?

How Close Are We to Completely Mapping the Ocean?

Of all the square miles of ocean floor all across the world, only a little bit of 20% of it has been mapped. In terms of raw square miles, that’s obviously a ton of ocean floor that has been mapped using modern high-resolution technology, like multibeam sonar systems. It also means a ton more that hasn’t been mapped at all, and thus, scientists have absolutely no clue what it looks like, how it rises and falls, or where it goes.

Here is something to put that into perspective: Because so little of the ocean floor has been mapped, the bottom of the sea is still a far more mysterious place than the surface of the moon or the surface of Mars. Not only that, but whenever explorers go down to the bottom of the sea in most parts of the world or use specialized underwater cameras to show them what’s down there, they nearly always see a spot on Earth for the very first time that no human has ever before laid eyes upon. That’s pretty cool—and pretty creepy.

As of late 2023, exactly 24.9% of the global seafloor has been mapped. So that means three out of every four square miles of the ocean bottom is still totally unaccounted for. That’s not just way out in the middle of the Pacific Ocean, away from all types of land masses, either.

Even when it comes to United States territorial waters, only about 50% of the nation’s ocean bottom has been mapped and plotted carefully with sonar systems attached to ships. So to say that we are nearly totally ignorant about what lies beneath is, uh, the understatement of the century![9]

1 Got Mud?

Boring Through The Earth’s Crust

As if the mysteries of the deepest waters of the ocean weren’t weird enough on their own, there is another major question down there that scientists can’t answer: What’s up with the mud that sits right under the very bottom of the water?

That area of mud and settled silt is commonly known as the Mohorovicic Discontinuity. It is one of the most unknown parts of the entire world while also still having major implications for how the earth works, how tectonic plates, shift around, how earthquakes come to be, and more.

About sixty years ago, scientists had a crazy idea for an experiment. They wanted to drill down all the way through the bottom of the sea bed and see if they could bore a hole into the mud way down there. They were hoping to gain access to the Mohorovicic Discontinuity and, in turn, pull up an actual piece of the earth’s mantle. A layer of earth that deep is something that no human has ever been able to observe before.

The experiment didn’t work, unfortunately, and experts weren’t able to bring up a part of the mantle at all. Modern-day scientists are hopeful that it could yet work one day with better technology. But until that happens, we’ll have to be content to stick to what we know about the Mohorovicic Discontinuity: next to nothing![10]

fact checked by Darci Heikkinen