A quick Google search will tell you that the ocean covers approximately 71% of the Earth’s surface, spanning roughly 139 million square miles (around 361 square kilometers). And despite more than a hundred years of scientific study, there is still a lot we don’t know.
Among them are some creepy facts that will likely induce a bad case of Thalassophobia. Here are some examples, as shared by people on Reddit when the topic came up in a recent thread.
From “rogue waves” to “dark fish,” here are some of the most disturbing things shared in the discussion.
#1

Diel vertical migration (DVM) is the largest daily animal migration on Earth, involving trillions of marine organisms—including zooplankton, krill, squid, and fish—moving from the deep sea to the surface at night to feed and returning to the depths by dawn. This behavior helps creatures avoid visual predators during daylight, driven by light cycles.
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20points
#2

I watched one of the David Attenborough documentaries and there’s actually a super salty lake somewhere in the ocean. It’s surrounded by all these dead fish and sea creatures because the salinity is so high it kills any living thing that ventures in it.
20points
#3

Many of us have heard about rogue waves, but apparently there exists the complete opposite of that, a "rogue hole" which is when one is suddenly met with a gap between the ocean waves that yawns open and can dip down to possibly a 100 ft.
I don't know why, but something tells me that if such a thing exists, it would be far more destructive and fatal compared to a rogue wave as it would seem impossible trying to maneuver out of literally being swallowed up by the ocean.
Edit: Here's some survival stories of those who encountered this deadly phenomenon.
Johnny Savage and the Anhinga (1998): Fisherman Johnny Savage describes encountering a "hole in the ocean" during a 350-mile trip from Key West to Cancun. He described it as a sudden, massive void ahead of them, causing the boat to fall completely off into it. The 56-foot boat was destroyed instantly, forcing Savage and his captain, Eric Bingham, into the water within minutes without any time to make a distress call or grab safety gear.
The Rose-Noelle Crew (1989): Four sailors survived 118 days adrift off the coast of New Zealand after their trimaran was upturned by a massive, violent wave, leaving them in an inverted hull, which is a common outcome of such, a "hole" or trough-related incident.
"Pitchpoling" off the Golden Gate: A sailor reported a "rogue hole" event during a race outside the Golden Gate, describing a sailboat dropping into a deep trough near a seamount, effectively sailing "off a cliff" and almost turning end-over-end (pitchpoling).
Yachting World Account (1980s): A sailor described being on a vessel that was hit by a massive wave that caused the world to go black, as they were thrown into a trough so deep they were effectively trapped inside a "hole." The wheel was ripped off, and the vessel was left severely damaged, but they survived. .
I don't know why, but something tells me that if such a thing exists, it would be far more destructive and fatal compared to a rogue wave as it would seem impossible trying to maneuver out of literally being swallowed up by the ocean.
Edit: Here's some survival stories of those who encountered this deadly phenomenon.
Johnny Savage and the Anhinga (1998): Fisherman Johnny Savage describes encountering a "hole in the ocean" during a 350-mile trip from Key West to Cancun. He described it as a sudden, massive void ahead of them, causing the boat to fall completely off into it. The 56-foot boat was destroyed instantly, forcing Savage and his captain, Eric Bingham, into the water within minutes without any time to make a distress call or grab safety gear.
The Rose-Noelle Crew (1989): Four sailors survived 118 days adrift off the coast of New Zealand after their trimaran was upturned by a massive, violent wave, leaving them in an inverted hull, which is a common outcome of such, a "hole" or trough-related incident.
"Pitchpoling" off the Golden Gate: A sailor reported a "rogue hole" event during a race outside the Golden Gate, describing a sailboat dropping into a deep trough near a seamount, effectively sailing "off a cliff" and almost turning end-over-end (pitchpoling).
Yachting World Account (1980s): A sailor described being on a vessel that was hit by a massive wave that caused the world to go black, as they were thrown into a trough so deep they were effectively trapped inside a "hole." The wheel was ripped off, and the vessel was left severely damaged, but they survived. .
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18points
#4

As soon as you go into it, you are not the top of the food chain.
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18points
#5

90% of the ocean receives zero sunlight, ever. It's 100% pitch darkness 100% of the time.
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17points
#6

A guy I talked to was a deep sea diver. It gets pitch black fairly quickly when you're diving down. He said you get used to things bumping into you down there.
16points
#7

We’ve discovered entire ecosystems can exist from thermal vents at super deep depths. Places where we assumed life was impossible and they’re basically isolated alien worlds which we have only had a glimpse of.
15points
#8

Point Nemo. It's not a an island, just a gps location in the South Pacific. If you go there the nearest human is on the ISS.
14points
#9

The largest sunken ships aren't even a speck in their vastness.
The Pacific is larger than every continent COMBINED, and it's surface area is greater than the surface area of Mars.
The Pacific is larger than every continent COMBINED, and it's surface area is greater than the surface area of Mars.
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14points
#10

A lot of folks think if you see a dolphin you’re safe from sharks, because they dislike each other. But it’s a myth. They feed on the same fish, so if one is in the area, the other is like to be as well.
Guess who saw a dolphin fin pop out of a wave next to them after learning this fun fact on the way to a morning surf?
Also, if you almost drown by getting whomped by an entire set of waves twice as big as anything you’ve been in the water for, and end up chilling on the beach to recover after being dragged across the bottom of the ocean in water well over your head, only knowing which way to fight towards the surface because of the tether pulling you straight into the next wave ready to throw a board a few feet too long right at your head, a sea lion might just come by and sit next to you, and it is way more frightening to be next to one of those than it sounds. Especially while sitting down, unsure of what happens if you try to get up and don’t have the energy to run.
Guess who saw a dolphin fin pop out of a wave next to them after learning this fun fact on the way to a morning surf?
Also, if you almost drown by getting whomped by an entire set of waves twice as big as anything you’ve been in the water for, and end up chilling on the beach to recover after being dragged across the bottom of the ocean in water well over your head, only knowing which way to fight towards the surface because of the tether pulling you straight into the next wave ready to throw a board a few feet too long right at your head, a sea lion might just come by and sit next to you, and it is way more frightening to be next to one of those than it sounds. Especially while sitting down, unsure of what happens if you try to get up and don’t have the energy to run.
14points
#11
The city of Thonis-Heracleion was discovered in 2000, after going missing for 1,200 years, having vanished overnight.
At the end of the last Ice Age, sea levels rose by about 120 metres. We have found thousands of human settlements. Rising sea levels is real. It has already happened and will continue to happen.
At the end of the last Ice Age, sea levels rose by about 120 metres. We have found thousands of human settlements. Rising sea levels is real. It has already happened and will continue to happen.
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14points
#12

I remember reading a thread someone was joking that physics got all the good stuff and biology never had anything spooky, as a joke they said 'there's dark energy but no dark birds'
Anyway someone responded that, apparently there's evidence of a huge amount of fish. Like the ecology suggests this huge population and there's sonar to support it but no-one has ever seen them.
Supposedly there's 'dark fish'.
Anyway someone responded that, apparently there's evidence of a huge amount of fish. Like the ecology suggests this huge population and there's sonar to support it but no-one has ever seen them.
Supposedly there's 'dark fish'.
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13points
#13

Occasionally I look through the Internet if something new was discovered. Like that nightmare bigfin squid.
I love the ocean.
I love the ocean.
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13points
#14
In Northern Queensland, there are several types of Cubozoa Jellyfish with deadly neurotoxins in their tentacles. They are all transparent, and several can paralyse your respiratory system within 5 minutes. One of the most lethal, the Irukandji, is not only transparent... it's smaller than your thumbnail. You literally will not know what hit you.
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13points
#15
When a whale dies, it will (eventually) sink to the bottom of the ocean. Given the lack of nutrients >1000 m below the surface, these whale carcasses (known as "whale falls") become their own little ecosystem sustaining life for decades at a time.
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13points
#16
It’s 95% unexplored… which is ocean-speak for “probably haunted, probably angry, and definitely judging your floaties.”.
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13points
#17

When you swim in the ocean you’re moving through a bacterial soup with millions of cells per teaspoon, a large proportion of which are actively dying microbes being lysed open by viruses.
12points
#18
Im a dive instructor so i know a bit about the ocean. Of all things ocean, the only thing that I find extremely errie, is how phucking dark it is. The real wild ocean is so dark you cant even see your hand. If you fell off a cliff without a flashlight, if you fell off a massive cargo ship, or oil rig, you're 100% dead. 0% chance of survival. If you had a chance, you have less than 10 minutes.
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11points
#19
Ghost Ships: Vessels are occasionally found perfectly intact with no sign of crew, a phenomenon reported even in recent years.
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11points



