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Uploaded:2021-04-21
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From spooky-looking towers that belch white "smoke" to a mountain range in the middle of the Atlantic ocean, the seafloor is full of features as dynamic as the surface! That's part of why we've done many SciShow episodes about the ocean. Here are 5 episodes about the intense, and sometimes invaluable features under the water!

Hosted by: Michael Aranda

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Original episodes and sources:

The Most Incredible Snowfall on Earth Occurs Deep Underwater
https://www.youtube.com/watch?v=BAvQ3t4ueZw

The Scientist Who Mapped the Seafloor: Marie Tharp | Great Minds
https://www.youtube.com/watch?v=-mOjsn5UrWM

The Lost City and the Origin of Life
https://www.youtube.com/watch?v=BFExaMByzYw

The Deep-Sea Snail with an Iron Shell
https://www.youtube.com/watch?v=_d-us3DL5Kk

How the Ocean Floor Got Filled with Riches
https://www.youtube.com/watch?v=J6uULoBsTJo

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MICHAEL: The ocean is an incredibly mysterious place which is part of the why we've done so many Sci Show episodes about it. But the ocean isn't just fascinating because cool things live there, there are also ghostly towers, mountain ranges longer than continents, and all kinds of other features you wouldn't expect under the water. So, let's dive in. 

First, when you think of the ocean, snow probably isn't what comes to mind. But arguably the most amazing snowfall on earth happens deep underwater, it's just not the kind of snow you're thinking about. Here's hank with more. 

HANK: If you're taking a trip to the deep ocean, you should know the forecast. It's going to be cold and dark with a high chance of snow. Okay, well, not snow as in ice crystals like up here on the surface of the planet, we're talking about marine snow. It looks like snow. It is not. It's comprised of fluffy buts of organic matter that range in size from about half a millimeter to several centimeters across. And this snow isn't just pretty, it's an essential part of our ocean food webs and our global climate. 

Now, organic matter can refer to pretty much anything that is or was alive, but in this case, we're generally talking bout the remains of plankton. Plankton is a catch-all term for the organisms that are largely at the mercy of water current. And they're often tiny, things like algae, bacteria, protozoans, little crustaceans like krill, and even the early life stages of much larger animals.

When these creatures die, what's left of their bodies starts to sink, becoming part of marine snow. Not all these snow particles are part of dead plankton though, some are fecal pellets. It's gotta go somewhere. Marine snow also contains decomposers like bacteria that attach themselves to the falling poo in tiny carcasses

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and as the different bits descend, they clump together to form larger and larger flakes, which eventually give the appearance of a blizzard far below the waves. 

And this snowfall brings something very important to deeper waters: food. See, in the shallow ocean where sunlight beams through the water, plankton that can photosynthesize are the base of the food web, just like the plants that are the base of the food web up on land. 

And in some places in the deep ocean, there are nutrient-rich areas like hydrothermal vents which provide food for special bacteria that can form the base of their own ecosystems. Instead of using light for energy, these bacteria turn carbon dioxide into sugars by tinkering with chemicals like hydrogen sulfide, a process called chemosynthesis.

But most of the deep seafloor doesn't have these vents, and in the water column below about a thousand meters, there is no sunlight, so locally produced food is very scarce. And yet, life persists because what they need drifts down from above. Many animals eat the falling particles as they drift down through the water column like this larvacean.

The animal itself is just a small tadpole-like thing in the middle, the rest is the giant mucous net it constructs to catch and concentrate the descending organic matter. Over time though, the net clogs, so the larvacean tosses it and makes a new one. Of course in the deep, nothing goes to waste, and Mbari researchers have found that the mucous snowballs are an important source of food for other animals, like this vampire squid.
And at the seafloor, other filter feeders and scavengers scoop up even more of the falling snow. Even with all these hungry mouths though, some of the snow sticks. The particles that don't get eaten settle on the bottom and as they decompose, they form a nutrient-rich top soil-like ooze that coats much of the vast seafloor. This is all part of one of the most important 




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biogeochemical processes on the planet, the carbon cycle which is key to understanding climate change.

As far as we know, all life on earth needs carbon. It's a key component in essential molecules like DNA and RNA and the fats that make up our cell membranes.

So the distribution of carbon in different environments can influence what lives there, like without the carbon and other nutrients that sink from the shallows, most deep-sea organisms wouldn't exist. But this snow doesn't just impact life in the deep by playing a role in the carbon cycle, it affects all life on earth, including us. That's because the carbon these plankton have in their bodies had to enter the seawater from somewhere.

That somewhere is generally the atmosphere because it falls with the rain or it directly diffuses into the water. Once in seawater, carbon can be used by organisms to build their bodies and shells. Then when those organisms are digested by predators or decomposers, the carbon can be released as carbon dioxide.

If this happens in the shallows, it can diffuse back into the atmosphere. But marine snow pulls carbon from this water to air cycle and tucks it away in oozes on the seafloor. In places that this ooze builds up, it's gradually been pressed into huge deposits of chalk and other forms of limestone.

These rocks now cover roughly 3 billion square kilometers of the seafloor. In some spots, they're hundreds of meters thick.  In fact, these carbon-loaded rocks are the earth's biggest carbon storage unit. The carbon can eventually return to the surface.

Techtonic activity can push these ocean rocks beneath continents, where they may melt, rise upwards, and fuel volcanoes that pump CO2 into the atmosphere when they erupt. but that takes many millions of years. Until then the carbon is essentially locked away. Over time, marine snow has been storing more and more carbon into the depths.

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