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  • Thanks to the Monterey Bay Aquarium Research Institute

  • for partnering with us on this episode of SciShow.

  • All of the amazing deep-sea videos you are about to see

  • were taken with their remotely operated vehicles.

  • [♪ INTRO]

  • If you're taking a trip to the deep ocean, you should know the forecast:

  • it's gonna be cold and dark, with a high chance of snow.

  • Okay, well, not snow as inice crystalslike 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 bits 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 mattercan refer to pretty much anything that is or was alive.

  • But in this case, we're generally talking about the remains of plankton.

  • Plankton is a catch-all term for organisms that are largely at the mercy of water currents.

  • 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 of these snow particles are 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 and tiny carcasses.

  • And as the different bits descend, they clump together to form larger and largerflakes”,

  • which eventually give the appearance of a blizzard far below the waves.

  • And thissnowfallbrings 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 sea floor 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 mucus 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.

  • MBARI researchers have found that these mucus 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, topsoil-like ooze that coats much of the vast seafloor.

  • This is all part of one of the most important 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.

  • Thatsomewhereis generally the atmosphere,

  • because it falls with 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 three billion square kilometers of the seafloor.

  • And 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.

  • Tectonic activity can push these ocean rocks beneath continents,

  • where they may melt, and rise upward,

  • 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 in the depths.

  • According to a 2019 modeling study,

  • around eighty million years ago during the Cretaceous Period,

  • when dinosaurs like Velociraptor roamed the land,

  • about one million tons of carbon in the form of carbonate

  • were stored each year in deep-sea sediments.

  • But today, scientists estimate over two hundred million are stored annually!

  • And all the carbon in the deep because of marine snow

  • may have paved the way for our current, comfortable climate.

  • See, over that same time period, our planet cooled dramatically,

  • shifting from the warmerhothouseof the Cretaceous Period

  • to our currenticehouseconditions, where we have permanent ice caps,

  • widespread grasslands, and a cooler climate.

  • That's because carbon dioxide in the atmosphere acts as a greenhouse gas,

  • one that absorbs and traps heat.

  • So though there are other things involved, in general,

  • the less CO2 we have in our atmosphere, the cooler our planet is.

  • And when more of the planet's carbon is in rocks, there's less in the atmosphere.

  • Of course these days, we've been reversing all of that carbon storage.

  • We're essentially doing what takes volcanoes millions of years in a geologic instant

  • by burning fossil fuels and cutting down forests.

  • And because of our actions, we're causing the CO2 level in our atmosphere to rise

  • and fundamentally changing our climate.

  • That's why scientists are so eager to understand

  • how our activities affect marine snow.

  • It will give them a better sense of

  • how the planet will change in the years, decades, and centuries to come.

  • We do not want to go back to the hothouse of the Cretaceous,

  • so in addition to taking some steps to reduce emissions,

  • we want marine snow to keep pulling carbon down into the depths.

  • Right now, our ocean is doing us a very big favor.

  • Thanks in part to MBARI's crew of robotic floats,

  • we know that it soaks up a quarter of the excess carbon dioxide

  • we pump into the atmosphere and more than 90% of the planet's excess heat.

  • But as atmospheric CO2 levels rise, more carbon dioxide enters the ocean,

  • and that makes the water more acidic,

  • which can disrupt the formation of carbon-storing oozes.

  • That acidity is also messing with plankton communities,

  • which could ultimately affect how much carbon makes it down to the ocean floor.

  • So scientists are keeping a close eye on marine snow

  • and how it is or isn't changing in response to our actions.

  • Because if current trends continue,

  • we're gonna need all the carbon-storing help we can get.

  • Thank you again to the amazing people at the Monterey Bay Aquarium

  • and their research and technology partner MBARI

  • for collaborating with us on this episode of SciShow.

  • MBARI's mission is to advance marine science and engineering

  • to understand our changing ocean.

  • You can learn more about their work by following their social media accounts.

  • They have an amazing YouTube channel

  • featuring weird and wonderful deep-sea creatures.

  • You can also visit their website at mbari.org.

  • [♪ OUTRO]

Thanks to the Monterey Bay Aquarium Research Institute

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B2 中高級

地球上最不可思議的降雪發生在水下深處。 (The Most Incredible Snowfall on Earth Occurs Deep Underwater)

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    林宜悉 發佈於 2021 年 01 月 14 日
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