The motion of the ocean: The concentration gradient - Sasha Wright
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0:06 - 0:10If you've ever floated on an ocean swell,
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0:10 - 0:13you'll know that the sea moves constantly.
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0:13 - 0:15Zoom out, and you'll see the larger picture:
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0:15 - 0:18our Earth, covered by 71 percent water,
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0:18 - 0:22moving in one enormous current around the planet.
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0:22 - 0:24This intimidating global conveyor belt
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0:24 - 0:26has many complicated drivers,
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0:26 - 0:28but behind it all is a simple pump
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0:28 - 0:31that moves water all over the earth.
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0:31 - 0:34The process is called thermohaline circulation,
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0:34 - 0:36and it's driven by a basic concept:
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0:36 - 0:43the concentration gradient.
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0:43 - 0:45Let's leave the ocean for one moment
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0:45 - 0:47and imagine we're in an empty room
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0:47 - 0:49with lots of Roombas sardined together
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0:49 - 0:51in one corner.
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0:51 - 0:52Turn them all on at once
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0:52 - 0:54and the machines glide outwards
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0:54 - 0:56bumping into and away from each other
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0:56 - 1:00until the room is filled with an evenly spaced distribution.
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1:00 - 1:02The machines have moved randomly
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1:02 - 1:04towards equilibrium,
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1:04 - 1:06a place where the concentration of a substance
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1:06 - 1:08is equally spread out.
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1:08 - 1:11That's what happens along a concentration gradient,
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1:11 - 1:13as substances shift passively from a high,
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1:13 - 1:15or squashed, concentration,
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1:15 - 1:18to a lower, more comfortable one.
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1:18 - 1:21How does this relate to ocean currents and thermohaline circulation?
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1:21 - 1:23Thermo means temperature,
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1:23 - 1:25and haline means salt
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1:25 - 1:27because in the real world scenario of the sea,
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1:27 - 1:30temperature and salinity drive the shift
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1:30 - 1:33from high to low concentrations.
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1:33 - 1:35Let's put you back in the ocean
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1:35 - 1:37to see how this works.
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1:37 - 1:38Snap!
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1:38 - 1:41You're transformed into a molecule of surface water,
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1:41 - 1:43off the temperate coast of New York
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1:43 - 1:45surrounded by a zillion rowdy others.
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1:45 - 1:48Here, the sun's rays act as an energizer
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1:48 - 1:50that set you and the other water molecules
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1:50 - 1:52jostling about, bouncing off each other
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1:52 - 1:54like the Roombas did.
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1:54 - 1:55The more you spread out,
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1:55 - 1:57the less concentrated the water molecules
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1:57 - 1:59at the surface become.
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1:59 - 2:00Through this passive motion,
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2:00 - 2:04you move from a high to a lower concentration.
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2:04 - 2:06Let's suspend the laws of physics for a moment,
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2:06 - 2:08and pretend that your molecular self
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2:08 - 2:11can plunge deep down into the water column.
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2:11 - 2:12In these colder depths,
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2:12 - 2:14the comparative lack of solar warmth
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2:14 - 2:16makes water molecules sluggish,
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2:16 - 2:20meaning they can sit quite still at high concentrations.
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2:20 - 2:21No jostling here.
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2:21 - 2:23But seeking relief
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2:23 - 2:24from the cramped conditions they're in,
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2:24 - 2:26they soon start moving upwards
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2:26 - 2:29towards the roomier situation at the surface.
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2:29 - 2:30This is how temperature
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2:30 - 2:32drives a shift of water molecules
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2:32 - 2:34from high to low concentrations,
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2:34 - 2:36towards equilibrium.
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2:36 - 2:39But sea water is made up of more than just H2O.
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2:39 - 2:43There are a great deal of salt ions in it as well.
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2:43 - 2:45And like you, these guys have a similar desire
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2:45 - 2:47for spacious real estate.
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2:47 - 2:48As the sun warms the sea,
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2:48 - 2:50some of your fellow water molecules
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2:50 - 2:52evaporate from the surface,
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2:52 - 2:55increasing the ration of salt to H2O.
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2:55 - 2:57The crowded salt ions left behind
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2:57 - 2:59notice that lower down,
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2:59 - 3:01salt molecules seem to be enjoying more space.
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3:01 - 3:03And so an invasion begins,
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3:03 - 3:06as they too move downwards in the water column.
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3:06 - 3:08In the polar regions,
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3:08 - 3:10we see how this small local process
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3:10 - 3:11effects global movement.
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3:11 - 3:13In the arctic and antarctic,
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3:13 - 3:15where ice slabs decorate the water's surface,
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3:15 - 3:17there's little temperature difference
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3:17 - 3:19between surface and deeper waters.
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3:19 - 3:21It's all pretty cold.
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3:21 - 3:22But salinity differs,
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3:22 - 3:23and in this scenario,
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3:23 - 3:25that's what triggers the action.
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3:25 - 3:27Here, the sun's rays melt surface ice,
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3:27 - 3:30depositing a new load of water molecules
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3:30 - 3:31into the sea.
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3:31 - 3:33That not only increases the proximity
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3:33 - 3:36between you and other water molecules,
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3:36 - 3:38leaving you vying for space again,
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3:38 - 3:40but it also conversely dilutes
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3:40 - 3:42the concentration of salt ions.
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3:42 - 3:43So, down you go,
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3:43 - 3:45riding along the concentration gradient
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3:45 - 3:47towards more comfortable conditions.
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3:47 - 3:49For salt ions, however,
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3:49 - 3:51their lower concentration at the surface,
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3:51 - 3:53acts like an advertisement
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3:53 - 3:55to the clamoring masses of salt molecules below
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3:55 - 3:57who begin their assent.
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3:57 - 3:59In both temperate and polar regions,
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3:59 - 4:02this passive motion along a concentration gradient,
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4:02 - 4:04can get a current going.
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4:04 - 4:06And that is the starting point
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4:06 - 4:07of the global conveyor
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4:07 - 4:09called thermohaline circulation.
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4:09 - 4:11This is how a simple concept
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4:11 - 4:13becomes the mechanism underlying
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4:13 - 4:14one of the largest
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4:14 - 4:16and most important systems on our planet.
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4:16 - 4:17And if you look around,
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4:17 - 4:19you'll see it happening everywhere.
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4:19 - 4:20Turn on a light, and it's there.
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4:20 - 4:22Concentration gradients govern
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4:22 - 4:24the flow of electricity,
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4:24 - 4:26allowing electrons squashed together in one space
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4:26 - 4:29to travel to an area of lower concentration
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4:29 - 4:31when a channel is opened,
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4:31 - 4:33which you do by flipping a switch.
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4:33 - 4:35Right now, in fact, there's some gradient action going on
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4:35 - 4:39inside you as you breath air into your lungs
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4:39 - 4:41letting the concentrated oxygen in that air
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4:41 - 4:43move passively out of your lungs
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4:43 - 4:45and into your blood stream.
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4:45 - 4:47We know that the world is filled
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4:47 - 4:49with complex physical problems,
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4:49 - 4:50but sometimes the first step
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4:50 - 4:53towards understanding them can be simple.
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4:53 - 4:54So when you confront the magnitude
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4:54 - 4:55of the ocean's currents,
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4:55 - 4:58or have to figure out how electricity works,
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4:58 - 4:59remember not to panic.
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4:59 - 5:02Understanding can be as simple as flipping a switch.
- Title:
- The motion of the ocean: The concentration gradient - Sasha Wright
- Description:
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View full lesson: http://ed.ted.com/lessons/the-motion-of-the-ocean-the-concentration-gradient-sasha-wright
The constant motion of our oceans represents a vast and complicated system involving many different drivers. Sasha Wright explains the physics behind one of those drivers -- the concentration gradient -- and illustrates how our oceans are continually engaging in a universal struggle for space.
Lesson by Sasha Wright, animation by Andrew Foerster.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:20
Jenny Zurawell edited English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright | ||
Jennifer Cody approved English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright | ||
Jennifer Cody accepted English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright | ||
Jennifer Cody edited English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright | ||
Jennifer Cody edited English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright | ||
Caroline Cristal edited English subtitles for The motion of the ocean: The concentration gradient - Sasha Wright |