00:00In 1992, a cargo ship carrying bath toys got caught in a storm.
00:12Shipping containers washed overboard,
00:14and the waves swept 28,000 rubber ducks and other toys into the North Pacific.
00:20But they didn't stick together.
00:22Quite the opposite.
00:24The ducks have since washed up all over the world,
00:27and researchers have used their paths to chart a better understanding of ocean currents.
00:33Ocean currents are driven by a range of sources—
00:36the wind, tides, changes in water density, and the rotation of the Earth.
00:43The topography of the ocean floor and the shoreline modifies those motions,
00:47causing currents to speed up, slow down, or change direction.
00:52Ocean currents fall into two main categories—
00:55surface currents and deep ocean currents.
00:58Surface currents control the motion of the top 10% of the ocean's water,
01:02while deep ocean currents mobilize the other 90%.
01:06Though they have different causes, surface and deep ocean currents influence each other
01:11in an intricate dance that keeps the entire ocean moving.
01:15Near the shore, surface currents are driven by both the wind and tides,
01:19which draw water back and forth as the water level falls and rises.
01:24Meanwhile, in the open ocean, wind is the major force behind surface currents.
01:29As wind blows over the ocean, it drags the top layers of water along with it.
01:34That moving water pulls on the layers underneath, and those pull on the ones beneath them.
01:39In fact, water as deep as 400 meters is still affected by the wind at the ocean's surface.
01:47If you zoom out to look at the patterns of surface currents all over the Earth,
01:51you'll see that they form big loops called gyres,
01:54which travel clockwise in the Northern Hemisphere
01:57and counterclockwise in the Southern Hemisphere.
02:00That's because of the way the Earth's rotation affects the wind patterns
02:04that give rise to these currents.
02:06If the Earth didn't rotate, air and water would simply move back and forth
02:10between low pressure at the equator and high pressure at the poles.
02:14But as the Earth spins, air moving from the equator to the North Pole is deflected eastward,
02:20and air moving back down is deflected westward.
02:24The mirror image happens in the Southern Hemisphere,
02:27so that the major streams of wind form loop-like patterns around the ocean basins.
02:32This is called the Coriolis effect.
02:35The winds push the ocean beneath them into the same rotating gyres.
02:40And because water holds onto heat more effectively than air,
02:43these currents help redistribute warmth around the globe.
02:48Unlike surface currents, deep ocean currents are driven primarily by changes in the density of seawater.
02:55As water moves towards the North Pole, it gets colder.
02:58It also has a higher concentration of salt because the ice crystals that form trap water
03:04while leaving salt behind.
03:05This cold, salty water is more dense, so it sinks,
03:09and warmer surface water takes its place,
03:12setting up a vertical current called thermohaline circulation.
03:17Thermohaline circulation of deep water and wind-driven surface currents
03:21combine to form a winding loop called the global conveyor belt.
03:26As water moves from the depths of the ocean to the surface,
03:29it carries nutrients that nourish the microorganisms which form the base of many ocean food chains.
03:35The global conveyor belt is the longest current in the world,
03:39snaking all around the globe, but it only moves a few centimeters per second.
03:44It could take a drop of water a thousand years to make the full trip.
03:49However, rising sea temperatures are causing the conveyor belt to seemingly slow down.
03:54Models show this causing havoc with weather systems on both sides of the Atlantic,
03:59and no one knows what would happen if it continues to slow or if it stopped altogether.
04:04The only way we'll be able to forecast correctly and prepare accordingly
04:09will be to continue to study currents and the powerful forces that shape them.
04:13What about the creatures that adapted to survive in these swirling seas?
04:19Take a closer look at some truly fascinating ocean dwellers with these two animations.
04:25What about the creatures that have fallen around the globe?
04:29Take a closer look at the planet.
04:31What about the creatures that
04:33are actually in a material space?
04:42It's a great dream.
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