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# Ocean Currents

## Making Waves: Episode 123

In this episode: You know about ocean tides, but how much do you know about ocean currents? Watch our three-minute video podcast to learn what puts the motion in the ocean.

### Transcript

This is Making Waves from NOAA's National Ocean Service. 

The ocean never stands still. Even here in this quiet marina,  you can see the water is slowly moving. 

If you stood at this spot for many hours, you'd witness one of  the most reliable and predictable features of the ocean: the rise and fall of  the tide, caused by the gravitational pull of the moon and the sun on our  planet. 

But what's causing the motion you see here with this gently  swaying anemone on the sea floor off the Atlantic Coast? This is ocean current.  The reason we have currents in the ocean is a bit more complicated. 

Let's go back to the shoreline to witness one cause of ocean  currents. Tides. 

**1. Tidal Currents**

Tidal currents are  strongest near the shore, in bays, and in estuaries along our coasts.  This illustration will give you an idea of how this works. As the tide rises, water moves inland. This  is called a flood current. As the tide recedes, the water moves seaward.  This is called an ebb current. You can  see the movement of water by watching the green seaweed. 

Now let's zoom out and look at what's happening near the surface  of the ocean on a global scale over time. At this scale, currents are driven primarily by two different  forces.  The first force is something we all know: wind. 

**2. Wind**

This animation is from NASA's Goddard Space Flight Center. It  shows surface ocean currents around the world during the period from June 2005  to December 2007. Check our show notes for a link to the full animation. 

Let's take a few moments to look at a few prominent surface  ocean currents.  See that? You've probably heard of this current. It's called the  Gulf Stream. 

The Gulf Stream is an intense, warm ocean current in the western  North Atlantic. It transports nearly four billion cubic feet of water per  second. 

Now let's speed up a bit and to go look at another special  current. 

Coming into view now is the Kuroshio Current, located off the  east coast of Japan. This is the ocean's largest current. It can travel between  25-75 miles a day and is equal in volume to 6,000 large rivers. 

Surface ocean currents on the open ocean are fantastically  complicated and beautiful, driven by a complex global wind system. 

But there's one more ocean current force that  you may have never heard of. It's called thermohaline circulation.

**3. Thermohaline Circulation**

Thermo means 'heat,' and 'haline' refers to salinity. This term  describes how changes in heat and salt content constantly change the density of  ocean water. Cold, salty water is dense and sinks to the bottom of the ocean and eventually returns to the surface through  mixing and wind driven upwelling. 

On a global scale, this sinking and rising of ocean water  creates what scientists call the 'great ocean conveyor belt.’ 

This conveyor belt affects the Earth's climate by driving warm  water from the Equator and cold water from the poles around the Earth. It takes  water almost 1000 years to move through the whole conveyor belt. 

So there you have it. Tides, wind, heat, and salinity are all  factors that put the motion in the ocean.

CREDITS: 

            - NOS Center for Operational Oceanographic Products and Services
            - NASA's Goddard Space Flight Center

From corals to coastal science, catch the current of the ocean with our audio and video podcast, **Making Waves**. 

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