3 Causes of Ocean Currents: Tide, Wind, and Thermohaline Circulation Which Takes Nearly 1,000 Years

1. Tidal Currents
Tidal currents are most powerful near the shore, particularly in bays and estuaries along our coasts. To understand this better, picture how water behaves as the tide changes. When the tide rises, water moves inland in what's called a flood current. When the tide recedes, the water flows back out to sea, forming an ebb current. A great way to visualize this is by watching the movement of green seaweed along the shore.
Now, let's zoom out to see what's happening on a global scale near the ocean's surface over time. At this broader level, ocean currents are primarily driven by two major forces. The first one is something we’re all familiar with: wind.
2. Wind
This animation, produced by NASA's Goddard Space Flight Center, shows surface ocean currents around the world between June 2005 and December 2007. You can find a link to the full animation in our show notes.
Let’s take a moment to explore some of the most significant surface ocean currents. See that swirling motion? That’s the Gulf Stream, a powerful, warm ocean current in the western North Atlantic. It moves nearly four billion cubic feet of water every second.
Now, let’s pick up the pace and look at another remarkable current.
Coming into view now is the Kuroshio Current, which flows off the east coast of Japan. This is the largest ocean current, traveling between 25 and 75 miles per day, and it's equivalent in volume to 6,000 large rivers.
Surface ocean currents in the open ocean are astonishingly complex and mesmerizing, driven by a global wind system. But there’s one more force behind ocean currents that you might not have heard of: thermohaline circulation.
3. Thermohaline Circulation
"Thermo" refers to heat, and "haline" refers to salinity. Together, these terms describe how changes in temperature and salt content continually alter the density of ocean water. Cold, salty water is dense and sinks to the ocean's depths, eventually rising back to the surface through mixing and wind-driven upwelling.
On a global scale, this continuous sinking and rising of ocean water creates what scientists call the "great ocean conveyor belt."
This conveyor belt plays a crucial role in regulating Earth's climate by circulating warm water from the Equator and cold water from the poles around the globe. It takes nearly 1,000 years for water to complete its journey through the entire conveyor belt.
So there you have it. Tides, wind, heat, and salinity are all forces that set the ocean in motion.
Credits:
Thermohaline Circulation using Improved Flow Field:
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The Thermohaline Circulation - The Great Ocean Conveyor Belt - Stereoscopic Version:
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Dynamic Earth:
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NOS Center for Operational Oceanographic Products and Services:
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