What Are Ocean Currents?

Ocean currents are steady flows of seawater in one direction. Wind drives the currents near the surface, tides drive currents near the coast, and differences in temperature and salt drive slow currents deep below.

Last updated 11 October 2026

How it works

1. Wind pushes the surface. Winds blowing across the ocean drag the top layer of water with them. This sets the surface currents moving, down to a depth of about 100 m.
2. Earth's spin bends the flow. The Coriolis effect Coriolis effect. Earth's rotation turns moving water and air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Source deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Over a whole ocean this turns the currents into giant loops called gyres Gyre. A large system of rotating ocean currents. There are five major gyres: the North and South Pacific, the North and South Atlantic, and the Indian Ocean. Source .
3. Coasts steer the loops. On the western side of each ocean the flow is squeezed into a strong, narrow, warm current such as the Gulf Stream Western boundary current. The strong, narrow, warm current on the western side of a gyre, such as the Gulf Stream. The eastern side has a weak, broad current. Source . On the eastern side the return flow is weak, broad and cool.
4. Cold, salty water sinks. Near the poles, sea ice forms and leaves its salt behind. The water around it gets saltier and denser and sinks, starting the deep currents of thermohaline circulation Thermohaline circulation. Deep ocean flow driven by differences in water density, which depend on temperature (thermo) and salt (haline). Also called the global conveyor belt. Source .
5. Deep water comes back up. The deep current spreads through the oceans, warms, rises to the surface Upwelling. Wind pushes surface water away and cold, nutrient-rich water rises from below to replace it. Source and flows back to the North Atlantic, closing the global conveyor belt.

Surface, tidal and deep currents compared

NOAA groups ocean currents by what drives them. The three kinds work at different depths and speeds.

Key facts

1. Ocean currents are driven by three main factors: tides, wind and thermohaline circulation. NOAA Ocean Service, What is a current?
2. Tidal currents are strongest near the shore and in bays and estuaries. In some places they reach eight knots (about 15 km/h) or more. NOAA Ocean Service, What is a current?
3. Wind moves surface water only to a depth of about 100 m. Each deeper layer moves more slowly, turned a little more by the Coriolis effect, in a pattern called the Ekman spiral. NOAA Ocean Service, The Ekman spiral
4. Currents affect climate by moving warm water away from the equator and cold water away from the poles. The warm Gulf Stream gives Bergen, Norway, milder winters than New York, far to the south. NOAA Ocean Service, What is a current?
5. It is estimated that a cubic meter of water takes about 1,000 years to complete the journey along the global conveyor belt. NOAA Ocean Service, The global conveyor belt
6. Where winds push surface water away, deep, cold, nutrient-rich water rises to replace it. Good fishing grounds are often found where this upwelling is common. NOAA Ocean Service, What is upwelling?

Real-world examples

The western and eastern sides of the five major gyres, from the NOAA gyre figure. Notice the pattern: on this figure the western side is warm in every gyre.

Data source: NOAA Ocean Service gyre figure, traced by EarthMapped, Public domain (US government work).

The global conveyor belt

The deep currents link every ocean into one loop. It begins at the surface near the pole in the North Atlantic, where the water is chilled and gets saltier as sea ice forms. This cold, dense water sinks and flows south along the bottom of the western Atlantic, past the equator, to Antarctica. There it is recharged with more cold, salty water, then splits: one branch heads into the Indian Ocean, the other into the Pacific. Both warm, rise and loop back to the South Atlantic and on to the North Atlantic, where the cycle starts again.

For students

Picture the ocean as a giant bathtub that never sits still. Wind blowing over it pushes the top layer of water along, like blowing across a cup of soup. Because Earth spins, that moving water does not go straight: it curves into big circles. Far below, very cold and salty water is heavier, so it sinks to the bottom and creeps slowly around the world. Together these flows carry heat from the warm tropics toward the cold poles, which changes the weather on land.

See every major current on the ocean currents map, the five loops on the ocean gyres map, the best known warm current on the Gulf Stream map, and the sea bed below on the ocean floor map.