ocean circulation

Water in the oceans is in constant motion driven by tidal forces, density^* differences, and winds. Winds create surface currents by transferring energy to the water by friction. The direction of a wind-driven surface current is determined by how the transferred wind energy interacts with Coriolis deflection, other currents, and geological features such as continents and island arcs.

A major feature of the surface current systems in all of Earth's large ocean basins is a central gyre. These gyres move water in large, roughly circular patterns around each ocean basin's center.

Circulation in the oceans helps transport the solar energy that falls at the equator towards the poles. Like the atmosphere, uneven heating drives this flow of energy poleward. Unlike the atmosphere, the oceans are warmed from the top-down rather than from the bottom up, so heat-driven convection is not enough to cause ocean circulation. For density-driven circulation to mix the oceans at a large enough scale to matter, changes in both temperature and salinity are required.