Ocean Currents

Global thermohaline circulation and surface wind-driven currents

Ocean currents are driven by two main mechanisms: wind (surface currents) and density differences (deep thermohaline circulation). Trade winds and westerlies push surface water, while the Coriolis effect deflects currents to the right in the Northern Hemisphere and left in the Southern. This creates circular gyres — clockwise in the north, counterclockwise in the south. Western boundary currents (like the Gulf Stream) are narrow, deep, and fast; eastern boundary currents are broad, shallow, and slow. Thermohaline circulation is driven by cold, salty water sinking in polar regions (high density) and warm water rising near the equator. This 'global conveyor belt' takes about 1000 years for a complete cycle and redistributes heat globally, moderating climate. Changes in thermohaline circulation (e.g., from melting ice reducing salinity) can have dramatic climate effects.