Large-scale, continuous movements of ocean water in definite directions, driven mainly by prevailing winds, differences in water density, and the Earth's rotation, and classified as warm or cold.
- Caused by planetary winds, the Coriolis force, temperature and salinity differences (density), and shaped by the position of continents.
- Warm currents flow from the equator towards the poles (for example the Gulf Stream, North Atlantic Drift, Kuroshio); cold currents flow from the poles towards the equator (for example the Labrador, Humboldt/Peru, Benguela).
- Coriolis effect makes currents move clockwise in the Northern Hemisphere and anticlockwise in the Southern Hemisphere (forming gyres).
- Warm currents raise coastal temperatures (the North Atlantic Drift keeps north-west Europe's ports ice-free); the meeting of warm and cold currents creates rich fishing grounds (for example the Grand Banks off Newfoundland).
- Upwelling of cold, nutrient-rich water (as off Peru) supports major fisheries; El Nino disrupts the cold Peru current.
Warm versus cold current names, the gyre rotation direction, the climate-moderating role, and the warm-cold meeting creating fishing grounds are recurring oceanography facts.
Warm currents flow away from the equator (poleward); cold currents flow towards the equator. The Gulf Stream/North Atlantic Drift is warm; the Labrador and Peru (Humboldt) currents are cold.
Wind and density driven water movements; warm currents flow poleward, cold currents equatorward; they moderate coastal climate.