Ocean waters are constantly on the move. How they move influences climate and living conditions for plants and animals, even on land.
Currents flow in complex patterns affected by wind, the water's salinity and heat content, bottom topography, and the earth's rotation.
Dynamic Ocean Topography (952 kbyte mpeg)
Animation of two years of satellite-derived Dynamic Ocean Topography data from the Topex/Poseidon Mission
Upwelling brings cold, nutrient-rich water from the depths up to the surface. Earth's rotation and strong seasonal winds push surface water away from some western coasts, so water rises on the western edges of continents to replace it. Marine life thrives in these nutrient-rich waters §.
Deep water forms when sea water entering polar regions cools or freezes, becoming saltier and denser. Colder or saltier water tends to sink §.
A global "conveyor belt" set in motion when deep water forms in the North Atlantic, sinks, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into the North Pacific §.
Warm surface currents invariably flow from the tropics to the higher latitudes, driven mainly by atmospheric winds, as well as the earth's rotation.
Western boundary currents are good examples of warm surface currents: they are warm and fast, and they move from tropical to temperate latitudes §.
Cold surface currents come from polar and temperate latitudes, and they tend to flow towards the equator. Like the warm surface currents, they are driven mainly by atmospheric forces §. Gyres form when the major ocean currents connect. Water flows in a circular pattern--clockwise in the Northern Hemisphere, and counterclockwise in the Southern Hemisphere §.
The California current is an eastern boundary current. It's broad, slow, cool, and shallow. Eastern boundary currents are often associated with upwelling.
The Somali current, off Africa's eastern coast, is unusual because it reverses direction twice a year. From May to September it runs north; from November to March it runs south. As it flows northward, upwelling supports productive marine life, but productivity falls when the current begins to move southward.
The ocean is layered: warmer on top, cold at the bottom. Organisms move from one layer to another, and plant and animal remains containing nutrients "rain" down, but the layers stay fairly separate in all but a few places.
Coastal upwelling occurs against the western sides of continents in the Atlantic, Indian, and Pacific. There, colder water rises to replace warm surface water blown out to sea by strong offshore winds. Upwelling supports about half of the world's fisheries, although these cool waters account for only 10 percent of the surface area of the global ocean §.
Ocean Planet Exhibition Floorplan
gene carl feldman (email@example.com) (301) 286-9428
Judith Gradwohl, Smithsonian Institution (Curator/Ocean Planet)