This field describes the major ocean currents found in the ocean basins. Oceanic currents describe the movement of water from one location to another. Currents are generally measured in meters per second or in knots (1 knot = 1.85 kilometers per hour or 1.15 miles per hour). Oceanic currents are driven by three main factors:
- The rise and fall of the tides. Tides create ocean currents, which are strongest near the shore, but also extend into bays and estuaries along the coast. These are called "tidal currents." Tidal currents change in a very regular pattern and can be predicted for future dates. In some locations, strong tidal currents can travel at speeds of eight knots or more.
- Wind. Winds drive currents that are at or near the ocean's surface. Near coastal areas winds tend to drive currents on a localized scale and can result in phenomena like coastal upwelling. On a more global scale, in the open ocean, winds drive currents that circulate water for thousands of miles throughout the ocean basins.
- Thermohaline circulation. This is a circulatory process driven by density differences in water due to temperature (thermo) and salinity (haline) variations in different parts of the ocean. Currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much more slowly than tidal or surface currents.
Currents affect the Earth's climate by driving warm water from the Equator and cold water from the poles around the Earth.
Two major, slow-moving, wind-driven currents (drift streams) dominate: a clockwise drift pattern in the Beaufort Gyre in the western part of the Arctic Ocean and a nearly straight line Transpolar Drift Stream that moves eastward across the ocean from the New Siberian Islands (Russia) to the Fram Strait (between Greenland and Svalbard); sea ice that lies close to the center of the gyre can complete a 360 degree circle in about 2 years, while ice on the gyre periphery will complete the same circle in about 7-8 years; sea ice in the Transpolar Drift crosses the ocean in about 3 years
Clockwise North Atlantic Gyre consists of the northward flowing, warm Gulf Stream in the west, the eastward flowing North Atlantic Current in the north, the southward flowing cold Canary Current in the east, and the westward flowing North Equatorial Current in the south; the counterclockwise South Atlantic Gyre composed of the southward flowing warm Brazil Current in the west, the eastward flowing South Atlantic Current in the south, the northward flowing cold Benguela Current in the east, and the westward flowing South Equatorial Current in the north
The counterclockwise Indian Ocean Gyre comprised of the southward flowing warm Agulhas and East Madagascar Currents in the west, the eastward flowing South Indian Current in the south, the northward flowing cold West Australian Current in the east, and the westward flowing South Equatorial Current in the north; a distinctive annual reversal of surface currents occurs in the northern Indian Ocean; low atmospheric pressure over southwest Asia from hot, rising, summer air results in the southwest monsoon and southwest-to-northeast winds and clockwise currents, while high pressure over northern Asia from cold, falling, winter air results in the northeast monsoon and northeast-to-southwest winds and counterclockwise currents
The clockwise North Pacific Gyre formed by the warm northward flowing Kuroshio Current in the west, the eastward flowing North Pacific Current in the north, the southward flowing cold California Current in the east, and the westward flowing North Equatorial Current in the south; the counterclockwise South Pacific Gyre composed of the southward flowing warm East Australian Current in the west, the eastward flowing South Pacific Current in the south, the northward flowing cold Peru (Humbolt) Current in the east, and the westward flowing South Equatorial Current in the north
The cold, clockwise-flowing Antarctic Circumpolar Current (West Wind Drift; 21,000 km long) moves perpetually eastward around the continent and is the world's largest and strongest ocean current, transporting 130 million cubic meters of water per second - 100 times the flow of all the world's rivers; it is also the only current that flows all the way around the planet and connects the Atlantic, Pacific, and Indian Oceans; the cold Antarctic Coastal Current (East Wind Drift) is the southernmost current in the world, flowing westward and parallel to the Antarctic coastline