Ocean Circulation

(currents)

Surface Circulation

Ocean currents are masses of ocean water that run from one place to another. The amount of water can be small or large. It can be simple or complex. They can be deep below or at the surface.

Surface Currents

A surface current is moving water that flows from side to side in the upper part of the surface of the ocean. Surface currents develop from friction between the wind that blows across the ocean surface and the ocean. Some currents are short lasting and those kinds only affect small areas. Those kinds of water movements are responses to seasonal or local influences. Other surface currents extend over large portions of the oceans and they are more permanent. These side to side movements of the surface water are very similar to the general circulation of the atmosphere.

Gyres

Gyres are large swirls of water within an ocean basin (gyros = a circle). There are five main ocean gyres: North Pacific Gyre, South Pacific Gyre, North Atlantic Gyre, South Pacific Gyre, and Indian Ocean Gyre.
Wind is the force that causes surface currents, but other factors also influence the flow of the ocean waters. The most important of these is the Coriolis effect. The Coriolis effect is the deflection of currents away from their original course as a result of Earth's rotation. The Earth's rotation causes the currents to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Gyres flow in opposite directions in the two different hemispheres.
Water moves north from Florida and the North Atlantic Current is deflected to the right/eastward. Water moving south in the Canary Current is deflected to the left/westward into the North Equatorial Current. The South Atlantic Gyre flows counterclockwise because of the Coriolis effect.
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Ocean Currents and Climate

When currents from low-latitude regions go into higher latitudes, they give heat from warmer to colder areas on Earth.
As cold water currents travel to the equator, it helps control warm temperatures of adjacent land areas.

Upwelling

Upwelling brings greater concentrations of nutrients that have been dissolved, such as phosphates and nitrates to the ocean bottom.
Upwelling-the rising of cold water from the deeper layers to replace the warmer bottom water.

Deep-Ocean Circulation

Density Currents

A decrease in temperature or an increase in salinity is the cause of an increase in seawater density.
Density Currents- density differences among water masses cause vertical currents of ocean water. Bringing cold water from the poles back to the equator, and warm water from the equator to the poles is called ocean circulation.

High Latitudes

Most water involved in deep-ocean density currents begins in high latitudes at the ocean's surface. In these regions, the water on the ocean's surface becomes cold or freezes, and its salinity increases because the sea salts do not become part of the sea ice that starts to form. And when that water gets dense enough, it sinks, which causes deep-ocean density currents. This water is then removed from the physical processes that first increased its density. After sinking from the ocean's surface, the deep waters will not reappear at the ocean's surface for about 500 to 2000 yrs.

Evaporation

Conditions in the Mediterranean Sea and the Atlantic Sea and the eastern part the Mediterranean Sea lead to annual bunches of evaporation compared to the precipitation amount. When the sea water gets evaporated, the salt gets left behind, and the salinity of the water increases.
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A Conveyor Belt

A conveyor belt is a simplified model of the ocean circulation. It travels from the Atlantic Ocean and through the Pacific and Indian oceans and back again.
Warm water in the upper layers of the ocean flows toward the poles. When it reaches the poles, the temperature of the water drops and the salinity increases, which makes it more dense. When the water gets dense, it sinks and goes toward the equator. When it returns to the equator as cool, deep water, it will soon start upwelling to complete the circuit of the conveyor belt. Since the conveyor belt moves around the globe, it turns warm water into cold water and it releases heat into the atmosphere.
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