Surface Currents

Ocean water move in predictable means along the ocean surface. Surface currents can flow for hundreds of kilometers and also can reach depth of hundreds of meters. These surface ar currents perform not count on weather; they stay unchanged also in huge storms since they count on factors that execute not change.

You are watching: A poleward-moving ocean current is considered a warm current.

Surface currents are developed by 3 things:

global wind patternsthe rotation that the Earththe form of the s basins

Surface currents are incredibly important due to the fact that they distribute heat around the planet and are a major factor affecting climate about the globe.

Global Wind Patterns

Winds on planet are either an international or local. Global winds blow in the very same directions every the time and are regarded the unequal heater of earth by the sunlight — that is, more solar radiation strikes the equator than the polar regions –- and also the rotation of the planet — the is, the Coriolis effect. The reasons of the worldwide wind patterns will be defined in information in the Earth’s setting chapter.

Water in the surface currents is propelled in the direction that the significant wind belts:

trade winds: east to west between the equator and also 30oN and 30oSwesterlies: west to eastern in the center latitudespolar easterlies: east to west between 50o and 60o north and south that the equator and also the north and south pole

Earth’s Rotation

Wind is not the only variable that affects ocean currents. The Coriolis effect defines how earth’s rotation steers winds and also surface ocean currents (Figure below). Coriolis causes freely moving objects to show up to move to the appropriate in the north Hemisphere and to the left in the southerly Hemisphere. The objects themselves room actually relocating straight, however the planet is rotating in ~ them, therefore they it seems ~ to bending or curve.

An example can make the Coriolis effect simpler to visualize. If an plane flies 500 mile due north, it will certainly not come at the city the was due phibìc of it once it started its journey. Over the time it takes because that the airplane to paris 500 miles, the city moved, in addition to the planet it sits on. The plane will therefore arrive in ~ a city to the west that the original city (in the northern Hemisphere), uneven the pilot has compensated for the change. So to with his plan destination, the pilot must also veer appropriate while flying north.

As wind or an ocean present moves, the earth spins under it. As a result, an object moving north or south along the planet will appear to relocate in a curve, instead of in a straight line. Wind or water the travels towards the poles from the equator is deflected to the east, when wind or water the travels towards the equator indigenous the poles it s okay bent to the west. The Coriolis effect bends the direction of surface currents to the right in the northern Hemisphere and left in the southerly Hemisphere.


The Coriolis effect reasons winds and also currents to form circular patterns. The direction the they spin relies on the hemisphere that they space in.

Coriolis result is demonstrated using a metal ball and also a rotating plate in this video. The ball moves in a one path just like a easily moving bit of gas or liquid moves on the rotating Earth (5b): (2:04).

Shape the the ocean Basins

When a surface present collides with land, the present must readjust direction. In the Figure below, the Atlantic south Equatorial present travels westward along the equator till it reaches south America. In ~ Brazil, few of it walk north and some go south. Since of Coriolis effect, the water goes ideal in the northern Hemisphere and left in the southerly Hemisphere.


The major surface s currents.

You can see top top the map that the major surface s currents the the surface ocean currents develop loops called gyres (Figure below). The Antarctic Circumpolar current is unique because it travels uninhibited approximately the globe. Why is the the only current to go all the method around?


The s gyres. Why perform the north Hemisphere gyres turn clockwise and also the southern Hemisphere gyres turn counterclockwise?

This video shows the surface ocean currents collection by worldwide wind belts (5a): (1:20).

Effect on global Climate

Surface currents pat an enormous role in earth’s climate. Also though the equator and poles have really different climates, these areas would have an ext extremely various climates if ocean currents did not transfer warmth from the equatorial regions to the greater latitudes.

The Gulf stream is a river of warm water in the Atlantic Ocean, around 160 kilometers vast and around a kilometer deep. Water the enters the Gulf stream is heated together it travels along the equator. The warm water climate flows up the east coastline of phibìc America and across the Atlantic ocean to Europe (Figure below). The energy the Gulf Stream transfers is enormous: an ext than 100 times the world’s energy demand.

The Gulf Stream’s heat waters raise temperatures in the phibìc Sea, which raises the wait temperatures end land between 3 to 6oC (5 come 11oF). London, U.K., for example, is at the very same latitude as Quebec, Canada. However, London’s mean January temperature is 3.8oC (38oF), if Quebec’s is only -12oC (10oF). Because air traveling over the warmth water in the Gulf Stream picks up a many water, London it s okay a lot of rain. In contrast, Quebec is much drier and receives that is precipitation together snow.

In a satellite image of water temperature in the west Atlantic it is simple to pick out the Gulf Stream, which bring warmer waters from the equator up east North America.

Deep CurrentsThermohaline circulation drives deep ocean circulation. Thermo means heat and haline refers to salinity. Distinctions in temperature and also in salinity readjust the thickness of seawater. Therefore thermohaline circulation is the an outcome of density differences in water masses due to the fact that of their different temperature and salinity.

What is the temperature and salinity of very dense water? lower temperature and greater salinity yield the densest water. Once a volume the water is cooled, the molecule move less vigorously so same number of molecules takes increase less space and the water is denser. If salt is added to a volume that water, over there are an ext molecules in the exact same volume for this reason the water is denser.

Changes in temperature and also salinity the seawater take location at the surface. Water becomes thick near the poles. Cold polar air cools the water and lowers the temperature, increasing its salinity. Fresh water freezes the end of seawater to become sea ice, which likewise increases the salinity that the continuing to be water. This an extremely cold, an extremely saline water is an extremely dense and sinks. This sinking is called downwelling.

This video clip lecture discusses the vertical distribution of life in the oceans. Seawater thickness creates currents, which administer different habitats for different creatures (5d): (6:12).

Two points then happen. The dense water pushes deeper water the end of its way and the water moves follow me the bottom of the ocean. This deep water mixes v less thick water as it flows. Surface currents relocate water right into the room vacated in ~ the surface where the thick water sank (Figure below). Water also sinks right into the deep s off the Antarctica.

Cold water (blue lines) sink in the phibìc Atlantic, flows follow me the bottom that the ocean and upwells in the Pacific or Indian. The water then travels in surface ar currents (red lines) earlier to the north Atlantic. Deep water also forms off of Antarctica.

Since unlimited amounts of water can not sink to the bottom the the ocean, water must rise native the deep ocean to the surface ar somewhere. This procedure is called upwelling (Figure below).

Upwelling pressures denser water from below to take the ar of less thick water at the surface that is moved away by the wind.

Generally, upwelling occurs follow me the coastline when wind blows water strongly away from the shore. This leaves a void the is fill by deep water that rises come the surface.

Upwelling is extremely important where the occurs. During its time ~ above the bottom, the cold deep water has built up nutrients that have actually fallen down with the water column. Upwelling bring those nutrients to the surface. Those nutrient assistance the growth of plankton and type the base of a affluent ecosystem. California, south America, south Africa, and the Arabian Sea all benefit from offshore upwelling.

An animation of upwelling is watched here:

Upwelling also takes place along the equator between the North and also South Equatorial Currents. Winds blow the surface ar water north and south that the equator therefore deep water experience upwelling. The nutrients increase to the surface and also support a good deal that life in the equatorial oceans.

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Lesson Summary

Ocean surface currents are developed by global winds, the Coriolis effect and the shape of each ocean basin.The Pacific and also Atlantic Oceans have a circular sample of surface currents called gyres that circle clockwise in the northern Hemisphere and counterclockwise in the Southern. The Indian ocean only has a counterclockwise gyre.Surface s circulation brings warmth equatorial waters in the direction of the poles and also cooler polar water in the direction of the equator.Thermohaline circulation cd driver deep ocean currents.Upwelling of cold, nutrient-rich waters creates biologically rich areas where surface ar waters space blown far from a shore, or wherein equatorial waters are blow outward.

Review Questions

What reasons the patterns of surface ar currents in the ocean?How do ocean surface currents influence climate?What is the Coriolis effect?What procedure can make deep, dense water climb to the surface?Why room upwelling areas important to marine life?

Further analysis / Supplemental Links

Points come Consider

Some scientists have hypothesized the if enough ice in Greenland melts, the Gulf Stream can be close up door down. Why can this happen?If the Gulf Stream shuts down, what would certainly be the result on climate in Europe?How execute the motions of ocean water contribute to the ocean’s life?