Surface Currents

Ocean water moves in predictable ways along the ocean surface. Surface currents can flow for hundreds of kilometers and also can reach depths of thousands of meters. These surface ar currents carry out not count on weather; they stay unchanged even in huge storms due to the fact that they count on determinants that perform not change.

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Surface currents are produced by 3 things:

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

Surface currents are incredibly important since they distribution heat around the planet and are a major factor influencing climate roughly the globe.

Global Wind Patterns

Winds on earth are either worldwide or local. Worldwide winds blow in the same directions every the time and also are concerned the unequal heater of earth by the sunlight — that is, much more solar radiation strikes the equator than the polar regions –- and also the rotation of the planet — that is, the Coriolis effect. The reasons of the global wind fads will be described 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 30oN and also 30oSwesterlies: west to eastern in the center latitudespolar easterlies: east to west between 50o and 60o north and also south of the equator and the north and south pole

Earth’s Rotation

Wind is no the only factor that affects ocean currents. The Coriolis effect defines how earth’s rotation steers winds and also surface ocean currents (Figure below). Coriolis reasons freely relocating objects to appear to move to the ideal in the northern Hemisphere and to the left in the southerly Hemisphere. The objects themselves are actually relocating straight, yet the earth is rotating beneath them, for this reason they it seems to be ~ to bending or curve.

An example could make the Coriolis effect less complicated to visualize. If an airplane flies 500 miles due north, it will certainly not arrive at the city the was due phibìc of it when it started its journey. Over the time it takes for the plane to fly 500 miles, that city moved, in addition to the earth it sit on. The plane will because of this arrive at a city come the west the the initial city (in the north Hemisphere), unless the pilot has compensated for the change. For this reason to reach his intended destination, the pilot must also veer right while flying north.

As wind or an ocean present moves, the earth spins underneath it. As a result, things moving phibìc or south along the earth will appear to move in a curve, rather of in a straight line. Wind or water the travels towards the poles from the equator is deflected come the east, while wind or water that travels towards the equator native the poles it s okay bent come the west. The Coriolis effect bends the direction of surface currents to the ideal in the north Hemisphere and also left in the southerly Hemisphere.


The Coriolis effect reasons winds and currents to kind circular patterns. The direction the they spin relies on the hemisphere the they room in.

Coriolis effect is demonstrated making use of a metal ball and a rotating plate in this video. The sphere moves in a one path similar to a openly moving particle of gas or fluid moves top top the rotating Earth (5b): (2:04).

Shape of the s Basins

When a surface existing collides v land, the existing must change direction. In the Figure below, the Atlantic southern Equatorial existing travels westward along the equator till it reaches southern America. At Brazil, several of it go north and some go south. Because of Coriolis effect, the water goes right in the north Hemisphere and also left in the southern Hemisphere.


The significant surface ocean currents.

You have the right to see on the map the the significant surface ocean currents the the surface ocean currents create loops called gyres (Figure below). The Antarctic Circumpolar current is unique due to the fact that it travels uninhibited around the globe. Why is the the only present to walk all the means around?


The s gyres. Why perform the north Hemisphere gyres rotate clockwise and also the southerly Hemisphere gyres rotate counterclockwise?

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

Effect on an international Climate

Surface currents play an enormous function in earth’s climate. Even though the equator and also poles have an extremely different climates, these regions would have much more extremely various climates if s currents did no transfer heat from the equatorial regions to the higher latitudes.

The Gulf stream is a flow of warm water in the Atlantic Ocean, about 160 kilometers broad and about a kilometer deep. Water that enters the Gulf currently is heated as it travels follow me the equator. The warmth water then flows increase the east coast of phibìc America and throughout the Atlantic s to Europe (Figure below). The power the Gulf Stream transfers is enormous: an ext than 100 time the world’s energy demand.

The Gulf Stream’s heat waters raise temperatures in the phibìc Sea, i beg your pardon raises the air temperatures over land in between 3 come 6oC (5 to 11oF). London, U.K., for example, is at the exact same latitude together Quebec, Canada. However, London’s average January temperature is 3.8oC (38oF), while Quebec’s is only -12oC (10oF). Since air traveling over the warmth water in the Gulf Stream picks up a the majority of water, London it s okay a many rain. In contrast, Quebec is lot drier and receives the precipitation as snow.

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

Deep CurrentsThermohaline circulation drives deep s circulation. Thermo method heat and also haline describes salinity. Distinctions in temperature and also in salinity change the density of seawater. For this reason thermohaline circulation is the result of density differences in water masses since of their various temperature and salinity.

What is the temperature and also salinity of very dense water? lower temperature and greater salinity productivity the densest water. Once a volume the water is cooled, the molecule move less vigorously therefore 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 much more molecules in the very same volume therefore the water is denser.

Changes in temperature and salinity the seawater take place at the surface. Water becomes dense near the poles. Cold polar air cools the water and lowers the temperature, increasing its salinity. New water freezes out of seawater to become sea ice, which likewise increases the salinity the the staying water. This an extremely cold, very saline water is very dense and also sinks. This sinking is called downwelling.

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

Two things then happen. The thick water pushes deeper water out of its method and the water moves follow me the bottom the the ocean. This deep water mixes with less dense water together it flows. Surface ar currents move water right into the an are vacated in ~ the surface ar where the dense water sank (Figure below). Water additionally sinks right into the deep s off that Antarctica.

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

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

Upwelling forces denser water from below to take the location of less dense water in ~ the surface ar that is driven away by the wind.

Generally, upwelling occurs follow me the shore when wind blows water strongly far from the shore. This pipeline a void the is fill by deep water the rises to the surface.

Upwelling is extremely essential where it occurs. During its time on the bottom, the cold deep water has built up nutrients that have actually fallen down with the water column. Upwelling brings those nutrients to the surface. Those nutrient assistance the expansion of plankton and kind the basic of a affluent ecosystem. California, south America, southern Africa, and the Arabian Sea all advantage from offshore upwelling.

An animation of upwelling is watched here:

Upwelling also takes ar along the equator between the North and also South Equatorial Currents. Winds blow the surface water north and south of the equator so deep water experience upwelling. The nutrients climb to the surface and support a great deal of life in the equatorial oceans.

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Lesson Summary

Ocean surface ar currents are created by worldwide winds, the Coriolis effect and the shape of each ocean basin.The Pacific and Atlantic Oceans have actually a circular sample of surface ar currents dubbed gyres the circle clockwise in the north Hemisphere and also counterclockwise in the Southern. The Indian ocean only has a counterclockwise gyre.Surface ocean circulation brings warmth equatorial waters in the direction of the poles and cooler polar water towards the equator.Thermohaline circulation drives deep s currents.Upwelling the cold, nutrient-rich waters create biologically rich locations where surface waters are blown away from a shore, or wherein equatorial waters room blow outward.

Review Questions

What reasons the trends of surface currents in the ocean?How do s surface currents influence climate?What is the Coriolis effect?What procedure can do deep, thick water rise to the surface?Why space upwelling areas important to marine life?

Further analysis / Supplemental Links

Points to Consider

Some scientists have hypothesized the if sufficient ice in Greenland melts, the Gulf Stream could be shut down. Why could this happen?If the Gulf Stream turn off down, what would be the an outcome on climate in Europe?How perform the motions of ocean water add to the ocean’s life?