Earth Science
Chapter 13
Section 4
A. Surface Currents:
A current is a large stream of moving water that flows through
the oceans.
Unlike waves a current moves water from one place to another
over great distances.
Some currents move water at the surface, while other currents
move deep water.
Surface currents, which affect water to a depth of several
hundred meters, are driven mainly by winds.
Surface currents move in circular patterns east or west and then
double back to complete a circle.
Surface currents and winds move in circular patterns due to the
Coriolis effect, which is caused by the Earth’s rotation.
Currents are deflected to the right in the N. Hemisphere and to
the left in the S. Hemisphere.
The largest and most powerful surface current in the North
Atlantic is the Gulf Stream. Caused by strong winds from the
west.
The Gulf Stream is about 30 Km wide and 300 meters deep. It
carries warm water from the Gulf of Mexico, to the Caribbean
then north along the U.S. coast then turns east out to sea.
B. How Surface Currents Affect Climate:
Climate is the pattern of temperature and precipitation typical
of an area over a long period of time.
A surface current warms or cools the air above it, influencing
the climate of the land near the coast.
C. Deep Currents:
Deep currents are caused by differences in density rather than
surface winds.
Deep currents move and mix water around the world.
They carry cold water from the poles back toward the equator.
D. Upwelling:
Upwelling is the upward movement of cold water from the
ocean depths.
This occurs as the wind blows warm surface water away from
the coast, and cold water rises to replace it.
Upwelling brings up tiny ocean organisms, minerals and other
nutrients from the deep. Which supports large schools of fish,
which in turn supports the fishing industry and other creatures.
One major area of upwelling is along the west coast of S.
America.
E. El Nino:
Change in winds and currents can greatly impact the oceans
and the neighboring land.
El Nino, is an abnormal climate event that occurs every 2-7
years in the Pacific Ocean.
El Nino begins when an unusual pattern of winds form over the
western Pacific.
This causes a vast sheet of warm water to move eastward
toward S. America.
What happens?
1. El Nino prevents upwelling along the coast.
2. Fish and food supplies are depleted
3. Weather patterns are changed, often bringing unusual or
severe conditions to different areas.

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