The world's oceans travel in well-defined circular patterns
called currents which flow like rivers. When the atmosphere
pushes over the surface of the ocean some of the energy goes
to forming waves while the rest goes to pushing the water in
the direction of the wind. North of the equator currents
bend to the right; south of the equator, they bend to the
left. This is called the Coriolis effect. Winds, continents
and the Coriolis effect make currents flow around the oceans
in huge loops called gyres.
The map shows a
generalized pattern of ocean currents. In each
ocean basin there is a roughly circular current
flow called a gyre.
Energy from the sun also causes currents to flow. Water
near the equator is heated more than water at middle
latitudes causing a surface flow toward the poles. Where two
currents meet, the colder water sinks pushing warmer water
up to the surface.
Each current has its own characteristic salinity, density
and temperature. The Gulf Stream, which was first mapped by
Benjamin Franklin, runs along the east coast of the United
States and is one of the strongest currents known. It is a
warm, salty current up to 37 miles wide, 2600 feet deep and
in some places it may travel more than 60 miles in a day.
The importance of currents can be seen when they change. On
the west coast of South America, the Humboldt current
normally brings cold water to the surface. With it come
minerals and other nutrients that feed huge schools of fish.
During an El Niño event, trade winds diminish and
warm water flows down western South America. This stops
nutrient-rich cold water from rising up and causes plankton
and fisheries to fail.
map of the Gulf Stream.