is surrounded by two great oceans: an ocean of air and an ocean
of water. Both are in constant motion, driven by the energy of
the sun and the gravity of the Earth. Their motions are linked;
the winds give energy to the sea surface and ocean currents are
the result. The currents carry heat from one location to another,
altering the Earth's surface temperature patterns and modifying
the air above.
Out in the
open sea, ocean waters are driven by two great wind systems. Close
to the equator the Trade Winds blow the surface waters westward.
In the temperate zone, the Westerlies blow the surface waters
back toward the east. The result is that in each great ocean basin
there is roughly circular movement of the surface waters. In the
northern hemisphere these wind driven currents move clockwise
and in the southern hemisphere they move counter clockwise. Both
surface and deep-water currents affect the world's climate by
moving cold water from the poles toward the tropics and vice versa.
are always in motion. Currents flow like rivers, waves crash against
seashores and tides rise and fall.