Ocean water moves in giant streams called currents. In the Northern Hemisphere the currents run clockwise, while in the Southern Hemisphere, they run counter clockwise. Likewise, currents on the West Coast are cold, while those on the East Coast are warm. These currents are powered by the sun and winds and are responsible for delivering heat from the tropics to polar regions, affecting the weather and climate of the world. At the same time, currents are responsible for distributing nutrients throughout the ocean.
Deep currents move much more slowly and are affected by gravity and density of water.
In unison, surface and deep currents comprise what are known as boundary currents. On the East Coast, there are five large western boundary currents, the largest being the Gulf Stream. The name of this current originates from the early belief that the current began in the Gulf of Mexico from the Mississippi River. In actuality, it is the currents off of Northern Belize and up through the Yucatan Strait that are responsible for the origin of the Gulf Stream. Eastern boundary currents, on the other hand, are very slow and only move about ten miles a day.