What Are Ocean Currents?

There is a constant flow of sea along  well-marked paths much like the flow of rivers over land. Quite a number of such rivers keep running across the oceans of the world, they are called ocean currents.

Ocean – currents exercise a good deal of influence on the climate of many paths of the world. The global networks of currents are a device used by nature to keep the temperature of various seas and oceans within a limited and responsible range.

There is another advantage of warm currents. These help rainfall. They bring with them moisture laden warm air which proves a source of rainfall.  Cold currents on the other hand hinder rainfall. The cool air they bring with them has little part to hold moisture. Such winds can't bring much rain.  

Around the globe the rays of sun fall almost vertically throughout the year. They heat up and expand water of the ocean,this rises the surface of the ocean. The polar regions, on the contrary always receive slanting rays of the sun and that is how this keeps the ocean water cold.

An ocean current is the movement of water from one direction to another on a horizontal plane. This movement can happen either at the surface of the ocean or underneath the surface of the ocean. When the movement is on the surface of the ocean, the current generated is called a surface current. When the movement is underneath the ocean's surface, the current is called sub-surface or deep water current. While these are essentially two types of currents, they have distinctive characteristics. A surface current operates from the top of the ocean's surface to a depth of about 400 meters, while a deep water current works below the depth mentioned for a surface current.

Different factors work on the ocean currents, and are responsible for their generation. These include heat from the sun, wind, gravity, coriolis, and surface circulation. The first four factors are called primary factors, while the last one is called a secondary factor.