What causes ocean currents?

          Most people think that the water in the oceans is still. But it is not so. It is always moving in regular patterns. This movement of water is called ocean currents. There are many kinds of currents. One kind is a ‘stream’. A stream is a current with distinct boundaries. Another kind is a ‘drift’. A drift does not have distinct boundaries. Do you know how ocean currents are produced?

          There are three main reasons for the occurrence of the ocean currents. (1) The density of sea water varies from place to place, because the salt content is not same at different places. Water flows from the regions of higher density to regions of lower density thus producing currents. (2) Sun’s rays fall on the surface of the sea at different angles and as such produce unequal heating. This generates ‘convection currents’ in the sea. (3) Winds blowing on the sea surface push water into current.

          Currents are also caused by the rotation of the earth. Generally, the earth’s rotation produces clockwise currents in the northern hemisphere and counter clockwise currents in the southern hemisphere.

          Amongst these, the Gulf Stream is the most important. The water of this stream is blue and warm. This stream flows from the Gulf of Mexico north to Canada like a river in the middle of the Atlantic Ocean. London and Paris are less cold, because of this stream. It keeps ports in Norway free of ice all year. In addition to these, Brazil current, Japan Current North Equatorial current, North Pacific current etc., are the main ocean currents of the world.

          A cool current like the Labrador Current, which flows from the Arctic to the Atlantic, may carry icebergs into the trans-Atlantic shipping lanes. Ocean currents are important to the plants and animals in the oceans. The movement of water brings them food and nutrients. It also helps them during migration. Currents also affect the climate of the land. Ocean currents move water from warm to cold areas and vice versa.

          The collective name for a complex system of ocean currents flowing in the environs of the equator in Atlantic, Pacific and Indian Ocean is known as ‘Equatorial Current’. The pacific north equatorial current is the part of clock-wise ocean current system with Japan Current, North Pacific current and California current. Similarly in Atlantic, the North Equatorial Current is the part of the clockwise system with Gulf Stream, and Canaries current.