Large amounts of water in the ocean move in a definite path on the surface. There are many such streams flowing all over the world oceans. These are called ocean currents. In short, they constitute a large mass of water flowing along a fixed path on the surface of the ocean. A current may be swift with a speed of up to 10 km/hr, or it may be broad and slow moving at an average speed of 2 km/hr, in which case it is called ocean drift.
The following factors cause ocean currents:
(a) The prevailing winds are the major cause of the ocean waters moving in a definite direction. The pushing action of these winds makes the waters flow as they do. Like the planetary winds, currents too are deflected from their original path due to the rotation of the Earth. All currents in the northern hemisphere move in a clockwise direction, while in the southern hemisphere they move in an anti-clockwise direction. Landmasses are also responsible for changing the course of a current.
(b) Differences in temperature and salinity are also responsible for the movement of ocean water. In the equatorial region, ocean water gets more heated than in the cold Polar Regions. This makes the water light. Water in the Polar Regions is cold and heavy, so it sinks and flows towards the equator. The light upper layers of water are forced to move towards the Poles where they get cooled.
Effects of Ocean Currents
Currents influence the climate of the costal regions. This determines the agricultural and hence all other economic activities of the region. Ocean currents have the following effects:
I. Winds blowing over a warm current become warm and at the same time, pick up moisture, as warm winds are able to retain more moisture. Thus, the wind that reaches the land brings down the temperature and causes heavy rainfall. The western coast of Europe is an example of such a region. Such winds bring down the temperature of the land like the kuroshio (warm) current, which flows along the east coast of Japan.
II. Winds blowing over a cold and dry. They help to bring down the temperatures in places, which would have been much hotter. The California (cold) current, which flows along the western coast of USA, makes the region much cooler than other places in the west coast on the same latitude.
Such winds are bereft of any moisture and bring little or no rainfall over the coastal regions where they blow. As most cold currents flow along the western coast of continents, some of the major deserts are found in such regions. The Atacama desert in South America is influenced by the cold Peru current.
III. Places where cold and warm currents meet are ideal for the growth of Plankton. These are very small organisms, which are food for fish. These regions thus support a great number of fish. They have developed into major fishing grounds of the world. Newfoundland on the eastern coast of North America is the meeting point of the Gulf Stream and the Labrador Current. It is one of the major fishing centers of the world.
However, these places may be dangerous for ships as the meeting of cold and warm currents gives rise to thick fog, which reduces visibility.
IV. Ships sailing with a current gain speed, which helps to save fuel and time. Ships moving against a current lose speed. Warm currents keep the Arctic regions free from icebergs, which can be dangerous for ships.