The Oceans

An ocean is a large saline water body of water which approx. covers 71% of Earth's surface. Customarily the water on this planet earth was divided into several principal oceans and smaller seas.

The oceans are in a state of continuous unrest and the water in the oceans is subjected to three kinds of motions, namely the tides, the waves and the currents. The tides in the oceans are rhythmic rise and fall of ocean waters due to the gravitational attraction of the sun and the moon. Generally a high tide is experienced at a longitude which faces the moon at a particular time. Another high tide is experienced at the longitude 180 degrees of longitude from this longitude which is called the indirect tide. As the earth completes one rotation on its axis in one day, every place experiences two high tides and two low tides every 24 hours. Generally the two high tides are about 12 hour apart from each other. However, the actual time difference between two high tides is more than 12 hours as the period of rotation of the earth with respect to the moon is nearly 25 hours. Due to this fact the time of the high tide every day is delayed from that on the previous day.

As the tides are produced by the gravitational pull of the moon and the sun, the relative position of the sun, the moon and the earth has an impact upon the tidal range. Tides of very high magnitude (spring tides) occur when the sun, the earth and the moon are in a straight line so that the tide producing forces of the sun and the moon complement each other. On the other hand the tides of relatively lower magnitude (neap tides) are produced when the sun, the earth and the moon form a triangle so that the tide producing forces of the sun and the moon neutralize each other. The spring tides occur around the new moon and the full moon.

The waves are oscillating movements in the oceans which are caused by factors like the friction of the winds on the ocean surface. They may be caused by earthquakes also. The high magnitude waves caused by earthquakes originating on the sea bottom are called tsunamis. One important fact about both the tides and the waves is that none of these motions involves an actual transportation of water from one place to the other.

The third important motion in the oceans are the currents. The currents are caused by density and salinity differences in the oceans. Unlike the tides and the waves the currents are well defined movements of water from one latitude to the other which involve an actual transportation of water. The currents are classified as cold and warm currents on the basis of the comparison of the temperature of the water moving as a current with that of the normal water of a given latitude. Generally the currents moving from the tropical regions towards the higher latitudes are warm currents and those flowing from higher latitudes towards the lower latitudes are the cold currents. They have an important impact on the climate of the coastal regions along which they flow. Generally the western coasts of the continents are washed by cold currents in the tropical and low latitudes and by warm currents in the higher latitudes. On the other hand the currents along the eastern coasts of the continents are warm in the low latitudes and cold in the higher latitudes. Therefore on the two sides of an ocean, in the tropical zone, the eastern coasts are warmer than the western coasts and the western coasts are warmer than the eastern coasts in the higher latitudes.