We know that about seventy one per cent of the earth’s surface is covered with water. The earth’s three main Oceans are the Atlantic, the Pacific and the Indian Ocean.
The Atlantic Ocean is a great mass of water that separates Europe and Africa from America. It is shaped like a great hour-glass-with a ‘waist’ where Africa and South America bulge out towards each other. Although in area it is less than half the Pacific, it has many ‘secondary’ seas, such as the Arctic Ocean and the Mediterranean Sea.
It is actually possible to distinguish where the waters of the Mediterranean Sea meet the Atlantic Ocean. This is because the former appears blue and the latter green.
Why is this so?
The Mediterranean Sea lies between southern Europe, Africa and south-west Asia. It is linked to the Atlantic Ocean through the narrow Strait of Gibraltar in the west and to the Black Sea in the north-east, via the sea of Marmara. The varying colours of the two depend mainly on the amount of sunlight scattered from their surface.
The colour of the scattered light depends upon the substances dissolved in seawater. Generally, of the seven colours of sunlight, blue is scattered most. That is why most oceans appear blue. However, in the case of the Atlantic Ocean, the decaying plants on the ocean bed produce a green effect. When these plants decay, yellow pigments are released which get dissolved in the water. This water now scatters both blue and yellow light and the resulting mixture produces the characteristic greenish shade.