When we pour a glass of water, we notice that the water is colourless. But if water is colourless, then why is the ocean blue?
Scientific reason
The ocean is blue because it reflects blue light. To understand properly, we must first understand how light works on the sea surface.
The light that comes from the Sun appears to be white to the naked eye. Hence, it is called white light.
When this white light passes through a medium, it gets scattered into seven colours of the rainbow, namely red, orange, yellow, green, blue, indigo, and violet. These colours are known as the colours of visible light.
Some of these coloured lights are of longer wavelengths, while others are shorter. Red light has the longest wavelength while violet has the shortest.
Water acts as a medium for light to pass through. As a result, lights of longer wavelengths like red and orange easily penetrate the sea bed and get absorbed into it while lights of shorter wavelengths, like blue and violet get reflected. This gives the ocean its blue colour.
When Do Sea looks greenish-blue
However, plenty of other factors can affect the colour of the ocean. You might have noticed that sometimes the ocean appears to be greenish-blue in colour. This is because shallow water tends to reflect green light. Sometimes algae also cause water to look green as they contain chlorophyll which absorbs green light.
Pure Ocean gives the bluish look
Water is only blue in those places where the ocean is pure and clean. If the water is crystal clear in shallow areas then it might appear to be turquoise in colour.
Role of sand & silt
Sand and silt can also play a role in changing the colour of the water as these sediments reflect lights of longer wavelengths and give the water a brownish colour.
As we go deeper, the ocean becomes darker. This is because light does not reach the very depths of the ocean. In these parts, animals use bioluminescence or light of their own to find food and mates.
Ms Kalinga