When we think of the ocean, our mind is invaded by the picture of a vast mass of blue water. But why does the sea appear in our eyes in bluish tones, even though water is perfectly clear?
A glass of water reveals nothing but a transparent liquid. However, when we get to the beach on a sunny summer morning, we're blessed by a wide and visibly infinite field of blue saltwater.
So, could it be that the ocean is blue because it reflects the sky? Does the color of marine life influence the hue of the sea? The answer to the enigma is pretty straightforward.
Light is a mixture of colors. The ocean is blue - and sometimes navy blue - because water absorbs more the red, orange and yellow (long wavelength light) colors of the light spectrum than the blue color (short wavelength light).
So, like a filter, when the sun's white light penetrates the sea only, or mostly, the blue tones get returned. Interestingly the ocean is blue for the same reason why the sky is blue.
Though, it is important to stress that most of the sea is entirely dark. The reason why it happens is that light cannot penetrate the ocean below the "midnight," or aphotic zone, i.e., 3,280 feet (1,000 meters).
Still, how do you compare a glass of transparent water with the blue of the ocean? A cup of water lets nearly the same amount of blue and red light through.
Water only gets blue when there is enough depth, and a small glass of still mineral water is not deep enough, so it appears colorless.
In the Caribbean and tropical areas, the shallow bottoms, the absence of suspended particles and phytoplankton, and the tendency of the coastline to scatter sunlight explain why the region has turquoise and crystal-clear waters.
In some places of the world, the ocean displays green, red and other colors. The bouncing of light off particles, algae, floating sediments explains that particularly remarkable phenomenon.