Glenn Smith, a professor at the Georgia Institute of Technology (USA), explained this issue as follows: ocean water is actually colorless, but it reflects the blue of the sky, which is why we often see it as blue. Therefore, when the sky has many gray clouds, the ocean appears gray.
Why is Ocean Water Blue While River Water Is Not?
The blue color of ocean water is not because the water itself is blue, as we perceive it. The blue of ocean water is entirely determined by sunlight.
Sunlight consists of seven colors: red, orange, yellow, green, blue, indigo, and violet. When sunlight shines on the ocean surface, there are many small particles suspended in the water. Long-wavelength light, such as red and orange, cannot penetrate these particles and travel straight through.
The blue color of ocean water is entirely determined by sunlight.
As light progresses forward, it is continuously absorbed by the ocean water and marine organisms. While shorter wavelengths like blue and violet light are also partially absorbed by ocean water and phytoplankton, the majority of it is scattered around or reflected back when encountering ocean water. What we see is the light that has been scattered or reflected. The deeper the water, the more blue light is scattered and reflected, which is why the ocean always appears deep blue.
In contrast, warm colors such as red and orange can penetrate through all obstacles and shine directly downwards, but this light is constantly absorbed by the ocean water and marine organisms. This is the reason why river water does not appear blue like ocean water.
Interestingly, there is the Red Sea, where a type of red algae thrives and grows abundantly. Meanwhile, the Black Sea appears very dark because its water contains a high concentration of H2S (which darkens the water starting at depths of about 100 meters and below).
So Why Are Ocean Waves White?
A clear glass is colorless and transparent, and even when a glass breaks into pieces, those pieces remain transparent. However, when we sweep them together, they form a white pile. Moreover, the more fragmented the glass becomes, the whiter the collected pile appears. If the glass is broken into tiny particles (like powder), it resembles a pile of snow.
Ocean waves are composed of shattered glass particles, which diffuse the light and create a white appearance.
Why Is This the Case?
In fact, glass can transmit sunlight and also reflect it. When glass accumulates in piles, as light passes through, multiple refractions occur alongside reflections. The light rays, after undergoing several optical phenomena, are refracted or scattered in different directions. When our eyes encounter this light, it appears white.
Ocean waves are similar in that they consist of shattered glass particles, which also diffuse the light, creating a white appearance. This is why ocean water is blue while ocean waves appear white.
