WHY IS THE OCEAN BLUE?
Sunlight is made up of all the colors of the rainbow: red, orange, yellow, green, blue, and violet. Some of the sunlight is reflected off the surface of the water, reflecting the color of the sky. Some of the sunlight penetrates the water and is scattered by ripples and particles in the water (this tinges the appearance of the ocean with the color of the particles). In deep water, much of the sunlight is scattered by the oxygen in the water, and this scatters more of the blue light.
Water absorbs more of the red light in sunlight; the water also enhances the scattering of blue light. Sir Chandrasekhar Venkata Raman (an Indian physicist) won the Nobel prize in 1930 for his work on light.
Some Oddly-Colored Seas:
The Red Sea often looks red because of red algae that live in this sea.
The Black Sea looks almost black because it has a high concentration of hydrogen sulfide (which appears black).
There are several theories:
- Blue wavelengths are absorbed the least by the deep ocean water and are scattered and reflected back to the observer’s eye
- Particles in the water may help to reflect blue light
- The ocean reflects the blue sky
Most of the time the ocean appears to be blue because this is the color our eyes see. But the ocean can be many other colors depending upon particles in the water, the depth of the water, and the amount of skylight.
The colors we see depend upon the reflection of the visible wavelengths of light to our eyes. The Franklin Institute provides a good explanation of how we see color at http://www.fi.edu/color/color.html.
Wavelengths of light pass through matter differently depending on the material’s composition. Blue wavelengths are transmitted to greater depths of the ocean, while red wavelengths are absorbed quickly. Water molecules scatter blue wavelengths by absorbing the light waves, and then rapidly reemitting the light waves in different directions. That is why there are mostly blue wavelengths that are reflected back to our eyes.
Sometimes oceans look green. This may be because there is an abundance of plant life or sediment from rivers that flow into the ocean. The blue light is absorbed more and the yellow pigments from plants mix with the blue light waves to produce the color green.
Sometimes parts of the oceans will look milky brown after a storm passes. This is because winds and currents associated with the storm churn up sand and sediment from the rivers that lead into the oceans.
The ocean may also reflect the blue sky. However this is prominent only at relatively low angles and when the water is smooth.