Question Why is the ocean blue?

Answer

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 Pantone.com website provides a good explanation of how we see color.External

Blue Ocean. Tadashi Ikai, 2015. Prints & Photographs Division, Library of Congress

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 re-emitting 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.