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SCIENCE FILE / An exploration of issues and trends
affecting science, medicine and the environment

I Didn't Know That. . .

May 18, 2000

Q: Why is the ocean blue? Because it reflects the sky?

A: The ocean is blue because all water--fresh and salt alike--is blue, albeit a very light, faint blue. The color is so faint that, if you look through a glass of water, it appears colorless. But if you fill a white bathtub, you will clearly see a blue tint. The color exists because water molecules absorb the orange and red portions of sunlight slightly more strongly than blue, thus reflecting more blue back to the viewer, according to chemist Robert L. Wolke, author of "What Einstein Told His Barber." Of course, the oceans contain a variety of other materials that influence color. Phytoplankton--very small plant life--scatters green light very effectively, giving ocean water that contains it a strong greenish coloration. Water also contains a variety of dissolved and suspended organic matter that is yellow when dry, and because of its absorption properties, higher concentrations of this matter shift the water's color from its normal pale blue to a deeper, purplish blue.

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