Why does the sea look blue

Why is the sea actually blue?

From TRAVELBOOK | March 11, 2021, 12:28 p.m.

At the moment we are dreaming more about traveling and vacationing. We can't wait until we can finally go to the beach without any worries. How nice would it be to feel sand under your feet again and then cool off in the sea? But why is the sea actually blue?

Sometimes it's storm-lashed and gray, sometimes green like a tilted garden pond. Dream beaches in the South Seas are often located on turquoise water. Mostly, however, the sea presents itself to us in a deep blue color. How does the human perception of the color of the sea come about? Why does an ocean mostly look blue to us? TRAVELBOOK asked an expert.

“Many people think the sea is blue because the sky is blue and it is reflected by the water. Unfortunately, it's not that simple, ”explains Prof. Dr. Tobias Kampfrath, Professor of Experimental Physics at the Free University of Berlin. So why is the ocean blue then? According to Kampfrath, this mainly has to do with the extent to which the molecules of the water react to light radiation.

Professor explains why the sea is blue

“As soon as a ray of sun penetrates the sea water, two processes take place simultaneously: On the one hand, the light is absorbed by the water. On the other hand, it is scattered in all directions by the water molecules and can thus reach our eyes, ”explains Kampfrath. These two processes ensure that the scattered light contains more blue than red components.

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On the one hand, this is due to the fact that red light is more strongly absorbed than blue light. "This allows blue light to penetrate deeper into the water and so be scattered to us by more water molecules," says Kampfrath. In addition, because of its shorter wavelength, blue light is much more strongly scattered than red light, which has a much longer wavelength. So it happens that the sea appears blue to us.

According to Kampfrath, there is a second reason for the intense perception of the color blue in addition to the radiation of light on the water - namely the human eye itself. “Our visual organ is much more sensitive to blue and green radiation than to red. That is why we recognize a blue or green color spectrum much better, ”explains Kampfrath.

The color of the sea can change for a number of reasons

But now we all know that the sea is unfortunately not always bright and blue. We all know the gray to brownish picture that the Baltic Sea gives off in bad weather. And sometimes the sea is also very green in color. Professor Kampfrath explains: “The lighting conditions just described apply above all when the sea is clean and deep. There can of course be umpteen circumstances under which our color perception changes. "

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For example, with a high proportion of plants and plankton that secrete the green substance chlorophyll, the sea is perceived as greener. Mud and heavy weather, on the other hand, can make the sea look gray and brown. Whereas a white sandy bottom makes the waters of the Caribbean appear lighter.

Sometimes, when the proportion of microorganisms, algae and saltwater crabs, which produce the red substance beta-carotene, is very high in a body of water, it can also appear reddish or pink, which repeatedly leads to supernatural images of pink-colored rivers and lakes . The color of the sea is therefore by no means just “blue”, but rather changeable and dependent on numerous factors.

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