Fun with Science Club®


			Why is the Ocean Blue? Naval Meterological and Oceanography Command 03.19.01 The calm blue Gulf Stream. The exotic turquoise Caribbean Sea. The Pacific Ocean reflecting a brilliant coral sunset. Although seawater is usually thought to be deep blue, the world's waterways actually form a rainbow of colors. The sea appears to be blue for the same reason that the sky looks blue. Sunlight, composed of electro-magnetic radiation ranging in color from red to blue, is scattered by particles suspended in the water. The shorter blue wavelengths scatter more effectively and are absorbed less quickly than the longer red and orange wavelengths. Seawater appears blue for about 100 feet under the surface although a small percentage of undetectable blue light remains in the water down to the 600 foot level. At about 400 feet, color becomes indistinguishable and shadows disappear. After 600 feet, light absorption is so complete that the ocean appears black. Because the sea is a mirror of the sky, clouds or a sunset can further alter the water's color. An overcast day can change a bright blue lake to a steely grey. Light absorption explains blue water, but why is the Red Sea red and the Yellow Sea yellow? These colors are caused by microscopic organisms, silt, and mud, suspended in the water. Near some coastlines, microscopic floating plants exude yellow pigments which turn the normally blue water to green. Some algae release brownish-red pigments, hence the Red Sea. The Yellow Sea owes its hue to mud carried in by its contributing rivers. The color deepens during floods. Unlike most bodies of water, the Black Sea is landlocked with only one narrow, shallow outlet connecting it to the Mediterranean Sea, so there is little oxygen in the water except near the surface. This results in a heavy concentration of hydrogen sulphide near the bottom which colors the water black. Despite the many scientific reasons for the shifting colors of the oceans, the sea and its hues remain a subject of mystery and legend. As seawater changes from serene blue, to vivid aqua, to turbulent black, the sea often seems as moody as the humans who sail its surface


			Naval Meterological and Oceanography Command Public Affairs Office 1100 Balch Boulevard Stennis Space Center, Mississippi 39529