The "color" of the ocean is determined by the interactions of light with
the water. We see color when light is reflected by objects around us. White
light is
made up of a spectrum or combination of colors, which are broken apart by water droplets in a rainbow. When light
hits the surface of an object, the different colors can be absorbed,
transmitted, scattered, or reflected in differing intensities. The color we see depends
on which colors are reflected. For example, a book that appears red to us
absorbs more of the green and blue
parts of the white light shining on it, and reflects the red parts. The
light which is scattered or transmitted by most objects is usually not
apparent to our eyes.
The substances in seawater which most affect the color reflected are,
phytoplankton, inorganic particles, dissolved organic chemicals, and the
water itself. Phytoplankton contain
chlorophyll, which absorbs red and blue light and reflects
green light. Particles can reflect and absorb light, which reduces
the clarity (light transmission) of the
water. Dissolved organic matter strongly absorbs blue light, and its
presence can interfere with measurements of chlorophyll.
When we look at the ocean or observe it from space, we see that the ocean
is blue because water absorbs red and reflects blue light. Using
instruments that are more sensitive than the
human eye, we can measure a wide array of blue shades, which reveal the
presence of varying amounts of phytoplankton, sediments, and dissolved
organic chemicals.