![]() ![]() In other words, phytoplankton respond very rapidly to changes in their environment. Scientists have found that a given population of phytoplankton can double its numbers about once per day. The larger the world's phytoplankton population, the more carbon dioxide gets pulled from the atmosphere, hence, the lower the average temperature due to lower volumes of this greenhouse gas. Phytoplankton use carbon dioxide for photosynthesis and in turn provide almost half the oxygen we breathe. These small organisms can affect a system on a very large scale such as climate change. The study of ocean color helps scientists gain a better understanding of phytoplankton and their impact on the Earth system. Since these substances are usually composed of organic carbon, researchers generally refer to these substances as colored dissolved organic matter, CDOM for short. There are other substances that may be found dissolved in the water that can also absorb light. The basic principle behind the remote sensing of ocean color from space is this: the more phytoplankton in the water, the greener it is.the less phytoplankton, the bluer it is. So, the ocean over regions with high concentrations of phytoplankton will appear as certain shades, from blue-green to green, depending upon the type and density of the phytoplankton population there. Due to this green pigment - chlorophyll - phytoplankton preferentially absorb the red and blue portions of the light spectrum (for photosynthesis) and reflect green light. The most important light-absorbing substance in the oceans is chlorophyll, which phytoplankton use to produce carbon by photosynthesis. The swirls of green are a phytoplankton bloom in the Gulf of California. Right Image: Although microscopic, phytoplankton can bloom in such large numbers that they can change the color of the ocean to such a degree that we can measure that change from space. ![]() All plants (on land and in the ocean) use chlorophyll to capture energy from the sun and through the process known as photosynthesis convert water and carbon dioxide into new plant material and oxygen. Left Image: Phytoplankton are very small, single-celled plants, generally smaller than the size of a pinhead that contain a green pigment called chlorophyll. Some types of particles (in particular, the cells of phytoplankton, also referred to as algae) can also contain substances that absorb certain wavelengths of light, which alters its characteristics. In coastal areas, runoff from rivers, resuspension of sand and silt from the bottom by tides, waves and storms and a number of other substances can change the color of the near-shore waters. If there are any particles suspended in the water, they will increase the scattering of light. The red, orange, yellow, and green wavelengths of light are absorbed so that the remaining light we see is composed of the shorter wavelength blues and violets. When sunlight hits the ocean, some of the light is reflected back directly but most of it penetrates the ocean surface and interacts with the water molecules that it encounters. The red, yellow, and green wavelengths of sunlight are absorbed by water molecules in the ocean. Almost all sunlight that enters the ocean is absorbed, except very close to the coast. In water, absorption is strong in the red and weak in the blue, thus red light is absorbed quickly in the ocean leaving blue. The blue wavelengths of light are scattered, similar to the scattering of blue light in the sky but absorption is a much larger factor than scattering for the clear ocean water. ![]() The reason the ocean is blue is due to the absorption and scattering of light. Pure water is perfectly clear, of course - but if there is a lot of water, and the water is very deep so that there are no reflections off the sea floor, the water appears as a very dark navy blue. For most of the world's oceans, your answer would be correct. If someone were to ask you what is the color of the ocean, chances are that you would answer that is was blue. Near the Bahama Islands, the lighter aqua colors are shallow water where the sunlight is reflecting off of the sand and reefs near the surface. This MODIS image of blue water in the Caribbean Sea looks blue because the sunlight is scattered by the water molecules. ![]()
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