[Athena] [Curriculum] [Oceans]

Ocean Color Viewed from Space

What color is the ocean? The ocean reflects the color of the sky, but even on cloudless days the color of the ocean is not a consistent blue. Phytoplankton, microscopic plant life that floats freely in the lighted surface waters, may alter the color of the water. When a great number of organisms are concentrated in an area, the plankton changes the color of the ocean surface. This is called a "bloom." This photograph shows such a change in color. It was taken by astronauts aboard the space shuttle looking down at the coast of Angola.

Microscopic plant life is at the base of the marine food web and is the primary food and energy source for the ocean ecosystem. Phytoplankton convert nutrients into plant material by using sunlight with the help of the green pigment chlorophyll. The chlorophyll pigments in the plants absorb light, and the plants themselves scatter light. Together, these processes change the color of the ocean as seen by an observer looking downward into the sea. Very productive water with a high concentration of plankton appears blue-green. Very pure water appears deep-blue, almost black.

From space, variations in ocean color can be measured with sensitive instruments. Ocean and land plants are green because chlorophyll absorbs red light but reflects blue and yellow light. Satellite instruments measure the amount of reflected light of different wavelengths. These amounts allow scientists to estimate the productivity of Earth's land masses and oceans. The false color images below show these estimates of plankton distribution and productivity in the world's oceans.

False Color Images of Ocean Color

Click on the map to see a larger view
The sunlit surface layer of the ocean can be full of microscopic plants and animals. As the legend shows, the red areas contain the most life, while the purple areas are nearly empty of life. The number values on the scale indicate the milligrams of phytoplankton per cubic meter of sea water. While the organisms are microscopic, large numbers result in a measurable mass when filtered from the water. Ocean areas of high productivity support more life than less productive areas. It is as simple as more food = more fish. More oxygen is produced and carbon dioxide consumed in these highly productive areas of the ocean.

The plankton populations are dependent on a variety of factors, including ocean currents, temperature, availability of nutrients, amount of sunlight, and ocean depth. Many different species of plankton contribute to ocean color, although only a few species, occurring in great numbers, are found at any one time or place. The individual plants live at various depths, from the surface to nearly 100 meters, but prefer the surface sunlit regions with sufficient light to support photosynthesis.

In the ocean, as on land, plants are the foundation of the food chain on which all other organisms depend. The productivity of the ocean is very important to human activities and to the overall health of the planet. Remote-sensing of the productivity of the oceans through the use of instruments aboard satellites helps us better understand this vast frontier.

Science Journal


Continental Vegetation Detected from Space

Click on the map to see a larger view
Variations in "greenness" in the image show the productivity of plant life on the continents. This is also a false color image. The image shows both the ocean and the land productivity by detecting variation in the presence of the pigment chlorophyll (the green coloring in plants) using remote-sensing instruments aboard satellites.

Science Journal

As you record your observations focus on the land areas.

Summary

On land, we can judge the productivity of an environment by observing its "greenness." Tropical rain forests are more productive than deserts or arctic tundra. These differences in color can be observed from space. From space, sensitive instruments can measure variations in amounts of reflected light. This data is then mathematically sorted with formulas that estimate productivity from the measurements. False color images are produced like those you have examined in this lesson. The images indicate the presence of plants through detection of the plant pigment clorophyll. Photographs taken from space can show differences in the productivity of the land and oceans, but not with the precision and detail that the false color images yield.
This movie shows the distribution of plant life on Earth from satellite measurements in space. As the movie plays and Earth rotates, observe the pattern visible in the different latitudes. Make some generalizations.


Image Credits

Images and movie from SeaWiFS Project Home Page
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Last Modified Thu Jul 27 10:15:02 1995