Background:
Phytoplankton are overlooked and for good reason! Each one is tiny and can only be viewed with a microscope. But their large numbers actually change the color of the ocean. Scientists estimate that phytoplankton contribute between 50 to 75% of Earth's atmospheric oxygen supply.

How does our world affect these tiny organisms? Even though they are tiny, they represent one of the most enduring forms of life on Earth. They have survived cataclysmic events such as asteroid hits, Ice Ages, tectonic changes and changes in the atmosphere's composition.
 
Phytoplankton are microscopic organisms that, tiny as they are, perform a huge service for our Earth. They provide food for marine life and oxygen for human life, and account for over half of photosynthesis on Earth. These tiny, floating, microscopic organisms produce more oxygen than all the tropical rain forests on the Earth. They also help to reduce the amount of carbon dioxide in the Earth's atmosphere through photosynthesis, the process of converting the solar energy to chemical energy. Phytoplankton are photosynthetic autotrophs (self-feeders) and “primary producers,” which means that they form the foundation of the food chain. Phytoplankton blooms have been called "the pasture of the sea" because they serve as a food source for heterotrophs (organisms that feed on others)!

Typical phytoplankton include diatoms, dinoflagellates and cyanobacteria (algae). A few examples are shown below, courtesy of http://bluebonnet.pai.utexas.edu/infores/utex/ and SeaWiFs.
 

Halochlorococcum

Halochlorococcum (or halosphaera) is famous because under certain conditions, it causes red tides.
Lauderia

Lauderia is a species of ocean dwelling diatom

 

For more pictures of freshwater phytoplankton visit http://dixon.gso.uri.edu/john/phyto.html.

 
Phytoplankton require a constant energy source. Because they are autotrophs, they obtain their energy from the sun. Like plants, they convert the sunlight energy into chemical energy (photosynthesis). As a result of this energy conversion, they also produce waste. Oxygen, nitrous oxide, sulfides, and methane are a few examples of phytoplankton's waste. Like all biotic factors, phytoplankton are affected by abiotic factors.
 
The Earth is a complex system composed of these subsystems: the hydrosphere(water), the lithosphere(solid earth), the atmosphere(air), and the biosphere(living things). All of these components are interrelated. Every interaction that occurs on the planet has impact on the other subsystems of Earth. For example, a volcano alters not only the landscape of Earth but also the atmospheric contents. This, in turn, alters the amount of precipitation, which can change the population growth rates of living organisms. These interactions have resulted in the evolution of the Earth system. This premise is essential to our understanding of Earth.
 
In the Earth system, abiotic factors have an impact on the living factors (biotic). This investigation will address relationships between these factors in the case of phytoplankton.

For more background on studying ocean color from space, and the role of phytoplankton in the Earth system, see the SeaWiFS Project’s “Studying Ocean Color From Space Teacher's Guide with Activities” (http://seawifs.gsfc.nasa.gov/SEAWIFS/LIVING_OCEAN/)

Procedure:

Using information resources on the Internet, we will examine the following variables from the abiotic spheres:
 
A. Light
1. What do the ocean colors represent in this map?
 
 
 
 
2. What does the notation, mg/m3, mean?
3. Phytoplankton are microscopic organisms. The amount of chlorophyll in each organism varies broadly, depending on their age, the depth at which they live, how much light they receive, and other factors. Chlorophyll is the green pigment that makes photosynthesis possible. How would you estimate the number of organisms you would need in order to extract 1 mg of this pigment? (This is the hot question for scientists who study the marine biosphere; it is the subject of much current research and controversy.)
4. The m3 indicates a cubic meter of water. Visualize how much space that would occupy. Given that each organism is 10-20 microns in diameter (1 micron = 10-6 meters), visualize how many phytoplankton would exists in 1 m3?
5. What factors do you think would influence the distribution of 0.1 mg in a m3 of sea water?

Compare the amount of phytoplankton that is produced under conditions of low or sharply angled light with the amount produced in conditions of plentiful light. The map above is a 9 year annual average. Locate an area that has very small amounts of phytoplankton and enter its name. Now locate an area that has abundant phytoplankton and enter the name of this region as well. With those two regions in mind, consider the following facts, then answer the questions at the end of this section.

Energy is radiated from the Sun to the Earth in the form of light. The angle of light rays hitting the Earth is known as the “angle of incidence” and is important in determining the amount of energy received by an organism. When the Sun is directly overhead, its angle of incidence is 90 degrees. Because of the Earth’s tilted axis, the further from the Equator, the more acute the angle of incidence, hence less energy is received in these regions.

Remember that the Northern hemisphere tilts toward the Sun between March and September. This means that the angle of incidence of sunlight is more direct. Would this result in the accumulation of more or less energy? Phytoplankton require light to perform photosynthesis. If there is sufficient light energy, the living organism can not only provide for its own needs, it will be able to reproduce rapidly. Can you tell which of the two images below represents a winter seasonal average, and which one represents spring?
 
 
Now examine the four seasonal averages below.
 
Global phytoplankton concentrations change seasonally, as revealed by these three-month "climatological" composites for all months between November 1978-June 1986, during which the CZCS collected data: January-March (upper left), April-June (upper right), July-September (lower left), and October-December (lower right). Note the phytoplankton bloom over the entire North Atlantic with the advent of northern hemisphere spring, and seasonal increases in equatorial phytoplankton concentrations in both Atlantic and Pacific Oceans, and off the western coasts of Africa and Peru
(Images & caption: http://daac.gsfc.nasa.gov/WORKINPROGRESS/OCDST/ocdst_global_seasonal_change.html)
 
6. Where do you see concentrations of phytoplankton located in each season? Enter this information into your worksheet.
7. During the time of highest phytoplankton population, is the angle of incidence of sunlight high or low?
8. In these images, red, yellow, and green indicate higher concentration of chlorophyll. Overlay graphpaper on the screen to estimate (in mg/m3) the combined areas covered by these colors in the Jan-Mar composite. [Optional extension: use an image processing software application, such as NIH Image, to do a precise pixel count for each color.]
9. Do the same for the April - June composite.
10. What areas seem to thrive regardless of season? Enter this information into your worksheet.
11. What conclusions can you state about phytoplankton growth under varied
conditions of light?
 
B. Temperature
Compare the amount of phytoplankton that is produced under conditions of high and low temperatures. Remember that the temperature of the ocean is higher near the Equator than it is near the Poles, but there are some significant departures from this trend: examine the set of four sea surface temperature maps (based on data from 1987) to get an idea of regional variations of seasonal temperature changes. Pay particular attention to the coastline of each continent: which ones seem to harbor cooler waters throughout the year?
 
 
C. Regional Studies
 
Go to Nimbus 7 Geographic Regions Maps to view the map of South America.
 
1. Identify areas of heavy plankton concentration by describing the characteristics of this geographic region.
(Refer to World map for additional help)
2. Are these areas close to the Equator or close to the South Pole?
3. What conclusions can you draw from these observations?
4. Repeat this procedure for the Mediterranean Sea and the North Sea.
5. Which of these areas is closest to the Equator?
6. Which has the largest concentration of phytoplankton?
7. What conclusions can you draw from comparison of the two areas?
8. Does sea temperature effect phytoplankton concentration? How?
D. Challenging your expectations
 
Go to the Nimbus 7 Interactive Region Map
 
1. Choose a zoom factor of 6.
2. Select a box of 1 X 1.
3. Place cursor on the west coast of Africa and click.
4. What do you suppose the average water temperature would be at this latitude?
5. Is the phytoplankton concentration consistent with your findings from the previous investigations?
6. Use the same procedure to check other equatorial regions.
7. Give possible explanations for your discoveries.
8. Repeat this procedure for the Arctic, Antarctica, Australia, the Indian Ocean, and the Northwest and Northeast Pacific regions.
E. Analysis and Conclusions
 
1. What conditions do phytoplankton life processes require?
2. What conditions produce the most abundant phytoplankton concentrations?
3. In what areas of the Earth do these conditions exist?
4. Are there other factors in addition to light energy and temperature that cause phytoplankton to grow? List some ideas.
5. How could you verify your ideas?
6. How does phytoplankton, a biotic component of Earth systems, respond to changes in the atmosphere and hydrosphere. Complete the chart by placing a + or - mg/m3 in the appropriate box. Fill in the last two columns with your suggested variables.
 

Phytoplankton

Growth 

 More Light  Less Light

More

Temp.

Less

Temp.

   
 Australia            
Indian Ocean            
Northwest Pacific            
South America            
Mediterranean            
Northeast Pacific            
North Atlantic            
Arctic            
Antarctica            

 

7. If phytoplankton are at the base of the food chain, where would you go to observe many different species of aquatic mammals feeding? What time of year would you go?
8. Refer to "Ocean Color from Space" at NASA: Goddard Space Flight Center http://daac.gsfc.nasa.gov//WORKINPROGRESS/OCDST/OCDST/ocean_color_from_space.html.
for more background information and as a starting point to discuss the results you've gathered in your table.
9. To continue your research with data from a current mission that is studying ocean color, go to the SeaWiFS home page and use the interactive image screen to see new data gathered since September 1997.
10. To continue your research on the marine biosphere up through higher levels of the food chain, go to Investigation 3.7: "Sea Mammals".
 
Coding:
 

Maryland Core Learning Goals (Science): 1.1, 2.2, 3.1, 3.3, 5.1
National Standards (Science): A.1, A.3, A.4, A.5, C.4, D.1, E.1, F.5
National Standards (Geography): 1, 3, 7, 8, 16.1
National Standards (Mathematics): 6.1, 6.3, 2.1, 7.2, 2.3

 
 
Credits:
Carolyn Ossont, Principal Investigator
David Kistler
David Hixson
Lisa Taschenberger
Editor: Farzad Mahootian
Scientist: Gene Feldman