Phytoplankton is the "grass" of oceans: microscopic plants that are the foundation of the food chain. Like land-based plants, phytoplankton requires sunlight, water and nutrients to grow. That's why it is mostly found at or near the surface of the ocean. There are many different species, each with a distinctive shape. But they all get their green color from chlorophyll, the pigment they use during photosynthesis.
Photosynthesis is the process by which plants convert carbon dioxide into oxygen and carbohydrates to make their own food. This involves a complicated series of chemical reactions, fueled by sunlight. First, the light energy converts water into an oxygen molecule, a positively charged hydrogen ion, and a free electron. Then all three combine to make a sugar molecule. Each of these reactions takes place in a reaction center -- a kind of chemical factory for producing energy.
Along with other algae and plants, phytoplankton is the source of most of the oxygen in the earth's atmosphere. Because phytoplankton relies on carbon dioxide for photosynthesis, the larger the world's population of phytoplankton, the more carbon dioxide gets pulled from the atmosphere. This reduces the volume of greenhouse gases and lowers the average temperature. Populations of phytoplankton are very sensitive to changes in climate conditions, capable of doubling in a single day in ideal conditions. A sudden decrease in phytoplankton alerts scientists to significant changes in environmental or climate conditions.
The American Meteorological Society contributed to the information in the TV report.