Source of Half Earth's Oxygen Gets Little Credit

John Roach
for National Geographic News
June 7, 2004

Fish, whales, dolphins, crabs, seabirds, and just about everything else that makes a living in or off of the oceans owe their existence to phytoplankton, one-celled plants that live at the ocean surface.

Phytoplankton are at the base of what scientists refer to as oceanic biological productivity, the ability of a water body to support life such as plants, fish, and wildlife.

"A measure of productivity is the net amount of carbon dioxide taken up by phytoplankton," said Jorge Sarmiento, a professor of atmospheric and ocean sciences at Princeton University in New Jersey.

The one-celled plants use energy from the sun to convert carbon dioxide and nutrients into complex organic compounds, which form new plant material. This process, known as photosynthesis, is how phytoplankton grow.

Herbivorous marine creatures eat the phytoplankton. Carnivores, in turn, eat the herbivores, and so on up the food chain to the top predators like killer whales and sharks.

But how does the ocean supply the nutrients that phytoplankton need to survive and to support everything else that makes a living in or off the ocean? Details surrounding that answer are precisely what Sarmiento hopes to learn.

Robert Frouin, a research meteorologist with the Scripps Institution of Oceanography in La Jolla, California, said understanding the process by which phytoplankton obtains ocean nutrients is important to understanding the link between the ocean and global climate.

"Marine biogeochemical processes both respond to and influence climate," Frouin said. "A change in phytoplankton abundance and species may result from changes in the physical processes controlling the supply of nutrients and sunlight availability."

Oxygen Supply

Phytoplankton need two things for photosynthesis and thus their survival: energy from the sun and nutrients from the water. Phytoplankton absorb both across their cell walls.

In the process of photosynthesis, phytoplankton release oxygen into the water. Half of the world's oxygen is produced via phytoplankton photosynthesis. The other half is produced via photosynthesis on land by trees, shrubs, grasses, and other plants.

Continued on Next Page >>


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