Microscopic ocean plants called phytoplankton account for about half the transfer of carbon dioxide (CO2) from the environment into plant cells by photosynthesis. Land plants pull in the other half. In the atmosphere, CO2 is a heat- trapping greenhouse gas.

Watson Gregg, a NASA GSFC researcher and lead author of the study, finds that the oceans' net primary productivity (NPP) has declined more than 6 percent globally over the last two decades, possibly as a result of climatic changes. NPP is the rate at which plant cells take in CO2 during photosynthesis from sunlight, using the carbon for growth. The NASA funded study appears in a recent issue of Geophysical Research Letters.

"This research shows ocean primary productivity is declining, and it may be a result of climate changes such as increased temperatures and decreased iron deposition into parts of the oceans. This has major implications for the global carbon cycle," Gregg said. Iron from trans-continental dust clouds is an important nutrient for phytoplankton, and when lacking can keep populations from growing.

Gregg and colleagues used two datasets from NASA satellites: one from the Coastal Zone Color Scanner aboard NASA's Nimbus- 7 satellite (1979-1986); and another from Sea-viewing Wide Field-of-view Sensor data on the OrbView-2 satellite (1997- 2002).

The satellites monitor the green pigment in plants, or chlorophyll, which leads to estimates of phytoplankton amounts. The older data was reanalyzed to conform to modern standards, which helped make the two data records consistent with each other. The sets were blende
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Contact: Krishna Ramanujan
kramanuj@pop900.gsfc.nasa.gov
301-286-3026
NASA/Goddard Space Flight Center
16-Sep-2003