Ocean Plant Life Slows Down and Absorbs Less Carbon

Credit: Images by Robert Simmon, NASA GSFC Earth Observatory, based on data provided by Watson Gregg, NASA GSFC
This image shows ocean net primary productivity distributions from the Coastal Zone Color Scanner (CZCS) aboard NASA's Nimbus-7 Satellite (1979-1986). The units are in grams of Carbon per meter squared per year.	This image shows ocean net primary productivity distributions from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data on the OrbView-2 satellite (1997-2002). The units are in grams of Carbon per meter squared per year. Light gray areas indicate missing data.

Plant life in the world's oceans has become less productive since the early 1980s, absorbing less carbon, which may in turn impact the Earth's carbon cycle, according to a study that combines NASA satellite data with NOAA surface observations of marine plants.

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.

For more information on the decline of ocean primary productivity, visit: http://www.gsfc.nasa.gov/topstory/2003/0815oceancarbon.html