How Green Is Thy Ocean?

A satellite that should give scientists the big picture of plant life in the oceans was launched this afternoon from an L-1011 jet flying at 10 kilometers over the Pacific Ocean. The NASA instrument, called the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), sits aboard a commercial satellite that rode a Pegasus rocket to its perch 700 kilometers up. There it will monitor the changing color of Earth's oceans, which in turn should reveal the growth and death cycles of microscopic ocean plants on a global scale and help establish their role in climate change.

After a month of final positioning and calibration, SeaWiFS will begin sending a complete color picture of Earth's surface every 2 days, offering broader and more frequent coverage than any earlier oceanographic satellite. "We know almost nothing about the biological time scales in the oceans. Our measuring ability has never been up to the task," says NASA oceanographer Gene Carl Feldman.

By measuring the cycles of plankton growth, scientists should learn how much carbon dioxide, a greenhouse gas, the plankton absorb from the atmosphere and refine models of global warming. "It's one of the biggest uncertainties in the model," Feldman says. "The data from SeaWiFS should help the modelers get their numbers right."

Scientists are also interested in watching how the El Niño current that is now warming the eastern Pacific affects phytoplankton growth, says SeaWiFS project scientist Charles McClain. Climatologists know that an El Niño can push back the cold water upwellings in the eastern Pacific that bring nutrients to phytoplankton there. "When the upwelling ceases, the plankton don't have anything to grow on, so they disappear," says McClain. Everything else in the ocean food web depends on phytoplankton, so the satellite data--contracted for 5 years from Orbital Sciences Corp. of Fairfax, Virginia--could reveal much about El Niño's impact on ocean ecosystems, says McClain.