Wednesday, December 6, 2006 03 12 PM
When the climate warms, there is a drop in the abundance of the ocean's phytoplankton, the tiny plants that feed krill, fish and whales, according to scientists who say the just-released research offers new clues to future life under global warming.
Ocean temperatures bounce up and down, but over the past century they have been warming along with the atmosphere. Nine years of NASA satellite data released today in the journal Nature show that the growth of phytoplankton drops in warm ocean years and increases in cooler ocean years.
Over the past decades, scientists have linked declining plankton numbers to warm-water El Nino years, which set off a domino effect of fewer krill and young fish, leading to failed reproduction of seabirds and even deaths of seals and sea lions.
"We've seen it on a regional scale. What's amazing is this is the first time we see it on a global scale. Now we have an inkling what will now happen to the ocean's biology in future climates,'' said Dave Siegel, a professor of marine science at UC Santa Barbara and a study author.
The scientists report that the association between warmer ocean waters and fewer plankton was born out in three-quarters of the ocean.
When the climate warms, the ocean's upper layer where the phytoplankton proliferate becomes separated from the colder ocean water below. The ocean waters then can't mix as well, and nutrients in the deeper, colder waters don't get up to the phytoplankton that uses them as a sort of fertilizer.
The lack of phytoplankton means less food for fish and other ocean life, but it also means less phytoplankton to absorb carbon dioxide, a greenhouse gas.
The research is the result of years of collaboration among UC Santa Barbara, Oregon State University, Princeton University, Rutgers University, University of Maine and NASA's Goddard Space Flight Center in Greenbelt, Md.
E-mail Jane Kay at jkay@sfchronicle.com.
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