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Plummeting plankton linked to warmer oceans

This image from NASA's SeaWiFs satellite documents summer phytoplankton concentrations between 1997 and 2000. Reds, yellows, greens and blues depict higher to lower population densities.
This image from NASA's SeaWiFs satellite documents summer phytoplankton concentrations between 1997 and 2000. Reds, yellows, greens and blues depict higher to lower population densities.  


By Richard Stenger
CNN

(CNN) -- Concentrations of microscopic plants that comprise the foundation of the ocean's food supply have fallen during the past 20 years as much as 30 percent in northern oceans, according to a satellite checkup of planetary health.

The shrinking population of phytoplankton could be associated with regional or global climate changes, said scientists, who combed through data from numerous U.S. orbiting spacecraft.

The mini-water plants, which thrive on sunlight and nutrients, have dwindled particularly in places characterized by rising ocean surface temperatures and declining ocean winds.

The reason for the lower numbers could be that warming water layers on top prevent cooler and more nutrient-rich waters down below from reaching the surface-dwelling plankton, which are crucial to the survival of many ocean species, the scientists said.

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"The whole marine food chain depends on the health and productivity of the phytoplankton," said researcher Watson Gregg of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

By measuring surface readings of chlorophyll concentrations, Gregg and colleague Margarita Conkright of the National Oceanic and Atmospheric Administration (NOAA) determined that phytoplankton levels in the Northern Pacific Ocean dropped more than 30 percent since the 1980s.

The North Atlantic Ocean experienced a 14 percent decline in the same period.

"This is the first time that we are really talking about the ocean chlorophyll and showing that the ocean's biology is changing, possibly as a result of climate change," Conkright said.

Whether the changes are caused by long-term global or short-term regional cycles remains unknown, the scientists said.

In some locations, especially the equatorial regions, phytoplankon concentrations actually increased during the time period. But overall, across the entire planet, there was a net decline, they said.

Besides fueling the food chain, phytoplankton plays a crucial role in cycling a primary greenhouse gas through the environment.

Phytoplankton accounts for 50 percent of the transfer of carbon dioxide from the atmosphere back into the biosphere through photosynthesis, the process through which plants absorb carbon dioxide gas to grow.