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Findings raise ocean concerns

Posted: Wednesday, Jul 21st, 2010

Study by OSU botany professor shows phytoplankton dilution

A new NASA-supported analysis published in the journal “Ecology” by Michael Behrenfeld, a botany professor at Oregon State University and a leading international expert in using remote sensing technology to examine ocean productivity, challenges a long-standing theory about the growth of phytoplankton in the world’s oceans.

Behrenfeld’s research calls into question what’s known as the “critical depth hypothesis” developed in 1953 that phytoplankton bloomed in temperate oceans in the spring due to longer and brighter days and warming of the ocean surface. The warming created a surface layer of warm water atop denser cold water below, slower wind-driven mixing and holding the phytoplankton in the upper layer longer, allowing for faster growth.

Although based on “the best science and data available at the time,” the hypothesis contained a fundamental flaw, according to Behrenfeld, who said it failed to account for seasonal changes in zooplankton (microscopic marine animals) activity, in particular how fast they feed on phytoplankton. A nine-year analysis of satellite sensing records show that phytoplankton accumulation actually begins to surge in the winter, when it’s cold and darker.

“We’ve been paying too much attention to phytoplankton growth and way too little attention to loss rates, particularly consumption by zooplankton,” said Behrenfeld. “When zooplankton are abundant and can find food, they eat phytoplankton almost as fast as it grows.”

For the complete article see the 07-21-2010 issue.

Click here to purchase an electronic version of the 07-21-2010 paper.

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