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Dust deposited in oceans may carry elements toxic to marine algae
Date:3/9/2009

SANTA CRUZ, CA--Dust blown off the continents and deposited in the open ocean is an important source of nutrients for marine phytoplankton, the tiny algae that are the foundation of the ocean food web. But new findings show that some sources of dust also carry toxic elements that can kill marine phytoplankton.

Researchers discovered the toxic effects during a study of how phytoplankton respond to atmospheric aerosols deposited in the northern Red Sea. The results will be published in the online early edition of the Proceedings of the National Academy of Sciences (PNAS) the week of March 9, 2009.

"This is the first time that toxicity from atmospheric aerosols has been reported for the ocean system," said first author Adina Paytan, an associate researcher in the Insitute of Marine Sciences at the University of California, Santa Cruz.

"Oceanographers have always thought of dust deposition as good for phytoplankton, because it provides nutrients such as nitrogen, phosphorus, and iron. But we know air pollution has negative effects on the terrestrial side, and we need to think about the effects of pollutants that may be deposited in the oceans," she said.

Paytan and her coworkers collected aerosols on filters, incubated the samples with seawater, and observed the responses of phytoplankton. They found that the results depended on the wind direction. Aerosols collected from air masses originating over Europe stimulated phytoplankton growth, whereas aerosols from air originating over Africa, which carried dust from the Sahara Desert, had the opposite effect.

Aerosols from both sources supplied key nutrients such as nitrogen and phosphorus, but the Sahara sources also contained high concentrations of copper. "When we added the Sahara dust, the phytoplankton died within 24 hours," Paytan said. "We found that copper was really high in those samples, so we suspected that copper was causing the toxicity."

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Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California - Santa Cruz
Source:Eurekalert

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