WASHINGTON - New findings have shown that some sources of dust that is deposited in oceans also carry toxic elements that can kill marine alagae.
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, in a study of how phytoplankton respond to atmospheric aerosols deposited in the northern Red Sea, researchers have discovered the toxic effects that some sources of dust can have on the marine algae.
“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.
According to Paytan, “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 added.
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,” she added.
To investigate the global implications of atmospheric copper deposition, the researchers gathered data from various sources on copper concentrations in aerosols, global distributions of aerosols, and aerosol deposition rates.
Using an atmospheric deposition model, they calculated rates of copper deposition in different areas of the oceans.
They also estimated the contribution of manmade sources of copper compared to pre-industrial rates of copper deposition.
Their analysis suggests that manmade sources account for about 40 percent of the copper deposited in the oceans from atmospheric aerosols.
“Although most of the copper deposition comes from natural sources of dust, the manmade sources are likely to increase over time,” Paytan said.
In addition, there may be other pollutants in atmospheric aerosols that could also have toxic effects on marine phytoplankton.
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