Science Scoops: Killer Dust!

It comes from Africa. It travels thousands of miles. And when it gets here, it kills huge numbers of fish, shellfish, marine animals, and birds. It can even cause sickness in humans.

What is “it”? “It” is Saharan dust clouds. In the Gulf of Mexico off the coast of West Florida, windblown Saharan dust ultimately falls every year.

In a NASA-funded study, graduate student Jason Lenes (University of South Florida's College of Marine Science) and his colleagues used data from an imager aboard the National Oceanic and Atmospheric Administration—Polar Orbiting Environmental Satellites, as well as ground-based measurements, to track large dust clouds leaving Africa.

It turns out that storm activity in the Sahara Desert region generates clouds of dust that originate from fine particles in the arid topsoil, which contains iron. Easterly trade winds carry the dust across the Atlantic Ocean and into the Gulf of Mexico, where it is deposited. Once the Saharan dust is deposited, it fertilizes the water with iron, setting off blooms of red toxic algae commonly referred to as “red tides.”

The blooms are huge. In Lenes' study, they formed in an 8,100-square-mile region between Tampa Bay and Fort Myers, Florida. Around the Gulf of Mexico, millions of fish and hundreds of manatees have reportedly died in a single red tide bloom. And humans who swim in the Gulf during a red tide, or those who eat shellfish affected by it, can suffer severe ailments.

By using satellites to monitor the dispersal of Saharan dust and the onset of blooms, Lenes believes he may soon be able to forecast red tides. “If you could predict when a red tide is coming, you could close beaches and fisheries ahead of time,” he says.

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  1. What happens to the habitat in the Gulf of Mexico when Saharan dust is deposited in its waters?
    [anno: The Saharan dust changes the habitat of the Gulf of Mexico. The dust contains iron, which allows blooms of red algae to grow.]
  2. Why do you think that so many organisms die after a red tide?
    [anno: Answers may vary, but could include that the red algae disrupts the entire food web that occurs naturally in the Gulf of Mexico. Students may theorize about what the red algae specifically disrupts, such as the growth of green algae.]
  3. Do you think that red tides might be beneficial in any way? Why or why not? Write a few sentences to explain your answer.
    [anno: Answers will vary.]