Killing dust

African dust clouds cause red tides that kill millions of fish in the Gulf of Mexico

Published: Monday 15 October 2001

huge dust clouds blowing across the Atlantic Ocean from the Sahara Desert cause red tides in the Gulf of Mexico, reveals a new study. Red tides, which are blooms of toxic algae, kill the gulf's marine life in large quantities. But this can be prevented, indicates the study done by students at University of South Florida's College of Marine Science, usa , (, August 31, 2001).

Usually, storm activities in the Sahara Desert region kick up fine particles of the arid soil, generating vast clouds of dust. This dust is carried by easterly trade winds across the Atlantic Ocean and into the Gulf of Mexico. The study shows that these clouds fertilise the water off the West Florida coast with iron. Plant-like bacteria use the iron to set the stage for red tides. When iron levels go up, these bacteria, called Trichodesmium , fix nitrogen in the water. The addition of biologically usable nitrogen in the water makes the Gulf of Mexico suitable for the toxic algae to bloom. "This is one of the first studies that quantitatively measures iron from the dust and links it to red tides through Trichodesmium ," says Jason Lenes, lead author of the study.

The study used satellite and ground-based measurements to track large dust clouds leaving Africa on June 17, 1999. The Saharan dust reached the West Florida region around July 1, increasing iron concentrations in the surface waters by 300 per cent. As a result, Trichodesmium counts shot up to 10 times what they had been prior to this event. Through a complex process involving a special enzyme called nitrogenase, the Trichodesmium used the iron to convert nitrogen in the water to a form more usable for other marine life. In October, after a 300 per cent increase of this biologically-accessible nitrogen, a huge bloom of toxic red algae had formed within the study area -- a 2,0976.9 square kilometre region between Tampa Bay and Fort Myers, Florida. For several years, scientists have tried to find ways to predict red tides because the results of these blooms can be devastating. This study might at least help in averting the disaster in the Gulf of Mexico. "If you could predict when a red tide is coming, you could close fisheries ahead of time," Lenes said. According to him space-based data can help scientists predict when red tides will strike the Gulf coast.

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