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Hitching a Ride on African Dust Plumes	February 26, 2000, A NASA satellite image captures one of the largest dust storms ever to come out of North Africa.
By Mary Kelley Hoppe Hurricanes aren't the only thing that barrel across the Atlantic toward Florida. Giant dust storms rising out of the Saharan desert blow an estimated billion tons of dust out of Africa each year; about half of that eventually reaches the Caribbean and Florida, at times, invading every state east of the Rockies.

Contributing to everything from stuffy heads to asthma, the iron-rich dust plumes also produce spectacular red sunsets and may be responsible for red tides.

While dust has been blowing for millennia, dust clouds have intensified since the early 1970s following a prolonged drought in northern Africa. As the drought worsened, the amount of dust hitchhiking on trade winds across the Atlantic and into the Gulf of Mexico increased dramatically. Typically, Florida can expect two to three African dust storms a month each summer, with some riding in on hurricanes. The amount deposited varies depending on rainfall and other factors.

The dusty scourge that reaches our shores is a mixture of fine particulate clay and silica, less than 2 microns each – about a hundred times smaller than the diameter of a human hair. Once a particulate that small is inhaled, it is rarely breathed out. It has been known to contain everything from DDT, mercury and arsenic to camel and goat dung.

More recent studies of the particulate have confirmed the presence of live bacteria and fungi, microbial riders of the storm responsible for a host of maladies from coral disease to human respiratory ailments. Caribbean nations downwind are at greatest risk. Asthma afflicts nearly onequarter of the populace of Trinidad and Barbados, the first landfall west of the Saharan desert. Barbados alone has seen a 17-fold increase in asthma since 1973, according to the Caribbean Respiratory Association.

Science-sleuths in Tampa Bay have been studying the connections for years. “The first thing that really caught our attention was when the corals started dying,” says USGS geologist Eugene Shinn.

“I’ve been studying the coral reefs for over 40 years,” he added. “I knew that the coral demise in the Caribbean really peaked in 1983 and 1984 – and that just happened to be the period in which the most dust was coming over from Africa.”

The supporting data, culled from a University of Miami dust monitoring station on Barbados in operation since 1965, gave Shinn and others confidence they were on the right track.

With funding from NASA in 2001, USGS hired microbiologist Dale Griffin, who had just completed his doctoral candidacy in public health and environmental microbiology. “Dale hit the ground running,” Shinn said. “Within six months he had cultured more than 120 live microbes from dust storm samples taken in the Virgin Islands.”

Of the 65 live microbes Griffin was able to identify, 25% were known to cause plant diseases and about 10% were opportunistic human pathogens. Besides impacts to marine life and human health, agricultural crops also may be affected by spores and other organisms riding transcontinental winds.

Microbes aren’t the only long-distance dust-hoppers. In 1988, biologists documented the arrival of millions of live African grasshoppers — some up to three inches long — that had survived the trans-Atlantic dust blow to the Caribbean. Airborne pesticides continue to rain down. Still, it remains an uphill battle for Griffin and other ‘dust busters’ who say research has been underfunded and undervalued, even after recent anthrax scares heightened awareness of the potential for airborne biohazards.

Is African Dust Causing Red Tide?

Scientists also suspect a connection between African dust and red tide, harmful algal blooms that can result in fish kills and force costly beach closures.

“The dust coming over from Africa contains a lot of iron,” says University of South Florida graduate student Jason Lenes, who is completing his doctorate in biological oceanography. When iron is deposited in the water, a certain percentage dissolves and sparks production of bluegreen algae.

“What’s special about the blue-green algae,” Lenes explains, “is its ability to ‘fix’ nitrogen, converting it from an unusable form to a usable form – and it takes a lot of iron to do that.”

While red tide is a naturally occurring phenomenon, it may be induced by manmade factors. “When you’re dealing with the west Florida shelf, there aren’t a lot of nutrients out there, so it’s hard for us to explain how we get the amount of red tide we do.”

Lenes is modeling data from 1998 to 2001 to try to establish concurrence between African dust, rainfall and red tide.

While researchers can’t halt red tides, Lenes hopes the study will give them a predictive tool that can help fingerprint the unwelcome events weeks before they occur.

August 8, 2001, Two massive African dust storms cross the Atlantic ocean, while another storm circles back into the Atlantic after dusting the mid-Atlantic states. The transoceanic crossing takes anywhere from five to seven days.

Satellite images courtesy of US Geological Survey

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