UNIVERSITY OF MIAMI ROSENSTIEL SCHOOL
OF MARINE AND ATMOSPHERIC SCIENCE
4600 Rickenbacker Causeway
Miami, Florida 33149
Home page: http://www.rsmas.miami.edu
More Science Snapshots

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Dust in the Wind: African Aerosolized Particles and its Many Impacts

Nearly 40 years ago scientists believed that Africa was too far away for its climate variations to have much, if any, effect on the United States and the Caribbean. We now know that those first assumptions were wrong. The clouds of dust blowing through the lower atmosphere from African deserts can have substantial effects on Western Atlantic weather. This dry, dusty layer is surprisingly influential on climate change, community health, and ocean environments, both positively and negatively.

African dust and the Saharan Air Layer refer generally to the dust-laden layer of the lower atmosphere where tiny particles of dust can accumulate that originate in the the areas south of the Sahara Desert, the Soudano - Sahel regions of Northern Africa. Propelled westward across the Atlantic Ocean by the motion of fierce trade winds and atmospheric waves, the dust is surprisingly still discernible in the Caribbean, as in the photos to the left, which were taken around Barbados. Satellite imagery is able to capture these tiny dust particles and their path, enabling scientists to study the aerosolized particles and their profound impacts.

Dissolved dust

Elemental iron inputs from the atmosphere to oceans are now recognized as capable of having a significant impact on the globe's chemical, physical, geological, and biological processes, as well as the reactions that govern the natural environment. Atmospheric dust (a major source of oceanic elemental iron) emerges as a concern to marine researchers as it falls from the atmosphere over the Atlantic Ocean, changing the chemistry of the open ocean. While some believe African dust deposits contribute to the amount of photosynthetic organisms in the upper ocean -- a process many believe results in more frequent and longer harmful algal blooms -- these particles are hardly the culprits that nitrates, phosphates and other pollutants are in causing red tide. These changes in marine chemistry can interrupt the fragile balance of life in ocean environments, however. Some Rosenstiel School scientists have noted Saharan dust transport in the Mediterranean region also, where this “dust” may be responsible for increases in marine productivity, thus provoking species overpopulation and the die-out of previously dominant organisms. Rosenstiel School scientists also study the effects dust has on cloud formation and precipitation over the Atlantic, hoping that their research may link climate variability in West Africa to that of the tropical Atlantic. This research could lead to faster and more accurate weather pattern forecasts in the United States.

Taming tropical cyclones

The Atlantic hurricane season of 2006 turned out to be a tame one, and most scientists credit African dust and its surprising and impressive way of “drying out” these wet, wild weather systems. In cooperation with several other research facilities, Rosenstiel School scientists are looking into the long-range impacts of African dust on tropical cyclones. The dust has a strong suppressant effect on hurricanes as it overtakes a cyclone and creates wind shear, stopping the storm and even wiping it out completely; this effect has been noted as far west as the coastal waters of the southern and eastern United States. With more research into these phenomena, scientists are hoping to understand the ways that African climate changes affect storms in the tropical Atlantic. This research may also help to improve meteorologic predictions.

Asthma aggravation?

The U.S. Environmental Protection Agency defines nearly half of the dust suspended in the atmosphere as “respirable” or particles that one can inhale. Some scientists have conjectured that African dust exacerbates asthma. However, Rosenstiel School scientists have not been able to confirm that phenomenon on a daily basis, seasonal basis, or even annual basis. One way of studying this issue, for example, has led to the scientist's accrual of two years of data on daily dust levels and daily patient load -- particularly children -- at the hospital's asthma clinic there.

Strong dust

Rosenstiel School researchers seek the “how” and “why” of these organisms' resilience as they travel through the harsh middle and upper layers of the troposphere. The researchers measure bacteria and fungi levels, and inferences have been made and theories established that connect various plant disease outbreaks in the Caribbean with disease outbreaks in western Africa.

By understanding the impact these small particles have on our continent, an ocean away, Rosenstiel School scientists may have global impacts on human health, shed light on climate change, and broaden our perspective on other environmental issues.