Aerosol studies have been carried out at a coastal site on Barbados, West Indies (13.18°N, 59.43°W) continuously since 1965. These show that during much of the year high concentrations of mineral dust are present in the trade winds with maximum concentrations occurring during the summer months. In 1996 we began a study of bacteria and fungi in aerosols at this site. Daily filters were collect during on-shore winds throughout 1996 and 1997. The filters were placed on nutrient media and the resulting growth of bacteria and fungi was followed. The concentration of colony-forming units (CFU) showed a strong seasonal cycle which matches that of African soil dust. During dust events concentrations of bacteria and fungi were typically several CFU m-3 air. The African origin is verified by satellite products and air mass back trajectories which show that it takes about one week for air parcels to travel from Africa to Barbados. In contrast air masses that originate from the North Atlantic, North America, and Europe yield no organisms that respond to culture. The strong association of viable organisms with African dust suggests mechanisms that might protect organisms during transit. These include the reduction of UV radiation by the dense dust clouds and the shielding of individual organisms on or within soil particles. Previous work [Prospero et al., 2002] has shown that on a global scale major dust sources are found in arid regions (rainfall less than about 200 mm) in topographical lows which had been flooded during the Pleistocene. The Georgia Institute of Technology ? Goddard Global Ozone Chemistry Aerosol Transport (GOCART) model has been shown to provide a good picture of dust transport on a global scale [Ginoux et al., 2001]. Here we use the model to see if it can provide insights on the sources of viable bacteria and fungi in Africa.

Prospero, J.M., P. Ginoux, O. Torres, S. Nicholson, and T. Gill. Environmental Characterization of Global Sources of Atmospheric Soil Dust Identified with the NIMBUS 7 TOMS Absorbing Aerosol Product. Reviews of Geophysics, in press.

Ginoux, P., M. Chin, I. Tegen, J. M. Prospero, B. Holben, O. Dubovik, and S.-J. Lin. Sources and distributions of dust aerosols simulated with the GOCART model, J. Geophys. Res., 106 (D17) 20,255 20,274, 2001.