Trends in aerosol nutrient solubility along a west-east transect of the Saharan dust plume

Simple leaching protocols have been used to examine trends in the solubility of aerosol nutrients ( Fe, P and Si) along a west - east transect through the Saharan dust plume ( German SOLAS cruise M55) and between Saharan and southern hemisphere-origin aerosols. Solubilities were in the range 0.5 - 7.9% for Fe, 2.3 - 67% for P and 0.02 - 1.1% for Si, with lower values corresponding to samples of Saharan origin. Previous laboratory studies have suggested that aerosol Fe solubility might be enhanced by acid- and/or photo-chemistry during transport through the atmosphere, but only the solubility of P was observed to be higher at the western end of the transect than the eastern. This implies that if ( photo) chemical processing of aerosol Fe occurs in the atmosphere, significant enhancement of Fe solubility requires longer than the 5 - 10 days associated with transport of Saharan dust across the tropical Atlantic Ocean.