Dynamics and composition of particles from an aeolian input event to the Sargasso Sea

Abstract

A major outbreak of Saharan dust ( >40 μg aerosols/m³ air) passed over the western Sargasso Sea in late June 1980. The flux of aeolian particles across the air‐sea interface was calculated based upon free‐floating sediment trap data (30‐m depth). During the early‐to‐middle portions of this event, we observed in the trap samples large numbers of “giant” (>20‐μm diameter) aeolian particles that were not observed in aerosol samples collected at Miami, Florida, 426 km to the west. To better intercompare data collected at the two sites, a simple aeolian particle settling model was developed. Scanning electron microscopy with automated image analysis and X ray energy spectroscopy of individual particles from the two sites provided size and compositional data as primary inputs to the model. The compositional differences between aerosols from the two sites, although not great, may have been due in part to the localized nature of particle sources and storm centers. The time history of the aerosol concentration over the western Sargasso during the month of June as simulated by the model was compared with the time history of aerosols arriving at Miami. These results suggest that a significant portion of the deposition flux is comprised of giant particles. Particles in this size range are not efficiently collected by conventional sampling techniques, and hence reported estimates of depositional fluxes could be significantly biased too low.