Vertical and areal distribution of Saharan dust over the western equatorial north Atlantic Ocean

Abstract

Aerosol measurements were made as a part of the Barbados Oceanographic and Meteorological Experiment (Bomex) during May, June, and July 1969. Maximum dust concentrations occurred between the altitudes of 1.5 km and 3.7 km, a region which we call the Saharan air layer. The average concentration of mineral aerosol within this layer was 61 μg m−3; in contrast, the average concentration in the low-level air was 22 μg m−3. These dust concentrations are comparable to those found in continental surface air. Because of the presence of a strong inversion at the base of the Saharan layer, sea salt was confined to te lower altitudes where the average concentration was 10 μg m−3. Thus, sea salt appears to be a relatively minor constituent of the trade wind aerosol during much of the year. On the basis of these measurements and of a model describing the movement of Saharan air outbreaks, we estimate that 25 to 37 million tons of dust are transported through the longitude of Barbados each year. This quantity of dust is sufficient to supply all the material required to maintain the present rate of pelagic sedimentation across the entire northern equatorial Atlantic Ocean.