Wet deposition of trace elements and radon daughter systematics in the South and equatorial Atlantic atmosphere

Atmospheric samples were collected aboard ship in the South and equatorial Atlantic (35°S–10°N) between 19 May and 20 June 1996. We measured 222 Rn in air, 210 Pb in aerosol, and trace elements (Fe, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210 Pb, and 210 Po in precipitation samples. The large variation of 222 Rn in air suggests a significant change in the incursion of continental air with time and latitude in the remote Atlantic. In the equatorial and subtropical Atlantic (20°S–10°N), 222 Rn activity was lower but 210 Pb/ 222 Rn ratios were higher than those at higher latitudes. The higher 210 Pb/ 222 Rn ratios in the equatorial Atlantic appear to be due to prevailing trade easterly winds which transport a supported source of 210 Pb in Saharan dust from the African Sahel. The enrichment of noncrustal trace elements in precipitation samples from the remote equatorial Atlantic was small on account of the remoteness from the continental emission regions and as a result of dilution with Saharan dust. The wet depositional fluxes of major crustal elements (Fe and Mn) were two‐ to three‐fold higher, while those of Cd and Zn were two‐ to ten‐fold lower, in the South and equatorial Atlantic relative to the western North Atlantic (Bermuda) or North Atlantic coast (Lewes, Delaware). Thus, dominant wet precipitation of Saharan dust in the Intertropical Convergence Zone (ITCZ) areas of the equatorial Atlantic appears to be a large potential source of micronutrients (i.e., Fe) to surface seawater.