Lead and aluminum in Atlantic surface waters (50°N to 50°S) reflecting anthropogenic and natural sources in the Eolian transport

Abstract

Lead and aluminum were measured with a 40–100 km resolution in surface water on two transects across the Atlantic Ocean, one in May 1990 from Cape Town to the North Sea, the other in November 1990 from the North Sea to the Strait of Magellan. Samples were drawn 14 m below surface at normal speed from a 2‐m‐long snorkel system mounted on the bottom of the ship directly into a clean‐room area. In the tropics, both Pb and Al show maximum concentrations in the Intertropical Convergence Zone (ITCZ) correlated with each other and with minimum salinities, indicating wet deposition as their common source. Even in this area characterized by large inputs of mineral aerosols, the Pb/Al ratio shows that the major source of soluble lead (>95%) is anthropogenic. At higher latitudes, Al is low throughout (10–20 nmol/kg), whereas enhanced Pb values show the anthropogenic inputs off south Africa, northern Argentina and especially western Europe. Very low Pb and especially Al concentrations in the upwelling areas associated with the Canary and Benguela currents show that the enhanced biogenic particle fluxes cause an efficient scavenging of both lithogenic particles known to arrive here by dry deposition, and of the adhering reactive trace metals.