Isotopic evidence of pollutant lead transport from North America to the subtropical North Atlantic gyre

Abstract

Lead isotope ratios have been measured in aerosols, seawater, and marine particles collected in 1990–1992 in the subtropical northeastern Atlantic Ocean as part of the JGOFS-EUMELI program. While the atmospheric input has unradiogenic 206Pb207Pb ratios (1.158 ± 0.006), typical of the tradewinds bringing lead from European countries, all the samples collected in the water column have more radiogenic 206Pb207Pb (from 1.170 to 1.196). This demonstrates that lead at the Eumeli sites contains a dominant input from American emissions, that has been circulated across the North Atlantic by the subtropical North Atlantic gyre. Using measurements in Sargasso Sea surface waters as an estimate of the isotopic composition of this input (206Pb207Pb = 1.195 ± 0.004), we calculate a contribution of 42–57% from America in these waters. This demonstrates that American emissions still dominated lead contamination over the North Atlantic in the early 1990s, in spite of the early reduction of leaded gasoline in the USA. These results also give new evidence of the equilibrium between dissolved and particulate phases during scavenging processes.