ISOTOPIC EVIDENCE OF POLLUTANT LEAD TRANSPORT FROM NORTH-AMERICA TO THE SUBTROPICAL NORTH-ATLANTIC GYRE

Lead isotope ratios have been measured in aerosols, seawater, and mari ne particles collected in 1990-1992 in the subtropical northeastern At lantic Ocean as part of the JGOFS-EUMELI program. While the atmospheri c input has unradiogenic Pb-206/Pb-207 ratios (1.158 +/- 0.006), typic al of the trade-winds bringing lead from European countries, all the s amples collected in the water column have more radiogenic Pb-206/Pb-20 7 (from 1.170 to 1.196). This demonstrates that lead at the Eumeli sit es contains a dominant input from American emissions, that has been ci rculated across the North Atlantic by the subtropical North Atlantic g yre. Using measurements in Sargasso Sea surface waters as an estimate of the isotopic composition of this input (Pb-206/Pb-207 = 1.195 +/- 0 .004), We calculate a contribution of 42-57% from America in these wat ers. This demonstrates that American emissions still dominated lead co ntamination over the North Atlantic in the early 1990s, in spite of th e early reduction of leaded gasoline in the USA. These results also gi ve new evidence of the equilibrium between dissolved and particulate p hases during scavenging processes. Copyright (C) 1997 Elsevier Science Ltd.