LEAD ISOTOPES IN THE WESTERN NORTH-ATLANTIC - TRANSIENT TRACERS OF POLLUTANT LEAD INPUTS

In the early 1980s, Patterson and colleagues demonstrated that most le ad in oceanic surface waters had an anthropogenic origin. Their discov ery occurred during the phasing out of leaded gasoline in North Americ a initiated in the previous decade. The corresponding decrease in anth ropogenic lead emissions, verified by Pb/Pb-210 ratios, accounted for the systematic decline in lead concentrations in surface waters of the western Sargasso Sea. Subsequent changes in anthropogenic lead inputs to the western Sargasso Sea surface waters have been documented by me asurements of lead concentrations, isotopic compositions (Pb-206/Pb-20 7, Pb-208/Pb-206), and Pb/Pb-210 ratios in precipitation and seawater for the period of 1981 to 1994. These data indicate the easterly trade winds are now the primary source of atmospheric lead in Bermuda, and they confirm that the decline of lead concentrations in the North Atla ntic is associated with the phasing out of leaded gasoline in North Am erica and western Europe over the past decade. Moreover, temporal vari ations in the relative contribution of industrial lead inputs from the two sides of the North Atlantic over that period can be quantified ba sed on differences in their isotopic composition. The transient charac ter of those isotopic signatures also allows calculations of pollutant lead penetration rates into the mixed layer and upper thermocline of the western Sargasso Sea. (C) 1998 Academic Press.