Role of oceanic circulation on contaminant lead distribution in the South Atlantic

Both the relatively high lead concentrations and their characteristic anthr opogenic isotopic compositions attest to the widespread contamination of in dustrial lead in the western Equatorial and South Atlantic Ocean. Spatial g radients in those isotopic signatures evidence the conservative lateral tra nsport of lead in oceanic water masses, while the discrete isotopic signatu res in deep oceanic waters substantiate the complementary hypothesis that t he release of lead from settling particles is relatively small on a decadal time-scale. Specifically, the relatively low radiogenic lead (e.g., Pb-206 /Pb-207, 1.148 +/- 0.009) in the Lower-North Atlantic Deep Water (1-NADW) s outh of 10 degrees North is primarily attributed to US industrial lead emit ted in the Northern Hemisphere prior to 1965, and the more radiogenic lead (e.g., Pb-206/Pb-207 = 1.180 +/- 0.006) in the Upper-North Atlantic Deep Wa ter (u-NADW) is primarily attributed to subsequent industrial lead emission s in that hemisphere. In contrast, the relatively radiogenic lead (e.g., Pb -206/Pb-207,1.186 +/- 0.007) in the Antarctic Bottom Water (AABW) seemingly reflects a mixture of natural and anthropogenic lead sources within the So uthern Hemisphere; and its isotopic dissimilarity with that (e.g., Pb-206/P b-207 = 1.159 +/- 0.002) of Antarctic Intermediate Water (AAIW) and the AAB W may be due to differences in either their aeolian or water-mass inputs. ( C) 2001 Published by Elsevier Science Ltd.