USE OF STABLE LEAD ISOTOPES TO CHARACTERIZE THE SOURCES OF ANTHROPOGENIC LEAD IN NORTH-ATLANTIC SURFACE WATERS

Stable lead isotopes are used to illustrate the impact of surface wate r circulation on dissolved lead distribution in North Atlantic surface waters during oligotrophic conditions. Using stable lead isotopic sig natures from (1) the Sargasso Sea and (2) direct tropospheric depositi on to the North Atlantic, we estimate that 10-40% of the lead accumula ted in surface waters of the European Basin is transported from the we stern North Atlantic by the North Atlantic Current. South of 50 degree s N, lead appears to be primarily distributed by the Subtropical North Atlantic Gyre that extends well beyond the western basins to 30 degre es W in the North African Basin (at 30-40 degrees N). There are differ ent lead isotopic signatures between the subtropical gyre to the Guian a and western Guinea Basins, which suggests that the Inter Tropical Co nvergence Zone acts as an efficient barrier limiting chemical exchange s between the gyre and the equatorial currents.