Stable lead isotopic ratios trace thermohaline circulation in the subarctic North Atlantic

Vertical profiles of lead concentrations in the subarctic North Atlantic at test to the predominance of anthropogenic lead inputs to those waters, whil e variations in their lead isotopic ratios (Pb-204:Pb-206:Pb-207: Pb-208) s how the multiplicity of those industrial lead inputs, Spatial gradients in the isotopic ratios are consistent with the thermohaline circulation of dif ferent water masses, which seemingly have relatively discrete isotopic sign atures. These include characteristic Pb-206/Pb-207 ratios of the North Atla ntic Drift (1.183-1.187), Iceland-Scotland Overflow Water (1.173-1.176), De nmark Straits Overflow Water (1.179-1.182), and Labrador Sea Water (1.190-1 .120). Based on parallels between these initial isotopic data and T-S measu rements, it is proposed that stable lead isotopic compositions may be emplo yed as complementary tracers of the mixing of source waters in the Nordic s eas, as they overflow the Iceland-Scotland Ridge and Denmark Strait, mixing into the Labrador Sea to form North Atlantic Deep Water. (C) 1999 Elsevier Science Ltd. All rights reserved.