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

Abstract

Vertical profiles of lead concentrations in the subarctic North Atlantic attest to the predominance of anthropogenic lead inputs to those waters, while variations in their lead isotopic ratios ( 204 Pb : 206 Pb : 207 Pb : 208 Pb ) show the multiplicity of those industrial lead inputs. Spatial gradients in the isotopic ratios are consistent with the thermohaline circulation of different water masses, which seemingly have relatively discrete isotopic signatures. These include characteristic 206 Pb/ 207 Pb ratios of the North Atlantic Drift (1.183–1.187), Iceland–Scotland Overflow Water (1.173–1.176), Denmark 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 measurements, it is proposed that stable lead isotopic compositions may be employed as complementary tracers of the mixing of source waters in the Nordic seas, as they overflow the Iceland–Scotland Ridge and Denmark Strait, mixing into the Labrador Sea to form North Atlantic Deep Water.