Vertical profile of lead isotopic compositions in the north-east Pacific

Abstract

Ratios of lead isotopes (^(204)Pb, ^(206)Pb, ^(207)Pb and ^(208)Pb) may be used to distinguish leads from different sources in sea water in a manner similar to neodymium isotopes. The following data from the north-east Pacific include the first vertical profile measurements of lead isotopic compositions in sea water. These preliminary data indicate that lead in offshore (48° N, 141° W) north-east Pacific surface waters (^(206)Pb/^(207)Pb = 1.164) was derived from aeolian inputs of Asian (Japanese) industrial leads (^(206)Pb/^(207)Pb = 1.160) (M. Murozumi, personal communication), but that lead in water immediately (400 m) below it (^(206)Pb/^(207)Pb = 1.211) was derived from North America industrial leads (^(206)Pb/^(207)Pb = 1.222). This remarkable contrast in isotopic compositions over such a relatively short distance reveals the potential of lead isotopic compositions to resolve the importance of horizontal transport processes on the lead cycle in the oceans, which were recently proposed to partially account for its oceanographic variability in the North Pacific.