Lead Isotopes and Selected Metals in Ice from Law Dome, Antarctica

The isotopic composition of Pb and the concentrations of.Pb, Ba and Bi were measured in selected ice-core samples from Law Dome, East AntarctIca, to a depth of 1196 m. The range of concentrations found in decontaminated ice was 0.03\.5 pg g I for Pb, 0.96.1pggl for Ba and 0.417 fgg I for Bi , excluding the deepest sample which contained rv I p:}6m of rock dust. The abundances of all four stable lead Isotopes were measured and gave 6Pb/207Pb ratios up to rv1.23. A value of208Pb/2o7Pb = 2.78 was measured in the deepest sample and is consistent with reported Pb isotope ratios of Antarctic granulites. Although the element concentrations in some samples were lower than have been reported elsewhere, geochemical and isotopic evidence indicated that a number of samples were contaminated with Pb not present in the original ice. However, it appears that the technical ski ll s now available are approaching the level where careful sample selection, decontamination and analysis can yield accurate results for the concentration and isotopic composition ofPb in Earth's purest naturally occurring ice.