An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g(-1) Pb concentrations

Measurements of Pb isotope ratios in ice containing sub-pg g(-1) concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g-1 and fg g(-1) concentrations in Polar ice, were also measured. The final blank amounted to 0.2 +/- 0.2 pg of Pb with Pb-206/Pb-207 and Pb-208/Pb-207 ratios of 1.16 +/- 0.12 and 2.35 +/- 0.16, respectively, 1.5 +/- 0.4 pg of Ba and 0.6 +/- 2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only similar to 5%, similar to 14% and similar to 0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g(-1), 0.3 pg g(-1) and 2.3 fg g(-1). Uncertainties in the Pb isotopic ratio measurements were degraded by only similar to 0.2%. © 2009, Elsevier Ltd.

Keywords

Antarctica, Ice, Mass spectroscopy, Lead isotopes, Barium, Indium

Citation

Burn, L. J., Rosman, K. J. R., Candelone, J. P., Vallelonga, P., Burton, G. R., Smith, A. M., Morgan, V. I., Barbante, C., Hone, S., & Boutron, C. F. (2009). An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g(-1) Pb concentrations. Analytica Chimica Acta, 634(2), 228-236. doi:10.1016/j.aca.2008.11.067