DETERMINATION OF LEAD, CADMIUM, INDIUM, THALLIUM AND SILVER IN ANCIENT ICES FROM ANTARCTICA BY ISOTOPE-DILUTION THERMAL IONIZATION MASS-SPECTROMETRY

The concentrations of five chalcophile elements (Pb, Cd, In, Tl and Ag ) and the lead isotope ratios in ancient ices from the Taylor Dome nea r coastal Antarctica, have been determined by the isotope dilution-the rmal ionization mass spectrometry (ID-TIMS), with ultra-clean laborato ry techniques. The samples were selected from segments of cores, one o f which included a visible ash layer. Electric conductivity measuremen t (ECM) or dielectric properties (DEP) gave distinctive sharp peaks fo r some of the samples chosen. Exterior portions of the sample segments were trimmed away by methods described here. Samples were evaporated to dryness and later separated into fractions for the five elements us ing an HBr-HNO3 anion exchange column method. The concentrations are i n the range 2.62-36.7 pg Pb/g of ice, 0.413-2.83 pg Cd/g, 0.081-0.34 p g In/g, 0.096-2.8 pg Tl/g and 0.15-0.84 pg Ag/g, respectively. The dis persions in duplicate analyses are about +/- 1% for lead and cadmium, +/- 2% for indium, +/- 4% for thallium and +/- 6% for silver, respecti vely. The concentrations of lead obtained are commonly higher than tho se in the present-day Antarctic surface snows, but the isotope ratios are distinctively higher than those of the present-day snows and close to those of the other ancient ice collected from a different Antarcti c area.