Seasonal δ34S variations in two high elevation snow pits measured by 33S-36S double spike thermal ionization mass spectrometry

delta S-34 and sulfate concentrations were determined in snow pit samples using a thermal ionization mass spectrometric technique capable of 0.2 parts per thousand. accuracy and requires approximate to 5 mu g (0.16 mu mol) natural S. The technique utilizes a S-33-S-36 double spike for instrumental mass fractionation correction, and has been applied to snow pit samples collected from the Inilchek Glacier, Kyrgyzstan and from Summit, Greenland. These delta S-34 determinations provide the first high-resolution seasonal data for these sites, and are used to estimate seasonal sulfate sources. Deuterium (delta D) and oxygen (delta O-18) isotope data show that the Inilchek and Summit snow pit samples represent precipitation over approximate to 20 months. The delta S-34 values for the Inilchek ranged from +2.6 +/- 0.4 parts per thousand to +7.6 +/- 0.4 parts per thousand on sample sizes ranging from 0.3 to 1.8 mu mol S. delta S-34 values for Greenland ranged from +3.6 +/- 0.7 parts per thousand to +13.3 +/- 5 parts per thousand for sample sizes ranging from 0.05 to 0.29 mu mol S. The SO42- concentration ranged from 92.6 +/- 0.4 to 1049 +/- 4 ng/g for the Inilchek and 18 +/- 9 to 93 +/- 6 ng/g for the Greenland snow pit. Anthropogenic sulfate dominates throughout the sampled time interval for both sites based on mass balance considerations. Additionally, both sites exhibit a seasonal signature in both delta S-34 and SO42- concentration. The thermal ionization mass spectrometric technique has three advantages compared to gas source isotopic methods: (1) sample size requirements of this technique are 10-fold less permitting access to the higher resolution S isotope record of low concentration snow and ice, (2) the double spike technique permits delta S-14 and S concentration to be determined simultaneously, and (3) the double spike is an internal standard. (C) 2008 Elsevier Ltd. All rights reserved.