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Updated: Jul 7, 2025

Preparation of Authigenic Pyrite from Methane-bearing Sediments for In Situ Sulfur Isotope Analysis Using SIMS
Published on: August 31, 2017
Stable-isotope ratios (δ18O and δD) in a firn core from West Antarctica
Manoela B P Portella1,2, Jefferson C Simões1,2,3, Ronaldo T Bernardo2
1Universidade Federal do Rio Grande do Sul, Programa de Pós-graduação em Geociências, Av. Bento Gonçalves, 9500, 91540-000 Porto Alegre, RS, Brazil.
Abstract:
A 22.48 m long ice core (BR-IC-4) was collected in the West Antarctic Ice Sheet (at 83°58'59.4" S, 80°07'01.4" W, 1,295 m above the sea level) during the Austral summer of 2004-2005, as a contribution to the International Trans-Antarctic Expedition program. The isotopic composition (δD and δ18O) of 599 samples, corresponding to the upper 12.98 m of the ice core, was determined by gas source mass spectrometry and cavity ring-down spectroscopy. Relative dating was based on the isotopic ratios and major ions (MS-, Na+, nssSO4 2-) and trace elements (Na, S, Sr) concentrations. The record covers approximately 13 years - from 1990 to 2003. The mean accumulation rate of 0.48 ± 0.09 m water equivalent per year (m eq H2O a1) is relatively high for the geographical area and possibly results from snowdrifting from near areas, as attested by ice glaze surfaces in other sites in the region. The stable isotope δD content varies between -367.90‰ and 256.30‰ (mean -314.42 ± 19.01‰); and δ18O ranges from -44.96‰ to 35.08‰ (mean -39.95 ± 2.05‰). Deuterium excess values (mean 3.70 ± 1.54‰) indicate episodic intense oceanic evaporation and high relative humidity in the moisture sources.
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