MC-ICP-MS measurements of sulfur isotopes in ice cores to reconstruct sea ice extent around the Antarctic Peninsula

Abstract:

A new method for sulfur isotope analysis is being developed at Cambridge University using multicollector inductively coupled mass spectrometry (MC-ICP-MS). This method is preferable to more traditional gas source mass spectrometry (GS-MS) because it can measure nmols of sulfur rather than the µmols necessary for GS-MS analysis. Because of its low detection limit, MC-ICP-MS is ideal to measure sulfur isotopes in ice cores, which have a background sulfate concentration of ~20 – 80 ppb. These ice core records can be used to constrain changes in sea ice extent over time and to examine the impact of sea ice on the local and global climate system. To facilitate these analyses at Cambridge, I have established an MC-ICP-MS coupled with a desolvating introduction system to measure δ³⁴SO₄ in samples with <30 nmol sulfur. I have tested this technique with dilute seawater standards and achieved a precision of ±0.08 – 0.14‰ (2 stdev). I will next use this method to measure δ³⁴SO₄ in an ice core from the Dyer Plateau in Antarctica and examine seasonal fluctuations in isotopic content. Ion chromatographic analysis of sea salt ions with also be conducted. Finally, I will assess the potential of this combined data as an improved proxy for sea ice extent around the Antarctic Peninsula.