Laser Ablation – ICP-MS measurements for high resolution chemical ice core analyses with a first application to an ice core from Skytrain Ice Rise (Antarctica)

For many ice core related scientific questions, like the analysis of fast changing climate signals, the depth resolution of conventional methods of analysis is not sufficient. In this study we present a setup of Laser Ablation Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) for high resolution glacier ice impurity analysis to the sub-millimetre scale. This setup enables chemical impurity ice core analysis to a depth resolution of ~ 80 μm while consuming only minimal amounts of ice. The system was used for simultaneous analysis of sodium, magnesium and aluminium incorporated in the ice structure. In a first case study within the framework of the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) project, the method was applied to a selection of samples from Skytrain ice core (West Antarctica), on a total length of 6.7 m consisting of about 130 single samples. The main goal of this study was to use the new LA-ICP-MS method to extract meaningful climate signals on a depth resolution level beyond the limits of Continuous Flow Analysis (CFA). A comparison between low resolution CFA data and the high resolution LA-ICP-MS data reveals generally good agreement on the decimetre scale. Stacking of parallel laser measurements together with frequency analysis is used to analyse the high resolution LA-ICP-MS data on the millimetre scale. Spectral analysis revealed that despite effects of impurity accumulation in ice crystal grain boundaries, periodic concentration changes in the Skytrain ice core on the millimetre scale can be identified in ice from 26 ka BP (kilo years before present; 1950 CE) and also from the Last Interglacial (LIG). These findings can open new possibilities for climate data interpretation with respect to fast changes in the last glacial and beyond.