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

The ice in the deepest and therefore oldest parts of polar ice cores is highly compressed. Annual layers, although potentially preserved, can be thinned to a millimeter scale or even below. However, for many palaeoclimate studies these are the most interesting sections. Within the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last Interglacial) project we aim to investigate particularly the basal part of an ice core recently drilled to bedrock at the Skytrain Ice Rise in West Antarctica. Our aim is to obtain unique information on the state of the Filchner-Ronne ice shelf during the last interglacial (LIG). To achieve this we have set up a system to perform using high-resolution laser-ablation inductively coupled plasma – mass spectrometry (LA-ICP-MS) measurements using a cryocell stage on selected segments of the ice core. Here we present first results of system performance including assessment of measurement sensitivity and precision with respect to analyses of the most relevant components, including sodium, magnesium, calcium and aluminium. We report on the sample preparation technique as well as the resulting process blank. We evaluate the horizontal variability of the LA-ICP-MS signal across the ice core and the representativity of the high-resolution signal for an overall impurity content for different depth levels in the core. The results of the laser ablation ICP-MS measurements are then compared to low-resolution chemistry data from continuous flow analysis of the Skytrain ice core performed on the ice from the same depth. This comparison aims to evaluate the capabilities of the method in terms of improving depth resolution and annual variability. In a first application, sections of 80cm of ice from five different depth intervals covering time frames from late Holocene to the LIG are analysed via LA-ICP-MS and compared for their overall impurity content as well their signal variability. Finally, the potential of the method for resolving annual layers and fast changing climate signals within the core section covering the time period of the late last interglacial (about 115 - 120 ky before present) is investigated.