Two-dimensional impurity imaging in deep Antarctic ice cores: snapshots of three climatic periods and implications for high-resolution signal interpretation

Pascal Bohleber,Marco Roman,Carlo Barbante,Martin Šala,Barbara Stenni,Barbara Delmonte

doi:10.5194/tc-15-3523-2021

Abstract

Abstract. Due to its micrometer-scale resolution and inherently micro-destructive nature, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is particularly suited to exploring the thin and closely spaced layers in the oldest sections of polar ice cores. Recent adaptions to the LA-ICP-MS instrumentation mean we have faster washout times allowing state-of-the-art 2-D imaging of an ice core. This new method has great potential especially when applied to the localization of impurities on the ice sample, something that is crucial, to avoiding misinterpretation of the ultra-fine-resolution signals. Here we present the first results of the application of LA-ICP-MS elemental imaging to the analysis of selected glacial and interglacial samples from the Talos Dome and EPICA Dome C ice cores from central Antarctica. The localization of impurities from both marine and terrestrial sources is discussed, with special emphasis on observing a connection with the network of grain boundaries and differences between different climatic periods. Scale-dependent image analysis shows that the spatial significance of a single line profile along the main core axis increases systematically as the imprint of the grain boundaries weakens. It is demonstrated how instrumental settings can be adapted to suit the purpose of the analysis, i.e., by either employing LA-ICP-MS to study the interplay between impurities and the ice microstructure or to investigate the extremely thin climate proxy signals in deep polar ice.

Highlights

Antarctic ice cores are a cornerstone of modern paleoclimatic research, archiving a unique variety of proxies such as greenhouse gases and aerosol-related atmospheric impurities over timescales from decades to hundreds of millennia (e.g., Petit et al, 1999; Kawamura et al, 2003; Ahn et al, 2004; EPICA Community Members, 2004)
Investigation of the oldest, deepest and thinnest ice core layers has become of special interest in state-of-the-art polar ice core research since the search has begun for a 1.5-million-year-old record that could be recovered from Antarctica (Brook et al, 2006; Fischer et al, 2013)
Through the integration of state-of-the-art imaging techniques, LA-ICP-MS ice core analysis has taken the step from 1-D into 2-D

Summary

Introduction

Antarctic ice cores are a cornerstone of modern paleoclimatic research, archiving a unique variety of proxies such as greenhouse gases and aerosol-related atmospheric impurities over timescales from decades to hundreds of millennia (e.g., Petit et al, 1999; Kawamura et al, 2003; Ahn et al, 2004; EPICA Community Members, 2004). The goal to obtain this record at the finest detail drives the demand for new analytical methods that surpass the depth resolution capabilities of established methods based on meltwater analysis, such as continuous flow analysis (CFA) (e.g., Röthlisberger et al, 2000; McConnell et al, 2002; Osterberg et al, 2006; Kaufmann et al, 2008). Within this framework, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has recently been re-established as a highresolution trace element technique for the characterization of ice cores (Müller et al, 2011; Sneed et al, 2015).

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Discussion

Conclusion