Investigating Antarctic Blue Ice Climate Archives Using Laser Ablation Impurity Imaging

Ice cores are indispensable archives for preserving terrestrial climate history, yet continuous Antarctic cores are limited to 1–1.5 million years due to basal melting, ice flow dynamics, and layer thinning, with the oldest continuous ice core (the EPICA Dome C core) extending to 800,000 years before present.  Recent discoveries of ice as old as 6 million years from shallow cores drilled in the Allan Hills Blue Ice Area (BIA) in Antarctica indicate that it is possible to extend the polar ice core record well beyond what is possible from continuous ice cores. However, developing robust paleoclimate archives from Antarctic BIA ice cores is challenging due to the uncertainties in the orientation and thickness of layering in such old, deformed, and often chronologically disturbed ice. Cryo-cell laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers a micro-destructive method to analyze spatial impurities in ice cores at a sub-millimeter scale, and preserves most of the ice material for paired, high-precision chemical analyses. This study investigates the application of LA-ICP-MS for high-resolution chemical layer analysis and orientation of Antarctic BIA cores. By imaging distribution of trace elements like Na, Mg, Ca, Al, and Sr at micrometer (µm) scales, LA-ICP-MS enables the chemical characterization of individual ice layers. To evaluate the technique’s effectiveness, we analyzed NIST 612 glass standard, Taylor Glacier ice, and an Allan Hills ice core (ALHIC 1903). Our findings reveal that LA-ICP-MS captures fine-scale spatial variations (65 µm) in elemental concentrations, highlighting the potential for annual layer identification within BIA ice cores. In the ALHIC 1903 sample, we identified a probable annual layer through a distinct peak in Na concentration across the length of a sample, demonstrating the ability of LA-ICP-MS to reveal layering within ice microstructure. The study emphasizes the importance of optimizing laser parameters and washout times to preserve microstructural details, ultimately enhancing the reconstruction of paleoclimate records from BIA ice cores.