Preprints
https://doi.org/10.5194/amt-2022-263
https://doi.org/10.5194/amt-2022-263
 
04 Oct 2022
04 Oct 2022
Status: this preprint is currently under review for the journal AMT.

Laser-induced sublimation extraction for cm-resolution multi-species greenhouse gas analysis on ice cores

Lars Mächler1, Daniel Baggenstos1, Florian Krauss1, Jochen Schmitt1, Bernhard Bereiter1,2, Remo Walther1, Christoph Reinhard1, Béla Tuzson2, Lukas Emmenegger2, and Hubertus Fischer1 Lars Mächler et al.
  • 1Climate and Environmental Physics and Oeschger Center for Climate Research, University of Bern, 3012 Bern, Switzerland
  • 2Laboratory for Air Pollution / Environmental Technology, Empa - Swiss Federal Laboratory for Materials Science and Technology, 8600 Dübendorf, Switzerland

Abstract. Precision, accuracy, and temporal resolution are key to make full use of atmospheric trace gas records in ice cores. These aspects will become especially crucial for ice cores that aim to extend the ice core record to the last 1.5 Myr, i.e., across the Mid Pleistocene Transition (as currently drilled within the European project Beyond EPICA – Oldest Ice Core (BE-OIC)). The ice from this period is expected to be close to bedrock and, due to glacier flow, extremely thinned with 15,000 years of climate history contained in only one meter of ice. Accordingly, for a century-scale resolution, the sample vertical extent must be reduced to a few cm containing only about 1−2 mL air STP.

We present a novel combined system for the extraction and the simultaneous measurement of CO2, CH4, and N2O concentrations, as well as δ13CO2, which achieves a vertical resolution of 1−2 cm with precisions of 0.4 ppm, 3 ppb, 1 ppb and 0.04 ‰, respectively. This is accomplished by employing a directional and continuous laser induced sublimation followed by analysis of the sample gas by quantum cascade laser absorption spectroscopy (QCLAS). Besides the low sample volume requirements and the vertical resolution capabilities, the described method holds additional advantages over previous methods, including the immunity of the highly specific QCLAS analysis to drilling fluid contamination as well as the non-destructive nature of the spectroscopic gas analysis. The combined extraction and analysis system was extensively tested by sublimating gas-free ice with introduction of a standard gas to determine the accuracy and characterize potential artefacts. Moreover, Antarctic ice samples were measured to confirm the measurement performance, covering the range of variability expected in Pleistocene ice and to highlight the vertical resolution capabilities critical for its application within BE-OIC.

Lars Mächler et al.

Status: open (extended)

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  • RC1: 'Comment on amt-2022-263', Anonymous Referee #1, 04 Nov 2022 reply

Lars Mächler et al.

Lars Mächler et al.

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Short summary
We present a new method to extract the gases from ice cores and measure their greenhouse gas composition. The ice is sublimated continuously with a near-infrared laser, releasing the gases, which are then analyzed on a laser absorption spectrometer. The main advantage over previous efforts is a low effective resolution of 1–2 cm. This capability is crucial for the analysis of highly thinned ice, as expected from ongoing drilling efforts to extend the ice core history further back in time.