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Author
Date
2024Type
- Doctoral Thesis
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Abstract
The technique of laser ablation accelerator mass spectroscopy (LA-AMS) has been developed and improved over the past decade. It promises faster and cheaper high-resolution ¹⁴C records of various carbonate archives, but these benefits come at the cost of measurement precision. Here, a routine analysis protocol is proposed, which can reduce uncertainties by about 55%. It achieves this by measuring two parallel tracks, applying a Savitzky-Golay filter to each of them, and then taking the mean over the resulting tracks. Additionally, corrections for the cell washout and the target memory effect are implemented. These corrections are crucial for recovering the amplitude and period of a periodic signal, as could be shown by using a box model to simulate the LA-AMS system. Both amplitude and period can be recovered by applying the appropriate correction parameters, as long as the signal is i) stronger than 2σ, and ii) the period longer than 6 measurement cycles.
The new data reduction procedure is applied to various carbonate samples to investigate three different research questions: i) Can intra-annual signals be resolved, ii) What are the effects of parallel tracks on results, and iii) How to use radiocarbon to support the interpretation of stable carbon records in stalagmites. So far, no intra-annual signals could be resolved with the method, but it is likely worthwhile to test this with a sample where seasonality is previously established at a sufficiently large amplitude. By studying the effect of parallel tracks, a method to map the distance from top between different LA-AMS tracks could be developed. Using confocal laser scanning microscopy, any two parallel tracks can be mapped onto a main distance from top, which not only improves the comparability of LA-AMS measurements, but increases their value in combination with other proxy records. While comparisons between separate proxy records remain challenging, it could be shown that having a highly-resolved ¹⁴C record available can be crucial when interpreting the stable carbon record of a stalagmite.
Thus, as a first step towards potential simultaneous carbon isotope measurements by LAAMS, a method for simultaneous measurements from any source of CO₂ was developed. In its current state, the method shows potential for carbonate measurements with precisions comparable to standalone measurements for both isotopes with sample sizes of 100 µg C. As the LAinterface produces both CO as well as CO₂, it might be possible to couple it to this novel method by either converting or removing the CO and measuring single spots. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000673437Publication status
publishedExternal links
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Contributors
Examiner: Eglinton, Timothy I.
Examiner: Welte, Caroline
Examiner: Bernasconi, Stefano M.
Examiner: Aeschbach, Werner
Publisher
ETH ZurichOrganisational unit
03868 - Eglinton, Timothy I. / Eglinton, Timothy I.
Related publications and datasets
Is supplemented by: https://doi.org/10.3929/ethz-b-000666702
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