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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Jul 2020

16 Jul 2020

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This preprint is currently under review for the journal BG.

Technical note: Single-shell δ11B analysis of Cibicidoides wuellerstorfi using femtosecond laser ablation MC-ICPMS and secondary ion mass spectrometry

Markus Raitzsch1,2,3, Claire Rollion-Bard4, Ingo Horn1, Grit Steinhoefel2, Albert Benthien2, Klaus-Uwe Richter2, Matthieu Buisson4, Pascale Louvat4, and Jelle Bijma2 Markus Raitzsch et al.
  • 1Institut für Mineralogie, Leibniz Universität Hannover, Callinstraße 3, 30167 Hannover, Germany
  • 2Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 3MARUM – Zentrum für Marine Umweltwissenschaften, Universität Bremen, Leobener Straße 8, 28359 Bremen, Germany
  • 4Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France

Abstract. The boron isotopic composition (δ11B) of benthic foraminifera provides a valuable tool to reconstruct past deep-water pH. As the abundance of monospecific species might be limited in sediments, microanalytical techniques can help to overcome this problem, but such studies on benthic foraminiferal δ11B are sparse. In addition, microanalytics provide information on the distribution of δ11B at high spatial resolution to increase the knowledge of e.g. biomineralization processes. For this study, we investigated the intra- and inter-shell δ11B variability of the epibenthic species Cibicidoides wuellerstorfi, which is widely used in paleoceanography, by secondary ion mass spectrometry (SIMS) and femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS). While the average δ11B values obtained from these different techniques agree remarkably well with bulk solution values to within ± 0.1 ‰, a relatively large intra-shell variability was observed. Based on multiple measurements within single shells, the SIMS and LA data suggest median variations of 4.8 ‰ and 1.3 ‰ (2σ), respectively, where the larger spread for SIMS is attributed to the smaller volume of calcite being analyzed in each run. When analytical uncertainties and volume-dependent differences in δ11B variations are taken into account for these methods, the intra-shell variability is presumably in the order of ~ 3 ‰ and ~ 0.4 ‰ (2σ) on a ~ 20 µm and 100 µm scale, respectively. In comparison, the δ11B variability between shells exhibits a total range of ~ 3 ‰ for both techniques, suggesting that several shells need to be analyzed for accurate mean δ11B values. Based on a simple resampling method, we conclude that ~ 7 shells of C. wuellerstorfi must be analyzed using LA-MC-ICPMS to obtain an accurate average value within ± 0.5 ‰ (2σ) to resolve pH variations of ~ 0.1. Based on our findings, we suggest to prefer the conventional bulk solution MC-ICPMS over the in-situ methods for e.g. paleo-pH studies. However, SIMS and LA provide powerful tools for high-resolution paleoreconstructions, or for investigating ontogenetic trends in δ11B, possibly due to vital effects during chamber formation.

Markus Raitzsch et al.

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Markus Raitzsch et al.

Markus Raitzsch et al.


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Publications Copernicus
Short summary
The isotopic composition of boron in carbonate shells of marine unicellular organisms is a popular tool to estimate seawater pH. Usually, many shells need to be dissolved and measured for boron isotopes, but the information on their spatial distribution is lost. Here, we investigate two techniques that allow for measuring boron isotopes within single shells, and show that they yield robust mean values, but provide additional information on the heterogeneity within and between single shells.
The isotopic composition of boron in carbonate shells of marine unicellular organisms is a...