In:
Biogeosciences, Copernicus GmbH, Vol. 17, No. 21 ( 2020-11-10), p. 5365-5375
Abstract:
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 biomineralization processes, for example. 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, while 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 estimated to be on the order of ∼3 ‰ and ∼0.4 ‰
(2σ) on a ∼20 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 ∼12
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 preferring the conventional bulk solution MC-ICPMS over the
in situ methods for paleo-pH studies, for example. However, SIMS and LA provide powerful tools for
high-resolution paleoreconstructions, or for investigating ontogenetic trends in
δ11B.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-17-5365-2020
DOI:
10.5194/bg-17-5365-2020-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2020
detail.hit.zdb_id:
2158181-2
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