Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 415-430, 2017
https://doi.org/10.5194/bg-14-415-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Jan 2017
Decoupled carbonate chemistry controls on the incorporation of boron into Orbulina universa
Ella L. Howes1,2, Karina Kaczmarek1, Markus Raitzsch3, Antje Mewes1, Nienke Bijma4, Ingo Horn5, Sambuddha Misra6, Jean-Pierre Gattuso2,7,8, and Jelle Bijma1 1Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
2Sorbonne Universités, UPMC Univ Paris 06, Observatoire Océanologique, 06230 Villefranche-sur-mer, France
3MARUM – Zentrum für Marine Umweltwissenschaften, Universität Bremen, Leobener Str., 28359 Bremen, Germany
4Christian-Albrechts-Universität, Kiel, Germany
5Institut für Mineralogie, Leibniz Universität Hannover, Callinstraße 3, 30167 Hannover, Germany
6University of Cambridge, Department of Earth Sciences, Godwin Laboratory for Paleoclimate Research, Downing Street, Cambridge, UK
7CNRS-INSU, Laboratoire d'Océanographie de Villefranche, 06230 Villefranche-sur-Mer, France
8Institute for Sustainable Development and International Relations, Sciences Po, 27 rue Saint Guillaume, 75007 Paris, France
Abstract. In order to fully constrain paleo-carbonate systems, proxies for two out of seven parameters, plus temperature and salinity, are required. The boron isotopic composition (δ11B) of planktonic foraminifera shells is a powerful tool for reconstructing changes in past surface ocean pH. As B(OH)4 is substituted into the biogenic calcite lattice in place of CO32−, and both borate and carbonate ions are more abundant at higher pH, it was suggested early on that B ∕ Ca ratios in biogenic calcite may serve as a proxy for [CO32−]. Although several recent studies have shown that a direct connection of B ∕ Ca to carbonate system parameters may be masked by other environmental factors in the field, there is ample evidence for a mechanistic relationship between B ∕ Ca and carbonate system parameters. Here, we focus on investigating the primary relationship to develop a mechanistic understanding of boron uptake.

Differentiating between the effects of pH and [CO32−] is problematic, as they co-vary closely in natural systems, so the major control on boron incorporation remains unclear. To deconvolve the effects of pH and [CO32−] and to investigate their impact on the B ∕ Ca ratio and δ11B, we conducted culture experiments with the planktonic foraminifer Orbulina universa in manipulated culture media: constant pH (8.05), but changing [CO32−] (238, 286 and 534 µmol kg−1 CO32−) and at constant [CO32−] (276 ± 19.5 µmol kg−1) and varying pH (7.7, 7.9 and 8.05). Measurements of the isotopic composition of boron and the B ∕ Ca ratio were performed simultaneously using a femtosecond laser ablation system coupled to a MC-ICP-MS (multiple-collector inductively coupled plasma mass spectrometer). Our results show that, as expected, δ11B is controlled by pH but it is also modulated by [CO32−]. On the other hand, the B ∕ Ca ratio is driven by [HCO3], independently of pH. This suggests that B ∕ Ca ratios in foraminiferal calcite can possibly be used as a second, independent, proxy for complete paleo-carbonate system reconstructions. This is discussed in light of recent literature demonstrating that the primary relationship between B ∕ Ca and [HCO3] can be obscured by other environmental parameters.


Citation: Howes, E. L., Kaczmarek, K., Raitzsch, M., Mewes, A., Bijma, N., Horn, I., Misra, S., Gattuso, J.-P., and Bijma, J.: Decoupled carbonate chemistry controls on the incorporation of boron into Orbulina universa, Biogeosciences, 14, 415-430, https://doi.org/10.5194/bg-14-415-2017, 2017.
Publications Copernicus
Download
Short summary
To calculate the seawater carbonate system, proxies for 2 out of 7 parameters are required. The boron isotopic composition of foraminifera shells can be used as a proxy for pH and it has been suggested that B / Ca ratios may act as a proxy for carbonate ion concentration. However, differentiating between the effects of pH and [CO32−] is problematic, as they co-vary in natural systems. To deconvolve the effects, we conducted culture experiments with the planktonic foraminifer Orbulina universa.
To calculate the seawater carbonate system, proxies for 2 out of 7 parameters are required. The...
Share