Calibration of the Boron Isotope Proxy in the Planktonic Foraminifera Globigerinoides ruber for use in palaeo-CO 2 reconstruction

The boron isotope-pH proxy, applied to mixed-layer planktic foraminifera, has great potential for estimating past CO2 levels, which in turn is crucial to advance our understanding of how this greenhouse gas influences Earth's climate. Previous culture experiments have shown that, although the b...

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Bibliographic Details
Published in:Earth and Planetary Science Letters
Main Authors: Henehan, Michael J., Rae, James William Buchanan, Foster, Gavin L., Erez, Jonathan, Prentice, Katherine C., Kucera, Michal, Bostock, Helen C., Martinez-Boti, Miguel A., Milton, J. Andy, Wilson, Paul A., Marshall, Brittney J., Elliott, Tim
Format: Article in Journal/Newspaper
Language:English
Published: 2013
Subjects:
boron isotopes
Globigerinoides ruber
MC-ICPMS
culture calibration
pCO2 reconstruction
planktic foraminifera
Planktonic foraminifera
Online Access:https://risweb.st-andrews.ac.uk/portal/en/researchoutput/calibration-of-the-boron-isotope-proxy-in-the-planktonic-foraminifera-globigerinoides-ruber-for-use-in-palaeoco2-reconstruction(93098840-a810-475d-9f08-0a1aaaca25c1).html
https://doi.org/10.1016/j.epsl.2012.12.029
http://www.sciencedirect.com/science/article/pii/S0012821X12007157
Description
Summary:The boron isotope-pH proxy, applied to mixed-layer planktic foraminifera, has great potential for estimating past CO2 levels, which in turn is crucial to advance our understanding of how this greenhouse gas influences Earth's climate. Previous culture experiments have shown that, although the boron isotopic compositions of various planktic foraminifera are pH dependent, they do not agree with the aqueous geochemical basis of the proxy. Here we outline the results of culture experiments on Globigerinoides ruber (white) across a range of pH (∼7.5–8.2) and analysed via multicollector inductively-coupled plasma mass spectrometry (MC-ICPMS), and compare these data to core-top and sediment-trap samples to derive a robust new species-specific boron isotope-pH calibration. Consistent with earlier culture studies, we show a reduced pH dependency of the boron isotopic composition of symbiont-bearing planktonic foraminifera compared to borate ion in seawater. We also present evidence for a size fraction effect in the δ11B of G. ruber. Finally, we reconstruct atmospheric CO2 concentrations over the last deglacial using our new calibration at two equatorial sites, ODP Site 999A and Site GeoB1523-1. These data provide further grounding for the application of the boron isotope-pH proxy in reconstructions of past atmospheric CO2 levels.

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