Calibration of the boron isotope proxy in the planktonic foraminifera Globigerinoides ruber for use in palaeo-CO2 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 W. B., 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:
pCO(2) reconstruction
culture calibration
SACCULIFER BRADY
ORBULINA-UNIVERSA
BORIC-ACID
CARBON-DIOXIDE CONCENTRATION
MARINE CARBONATES
boron isotopes
MOLECULAR-ORBITAL CALCULATIONS
ARABIAN SEA
PH PROXY
PALEO-PH
MC-ICPMS
Globigerinoides ruber
planktic foraminifera
SCLERACTINIAN CORALS
Planktonic foraminifera
Online Access:https://hdl.handle.net/1983/4d5b00c8-fe42-4fc6-995a-2db955305277
https://research-information.bris.ac.uk/en/publications/4d5b00c8-fe42-4fc6-995a-2db955305277
https://doi.org/10.1016/j.epsl.2012.12.029
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 (similar to 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 delta B-11 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. (C) 2012 Elsevier B.V. All rights reserved.

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