Calibration of the boron isotope proxy in the planktonic foraminifera Globigerinoides ruber for use in palaeo-CO₂ reconstruction

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• 作者：Michael J. Henehan^a ; ^{M.J.Henehan@soton.ac.uk} ; James W.B. Rae^b ; Gavin L. Foster^a ; Jonathan Erez^c ; Katherine C. Prentice^d ; Michal Kucera^e ; Helen C. Bostock^f ; Miguel A. Martí ; nez-Botí ; ^a ; J. Andy Milton^a ; Paul A. Wilson^a ; Brittney J. Marshall^g ; Tim Elliott^b
• 关键词：boron isotopes ; Globigerinoides ruber ; MC-ICPMS ; culture calibration ; pCO2 reconstruction ; planktic foraminifera
• 刊名：Earth and Planetary Science Letters
• 出版年：2013
• 出版时间：15 February, 2013
• 年：2013
• 卷：364
• 期：Complete
• 页码：111-122
• 全文大小：1257 K

文摘

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 ¦Ä¹¹B 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.