Journal
GEOCHIMICA ET COSMOCHIMICA ACTA
Volume 75, Issue 4, Pages 1003-1012Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.gca.2010.11.023
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Funding
- TGE RMN THC [Fr3050]
- Conseil Regional du Nord-Pas de Calais
- European Regional Development Fund (ERDF)
- Institut National des Sciences de l'Univers (INSU, CNRS)
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Dissolved boron in modern seawater occurs in the form of two species, trigonal boric acid B(OH)(3) and tetrahedral borate ion B(OH)(4)(-). One of the key assumption in the use of boron isotopic compositions of carbonates as pH proxy is that only borate ions, B(OH)(4)(-), are incorporated into the carbonate. Here, we investigate the speciation of boron in deep-sea coral microstructures (Lophelia pertusa specimen) by using high field magic angle spinning nuclear magnetic resonance (B-11 MAS NMR) and electron energy-loss spectroscopy (EELS). We observe both boron coordination species, but in different proportions depending on the coral microstructure, i.e. centres of calcification versus fibres. These results suggest that careful sampling is necessary before performing boron isotopic measurements in deep-sea corals. By combining the proportions of B(OH)(3) and B(OH)(4)(-) determined by NMR and our previous ion microprobe boron isotope measurements, we propose a new equation for the relation between seawater pH and boron isotopic composition in deep-sea corals. (C) 2010 Elsevier Ltd. All rights reserved.
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