Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 5
Biogeosciences, 15, 1447–1467, 2018
https://doi.org/10.5194/bg-15-1447-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 15, 1447–1467, 2018
https://doi.org/10.5194/bg-15-1447-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Mar 2018

Research article | 08 Mar 2018

δ11B as monitor of calcification site pH in divergent marine calcifying organisms

Jill N. Sutton1, Yi-Wei Liu1,2, Justin B. Ries3, Maxence Guillermic2, Emmanuel Ponzevera4, and Robert A. Eagle1,5,6 Jill N. Sutton et al.
  • 1Université de Brest, UMR 6539 CNRS/UBO/IRD/Ifremer, LEMAR, IUEM, 29280, Plouzané, France
  • 2Université de Brest, UMR 6539 CNRS/UBO/IRD/Ifremer, LGO, IUEM, 29280, Plouzané, France
  • 3Department of Marine and Environmental Sciences, Marine Science Center, Northeastern University, 430 Nahant Rd, Nahant, MA 01908, USA
  • 4Unité de Recherche Géosciences Marines, Ifremer, 29280, Plouzané, France
  • 5Institute of the Environment and Sustainability, University of California, Los Angeles, LaKretz Hall, 619 Charles E Young Dr E no. 300, Los Angeles, CA 90024, USA
  • 6Atmospheric and Oceanic Sciences Department, University of California, Los Angeles, Math Sciences Building, 520 Portola Plaza, Los Angeles, CA 90095, USA

Abstract. The boron isotope composition (δ11B) of marine biogenic carbonates has been predominantly studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. However, a number of assumptions regarding chemical kinetics and thermodynamic isotope exchange reactions are required to derive seawater pH from δ11B biogenic carbonates. It is also probable that δ11B of biogenic carbonate reflects seawater pH at the organism's site of calcification, which may or may not reflect seawater pH. Here, we report the development of methodology for measuring the δ11B of biogenic carbonate samples at the multi-collector inductively coupled mass spectrometry facility at Ifremer (Plouzané, France) and the evaluation of δ11BCaCO3 in a diverse range of marine calcifying organisms reared for 60 days in isothermal seawater (25 °C) equilibrated with an atmospheric pCO2 of ca. 409 µatm. Average δ11BCaCO3 composition for all species evaluated in this study range from 16.27 to 35.09 ‰, including, in decreasing order, coralline red alga Neogoniolithion sp. (35.89 ± 3.71 ‰), temperate coral Oculina arbuscula (24.12 ± 0.19 ‰), serpulid worm Hydroides crucigera (19.26 ± 0.16 ‰), tropical urchin Eucidaris tribuloides (18.71 ± 0.26 ‰), temperate urchin Arbacia punctulata (16.28 ± 0.86 ‰), and temperate oyster Crassostrea virginica (16.03 ‰). These results are discussed in the context of each species' proposed mechanism of biocalcification and other factors that could influence skeletal and shell δ11B, including calcifying site pH, the proposed direct incorporation of isotopically enriched boric acid (instead of borate) into biogenic calcium carbonate, and differences in shell/skeleton polymorph mineralogy. We conclude that the large inter-species variability in δ11BCaCO3 (ca. 20 ‰) and significant discrepancies between measured δ11BCaCO3 and δ11BCaCO3 expected from established relationships between abiogenic δ11BCaCO3 and seawater pH arise primarily from fundamental differences in calcifying site pH amongst the different species. These results highlight the potential utility of δ11B as a proxy of calcifying site pH for a wide range of calcifying taxa and underscore the importance of using species-specific seawater-pH–δ11BCaCO3 calibrations when reconstructing seawater pH from δ11B of biogenic carbonates.

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The boron isotope composition of marine biogenic carbonates has been studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. We highlight the potential utility of the boron isotope composition of marine biogenic carbonates as a proxy of calcifying site pH for a wide range of calcifying taxa and the importance of using species-specific seawater-pH–boron isotope calibrations when reconstructing seawater pH from the boron isotope composition of biogenic carbonates.
The boron isotope composition of marine biogenic carbonates has been studied as a proxy for...
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