δ11B as monitor of calcification site pH in marine calcifyingorganisms

Type Publication
Acceptance Date 2017-05-15 IN PRESS
Language English
Copyright Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License.
Author(s) Sutton Jill N.1, Liu Yi-Wei1, Ries Justin B.2, Guillermic Maxence1, Ponzevera Emmanuel3, Eagle Robert A.1, 4, 5
Affiliation(s) 1 : Université de Brest, UBO, CNRS, IRD, Ifremer, Institut Universitaire Européen de la Mer, LEMAR, Rue Dumont d'Urville, 29280, Plouzané, France
2 : Department of Marine and Environmental Sciences, Marine Science Center, Northeastern University, 430 Nahant Rd, Nahant, MA 01908, USA
3 : Unité de Recherche Géosciences Marines, Ifremer, 29280, Plouzané, France
4 : Institute of the Environment and Sustainability, University of California, Los Angeles, LaKretz Hall, 619 Charles E Young Dr E #300, Los Angeles, CA 90024, USA
5 : Atmospheric and Oceanic Sciences Department, University of California – Los Angeles, Maths Science Building, 520 Portola Plaza, Los Angeles, CA 90095, USA
Source Biogeosciences Discussions (1810-6285) (Copernicus GmbH) In Press
DOI 10.5194/bg-2017-154
Abstract

The isotope composition of boron (B) in marine biogenic carbonates has been predominantly studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. In order to derive seawater pH from boron isotope ratio data, a number of assumptions related to chemical kinetics and themodynamic isotope exchange reactions are necessary. Furthermore, the boron isotope composition (δ11B) of biogenic carbonates (δ11BCaCO3) is assumed to reflect the δ11B of dissolved borate (B(OH)4−) in seawater. Here we report the development of methodology for measuring the δ11B in 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. We evaluated the δ11BCaCO3 of 6 species of marine calcifiers (a temperate coral, Oculina arbuscula; a coralline red alga, Neogoniolithion sp.; a tropical urchin, Eucidaris tribuloides; a temperate urchin, Arbacia punctulata; a serpulid worm, Hydroides crucigera; and an American oyster, Crassostrea virginica) that were reared for 60 days in isothermal seawater (25 °C) equilibrated with an atmospheric pCO2 of ca. 409 μatm. We observe large inter-species variability in δ11BCaCO3 (ca. 20 ‰) and significant discrepancies between measured δ11BCaCO3 and δ11BCaCO3 expected from established relationships between δ11BCaCO3 and seawater pH. We discuss these results in the context of various proposed mechanisms of biocalcification, including the potential dominant role that internal calcifying site pH plays in regulating CaCO3 saturation state and borate δ11B at the site of calcification and, thus, the δ11B composition of calcifers’ shells and skeletons.

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