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

Type Article
Date 2018-03
Language English
Author(s) Sutton Jill N.1, Liu Yi-Wei1, 2, Ries Justin B.3, Guillermic Maxence2, Ponzevera Emmanuel4, Eagle Robert A.1, 5, 6
Affiliation(s) 1 : Univ Brest, UMR CNRS UBO IRD Ifremer 6539, LEMAR, IUEM, F-29280 Plouzane, France.
2 : Univ Brest, UMR CNRS UBO IRD Ifremer 6539, LGO, IUEM, F-29280 Plouzane, France.
3 : Northeastern Univ, Dept Marine & Environm Sci, Ctr Marine Sci, 430 Nahant Rd, Nahant, MA 01908 USA.
4 : IFREMER, Unite Rech Geosci Marines, F-29280 Plouzane, France.
5 : Univ Calif Los Angeles, Inst Environm & Sustainabil, LaKretz Hall,619 Charles E Young Dr E 300, Los Angeles, CA 90024 USA.
6 : Univ Calif Los Angeles, Atmospher & Ocean Sci Dept, Math Sci Bldg,520 Portola Plaza, Los Angeles, CA 90095 USA.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2018-03 , Vol. 15 , N. 5 , P. 1447-1467
DOI 10.5194/bg-15-1447-2018
WOS© Times Cited 21
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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