Investigating controls on boron isotope ratios in shallow marine carbonates

Shuang Zhang, Michael J. Henehan, Pincelli M. Hull, Pamela R Reid, Dalton S. Hardisty, Ashleigh v S Hood, Noah J. Planavsky

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The boron isotope-pH proxy has been widely used to reconstruct past ocean pH values. In both planktic foraminifera and corals, species-specific calibrations are required in order to reconstruct absolute values of pH, due to the prevalence of so-called vital effects — physiological modification of the primary environmental signals by the calcifying organisms. Shallow marine abiotic carbonate (e.g. ooids and cements) could conceivably avoid any such calibration requirement, and therefore provide a potentially useful archive for reconstructions in deep (pre-Cenozoic) time. However, shallow marine abiotic carbonates could also be affected by local shifts in pH caused by microbial photosynthesis and respiration, something that has up to now not been fully tested. In this study, we present boron isotope measurements from shallow modern marine carbonates, from the Bahama Bank and Belize to investigate the potential of using shallow water carbonates as pH archives, and to explore the role of microbial processes in driving nominally ‘abiogenic’ carbonate deposition. For Bahama bank samples, our boron-based pH estimates derived from a range of carbonate types (i.e. ooids, peloids, hardground cements, carbonate mud, stromatolitic micrite and calcified filament micrite) are higher than the estimated modern mean-annual seawater pH values for this region. Furthermore, the majority (73%) of our marine carbonate-based pH estimates fall out of the range of the estimated pre-industrial seawater pH values for this region. In shallow sediment cores, we did not observe a correlation between measured pore water pH and boron-derived pH estimates, suggesting boron isotope variability is a depositional rather than early diagenetic signal. For Belize reef cements, conversely, the pH estimates are lower than likely in situ seawater pH at the time of cement formation. This study indicates the potential for complications when using shallow marine non-skeletal carbonates as marine pH archives. In addition, variability in δ11B based pH estimates provides additional support for the idea that photosynthetic CO2 uptake plays a significant role in driving carbonate precipitation in a wide range of shallow water carbonates.

Original languageEnglish (US)
Pages (from-to)380-393
Number of pages14
JournalEarth and Planetary Science Letters
Volume458
DOIs
StatePublished - Jan 15 2017

Fingerprint

boron isotopes
boron isotope
Boron
Carbonates
isotope ratios
Isotopes
carbonates
carbonate
Cements
cement
cements
Seawater
Belize
micrite
Bahamas
seawater
boron
estimates
Water
shallow water

Keywords

  • Bahama Bank
  • boron isotopes
  • micrite
  • ooids
  • pH proxy
  • shallow marine carbonates

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Zhang, S., Henehan, M. J., Hull, P. M., Reid, P. R., Hardisty, D. S., Hood, A. V. S., & Planavsky, N. J. (2017). Investigating controls on boron isotope ratios in shallow marine carbonates. Earth and Planetary Science Letters, 458, 380-393. https://doi.org/10.1016/j.epsl.2016.10.059

Investigating controls on boron isotope ratios in shallow marine carbonates. / Zhang, Shuang; Henehan, Michael J.; Hull, Pincelli M.; Reid, Pamela R; Hardisty, Dalton S.; Hood, Ashleigh v S; Planavsky, Noah J.

In: Earth and Planetary Science Letters, Vol. 458, 15.01.2017, p. 380-393.

Research output: Contribution to journalArticle

Zhang, S, Henehan, MJ, Hull, PM, Reid, PR, Hardisty, DS, Hood, AVS & Planavsky, NJ 2017, 'Investigating controls on boron isotope ratios in shallow marine carbonates', Earth and Planetary Science Letters, vol. 458, pp. 380-393. https://doi.org/10.1016/j.epsl.2016.10.059
Zhang, Shuang ; Henehan, Michael J. ; Hull, Pincelli M. ; Reid, Pamela R ; Hardisty, Dalton S. ; Hood, Ashleigh v S ; Planavsky, Noah J. / Investigating controls on boron isotope ratios in shallow marine carbonates. In: Earth and Planetary Science Letters. 2017 ; Vol. 458. pp. 380-393.
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