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A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects'

A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects'
A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects'
Boron isotope ratios, as measured in planktic foraminifera, can be a useful tracer of past ocean pH, and hence help to discern the concentration of CO2 in the ancient atmosphere. However, different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater pH. Therefore when applying the proxy to questions in the geological past, species-specific calibrations are preferable. Beyond the evolutionary history of a calibrated species, we must rely on our understanding of the causes of the observed “vital effects” in the modern ocean, and the applicability of that understanding to extinct species. Here we present a new open-ocean calibration of the planktic foraminifera Orbulina universa, measured via Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS). Unlike other symbiont-bearing foraminifera, O. universa record a ?11B?11B (and hence pH) that is lower than its surrounding seawater, but with a pH-sensitivity roughly equal to that of aqueous borate ion. We discuss the significance of this for application of the boron isotope proxy in deep time, with recommendations for best practice and future research directions.
boron isotopes, palaeo-CO2, planktic foraminifera, vital effects, Orbulina universa
0012-821X
282-292
Henehan, Michael J.
e64fc230-0233-4660-9811-8252e8a1ddf9
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Bostock, Helen C.
a2c12519-6e77-4663-aeb3-37383b10b36f
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Marshall, Brittney J.
4c1f0ae8-6038-427b-b58f-eb151adf1815
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Henehan, Michael J.
e64fc230-0233-4660-9811-8252e8a1ddf9
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Bostock, Helen C.
a2c12519-6e77-4663-aeb3-37383b10b36f
Greenop, Rosanna
9a08d945-03bb-41b9-b8f2-f6e84731057e
Marshall, Brittney J.
4c1f0ae8-6038-427b-b58f-eb151adf1815
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Henehan, Michael J., Foster, Gavin L., Bostock, Helen C., Greenop, Rosanna, Marshall, Brittney J. and Wilson, Paul A. (2016) A new boron isotope-pH calibration for Orbulina universa, with implications for understanding and accounting for ‘vital effects'. Earth and Planetary Science Letters, 454, 282-292. (doi:10.1016/j.epsl.2016.09.024).

Record type: Article

Abstract

Boron isotope ratios, as measured in planktic foraminifera, can be a useful tracer of past ocean pH, and hence help to discern the concentration of CO2 in the ancient atmosphere. However, different species of planktic foraminifera demonstrate different patterns of boron isotope variation with ambient seawater pH. Therefore when applying the proxy to questions in the geological past, species-specific calibrations are preferable. Beyond the evolutionary history of a calibrated species, we must rely on our understanding of the causes of the observed “vital effects” in the modern ocean, and the applicability of that understanding to extinct species. Here we present a new open-ocean calibration of the planktic foraminifera Orbulina universa, measured via Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS). Unlike other symbiont-bearing foraminifera, O. universa record a ?11B?11B (and hence pH) that is lower than its surrounding seawater, but with a pH-sensitivity roughly equal to that of aqueous borate ion. We discuss the significance of this for application of the boron isotope proxy in deep time, with recommendations for best practice and future research directions.

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Published date: 2016
Keywords: boron isotopes, palaeo-CO2, planktic foraminifera, vital effects, Orbulina universa
Organisations: Geochemistry, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 402105
URI: https://eprints.soton.ac.uk/id/eprint/402105
ISSN: 0012-821X
PURE UUID: 418bc9c1-bc6b-4c58-99e4-a89ddb214f2b
ORCID for Gavin L. Foster: ORCID iD orcid.org/0000-0003-3688-9668

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Date deposited: 27 Oct 2016 15:14
Last modified: 03 Dec 2019 01:42

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