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Evaluating the utility of B/Ca ratios in planktic foraminifera as a proxy for the carbonate system: A case study of Globigerinoides ruber

Evaluating the utility of B/Ca ratios in planktic foraminifera as a proxy for the carbonate system: A case study of Globigerinoides ruber
Evaluating the utility of B/Ca ratios in planktic foraminifera as a proxy for the carbonate system: A case study of Globigerinoides ruber
B/Ca ratios in foraminifera have attracted considerable scientific attention as a proxy for past ocean carbonate system. However, the carbonate system controls on B/Ca ratios are not straightforward, with ?[ inline image] ([ inline image]in situ – [ inline image]at saturation) correlating best with B/Ca ratios in benthic foraminifera, rather than pH, inline image, or inline image (as a simple model of boron speciation in seawater and incorporation into CaCO3 would predict). Furthermore, culture experiments have shown that in planktic foraminifera properties such as salinity and [B]sw can have profound effects on B/Ca ratios beyond those predicted by simple partition coefficients. Here, we investigate the controls on B/Ca ratios in G. ruber via a combination of culture experiments and core-top measurements, and add to a growing body of evidence that suggests B/Ca ratios in symbiont-bearing foraminiferal carbonate are not a straightforward proxy for past seawater carbonate system conditions. We find that while B/Ca ratios in culture experiments covary with pH, in open ocean sediments this relationship is not seen. In fact, our B/Ca data correlate best with [ inline image] (a previously undocumented association) and in most regions, salinity. These findings might suggest a precipitation rate or crystallographic control on boron incorporation into foraminiferal calcite. Regardless, our results underscore the need for caution when attempting to interpret B/Ca records in terms of the ocean carbonate system, at the very least in the case of mixed-layer planktic foraminifera.
Globigerinoides ruber, B/Ca ratios, planktic foraminifera, pH proxy, trace elements, proxy calibration
1525-2027
1052-1069
Henehan, Michael J.
e64fc230-0233-4660-9811-8252e8a1ddf9
Foster, Gavin L.
fbaa7255-7267-4443-a55e-e2a791213022
Rae, James W.B.
8788a3a1-fec8-46c2-95a4-a59ce25416f5
Prentice, Katy C.
8accbbe6-8dcd-4e32-9ab2-906dd1779224
Erez, Jonathan
ed56a557-377e-4b63-8ba8-3d23e506e5c0
Bostock, Helen C.
a2c12519-6e77-4663-aeb3-37383b10b36f
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
Rae, James W.B.
8788a3a1-fec8-46c2-95a4-a59ce25416f5
Prentice, Katy C.
8accbbe6-8dcd-4e32-9ab2-906dd1779224
Erez, Jonathan
ed56a557-377e-4b63-8ba8-3d23e506e5c0
Bostock, Helen C.
a2c12519-6e77-4663-aeb3-37383b10b36f
Marshall, Brittney J.
4c1f0ae8-6038-427b-b58f-eb151adf1815
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6

Henehan, Michael J., Foster, Gavin L., Rae, James W.B., Prentice, Katy C., Erez, Jonathan, Bostock, Helen C., Marshall, Brittney J. and Wilson, Paul A. (2015) Evaluating the utility of B/Ca ratios in planktic foraminifera as a proxy for the carbonate system: A case study of Globigerinoides ruber. Geochemistry, Geophysics, Geosystems, 16 (4), 1052-1069. (doi:10.1002/2014GC005514).

Record type: Article

Abstract

B/Ca ratios in foraminifera have attracted considerable scientific attention as a proxy for past ocean carbonate system. However, the carbonate system controls on B/Ca ratios are not straightforward, with ?[ inline image] ([ inline image]in situ – [ inline image]at saturation) correlating best with B/Ca ratios in benthic foraminifera, rather than pH, inline image, or inline image (as a simple model of boron speciation in seawater and incorporation into CaCO3 would predict). Furthermore, culture experiments have shown that in planktic foraminifera properties such as salinity and [B]sw can have profound effects on B/Ca ratios beyond those predicted by simple partition coefficients. Here, we investigate the controls on B/Ca ratios in G. ruber via a combination of culture experiments and core-top measurements, and add to a growing body of evidence that suggests B/Ca ratios in symbiont-bearing foraminiferal carbonate are not a straightforward proxy for past seawater carbonate system conditions. We find that while B/Ca ratios in culture experiments covary with pH, in open ocean sediments this relationship is not seen. In fact, our B/Ca data correlate best with [ inline image] (a previously undocumented association) and in most regions, salinity. These findings might suggest a precipitation rate or crystallographic control on boron incorporation into foraminiferal calcite. Regardless, our results underscore the need for caution when attempting to interpret B/Ca records in terms of the ocean carbonate system, at the very least in the case of mixed-layer planktic foraminifera.

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More information

e-pub ahead of print date: 4 April 2015
Published date: April 2015
Keywords: Globigerinoides ruber, B/Ca ratios, planktic foraminifera, pH proxy, trace elements, proxy calibration
Organisations: Geochemistry, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 375881
URI: https://eprints.soton.ac.uk/id/eprint/375881
ISSN: 1525-2027
PURE UUID: 296bfbb8-097e-418d-a717-b1478b7dab45

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Date deposited: 09 Apr 2015 12:53
Last modified: 20 Apr 2018 16:32

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