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Calibration and application of B/Ca, Cd/Ca, and δ^(11)B in Neogloboquadrina pachyderma (sinistral) to constrain CO_2 uptake in the subpolar North Atlantic during the last deglaciation

Yu, Jimin and Thornalley, David J. R. and Rae, James W. B. and McCave, Nick I. (2013) Calibration and application of B/Ca, Cd/Ca, and δ^(11)B in Neogloboquadrina pachyderma (sinistral) to constrain CO_2 uptake in the subpolar North Atlantic during the last deglaciation. Paleoceanography, 28 (2). pp. 237-252. ISSN 0883-8305. doi:10.1002/palo.20024.

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The North Atlantic and Norwegian Sea are prominent sinks of atmospheric CO_2 today, but their roles in the past remain poorly constrained. In this study, we attempt to use B/Ca and δ^(11)B ratios in the planktonic foraminifera Neogloboquadrina pachyderma (sinistral variety) to reconstruct subsurface water pH and pCO_2 changes in the polar North Atlantic during the last deglaciation. Comparison of core-top results with nearby hydrographic data shows that B/Ca in N. pachyderma (s) is mainly controlled by seawater B(OH)_4−/HCO_3− with a roughly constant partition coefficient (K_D = [B/Ca]_(CaCO_3) / [B(OH)_4−/HCO_3− (seawater)) of 1.48 ± 0.15 × 10^(−3) (2σ), and δ^(11)B in this species is offset below δ^(11)B of the borate in seawater by 3.38 ± 0.71‰ (2σ). These values represent our best estimates with the sparse available hydrographic data close to our core-tops. More culturing and sediment trap work is needed to improve our understanding of boron incorporation into N. pachyderma (s). Application of a constant K_D of 1.48 × 10^(−3) to high resolution N. pachyderma (s) B/Ca records from two adjacent cores off Iceland shows that subsurface pCO_2 at the habitat depth of N. pachyderma (s) (~50 m) generally followed the atmospheric CO_2 trend but with negative offsets of ~10–50 ppmv during 19–10 ka. These B/Ca-based reconstructions are supported by independent estimates from low-resolution δ^(11)B measurements in the same cores. We also calibrate and apply Cd/Ca in N. pachyderma (s) to reconstruct nutrient levels for the same down cores. Like today's North Atlantic, past subsurface pCO_2 variability off Iceland was significantly correlated with nutrient changes that might be linked to surface nutrient utilization and mixing within the upper water column. Because surface pCO_2 (at 0 m water depth) is always lower than at deeper depths and if the application of a constant KD is valid, our results suggest that the polar North Atlantic has remained a CO_2 sink during the calcification seasons of N. pachyderma (s) over the last deglaciation.

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Rae, James W. B.0000-0003-3904-2526
Additional Information:© 2013 American Geophysical Union. Received 26 November 2012; revised 18 February 2013; accepted 22 February 2013; published 30 May 2013. We thank T. Takahashi, R. Ryderson, H. Elderfield, and F. He for very helpful discussions, O. Hyams-Kaphzan, Z. Jin, M. Greaves, and Chris Coath for excellent lab assistance, and T. Dokken for providing three core-tops from the Norwegian Sea. We also thank constructive comments from two anonymous reviewers. This research is funded by Lamont-Doherty Postdoctoral Fellowship, Lawrence Livermore Fellowship and the Australian National University (J.Y.), by NERC RAPID grant NER/T/S/2002/00436 (N. M. and D. T.), and by a NERC PhD studentship (J.R.). The cores examined in this study were obtained during cruise CD-159 of RRS Charles Darwin funded by the RAPID Climate Change programme of NERC (UK).
Funding AgencyGrant Number
Lamont-Doherty Postdoctoral FellowshipUNSPECIFIED
Lawrence Livermore FellowshipUNSPECIFIED
Australian National UniversityUNSPECIFIED
NERC RAPIDNER/T/S/2002/00436
NERC RAPID Climate Change ProgrammeUNSPECIFIED
Subject Keywords:Neogloboquadrina pachyderma (s); B; Ca; Cd; Ca; d11B; subsurface pH and pCO2 and nutrients
Issue or Number:2
Record Number:CaltechAUTHORS:20130829-111854958
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Official Citation:Yu, J., D. J. R. Thornalley, J. W. B. Rae, and N. I.McCave (2013), Calibration and application of B/Ca, Cd/Ca, and d11B in Neogloboquadrina pachyderma (sinistral) to constrain CO2 uptake in the subpolar North Atlantic during the last deglaciation, Paleoceanography, 28, 237–252, doi:10.1002/palo.20024
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40995
Deposited By: Tony Diaz
Deposited On:29 Aug 2013 23:41
Last Modified:10 Nov 2021 04:24

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