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Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

Haynes, Laura L. and Hönisch, Bärbel and Dyez, Kelsey A. and Holland, Kate and Rosenthal, Yair and Fish, Carina R. and Subhas, Adam V. and Rae, James W. B. (2017) Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions. Paleoceanography, 32 (6). pp. 580-599. ISSN 0883-8305.

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The B/Ca ratio of planktic foraminiferal calcite, a proxy for the surface ocean carbonate system, displays large negative excursions during the Paleocene-Eocene Thermal Maximum (PETM, 55.9 Ma), consistent with rapid ocean acidification at that time. However, the B/Ca excursion measured at the PETM exceeds a magnitude that modern pH calibrations can explain. Numerous other controls on the proxy have been suggested, including foraminiferal growth rate and the total concentration of dissolved inorganic carbon (DIC). Here we present new calibrations for B/Ca versus the combined effects of pH and DIC in the symbiont-bearing planktic foraminifer Orbulina universa, grown in culture solutions with simulated Paleocene seawater elemental composition (high [Ca], low [Mg], and low total boron concentration ([B]_T). We also investigate the isolated effects of low seawater [B]_T, high [Ca], reduced symbiont photosynthetic activity, and average shell growth rate on O. universa B/Ca in order to further understand the proxy systematics and to determine other possible influences on the PETM records. We find that average shell growth rate does not appear to determine B/Ca in high calcite saturation experiments. In addition, our “Paleocene” calibration shows higher sensitivity than the modern calibration at low [B(OH)_4−]/DIC. Given a large DIC pulse at the PETM, this amplification of the B/Ca response can more fully explain the PETM B/Ca excursion. However, further calibrations with other foraminifer species are needed to determine the range of foraminifer species-specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations.

Item Type:Article
Related URLs:
URLURL TypeDescription
Haynes, Laura L.0000-0003-1914-3282
Hönisch, Bärbel0000-0001-5844-3398
Dyez, Kelsey A.0000-0001-8347-3089
Holland, Kate0000-0003-4197-9377
Fish, Carina R.0000-0001-9400-3517
Subhas, Adam V.0000-0002-7688-6624
Rae, James W. B.0000-0003-3904-2526
Additional Information:© 2017 American Geophysical Union. Received 3 DEC 2016; Accepted 8 MAY 2017; Accepted article online 17 MAY 2017; Published online 17 JUN 2017. We thank Jordan Snyder, Alex Gagnon, Sam Phelps, Jennifer Fehrenbacher, Catherine Davis, and Ann Russell, who assisted in the collection of foraminifers, and Caroline Baptist and Nina Ruprecht for their laboratory assistance. Stella Woodard, Ryan Bu, and Paola Moffa-Sanchez provided assistance with ICP-MS analyses at Rutgers. We thank Richard Zeebe for access to LOSCAR model output. Special thanks to Bill Rosado, Govind Nadathur, and Orlando Espinosa for assistance in the lab and on the boat in Puerto Rico. We also thank Kat Allen, Jesse Farmer, Don Penman, and Sidney Hemming for their helpful discussion of the data. This manuscript was greatly improved by the constructive comments of Howie Spero, Michael Henehan, and one anonymous reviewer. This research is funded by NSF [OCE12-32987] to B.H. All data presented in this manuscript can be found in the main text and the supporting information.
Funding AgencyGrant Number
Subject Keywords:Orbulina universa; B/Ca; Paleocene-Eocene Thermal Maximum; ocean acidification; planktic foraminifera
Issue or Number:6
Record Number:CaltechAUTHORS:20170803-075555492
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Official Citation:Haynes, L. L., B. Hönisch, K. A. Dyez, K. Holland, Y. Rosenthal, C. R. Fish, A. V. Subhas, and J. W. B. Rae (2017), Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions, Paleoceanography, 32, 580–599, doi:10.1002/2016PA003069
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:79811
Deposited By: Tony Diaz
Deposited On:05 Aug 2017 21:00
Last Modified:03 Oct 2019 18:24

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