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Controls on boron incorporation in cultured tests of the planktic foraminifer Orbulina universa

Katherine Ann Allen; Baerbel Hoenisch; Stephen M. Eggins; Jimin Yu; Howard J. Spero; Henry Elderfield

Title:
Controls on boron incorporation in cultured tests of the planktic foraminifer Orbulina universa
Author(s):
Allen, Katherine Ann
Hoenisch, Baerbel
Eggins, Stephen M.
Yu, Jimin
Spero, Howard J.
Elderfield, Henry
Date:
Type:
Articles
Department:
Lamont-Doherty Earth Observatory
Volume:
309
Permanent URL:
Book/Journal Title:
Earth and Planetary Science Letters
Abstract:
Culture experiments with living planktic foraminifers reveal that the ratio of boron to calcium (B/Ca) in Orbulina universa increases from 56 to 92 μmol mol−1 when pH is raised from 7.61+/–0.02 to 8.67+/–0.03 (total scale). Across this pH range, the abundances of carbonate, bicarbonate, and borate ions also change (+530, −500, and +170 μmol kg−1, respectively). Thus specific carbonate system control(s) on B/Ca remain unclear, complicating interpretation of paleorecords. B/Ca in cultured O. universa also increases with salinity (55–72 μmol mol−1 from 29.9–35.4‰) and seawater boron concentration (62–899 μmol mol−1 from 4–40 ppm B), suggesting that these parameters may need to be taken into account for paleorecords spanning large salinity changes (~ 2‰) and for samples grown in seawater whose boron concentration ([B]SW) differs from modern by more than 0.25 ppm. While our results are consistent with the predominant incorporation of the charged borate species B(OH)4−into foraminiferal calcite, the behavior of the partition coefficient KD (defined as [B/Ca]calcite/[B(OH)4−/HCO3−]seawater) cannot be explained by borate incorporation alone, and suggests the involvement of other pH-sensitive ions such as CO3 2− For a given increase in seawater B(OH)4−, the corresponding increase in B/Ca is stronger when B(OH)4− is raised by increasing [B]SW than when it is raised by increasing pH. These results suggest that B incorporation controls should be reconsidered. Additional insight is gained from laser-ablation ICP-MS profiles, which reveal variable B/Ca distributions within individual shells.
Subject(s):
Biological oceanography
Publisher DOI:
http://dx.doi.org/10.1016/j.epsl.2011.07.010
Item views:
561
Metadata:
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