Calcification rate and shell chemistry response of the planktic foraminifer Orbulina universa to changes in microenvironment seawater carbonate chemistry

Holland, K. and Eggins, S.M. and Hönisch, B. and Haynes, L.L. and Branson, O. (2017) Calcification rate and shell chemistry response of the planktic foraminifer Orbulina universa to changes in microenvironment seawater carbonate chemistry. Earth and Planetary Science Letters, 464. pp. 124-134. ISSN 0012-821X DOI https://doi.org/10.1016/j.epsl.2017.02.018

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Abstract

We use LA-ICP-MS depth profiling to explore the sensitivity of shell chemistry of the symbiotic planktic foraminifer Orbulina universa to diurnal changes in the holobiont physiology, over a wide range of seawater pH and DIC compositions. B/Ca and U/Ca vary in concert with diurnal Mg/Ca banding, forming compositional bands that are qualitatively consistent with physiological modification of seawater carbonate chemistry (pH, [] and []) within the foraminiferal microenvironment by the net effects of photosynthesis, respiration and calcification. The amplitude of B/Ca banding broadly conforms to banding predicted using the bulk-shell B/Ca sensitivity to the carbonate chemistry changes in the foraminiferal microenvironment. U/Ca banding tends to be greater than predicted using the published bulk-shell sensitivity of this proxy to carbonate chemistry. This either suggests that carbonate chemistry changes in the foraminiferal microenvironment are greater than predicted by modeling and/or the published bulk shell calibration does not accurately reflect the U/Ca sensitivity at the micro-scale. A fourfold increase in seawater DIC composition (1026 to 4019 μmol kg−1) is associated with significant increases in Sr/Ca and Mg/Ca partitioning, and a decrease in Mn/Ca partitioning into shell calcite. The accompanying fourfold increase in calcite saturation produces only a twofold increase in calcification rate (0.14 to 0.28, ±0.02 μm hr−1), suggesting that seawater carbonate chemistry exerts only a small effect on foraminiferal calcification rates, but does have a significant influence on trace element incorporation at both the inter-shell and bulk-shell scale.

Item Type: Article
Uncontrolled Keywords: NILAREP
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 464
Page Range: pp. 124-134
Identification Number: https://doi.org/10.1016/j.epsl.2017.02.018
Depositing User: Sarah Humbert
Date Deposited: 13 Dec 2019 16:51
Last Modified: 13 Dec 2019 16:51
URI: http://eprints.esc.cam.ac.uk/id/eprint/4598

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