The coordination and distribution of B in foraminiferal calcite
The isotopic ratio and concentration of B in foraminiferal calcite appear to reflect the pH and bicarbonate concentration of seawater. The use of B as a chemical proxy tracer has the potential to transform our understanding of the global carbon cycle, and ocean acidification processes. However, disc...
Published in: | Earth and Planetary Science Letters |
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Main Authors: | , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2015
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Subjects: | |
Online Access: | http://eprints.esc.cam.ac.uk/3268/ http://eprints.esc.cam.ac.uk/3268/1/branson.pdf http://eprints.esc.cam.ac.uk/3268/2/1-s2.0-S0012821X15000849-gr001.jpg http://eprints.esc.cam.ac.uk/3268/3/mmc1.pdf http://eprints.esc.cam.ac.uk/3268/4/mmc2.pdf http://eprints.esc.cam.ac.uk/3268/5/mmc3.pdf http://eprints.esc.cam.ac.uk/3268/6/mmc4.pdf http://www.sciencedirect.com/science/article/pii/S0012821X15000849 https://doi.org/10.1016/j.epsl.2015.02.006 |
Summary: | The isotopic ratio and concentration of B in foraminiferal calcite appear to reflect the pH and bicarbonate concentration of seawater. The use of B as a chemical proxy tracer has the potential to transform our understanding of the global carbon cycle, and ocean acidification processes. However, discrepancies between the theory underpinning the B proxies, and mineralogical observations of B coordination in biomineral carbonates call the basis of these proxies into question. Here, we use synchrotron X-ray spectromicroscopy to show that B is hosted solely as trigonal BO3 in the calcite test of Amphistegina lessonii, and that B concentration exhibits banding at the micron length scale. In contrast to previous results, our observation of trigonal B agrees with the predictions of the theoretical mechanism behind B palaeoproxies. These data strengthen the use of B for producing palaeo-pH records. The observation of systematic B heterogeneity, however, highlights the complexity of foraminiferal biomineralisation, implying that B incorporation is modulated by biological or crystal growth processes. |
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