Factors affecting B/Ca ratios in synthetic aragonite
Factors affecting B/Ca ratios in synthetic aragonite
Date
2015-09
Authors
Holcomb, Michael
DeCarlo, Thomas M.
Gaetani, Glenn A.
McCulloch, Malcolm
DeCarlo, Thomas M.
Gaetani, Glenn A.
McCulloch, Malcolm
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Keywords
Boron
Aragonite
Coral
Proxy
Carbonate
Aragonite
Coral
Proxy
Carbonate
Abstract
Measurements of B/Ca ratios in marine carbonates have been suggested to record
seawater carbonate chemistry, however experimental calibration of such proxies based on
inorganic partitioning remains limited. Here we conducted a series of synthetic aragonite
precipitation experiments to evaluate the factors influencing the partitioning of B/Ca
between aragonite and seawater. Our results indicate that the B/Ca ratio of synthetic
aragonites depends primarily on the relative concentrations of borate and carbonate ions
in the solution from which the aragonite precipitates; not on bicarbonate concentration as
has been previously suggested. The influence of temperature was not significant over the
range investigated (20 – 40°C), however, partitioning may be influenced by saturation
state (and/or growth rate). Based on our experimental results, we suggest that aragonite
B/Ca ratios can be utilized as a proxy of [CO32-]. Boron isotopic composition (δ11B) is an
established pH proxy, thus B/Ca and δ11B together allow the full carbonate chemistry of
the solution from which the aragonite precipitated to be calculated. To the extent that
aragonite precipitation by marine organisms is affected by seawater chemistry, B/Ca may
also prove useful in reconstructing seawater chemistry. A simplified boron purification
protocol based on amberlite resin and the organic buffer TRIS is also described.
Description
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Chemical Geology 437 (2016): 67-76, doi:10.1016/j.chemgeo.2016.05.007.