Reconstructing coral calcification fluid dissolved inorganic carbon chemistry from skeletal boron: An exploration of potential controls on coral aragonite B/Ca

The boron geochemistry of coral skeletons reflects the dissolved inorganic carbon (DIC) chemistry of the calcification fluid from which the skeletons precipitates and may be a valuable tool to investigate the effects of climate change on coral calcification. In this paper I calculate the predicted B/Ca of aragonite precipitating from seawater based fluids as a function of pH, [DIC] and [Ca(2+)]. I consider how different co-precipitating DIC species affect aragonite B/Ca and also estimate the impact of variations in the B(OH)(4)(−)/co-precipitating DIC aragonite partition coefficient (K(D)), which may be associated with changes in the DIC and Ca(2+) chemistry of the calcification fluid. The coral skeletal B/Ca versus calcification fluid pH relationships reported previously can be reproduced by estimating B(OH)(4)(−) and co-precipitating DIC speciation as a function of pH(CF) and assuming that K(D) are constant i.e. unaffected by calcification fluid saturation state. Assuming that B(OH)(4)(−) co-precipitates with CO(3)(2−), then observed patterns can be reproduced by a fluid with approximately constant [DIC] i.e. increasing pH(CF) concentrates CO(3)(2−), as a function of DIC speciation. Assuming that B(OH)(4)(−) co-precipitates with HCO(3)(−) only or CO(3)(2−) + HCO(3)(−) then the observed patterns can be reproduced if [DIC](CF) and pH(CF) are positively related i.e. if DIC is increasingly concentrated in the calcification fluid at higher pH(CF) probably by CO(2) diffusion into the calcification site.