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

ABSTRACT: 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 [Ca²⁺]. 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 Ca²⁺ 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 CO₃^2-, then observed patterns can be reproduced by a fluid with approximately constant [DIC] i.e. increasing pH_CF concentrates CO₃^2-, as a function of DIC speciation. Assuming that B(OH)₄^- co-precipitates with HCO₃^- only or CO₃^2- + HCO₃^- 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 CO₂ diffusion into the calcification site.

SUBMITTER: Allison N

PROVIDER: S-EPMC5576960 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Coral reefs are facing major global and local threats due to climate change-induced increases in dissolved inorganic carbon (DIC) and because of land-derived increases in organic and inorganic nutrients. Recent research revealed that high availability of labile dissolved organic carbon (DOC) negatively affects scleractinian corals. Studies on the interplay of these factors, however, are lacking, but urgently needed to understand coral reef functioning under present and near future conditions. This experimental study investigated the individual and combined effects of ambient and high DIC (pCO2 403 ?atm/ pHTotal 8.2 and 996 ?atm/pHTotal 7.8) and DOC (added as Glucose 0 and 294 ?mol L-1, background DOC concentration of 83 ?mol L-1) availability on the physiology (net and gross photosynthesis, respiration, dark and light calcification, and growth) of the scleractinian coral Acropora millepora (Ehrenberg, 1834) from the Great Barrier Reef over a 16 day interval. High DIC availability did not affect photosynthesis, respiration and light calcification, but significantly reduced dark calcification and growth by 50 and 23%, respectively. High DOC availability reduced net and gross photosynthesis by 51% and 39%, respectively, but did not affect respiration. DOC addition did not influence calcification, but significantly increased growth by 42%. Combination of high DIC and high DOC availability did not affect photosynthesis, light calcification, respiration or growth, but significantly decreased dark calcification when compared to both controls and DIC treatments. On the ecosystem level, high DIC concentrations may lead to reduced accretion and growth of reefs dominated by Acropora that under elevated DOC concentrations will likely exhibit reduced primary production rates, ultimately leading to loss of hard substrate and reef erosion. It is therefore important to consider the potential impacts of elevated DOC and DIC simultaneously to assess real world scenarios, as multiple rather than single factors influence key physiological processes in coral reefs.

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

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