The effect of ocean acidification on tropical coral calcification : insights from calcification fluid DIC chemistry

• Published in: Chemical Geology
• Main Authors: Allison, Nicola, Cole, Catherine, Hintz, Chris, Hintz, Ken, Rae, James, Finch, Adrian
• Other Authors: NERC, University of St Andrews. School of Earth & Environmental Sciences, University of St Andrews. Marine Alliance for Science & Technology Scotland, University of St Andrews. Scottish Oceans Institute, University of St Andrews. St Andrews Isotope Geochemistry
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: B/Ca; Dissolved inorganic carbon; Coral; Calcification; Calcification fluid; δ11B; QE Geology; QD Chemistry; NDAS; SDG 14 - Life Below Water; QE; QD; Ocean acidification
• Online Access: http://hdl.handle.net/10023/18421; https://doi.org/10.1016/j.chemgeo.2018.09.004

This work was supported by the UK Natural Environment Research Council (award NE/I022973/1) to AAF and NA. Ocean acidification typically reduces calcification in tropical marine corals but the mechanism for this process is not understood. We use skeletal boron geochemistry (B/Ca and δ11B) to reconstruct the calcification fluid DIC of corals cultured over both high and low seawater pCO2 (180, 400 and 750 μatm). We observe strong positive correlations between calcification fluid pH and concentrations of the DIC species potentially implicated in aragonite precipitation (be they CO32- , HCO3- or HCO3-+CO32- ). Similarly, with the exception of one outlier, the fluid concentrations of precipitating DIC species are strongly positively correlated with coral calcification rate. Corals cultured at high seawater pCO2 usually have low calcification fluid pH and low concentrations of precipitating DIC, suggesting that a reduction in DIC substrate at the calcification site is responsible for decreased calcification. The outlier coral maintained high pHCF and DICCF at high seawater pCO2 but exhibited a reduced calcification rate indicating that the coral has a limited energy budget to support proton extrusion from the calcification fluid and meet other calcification demands. We find no evidence that increasing seawater pCO2 enhances diffusion of CO2 into the calcification site. Instead the overlying [CO2] available to diffuse into the calcification site appears broadly comparable between seawater pCO2 treatments, implying that metabolic activity (respiration and photosynthesis) generates a similar [CO2] in the vicinity of the calcification site regardless of seawater pCO2. Postprint Peer reviewed