The boron isotopic composition (δ11B) of coral skeleton is a proxy for seawater pH. However, δ11B-based pH estimates must account for the pH difference between seawater and the coral calcifying fluid, ∆pH. We report that skeletal δ11B and ∆pH are related to the skeletal carbon isotopic composition (δ13C) in four genera of deep-sea corals collected across a natural pH range of 7.89–8.09, with ∆pH related to δ13C by ∆pH=0.029×δ13C+0.929, r2=0.717. Seawater pH can be reconstructed by determining ∆pH from δ13C and subtracting it from the δ11B-derived calcifying fluid pH. The uncertainty for reconstructions is ±0.12 pH units (2 standard deviations) if estimated from regression prediction intervals, or between ±0.04 and ±0.06 pH units if estimated from confidence intervals. Our new approach quantifies and corrects for vital effects, offering improved accuracy relative to an existing δ11B versus seawater pH calibration with deep-sea scleractinian corals.
Martin P., Goodkin N. F., Stewart J. A, Foster G. L., Sikes E. L., White H. K., Hennige S. & Roberts J. M., in press. Deep-sea coral δ13C: A tool to reconstruct the difference between seawater pH and δ11B-derived calcifying fluid pH. Geophysical Research Letters. Article.
