Deep-sea coral C-13: A tool to reconstruct the difference between seawater pH and B-11-derived calcifying fluid pH

摘要

The boron isotopic composition (B-11) of coral skeleton is a proxy for seawater pH. However, B-11-based pH estimates must account for the pH difference between seawater and the coral calcifying fluid, pH. We report that skeletal B-11 and pH are related to the skeletal carbon isotopic composition (C-13) in four genera of deep-sea corals collected across a natural pH range of 7.89-8.09, with pH related to C-13 by pH=0.029x(13)C+0.929, r(2)=0.717. Seawater pH can be reconstructed by determining pH from C-13 and subtracting it from the B-11-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 B-11 versus seawater pH calibration with deep-sea scleractinian corals.