Extended Data Fig. 3. Illustration of δ¹¹B to pH conversion as well as age model differences.

(a) Comparison of pH evolution at Site 401 over the PETM CIE using either the borate ion⁴⁷ (red) or alternatively the T. sacculifer⁴³ (green) calibration. Age scale used is following Röhl et al.²⁵. (b) Direct comparison of our two age models, showing the reconstructed pH evolution of Site 401 plotted using either the age model of Farley and Eltgroth⁵⁷ or our preferred age model of Röhl et al.²⁵. (c) Expanded view of (b).