Extended Data Fig. 9. Down-core model-data evaluation at four data-rich sites.

Shown are comparisons for four ocean drilling sites for which surface ocean pH has been reconstructed across the PETM (Fig. 2) – 401, 865, 1209, and 1263 (this study and ref. 20). Their paleo locations in the cGENIE Earth system model are shown to the side (panel q). Model-data comparisons are made for: (i) wt% CaCO₃ (far LH panel for each site), (ii) δ¹³C of bulk carbonate (second-from-left series of panels), and (iii) surface ocean pH (third-from-left series of panels). To provide an orientation in time with regard to the evolution across the PETM event, the farthest-right series of panels shows the projected evolution of atmospheric δ¹³C of CO₂ in the model. For wt% CaCO₃ and δ¹³C of bulk carbonate, model points (resolved at 1 cm resolution) are plotted as filled yellow circles. Model-projected pH (global and annual mean, as per shown in Fig. 3j and Extended Data Fig. 6a) and atmospheric δ¹³C of CO₂ are shown as continuous red lines. In all cases, observed data values are shown as stars (*). The age models for Sites 865, 1209 and 1263 employing original relative age model constraints²⁰ used to convert from model-simulated sediment depth (resolved at 1 cm intervals) at each location in the cGENIE Earth system model, are calculated using a constant detrital flux accumulation rate. The observed data are plotting on their respective site 690-derived age models²⁵. Both model and data age scales are synchronized to age zero at PETM onset (horizontal line). See SI for details.