Fig. 2.

Paired benthic–planktic foraminiferal δ¹¹B measurements from 4 time slices following the K-Pg boundary at ODP Site 1209 (Shatsky Rise) are used to calculate the difference in surface and deep ocean pH (∆pH; red diamonds, A). These data show a trend from “normal” patterns of higher δ¹¹B/pH in the surface ocean relative to the deep until 65.92 Ma, where this gradient disappears (see also SI Appendix, Fig. S12). Shown for context is the convergence in δ¹³C from surface waters (bulk CaCO₃, in green) and deep ocean waters (benthic foraminifera, navy) (A). Water column δ¹³C and pH profiles in the cGENIE model the location of Shatsky Rise (see also Fig. 3) are shown in B and C, respectively. A weakened or reversed δ¹³C gradient can arise in a number of ways (B), but only a shallow remineralization (or “Living Ocean,” red dot-dashed line) model can produce a flat gradient in pH between the surface 80 m and 2,500-m water depth (C). Carbonate data from ODP 1209 include new data and benthic data from ref. 34. See SI Appendix for more details.