Fig. 3.

Pacific zonal means of the simulated depth distribution of δ¹³C_DIC in the Maastrichtian ocean for (A) the default (full-strength) biological pump, (B) global export production reduced to 50% of the default, and (C) no biological pump. The approximate paleo-latitude of ODP Site 1209 (Shatsky Rise) is marked by the vertical dashed white line. The action of the solubility pump, which absorbs atmospheric CO₂ at high latitudes due to increased solubility of surface waters with respect to CO₂ as they cool, imparts an inverse vertical δ¹³C_DIC gradient at low latitudes in the absence of biological productivity (C; see the main text for explanation).