Fig. 6. Simulated North Pacific ventilation changes versus observed Pliocene δ¹³C differences from the Late Pleistocene interglacial values.

Pliocene-control changes in ventilation age along (A) 158°E (the longitude of ODP Sites 586 and 1208) and (B) the average between 111° and 123°W (the longitude range of ODP Sites 849, 1014, and 1018). Superimposed circles show Pliocene δ¹³C differences from Late Pleistocene interglacial values for Sites 586, 849, 1014, and 1018 [see Table 2 of Ravelo and Andreasen (47)] and for Site 2018 [(40); using the same approach as by Ravelo and Andreasen (47) for the 1208 record, with average Holocene values serving as the Late Pleistocene estimate, and 3.1- to 3.37-Ma values as the Pliocene estimate, and with Site 849 used to correct for global ocean δ¹³C changes]. Note that whereas the PMOC results in varying degrees of enhanced North Pacific ventilation for all depths above ~3500 m, the presence of a deep western boundary current (see fig. S15) leads to increased ventilation in the western Pacific, thus accounting for the higher Pliocene δ¹³C observed at Site 586.