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In contrast to the modern‐day climate, North Pacific deep water formation and a Pacific meridional overturning circulation (PMOC) may have been active during past climate conditions, in particular during the Pliocene epoch (some 3–5 million years ago). Here, we use a climate model simulation with a robust PMOC cell to investigate the pathways of the North Pacific deep water from subduction to upwelling, as revealed by Lagrangian particle trajectories. We find that similar to the present‐day Atlantic Meridional Overturning Circulation (AMOC), most subducted North Pacific deep water upwells in the Southern Ocean. However, roughly 15% upwells in the tropical Indo‐Pacific Oceans instead—a key feature distinguishing the PMOC from the AMOC. The connection to the Indian Ocean is relatively fast, at about 250 years. The connection to the tropical Pacific is slower (∼800 years) as water first travels to the subtropical South Pacific then gradually upwells through the thermocline.

The Atlantic Meridional Overturning Circulation (AMOC) is expected to weaken in the 21st century due to increased surface buoyancy. Such AMOC changes in ocean models are often accompanied by a subsurface reduction in density. Here we perform freshwater perturbation experiments with both a 1° coupled model and an idealized zonally averaged ocean‐only model to demonstrate that slow subsurface property changes (1) introduce a negative feedback that erodes the stratification and partially reinvigorates convection and the AMOC and (2) ensure the meridional heat transport weakens less than the AMOC. In the coupled model with a 0.1‐Sv net freshwater flux introduced around Greenland, an initial 22% AMOC reduction over 40 years is followed by a recovery of almost half the lost strength after 400 years. The final heat transport, however, is weakened by only 7%. Similar responses in the idealized model demonstrate that 2‐D ocean‐only dynamics control the changes.