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Abstract The Miocene (∼23–5 Ma) is a past warm epoch when global surface temperatures varied between ∼5 and 8°C warmer than today, and CO₂concentration was ∼400–800 ppm. The narrowing/closing of the tropical ocean gateways and widening of high‐latitude gateways throughout the Miocene is likely responsible for the evolution of the ocean's overturning circulation to its modern structure, though the mechanisms remain unclear. Here, we investigate early and middle Miocene ocean circulation in an opportunistic climate model intercomparison (MioMIP1), using 14 simulations with different paleogeography, CO₂, and vegetation. The strength of the Southern Ocean‐driven Meridional Overturning Circulation (SOMOC) bottom cell is similar in the Miocene and Pre‐Industrial (PI) but dominates the Miocene global MOC due to weaker Northern Hemisphere overturning. The Miocene Atlantic MOC (AMOC) is weaker than PI in all the simulations (by 2–21 Sv), possibly due to its connection with an Arctic that is considerably fresher than today. Deep overturning in the North Pacific (PMOC) is present in three simulations (∼5–10 Sv), of which two have a weaker AMOC, and one has a stronger AMOC (compared to its PMOC). Surface freshwater fluxes control northern overturning such that the basin with the least freshwater gain has stronger overturning. While the orography, which impacts runoff direction (Pacific vs. Atlantic), has an inconsistent impact on northern overturning across simulations, overall, features associated with the early Miocene—such as a lower Tibetan Plateau, the Rocky Mountains, and a deeper Panama Seaway—seem to favor PMOC over AMOC. 

Abstract The Intertropical Convergence Zone (ITCZ) has an annual mean location north of the equator today. The factors determining this location and the evolution to its modern state are actively debated. Here we investigate how the Atlantic Meridional Overturning Circulation (AMOC) influences the ITCZ during the early‐to‐middle Miocene. By conducting a sensitivity study with an open Canadian Arctic Archipelago gateway, we show that North Atlantic Deep‐Water formation strengthens the AMOC, in alignment with Miocene North Atlantic ventilation proxies. A vigorous AMOC increases northward Atlantic Ocean heat transport and cross‐equatorial atmospheric energy transport shifts southwards to compensate, pushing the ITCZ northwards. Our study supports AMOC development as a strong contributor to the ITCZ's northern location today. Existing proxy‐based interpretations of ITCZ history are too sparse to strongly confirm these results. We predict a strong in‐phase relationship between AMOC strength and ITCZ's northward location, which should be testable in high resolution paleoclimate records.