Can Andean Uplift Enhance the Pacific Meridional Overturning Circulation?

Abstract

The uplift of major mountain ranges can exert a strong influence on ocean circulation through large-scale atmosphere–ocean interactions. Using topography-sensitive simulations with the Community Earth System Model 1.0, we isolate the role of the Andes in shaping Pacific climate and ocean circulation. Andean uplift weakens the equatorial easterlies and shifts the Hadley circulation, leading to surface warming along the equator and in the eastern North Pacific, accompanied by regional cooling in the southeastern Pacific. These atmospheric changes drive basin-scale oceanic adjustments, including the intensification of the North Pacific subtropical gyre and a strengthening of the Pacific Meridional Overturning Circulation (PMOC). The enhanced subtropical gyre increases warm-water transport into the subpolar northeastern Pacific, leading to pronounced surface warming and salinification. However, these surface buoyancy changes alone are insufficient to explain the intensified deep-water formation. Instead, they occur in concert with large-scale ocean dynamical adjustments that favor the development of North Pacific Deep Water (NPDW). The resulting PMOC intensification emerges through coupled dynamical and thermohaline adjustments on multicentennial timescales. Our results demonstrate that Andean topography alone can promote a vigorous PMOC without requiring elevated atmospheric CO 2 concentrations or changes in tropical seaways, highlighting an important role of continental-scale tectonics in regulating Pacific overturning circulation.