The effect of mountain uplift on eastern boundary currents and upwelling systems

Abstract

All major mountain ranges are assumed to have been subject to increased uplifting processes during the late Miocene and Pliocene. Previous work has demonstrated that African uplift is an important element to explain Benguela upper-ocean cooling in the late Miocene–Pliocene. According to proxy records, a surface ocean cooling also occurred in other eastern boundary upwelling regions during the late Neogene. Here we investigate a set of sensitivity experiments altering topography in major mountain regions (Andes, North American Cordillera, and southern and East African mountains) separately with regard to the potential impact on the intensity of near-coastal low-level winds, Ekman transport and Ekman pumping, and upper-ocean cooling. The simulations show that mountain uplift is important for upper-ocean temperature evolution in the area of eastern boundary currents. The impact is primarily on the atmospheric circulation which is then acting on upper-ocean temperatures through changes in strengths of upwelling, horizontal heat advection and surface heat fluxes. Different atmosphere–ocean feedbacks additionally alter the sea surface temperature response to uplift. The relative importance of the different feedback mechanisms depends on the region, but it is most likely also influenced by model and model resolution.