Pivotal Role of Tibetan Plateau and Antarctic in Shaping Present-Day Atlantic Meridional Overturning Circulation

Abstract The roles of the Tibetan Plateau and Antarctic orography in the formation of the Atlantic meridional overturning circulation (AMOC) have been recently demonstrated. This study further elucidates physical processes of the combined effect of the Tibetan Plateau and Antarctic orography by comparing two different sets of experiments, starting from a global flat orography: 1) to incorporate the Tibetan Plateau (TP) first followed by Antarctica (TP2AT) and 2) to introduce Antarctica first followed by the TP (AT2TP). The uplift of the TP significantly modifies moisture transport in the Northern Hemisphere, leading to a fresher North Pacific and a more saline North Atlantic. This alteration of atmospheric moisture transport is essential for the transition of deep-water formation from the North Pacific to the North Atlantic, which activates the AMOC. The role of the Antarctic orography is mainly associated with its influence on the atmospheric westerlies over the subpolar Southern Hemisphere, which can strengthen the AMOC by boosting Ekman pumping and Agulhas leakage in the Southern Ocean. The combined influence of the TP and Antarctica is the key driving factor for establishing the current configuration of the AMOC. The sequence of the TP going before Antarctica (TP2AT) is more effective in setting up the AMOC than the other way around (AT2TP). This is because in AT2TP, it takes time to terminate a strong Pacific meridional overturning circulation (PMOC) before the AMOC gets into a full swing.