Simulation of the mid-to-low latitudes seaways changes and the impact on the Atlantic Meridional Overturning Circulation and climate during the Miocene

Since the Middle Miocene, the opening and closing of the Tethys and Panama seaways may have directly affected the intensity and spatial morphology of the Atlantic Meridional Overturning Current (AMOC). However, systematic studies on the connection between the two key mid- and low-latitude seaways and the AMOC are few. Based on the boundary conditions of the Middle Miocene, we conducted a Middle Miocene climate simulation experiment using a coupled climate model and a sensitivity experiment of the successive closure of the Tethys and Panama seaways. Results show that the openings of Tethys and Panama seaways provided "shortcuts" for tropical Indian and Pacific Ocean waters to enter the North Atlantic, respectively, and transported high-salinity and low-salinity seawater to the North Atlantic, respectively, which played opposite roles in the change of AMOC intensity. The opening of the Tethys Seaway enhanced the AMOC, which offset the weakening of the AMOC caused by the opening of the Panama Seaway. The closure of these two mid- and low-latitude seaways could cause a north-south asymmetric response of global sea surface temperature, and the dividing line was roughly located at the latitude of the Panama Seaway. This study showed that the modern spatial structure of AMOC could be formed only when the Tethys Seaway and the Panama Seaway were closed. Therefore, the closure time of these two mid- and low-latitude seaways is of great significance for studying the evolution of AMOC.