The Seesaw between the Atlantic Meridional Overturning Circulation and the North Pacific Meridional Overturning Circulation

The variability of ocean meridional overturning circulations could redistribute ocean heat and materials, and induce climate and biogeochemical changes. Paleo records show robust seesaw between the Atlantic Meridional Overturning Circulation (AMOC) and the North Pacific Meridional Overturning Circulation (PMOC), and it is believed to be caused by changes of salinity in the North Atlantic and Pacific Ocean. Here we show that the seesaw of AMOC and PMOC can be explained by the Bjerknes compensation of meridional heat transport (MHT). The weakened AMOC will decrease the oceanic MHT. To keep the climate system in a relatively steady state, the atmospheric MHT strengthened, making the westerly wind moving southward and storm activities strengthened in mid-latitude in the North Pacific Ocean. The strengthened wintertime storm activities induced more oceanic turbulent heat loss and triggered deep convections in the North Pacific Ocean, and further increased PMOC. This mechanism is also valid in the modern climate with low-frequency variability above decadal time scale.