Role of Sea Level and Seaway in Modulating the Hadley Circulation Change During the Last Glacial Period

The Hadley circulation, which is the most prominent meridional atmospheric circulation in Earth's system, is widely suggested to contract during the Last Glacial (LG) period by paleoclimate modeling studies. Although ice sheet expansion and sea level fall often exert coupled influences on Hadley circulation changes, most existing studies have focused on ice sheet and overlooked the role of sea level fall. Here, using climate simulations based the Norwegian Earth System Model (NorESM1-F), we show that sea level fall and associated closure/constriction of seaways play roles comparable to ice sheet expansion in modulating Hadley circulation changes during the initial stage of the LG period (∼70 ka). The sea level fall leads to an interhemispheric energy imbalance, which in turn causes the southward shift of the ascending branch of the Hadley circulation associated with the Intertropical Convergence Zone (ITCZ). The closure/constriction of seaways weakens (strengthens) the Hadley circulation in the Northern (Southern) Hemisphere and shifts its poleward edges equatorward in both hemispheres through influencing the meridional temperature gradient. Our results demonstrate the importance of taking changes in global mean sea level and seaways into account when simulating the glacial climate.