Deciphering the migration of the intertropical convergence zone during the last deglaciation

Proxy evidences suggest abrupt southward displacements of the intertropical convergence zone (ITCZ) during Heinrich Stadial 1 (HS1) and Younger Dryas (YD) against a long-term trend of northward ITCZ migration from Last Glacial Maximum to modern climate. Climate model simulations reveal that the abrupt ITCZ changes in HS1 and YD are mainly driven by ice-sheet-induced meltwater while the long-term ITCZ trend primarily results from orbital variations, rising atmospheric greenhouse gases and ice-sheet retreats during the last deglaciation. Atmospheric energetics analysis elucidates two important processes driven by meltwater—less net radiation entering the top-of-atmosphere (TOA) in the Northern Hemisphere than the Southern Hemisphere and a reduced global cross-equatorial oceanic heat transport from the compensation between Atlantic and Indo-Pacific heat transports—induce the southward ITCZ shift during HS1. Ice sheet extent changes also create a large interhemispheric TOA radiation asymmetry during HS1, which, however, is not via the surface albedo feedback.