34°S Atlantic Meridional Freshwater Transport Set by Northern Hemisphere Ice Sheets and Meltwater in the Past 22,000 years

Abstract Freshwater transport by the Atlantic Meridional Overturning Circulation (AMOC) at the southern boundary () has been proposed as an instability indicator of the AMOC. However, its applicability remains controversial. Based on transient model experiment results of the past 22 ka, it is found that whether imports or exports freshwater is governed by the salinity contrast between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) instead of AMOC strength. With minor freshwater forcing in the Southern Ocean, the Northern Hemisphere ice sheets as well as meltwater flux play key roles in shaping the salinity gradient between these two water masses. We conclude that though is a useful metric to diagnose freshwater budget in the Atlantic, its application in indicating AMOC instability should be applied with caution, particularly under changing background climate conditions. Our study advances our understanding of feedback mechanisms in the Atlantic freshwater budget and AMOC hysteresis behavior in different climates.