Nonlinear response of global monsoon precipitation to Atlantic overturn-ing strength variations during Marine Isotope Stage 3

Monsoon rainfall proxy records show clear millennial variations corresponding to abrupt climate events in Greenland ice cores during Marine Isotope Stage 3 (MIS3). The occurrence of these abrupt climate changes is associated with Atlantic Meridio-nal Overturning Circulation (AMOC) strength variations which greatly impact the global oceanic energy transport. Hence, the AMOC most likely plays a key role in modulating the global monsoon rainfall at millennial time scale. No modeling work has hitherto investigated the global monsoon system response to AMOC changes under a MIS3 background climate. Using a coupled climate model CCSM3, we simu-lated MIS3 climate using true 38 ka before present boundary conditions and per-formed a set of freshwater hosing/extraction experiments. We show not only agreement between modeling results and proxies of monsoon rainfall within global monsoon domain but also highlights a nonlinear relationship between AMOC strength and annual mean global monsoon precipitation related to oceanic heat transport constraints. During MIS3, a weakened AMOC could lead to an increase of annual mean global monsoon rainfall dominated by the southern hemisphere, whereas northern hemisphere monsoon rainfall decreases. Above about 16 Sverdrups a further strengthening of the AMOC has no significant impact on hemi-spheric and global monsoon domain annual mean rainfall. The seasonal monsoon rainfall showed same asymmetric response like annual mean both hemispherical and globally.