The Atlantic freshwater budget as a diagnostic for the existence of a stable shut-down of the meridional overturning circulation

Which physical processes effectively determine the
stability regime of the Atlantic meridional overturning circulation (MOC) is not yet fully understood. We investigate the role of the oceanic freshwater transport into the basin, employing a coupled atmosphere/ocean/sea-ice model of intermediate complexity. By modifying the longitudinal variation of surface salinities near the southern border at 33S,the amount of salt flowing out of the Atlantic via the Brazil Current can be regulated. In turn, this will influence whether the MOC exports or imports salt water. The latter is associated with a basin-scale salinity-overturning feedback, which can be either positive or negative. Pulse experiments strongly suggest that its sign determines the existence of a monostable or bistable regime in our model.