Thursday, October 23rd, Nanne Weber (KNMI, The Netherlands) talks about Stability and restoring timescales of the Atlantic MOC.

ABSTRACT.
Which physical processes and variables effectively determine the stability 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 model of intermediate complexity, we show that the stability properties can
be established a priori. By modifying the longitudinal variation of surface salinites
near 30S, 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 determining the existence of a monstable of bistable
regime. This diagnostic is found to hold for the present as well as the glacial climate.

The glacial circulation is more easily perturbed than the modern and restoring
timescales are considerably longer, while recovery only sets in well after termination
of an imposed freshwater pulse matching the temporal pattern of Heinrich events.
Analysing coupled model runs from the Paleoclimate Modelling Intercomparison
Project, we find a remarkably consistent response of the overturning freshwater
transport into the Atlantic basin.