The strength of the Meridional Overturning Circulation (MOC) is controlled by just a few key elements, apparently minor in size but not in importance. They constitute the tipping points of the MOC, i.e. subsystems that may switch from one state into another through relatively small perturbations but have major impacts on the whole system, in our case the strength of the MOC and, ultimately, the climate of the Earth System. Here we propose to study three such tipping corners: the Mediterranean Outflow Water (Tipping Corner 1, or TC1), the North Brazil Current system (Tipping Corner 2, or TC2), and the strength of Southern Ocean stratification (Tipping Corner 3, or TC3).

The spreading of Mediterranean Water is controlled to a large degree by the initial plunging of Mediterranean Outflow Water (MOW) in the eastern Gulf of Cadiz, it leads to heat and salt fluxes which oppose current freshening by increased ice melting at high latitudes. The only significant upper and intermediate path between the southern and northern Atlantic is the North Brazil Current system, responsible for the returning path of the MOC to its source region in the North Atlantic subpolar gyre, bringing with it a large load of heat to the North Atlantic. Southern Ocean stratification arises as the combination of several local factors, from insolation to the wind regime, and controls both the high-latitude atmospheric CO₂ physical pump and the rate of formation of Antarctic Bottom Waters.

This proposal constitutes a logical extension of ongoing research by the team members, sharply focusing on specific oceanic subsystems with global impact. It represents a methodological opportunity to joint field measurements with idealized and numerical models, as well as a conceptual opportunity to link together key ocean subsystems that control the climate of the Earth System.