| Summary: | International audience Despite its role in heat, salt, and nutrient transport, the state of the Atlantic MeridionalOverturning Circulation (AMOC) at the Last Glacial Maximum (LGM) is still debated. Here, using a carbon-isotope enabled Earth system model, we perform a series of LGM experiments in which the AMOC state is varied. The simulated phosphate, δ13C, ventilation age and eps(Nd) distributions are compared to available North Atlantic LGM records. We find that proxy records are consistent with a shallower and ∼50% weaker AMOC compared to PI. This is associated with a 3º equatorward shift of the sea ice edge and convection sites in the Norwegian Sea. The shoaling of North Atlantic Deep Waters (NADW) allows for an incursion of Antarctic Bottom Water (AABW) in the North Atlantic, despite a 40% weakening of AABW transport. While the Deep Western Boundary Current in the northwest Atlantic weakens with NADW, the mid-depth southward flow on the east side of the north Mid-Atlantic Ridge strengthens, consistent with paleo-records. This northeast Atlantic intensification is due to a change in density gradients: a weaker AMOC reduces the transport of equatorial waters to the northeast Atlantic, thus weakening the North Atlantic zonal density gradient. Such a weaker oceanic circulation at the LGM leads to an increase in deep ocean dissolved inorganic carbon (DIC) concentration, and thus a larger vertical DIC gradient, which would have contributed to lowering atmospheric CO2 concentration
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