Weakening of AMOC linked to past Greenland Ice Sheet retreat

Daniel Parkes , David J. Thornalley, Erin McClymont, Sophie Nuber, David Fairman, Mia Cousins, Adrian Palmer, Ian Matthews, Jack Wharton, Ian Candy

A weakening of the Atlantic Meridional Overturning Circulation (AMOC) is predicted to occur under multiple scenarios of future warming. However, the effect of meltwater from a decaying Greenland Ice Sheet (GrIS) on AMOC is uncertain. Using a basin-wide network of North Atlantic sediment cores, we show that the largescale melting of the GrIS during a previous interglacial (Marine Isotope Stage 11c (MIS11c); 397 – 427 ka) led to a millennial-scale, 30±15% weakening of AMOC and an associated abrupt 2 – 7⁰C cooling event over the subpolar North Atlantic. Furthermore, we reveal that this AMOC weakening occurred due to a combination of an abrupt transient weakening of Iceland Scotland Overflow Water and a preceding long-term decline in the strength of Denmark Straits Overflow Water, as well as an earlier cooling of the western subpolar gyre. Paleoclimate datasets indicate that this re-arrangement of ocean circulation had an impact on terrestrial ecosystems and atmospheric/oceanic circulation across the northern hemisphere and the low latitudes. This study suggests that modern oceanographic conditions are analogous to those prior to the MIS11c AMOC weakening event, with comparable modern rates of GrIS melt to those modelled for MIS11c. Critically, these findings provide empirical evidence that suggests the potential vulnerability of AMOC weakening to GrIS decay.