Vegetation parameters control AMOC interstadials in Penultimate Deglaciation perturbed parameter ensemble simulations

The Penultimate Deglaciation (PDG, ~ 136-129 ka) saw warming from the Penultimate Glacial Maximum to the Last Interglacial (LIG), which was likely the most recent time Earth was as hot as today. The PDG may have seen a different pattern of AMOC behaviour compared to the more widely-studied Last Deglaciation. Using a low-resolution Earth System model with 3-D dynamic atmosphere and oceans and interactive sea-ice and vegetation, we run 18,000-year-long transient, perturbed parameter ensemble simulations varying 31 model parameters. Simulations span the entire PDG and the early LIG. AMOC can display either one, two or three phases of weakening and recovery, dependent on meltwater forcing uncertainty and parametric uncertainty. Surprisingly, vegetation parameters are shown to have a strong influence on PDG AMOC behaviour, including whether or not a brief interstadial occurs in the late stage of the PDG around 131 ka. The early AMOC stadial drives a reduction in Northern Hemisphere vegetation cover, particularly in Eurasia, which causes a multi-millennial cooling persisting beyond the termination of meltwater forcing. The ensemble spread of LIG global temperature is also strongly linked to vegetation parameters, and a stronger 131 ka AMOC interstadial is associated with a cooler (less realistic) LIG.