Drivers of the evolution and amplitude of African Humid Periods

During orbital precession minima, the Sahara was humid and more vegetated. Uncertainties remain over the climatic processes controlling the initiation, demise and amplitude of these African Humid Periods (AHPs). Here we study these processes using a series of transient simulations of the penultimate deglaciation and Last Interglacial period performed with an Earth system model of intermediate complexity (LOVECLIM). These results are compared to a transient simulation of the last deglaciation and Holocene. We find that the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) at the end of deglacial millennial-scale events exerts a dominant control on the abrupt initiation of AHPs, as the AMOC modulates the position of the Intertropical Convergence Zone. In addition, residual Northern Hemispheric ice-sheets can delay the peak of the AHPs. Through its impact on Northern Hemispheric ice-sheets disintegration and thus AMOC, the larger rate of insolation increase during the penultimate compared to the last deglaciation can explain the earlier and more abrupt onset of the AHP during the Last Interglacial period. Finally, we show that the mean climate state modulates precipitation variability, with higher variability under wetter background conditions.