North African Humid Periods over the past 800000 years – Timing, Amplitude and Forcing

The Sahara region has experienced periodic wet periods over the Quaternary and beyond. These North African Humid Periods (NAHPs) are astronomically paced by precession which controls the position of the African monsoon system. However, most IPCC-class climate models cannot generate enough precipitation to reconcile the magnitude of these events and so the driving mechanisms remain poorly constrained. Here, we present an 800kyr climate dataset produced using a recently developed version of the HadCM3B coupled climate model that simulates 20 NAHPs over the past 800kyr which have good agreement with the timing and amplitude of NAHPs identified in proxy data. Our results confirm that precession determines their pacing, but we identify that their amplitude is strongly linked to eccentricity via its control over ice sheet extent. During glacials, cooling due to enhanced ice-sheet albedo suppresses the amplitude of the NAHPs during periods of precession minima. Our results highlight the importance of both precession and eccentricity, and the role of high latitude processes in determining the timing and amplitude of the NAHPs. This may have implications for the out of Africa dispersal of plants and animals throughout the Quaternary.