Orbital forcing of African hydroclimate over the past 800,000 years

Abstract

The African hydroclimate played a key role in shaping the evolutionary environment of numerous species including hominins. African precipitation is sensitive to insolation and is consequently strongly linked to Earth’s orbital variations. Here, we utilise singular spectrum analysis to extract key orbital frequencies from a range of proxy records and a climate model dataset generated using the HadCM3B-V1.0 model, to reveal key patterns of pan-African orbital forcing of hydroclimate variability over the past 800,000 years. The model and proxies show good agreement. Eccentricity modulated precession forcing is the dominant mode of variability in both proxies and model, driving enhanced summer monsoon precipitation across a North-South interhemispheric antiphase. The impact of eccentricity is complex and associated with precession modulation, direct insolation change, and indirect feedbacks linked to greenhouse gases and ice-sheet extent. Obliquity primarily influences the amplitude of precession forcing. Our results suggest that the combination of different orbital forcings created complex spatio-temporal precipitation patterns, and consequent ecosystem dynamics in Africa.