HYDROCLIMATE VARIABILITY IN CENTRAL NORTH AFRICA DURING THE PLIO-PLEISTOCENE

Central North Africa underwent major hydroclimate fluctuations in the past, most recently during the early Holocene. The Plio-Pleistocene climate of the African continent is of much interest because hominin speciation, extinction and migration events have been linked to changes in global or regional climate. However, long and continuous records of North African climate are relatively rare. Here, we investigate the hydroclimate of central North Africa during the Plio-Pleistocene by examining concentrations of plant leaf waxes and their deuterium isotopic composition (ẟD) at ODP site 660 (10°N), located offshore Guinea in the tropical Eastern Atlantic. We find that concentrations of leaf waxes are low in the older portion of the record but increase dramatically at ca. 2.5 Ma, reflecting the intensification of the trade winds, in agreement with other studies. Leaf wax ẟD values at ODP 660 fluctuate by over ca. 70‰, attesting to dramatic fluctuations between wet and arid conditions in central North Africa from 4.0 and 0.5 Ma, the interval examined in this study. Interestingly, the most depleted values of the entire record occur at ca. 3.3-3.2 Ma, coinciding with Marine Isotope Stage M2 (~ 3.3 Ma), indicating wet conditions. The M2 event is recognized globally as a cooling event, which interrupted an otherwise relatively warm Pliocene. Prior to 2.5 Ma, our ẟD records suggest several major fluctuations between wet and arid conditions within the Pliocene. From ca. 2.5-1.7 Ma, a progressive enrichment in ẟD occurs, reflecting an overall trend to increasing aridity. Subsequently, a gradual depletion in ẟD occurs until 0.4 Ma, indicating a progressive return to wetter conditions. Our new hydroclimate records reveal that dynamic hydroclimate shifts in central North Africa, which are believed to have influenced hominin and faunal migration patterns, characterize the past 4.0 Ma, with especially variable conditions noted during the Pliocene.