Low-frequency orbital variations controlled climatic and environmental cycles, amplitudes, and trends in northeast Africa during the Plio-Pleistocene

Abstract

The eastern Mediterranean sapropels, paced by insolation, provide a unique archive of African monsoon strength over the Late Neogene. However, the longer-term climate of this region lacks characterization within the context of changes in ice volume, sea surface temperature gradients, and terrestrial ecosystems. Here, we examine C28n-alkanoic acid leaf wax hydrogen and carbon isotopes in sapropels, sourced from northeast Africa, along with vegetation-corrected precipitation isotopes, derived from astronomically dated sediment cores from ODP 160 Sites 966 and 967 since 4.5 million years ago. Despite sampling only wet-phase sapropels for African monsoon variability, we find a larger range in hydrogen isotopes than previously published data across wet-dry precession cycles, indicating the importance of long-term modulation of Green Sahara phases throughout the Neogene. An influence of orbital properties on regional monsoonal hydroclimate is observed, controlling up to 50% of total hydrogen isotope variance, but large changes outside of these typical frequencies account for at least 50% of the total variance. This secular trend may track changes in ice volume, tropical sea surface temperature, sea surface temperature gradients, or even lower-frequency orbital cycles. Long-term hydroclimate and environmental shifts provide new contexts for milestone events in northeast African hominin dispersal and evolution.