Orbital controls on eastern African hydroclimate in the Pleistocene

Understanding eastern African paleoclimate is critical for contextualizing early human evolution, adaptation, and dispersal, yet Pleistocene climate of this region and its governing mechanisms remain poorly understood due to the lack of long, orbitally-resolved, terrestrial paleoclimate records. Here we present leaf wax hydrogen isotope records of rainfall from paleolake sediment cores from key time windows that resolve long-term trends, variations, and high-latitude effects on tropical African precipitation. Eastern African rainfall was dominantly controlled by variations in low-latitude summer insolation during most of the early and middle Pleistocene, with little evidence that glacial-interglacial cycles impacted rainfall until the late Pleistocene. We observe the influence of high-latitude-driven climate processes emerging from the last interglacial (Marine Isotope Stage 5) to the present, an interval when glacial-interglacial cycles were strong and insolation forcing was weak. Our results demonstrate a variable response of eastern African rainfall to low-latitude insolation forcing and high-latitude-driven climate change, likely related to the relative strengths of these forcings through time and a threshold in monsoon sensitivity. We observe little difference in mean rainfall between the early, middle, and late Pleistocene, which suggests that orbitally-driven climate variations likely played a more significant role than gradual change in the relationship between early humans and their environment.

Automated summary

Understanding the ancient climate of eastern Africa is crucial for understanding early human evolution and migration. This study presents records of rainfall from ancient lake sediments, providing insights into the control mechanisms of Pleistocene climate in the region. The results suggest that eastern African rainfall was mainly influenced by low-latitude summer insolation during the early and middle Pleistocene, with little impact from glacial-interglacial cycles. However, high-latitude-driven climate processes emerged during the last interglacial to the present, when glacial-interglacial cycles were strong. The findings highlight the variable response of eastern African rainfall to different forcing mechanisms throughout time.