46 000 years of alternating wet and dry phases on decadal to orbital timescales in the cradle of modern humans: the Chew Bahir project, southern Ethiopia

Abstract. Rapid changes in environmental conditions are considered to be an important driver for human evolution, cultural and technological innovation, and expansion out of Africa. However, the nature of these environmental changes, their amplitude and correlation with steps in human evolution is the subject of current debates. Here we present a high-resolution (~3–12 yr) and well-dated (32 AMS ¹⁴C ages) lake-sediment record of the last 46 000 yr from the Chew Bahir basin in the southern Ethiopian Rift. The record was obtained from six cores along a NW–SE transect across the basin, which has been selected as the drilling location within the ICDP Hominin Sites and Paleolakes Drilling Project (HSPDP). Multi-proxy data and the comparison between the transect coring sites provide initial insight into intra-basin dynamics and major mechanisms controlling the sedimentation of the proxies that was used to develop a basic proxy concept for Chew Bahir for the last two wet-dry cycles. The environmental response to orbitally induced sinusoidal insolation changes is usually nonlinear, as climate changes abruptly compared to changes in the forcing, or gradual but punctuated by multi-decadal intervals of drier conditions. The second major control on the environment is millennial-scale climate variability lasting ~1500 yr, similar in duration to the high-latitude Dansgaard–Oeschger cycles and Heinrich events including the Younger Dryas cold reversal at the end of the last glacial, mostly causing abrupt shifts from extreme arid to wet conditions. The duration and character of orbitally induced, high-latitude controlled, and multi-decadal climate shifts provides important constraints for the adaptation of humans to the changing environment. Therefore, Chew Bahir is a perfect site to study and understand climatic variability on different timescales.