Orbital control of Pleistocene euxinia in Lake Magadi, Kenya

Lake Magadi is an internally drained, saline and alkaline terminal sump in the southern Kenya Rift. Geochemistry of samples from an ∼200 m core representing the past ∼1 m.y. ofthe lake’s history shows some of the highest concentrations of transition metals and metalloidsever reported from lacustrine sediment, including redox-sensitive elements molybdenum,arsenic, and vanadium. Elevated concentrations of these elements represent times when thelake’s hypolimnion was euxinic—that is, anoxic, saline, and sulfide-rich. Euxinia was commonafter ca. 700 ka, and after that tended to occur during intervals of high orbital eccentricity.These were likely times when high-frequency hydrologic changes favored repeatedepisodes of euxinia and sulfide precipitation. High-amplitude environmental fluctuations atpeak eccentricity likely impacted water balance in terrestrial habitats and resource availabilityfor early hominins. These are associated with important events in human evolution,including the first appearance of Middle Stone Age technology between ca.