Response of the East African climate to orbital forcing during the last interglacial (130-117 ka) and the early last glacial (117-60 ka)

Variations in the temporal and spatial distribution of solar radiation caused by changes in Earth's orbit provide a partial explanation for observed long-term fluctuations in African lake levels. The understanding of causal links between insolation changes and lake- level fluctuations is essential for the design of models predicting future changes in the hydrological budgets and water supply in Africa. Here we present a record of climate change in East Africa between 175 and 60 ka. This time span includes the last interglacial (the Eemian, 130-117 ka), which may provide the closest analogue to the present interglacial. Assessments of the nature and timing of East African climate changes are based on lake-level fluctuations of Lake Naivasha (Kenya) inferred from sediment characteristics, diatom assemblages, and (super 40) Ar/ (super 39) Ar dating. Our results show dramatic alternation between deep, freshwater and shallow, highly alkaline lake conditions. The Lake Naivasha record demonstrates that periods of increased humidity in East Africa mainly follow precessional insolation forcing in spring, causing more intense April-May rains every 23 k.y.