Résumé
A borehole core from Lake Ifrah (Middle Atlas, Morocco) provided a unique, continuous record of environmental change spanning the past c. 29,000 years cal BP (29 ka). A study of its organic matter, carbonates and magnetic susceptibility allowed us to reconstruct past climate changes and their impact on the lake's catchment area. The geochemical and pollen data show that the prevailing climate in the Middle Atlas from c. 29 ka to c. 12 ka was cold with a succession of dry and more humid periods. Prior to 24 ka the area surrounding Lake Ifrah enjoyed a relatively wet climate that allowed the survival of rare tree vegetation despite the overall cold conditions. After 12 ka, an increase in primary productivity and arboreal pollen is documented indicating the development of forest vegetation.