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The western Sahara Desert in Mauritania is dominated by extensive sand seas consisting largely of linear dunes. Analyses of Landsat images, geomorphic and stratigraphic studies, and optically stimulated luminescence dating of dunes in the Azefal, Agneitir, and Akchar sand seas provide evidence that three main generations of dunes were formed during the periods 25-15 ka (centered around the Last Glacial Maximum), 10-13 ka (spanning the Younger Dryas event), and after 5 ka. The wind regimes that occurred during each of these periods were significantly different, leading to the formation of dunes on three distinct superimposed trends-northeast, north-northeast, and north-and the development of the sand seas as composite geomorphic features.