A predominantly tropical influence on late Holocene hydroclimate variation in the hyperarid central Sahara.

The climate history of the Sahara desert during recent millennia is obscured by the near absence of natural climate archives, hampering insight in the relative importance of southerly (tropical) and northerly (midlatitude) weather systems at submillennial time scales. A new lake sediment record from Ounianga Serir oasis in northern Chad, spanning the Late Holocene without interruption, confirms that immediately before ca 4200 years ago, the Sahara experienced an episode of hyperaridity even more extreme than today's desert climate. The hypersaline terminal lake which formed afterwards never desiccated during the late Holocene due to continuous inflow of fossil groundwater, yet its water balance was sensitive to temporal variation in local rainfall and lake surface evaporation. Our in-lake geochemical proxies show that, during the last 3000 years, century-scale hydroclimate variation in the central Sahara primarily tracked the intensity of the tropical West African monsoon, modulated at shorter time scales by weather patterns linked to shifts in midlatitude Atlantic Ocean circulation.