Decadal-scale droughts disrupted the African Humid Period in the Sahara

During the early and mid-Holocene, the Sahara and Sahel experienced a humid phase, the so-called African Humid Period (AHP)¹. The AHP started around 14.8 thousand years before present (kyr BP), peaked between 9.0 kyr BP and 6.0 kyr BP and experienced short-lived droughts of as yet poorly constrained age and duration^2,3. Here we show that the AHP was punctuated by two droughts of decadal-scale duration, at about 9.3 kyr BP and 8.2 kyr BP, and another more tentatively identified drought at 6.3 kyr BP. Our findings arise from a multiproxy time series from the annually layered (varved) sedimentary archive of Lake Yoa in Chad, which covers the past 10.25 kyr continuously. During the more prominent drought at 8.2 kyr BP, pollen and diatom data, along with leaf-wax isotopes and geochemical source area indicators, imply that a reduction in local precipitation and fluvial supply to Lake Yoa caused a lake-level drop accompanied by an expansion of reed belts along the shore. The proxy data, together with our climate simulations, suggest that the 8.2 kyr BP drought event was a direct and rapid response to a potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) owing to sudden freshwater input into the North Atlantic. The results underline the need for improved decadal predictions⁴ to better anticipate such drought risks in the future.