Green Sahara periods and climate-human interactions during the Last Glacial Period: Evidence from Northwest African speleothems

<p>North Africa is a key region to study the interactions between low-latitude African monsoon systems and high-latitude millennial-scale climate change. Here, we present new high&#8208;resolution &#948;¹⁸O records and preliminary &#916;¹⁷O data (deviation of triple oxygen isotope data between &#948;¹⁷O and &#948;¹⁸O) from four Southwest Moroccan speleothems (&#8275;31&#176;N) spanning the last glacial period. Our &#948;¹⁸O records provide evidence of humid conditions during the Marine Isotope Stage (MIS) 5 and the early to mid&#8208;Holocene. The apparent increase in moisture during these Green Sahara periods is linked to the increase of summer insolation and the resulting expansion of the West African monsoon fringe, which could reach 31&#176;N in NW Africa. Furthermore, the preliminary &#916;¹⁷O results support our interpretation of &#948;¹⁸O data and reveal substantial changes in moisture sources and climate regimes between glacial and interglacial cycles.</p><p>Additionally, the Green Sahara periods are good examples to illustrate how dramatic climate change could shape human life in Africa &#8211; the original home of anatomically modern humans (AMH). Archaeological evidence shows that the human populations in North Africa during MIS5 were geographically well placed to disperse after the &#8220;Green Sahara&#8221; faded. Our climate record shows an abrupt deterioration of climate conditions during the MIS5-MIS4 transition, which has been proposed as one of the main factors that pushed AMH to move into Eurasia. Interestingly, the MIS5-MIS4 transition is characterized by a decrease of summer insolation and the occurrence of the Heinrich events 7a and 7b, which possibly induced a southern shift of the Intertropical Convergence Zone (ITCZ) and, therefore, a retreat of the African monsoon during this period.</p>