Timing and causes of North African wet phases during the last glacial period and implications for modern human migration

Abstract

We present the first speleothem-derived central North Africa rainfall record for the last glacial period. The record reveals three main wet periods at 65-61 ka, 52.5-50.5 ka and 37.5-33 ka that lead obliquity maxima and precession minima. We find additional minor wet episodes that are synchronous with Greenland interstadials. Our results demonstrate that sub-tropical hydrology is forced by both orbital cyclicity and North Atlantic moisture sources. The record shows that after the end of a Saharan wet phase around 70 ka ago, North Africa continued to intermittently receive substantially more rainfall than today, resulting in favourable environmental conditions for modern human expansion. The encounter and subsequent mixture of Neanderthals and modern humans – which, on genetic evidence, is considered to have occurred between 60 and 50 ka – occurred synchronously with the wet phase between 52.5 and 50.5 ka. Based on genetic evidence the dispersal of modern humans into Eurasia started less than 55 ka ago. This may have been initiated by dry conditions that prevailed in North Africa after 50.5 ka. The timing of a migration reversal of modern humans from Eurasia into North Africa is suggested to be coincident with the wet period between 37.5 and 33 ka.

Precessional Drivers of Late Miocene Mediterranean Sedimentary Sequences: African Summer Monsoon and Atlantic Winter Storm Tracks

“…The African summer monsoon is often considered as the sole driver, even at locations that are outside the areas of influence of the monsoonal system, likely due to the lack of evidence for winter precipitation in the observational record. The potential for a significant role of the Atlantic winter storm tracks on the Mediterranean regions has been suggested by some other modeling (Brayshaw et al, 2011;Kutzbach et al, 2013) and observational studies (Hoffmann et al, 2016;Toucanne et al, 2015). Here, we have provided further support for this hypothesis, based on nonidealized fully-coupled climate simulations, which confirm the link between winter precipitation changes in the Mediterranean and large-scale atmospheric circulation.…”

“…The combination of the two seasonally‐distinct moisture sources could have led to year‐round wetter conditions during times of precession minima from North Africa to the Mediterranean and the Middle East. This may not only be relevant for the late Miocene, but also during the more recent African humid periods, with potentially important implications for human migrations (Hoffmann et al, ; Kutzbach et al, ; Toucanne et al, ).…”

Western Mediterranean Climate Response to Dansgaard/Oeschger Events: New Insights From Speleothem Records

“…Speleothem records are indicated by triangles. CV = Cueva Victoria (this study, red triangle); GC = Gitana Cave (Hodge, Richards, Smart, Andreo, et al, 2008); BG = Buraca Gloriosa (Denniston et al, 2018); NSpC = caves in North Spain (Muñoz-García et al, 2007;Stoll et al, 2013); VC = Villars Cave (Genty et al, 2010); MC = Mallorcan Caves (Dumitru et al, 2018;Hodge, Richards, Smart, Ginés, & Mattey, 2008); SuC = Susah Cave (Hoffmann et al, 2016); DC = Dim Cave (Ünal-İmer et al, 2015); SoC = Soreq Cave (Bar-Matthews et al, 2003). Marine sediment cores are indicated by blue circles.…”

“…and lower speleothem δ 18 O values and growth phases in northern Libya(Hoffmann et al, 2016). Thus, it was more humid during the D/O events in the whole Mediterranean area and western Europe.…”

Sediment micromorphology and site formation processes during the Middle to Later Stone Ages at the Haua Fteah Cave, Cyrenaica, Libya

“…71-57 ka) to MIS 2 (ca. 29-14 ka)-albeit with shorter humid periods during intervening MIS 3 (Giraudi, 2005;Hoffmann et al, 2016;Tjallingii et al, 2008)-are argued to have forced populations to contract to the edges of the continent (Ambrose, 1998(Ambrose, , 2003Garcea, 2012), or to small yet viable areas of the Nile Valley (Van Peer, Vermeersch, & Paulissen, 2010, p. 241;Vermeersch & Van Neer, 2015).…”