East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins

Abstract

The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early latePleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after Ϸ70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations.human origins ͉ Lake Malawi ͉ paleoclimate ͉ Pleistocene

Old fossils–young species: evolutionary history of an endemic gastropod assemblage in Lake Malawi

“…Thus, we conclude that appropriate limnological conditions for the evolution of the extant Lanistes radiation have (re-)emerged only very recently; for example, after recovery from a severe lake level low stand. The existence of such low stands in the history of Lake Malawi was reported on the basis of deep drilling core data and linked to phases of pronounced tropical African aridity (Cohen et al 2007;Scholz et al 2007). The authors describe two events 135 000 and 75 000 years ago when Malawi's lake level dropped at least 600 and 350 metres, respectively.…”

“…At present, the lake (maximum depth 706 m; Spigel & Coulter 1996) largely fills the Malawi Rift, which started to develop approximately 8.6 Myr ago (Ebinger et al 1987(Ebinger et al , 1989Delvaux 1995;Ring & Betzler 1995). Owing to its very small catchment area, the water balance of Lake Malawi is strongly influenced by regional and even local climate fluctuations (DeBusk 1998;Barker et al 2007), and lake-level changes from a few dozen metres to several hundred metres take place on various time scales (Delvaux 1995;Finney et al 1996;Scholz et al 2007).…”

The puzzling phylogeography of the haplochromine cichlid fishAstatotilapia burtoni

“…The observed distribution of the main mtDNA haplotype lineages was interpreted to reflect past lake‐level oscillations (Theis et al., 2014). Such fluctuations in the lake level, caused by variation in hydrology through time (Cohen, Lezzar, Tiercelin, & Soreghan, 1997; McGlue et al., 2010; Scholz et al., 2007), have previously been documented to affect population dynamics in rock‐dwelling, littoral cichlid species from lakes Tanganyika (Baric, Salzburger, & Sturmbauer, 2003; Koblmüller et al., 2011; Sturmbauer, Baric, Salzburger, Rüber, & Verheyen, 2001) and Malawi (Genner, Knight, Haesler, & Turner, 2010). In a follow‐up study based on single nucleotide polymorphisms (SNPs) derived from genomic DNA (via restriction site‐associated DNA sequencing; RADseq), we confirmed a deep divergence in A. burtoni populations in the South of Lake Tanganyika, in this case, however, between the Lufubu River and all remaining populations including the fish sampled at the estuary of the Lufubu River (Egger et al., 2017).…”

Phylogeny and phylogeography of Altolamprologus: ancient introgression and recent divergence in a rock-dwelling Lake Tanganyika cichlid genus

“…In Lake Tanganyika, severe lake level drops down to 435 below the present level associated with the megadrought events at 75-135 KYA affected the distributions of littoral cichlid communities McGlue et al, 2008). Smaller fluctuations in the more recent past, especially the lake level drop of *260 m during the last glacial maximum (*20 KYA), also had a profound impact on the current genetic structure of rock-dwelling cichlid species Scholz et al, 2007;McGlue et al, 2008). We have previously noted difficulties in aligning molecular datings of population divergence and growth with the geological datings of lake level fluctuations (Koblmüller et al, 2011;Sefc et al, 2016); in particular, the age of recent demographic events may be overestimated due to the potential time dependency of the molecular clock (Ho et al, 2007) in combination with comparatively ancient calibration points ) and large confidence intervals around substitution rates inferred from recent events (Genner et al, 2010b).…”