150,000-year palaeoclimate record from northern Ethiopia supports early, multiple dispersals of modern humans from Africa

Abstract

Climatic change is widely acknowledged to have played a role in the dispersal of modern humans out of Africa, but the timing is contentious. Genetic evidence links dispersal to climatic change ~60,000 years ago, despite increasing evidence for earlier modern human presence in Asia. We report a deep seismic and near-continuous core record of the last 150,000 years from Lake Tana, Ethiopia, close to early modern human fossil sites and to postulated dispersal routes. The record shows varied climate towards the end of the penultimate glacial, followed by an abrupt change to relatively stable moist climate during the last interglacial. These conditions could have favoured selection for behavioural versatility, population growth and range expansion, supporting models of early, multiple dispersals of modern humans from Africa.

Figure 1

(a) Location and climatic context of Lake Tana. Blue arrows indicate paths of rain-bearing monsoon air masses in boreal summer, when the Intertropical Convergence Zone (ICTZ) moves northward. From October to May, the ITCZ shifts southwards and dry airflows dominate (red arrows). Marine and lacustrine core sites, earliest Homo sapiens sites (Herto, Omo), and Bab el Mandeb strait are also shown. (b) Position of core PT07 in Lake Tana at 12°N, 37° 15′ E. Maps generated in Adobe Illustrator CS6 Version:16.0.4. https://www.adobe.com/uk/.

Figure 2

Type-section data extracts of the three major seismic facies in the vicinity of core PT07. (a) Basin fill facies of unit 1 showing conformable strata onlapping onto seismic basement. (b) Wedge facies of unit 2, showing progradational phase. (c) Cyclic facies of unit 3 showing repeating reflectors, and pronounced cut-and-fill features. Reflector labels as in Supplementary Table 3. Only the uppermost 70 m of the >100 m seismic profile is shown here. Seismic acquired using SonatWiz, v5, Chesapeake Inc. (https://chesapeaketech.com/) and processed with Kingdom, IHS Markit https://kingdom.ihs.com/.

Figure 3

Selected elemental ratios determined by Itrax® XRF scanning of core PT07 at 2 mm intervals, plotted as 25-point running means against a 150 kyr timescale and a non-linear depth scale, with approximate boundaries of the major seismic units and Marine Isotope Stages (MIS). Blue shading indicates intervals of predominantly high lake level. Note reversed scale for Ca/Ti ratios. Figure generated in Adobe Illustrator CS6 Version:16.0.4. https://www.adobe.com/uk/.

Figure 4

Regional expression of the climate changes at Lake Tana. (A) June insolation at 12° N. (B) Sea-surface salinity in the Gulf of Guinea, core MD03-2707. (C) Ca/ Ti ratios, Lake Tana. (D) Fe XRF counts in core MS27PT, Nile delta margin. (E) Smectite/(chlorite + illite) ratios in core Geo Tü SL110, Nile plume, eastern Mediterranean. (F) Lake Malawi. Solid bars indicate high lake levels (C), and high Nile discharge (D,E). Approximate positions of Heinrich events (H1–H6) and P-reflectors (P1–P5) shown. Figure generated in Adobe Illustrator CS6 Version:16.0.4. https://www.adobe.com/uk/.