A progressively wetter climate in southern East Africa over the past 1.3 million years

Abstract

African climate is generally considered to have evolved towards progressively drier conditions over the past few million years, with increased variability as glacial-interglacial change intensified worldwide. Palaeoclimate records derived mainly from northern Africa exhibit a 100,000-year (eccentricity) cycle overprinted on a pronounced 20,000-year (precession) beat, driven by orbital forcing of summer insolation, global ice volume and long-lived atmospheric greenhouse gases. Here we present a 1.3-million-year-long climate history from the Lake Malawi basin (10°-14° S in eastern Africa), which displays strong 100,000-year (eccentricity) cycles of temperature and rainfall following the Mid-Pleistocene Transition around 900,000 years ago. Interglacial periods were relatively warm and moist, while ice ages were cool and dry. The Malawi record shows limited evidence for precessional variability, which we attribute to the opposing effects of austral summer insolation and the temporal/spatial pattern of sea surface temperature in the Indian Ocean. The temperature history of the Malawi basin, at least for the past 500,000 years, strongly resembles past changes in atmospheric carbon dioxide and terrigenous dust flux in the tropical Pacific Ocean, but not in global ice volume. Climate in this sector of eastern Africa (unlike northern Africa) evolved from a predominantly arid environment with high-frequency variability to generally wetter conditions with more prolonged wet and dry intervals.

A climatic context for the out-of-Africa migration

“…3), confirming that the north African monsoon was greatly expanded and invigorated during these times. This contrasts with paleoclimate evidence from southeast Africa (Lake Malawi), which indicate a series of precessionally paced "megadroughts" during MIS 6-5 (Johnson et al, 2016). The combination of a deteriorating climate in southeast Africa and a favorable climate in northern Africa may have facilitated expansion of Homo sapiens from their place of origin across Africa during MIS 5 (Figs.…”

Homo naledi and Pleistocene hominin evolution in subequatorial Africa

“…During most of the Pleistocene, the area suitable for hominins located to the south of the equatorial forests was vastly larger than that to the north or east. During the last 1.3 million years of this period, the Lake Malawi basin became increasingly moist with greater climate stability (Johnson et al, 2016). The paleoclimate record for the Kalahari is not as deep, but during the last 200,000 years, this area underwent both arid periods with dune formation and wetter periods with vast paleolakes (Robbins et al, 2016), a pattern that likely held during earlier climate cycles.…”

Middle Stone Age Technology and Cultural Evolution at Magubike Rockshelter, Southern Tanzania

“…Large-scale climatic trends are thought to have spurred considerable changes in regional economic and settlement systems in many parts of the continent, resulting in the emergence of a range of new material behaviours, including stone technology (Marean et al 2007;McCall 2007). While climate forcing remains a plausible hypothesis for technological change in eastern Africa, little direct supporting evidence has emerged (Blome et al 2012;Douze and Delagnes 2016;Johnson et al 2016;Tryon and Faith 2013). On a coarse scale, eastern African climate appears to have become wetter after 800,000 years ago, succeeding a long period of aridity, but was increasingly subject to longer and more severe periods of drought lasting tens of thousands of years (Lyons et al 2015).…”