Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity


Lyons, Robert P.
Scholz, Christopher A.
Cohen, Andrew S.
King, John W.
Brown, Erik T.; Ivory, Sarah J.; Johnson, Thomas C.; Deino, Alan L.; Reinthal, Peter N.; McGlue, Michael M. and Blome; Margaret W.

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9–15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world’s largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.

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Fig. 1. (A and B) Continental TRMM 2B31 [combined TRMM microwave imager (TMI) and precipitation radar (PR)] precipitation estimates from 1998 to 2009 for January and July (SI Appendix) across Africa. Drill site 1 from the Lake Malawi Drilling Project and the interpreted ITCZ and CAB are labeled. (C) Bathymetric map of Lake Malawi (maximum water depths of north and central basin are ∼600 and ∼700 m, respectively), with digital elevation model of the region surrounding the lake. The lake surface elevation is 474 m, and maximum relief on map is ∼2,600 m. Red circle is central basin drill site. Yellow circle is location of Rungwe volcanoes, the presumptive source of the tephras dated in the core. Main border faults, which accommodate most of the basin subsidence, are shown in red.

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Proceedings of the National Academy of Sciences.