Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity
Robert P. Lyons a,1, Christopher A. Scholz 2,3, Andrew S. Cohen b, John W. King c, Erik T. Brown d, Sarah J. Ivory e, Thomas C. Johnson d, Alan L. Deino f, Peter N. Reinthal g, Michael M. McGlue h, and Margaret W. Blome b,3
aDepartment of Earth Sciences, Syracuse University, Syracuse, NY 13244;
bDepartment of Geosciences, University of Arizona, Tucson, AZ 85721;
cGraduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882;
dLarge Lakes Observatory and Department of Earth and Environmental Sciences, University of Minnesota, Duluth, MN 55812;
eInstitute at Brown for the Study of the Environment and Society, Brown University, Providence, RI 02912;
fBerkeley Geochronology Center, Berkeley, CA 94709;
gDepartment of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721;
hDepartment of Earth and Environmental Sciences, University of Kentucky, Lexington, KY 40506
Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved October 29, 2015 (received for review June 30, 2015)
Significance
Lake Malawi is one of the world’s oldest and deepest lakes, with >1,000 species of endemic cichlid fish; its water bottom anoxia prevents bioturbation of deep-water sediments, which preserve exceptional paleoclimate signals. The Lake Malawi Drilling Project recovered the first continuous 1.3-My record of past climates of the African interior. These sediments show that the catchment experienced 24 dry periods over that time, when lake levels dropped more than 200 m. After ∼800,000 years ago, the lake was commonly deeper and overflowing, indicating wetter conditions, but lowstand intervals became more prolonged and extreme. These changes promoted the evolution of the endemic cichlid fishes, through shifting of habitats, and through isolation and restriction of populations.
Abstract
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.
Lake Malawi tropical paleoclimatology East African rift cichlid fish quaternary
Footnotes
1Present address: Chevron Corporation, Houston, TX 77002.
2To whom correspondence should be addressed. Email: cascholz{at}syr.edu.
3Present address: BP L48 Onshore, Houston, TX 77079.
Author contributions: C.A.S., A.S.C., J.W.K., and T.C.J. designed research; R.P.L., C.A.S., A.S.C., J.W.K., E.T.B., S.J.I., T.C.J., P.N.R., M.M.M., and M.W.B. performed research; J.W.K., E.T.B., and A.L.D. contributed new reagents/analytic tools; R.P.L., C.A.S., A.S.C., J.W.K., E.T.B., S.J.I., T.C.J., A.L.D., M.M.M., and M.W.B. analyzed data; and R.P.L., C.A.S., A.S.C., T.C.J., and P.N.R. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: The paleoclimate proxy data and geochronology data have been deposited with the NOAA paleoclimatology database of the National Centers for Environmental Information:
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1512864112/-/DCSupplemental.
Freely available online through the PNAS open access option.
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