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Orbital precession modulates interannual rainfall variability, as recorded in an Early Pleistocene speleothem

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posted on 2019-09-24, 13:06 authored by PJ Hopley, GP Weedon, CM Brierley, C Thrasivoulou, AIR Herries, A Dinckal, DA Richards, DC Nita, RR Parrish, NMW Roberts, D Sahy, CL Smith
Interannual variability of African rainfall impacts local and global communities, but its past behavior and response in future climate projections are poorly understood. This is primarily due to short instrumental records and a lack of long high-resolution palaeoclimate proxy records. Here we present an annually resolved 91,000 year Early Pleistocene record of hydroclimate from the early hominin-bearing Makapansgat Valley, South Africa. Changes in speleothem annual band thickness are dominated by precession over four consecutive orbital cycles with strong millennial-scale periodicity. The frequency of interannual variability (2.0–6.5 yr oscillations) does not change systematically, yet its amplitude is modulated by the orbital forcing. These long-term characteristics of interannual variability are reproduced with transient climate model simulations of water balance for South Africa from the Late Pleistocene to Recent. Based on these results, we suggest that the frequency of interannual variations in southern African rainfall is likely to be stable under anthropogenic warming, but that the size of year-to-year variations may increase. We see an orbitally forced increase in the amplitude of interannual climate variability between 1.8 Ma and 1.7 Ma coincident with the first evidence for the Acheulean stone tool technology.


We thank Mark Maslin for reading the manuscript and for supporting this project from its initiation. Thanks to Steve Noble for technical support at NERC Isotope Geosciences Laboratories and to Ming Tan and two anonymous reviewers for their constructive comments. Funding was provided to Hopley by the Natural Environment Research Council (NERC, UK), awards NE/J00443X/1 and IP/1065/1108. Weedon was supported by the Joint UK DECC/Defra Met Office Hadley Climate Centre Programme (GA01101). Herries was supported by Australian Research Council Future Fellowship FT120100399. Brierley is grateful to the substantial effort of the TraCE modeling and the Paleoclimate Modelling Intercomparison Project (PMIP) modeling groups, who have kindly donated all the simulation output. TraCE-21ka was made possible by the U.S. Department of Energy (DOE) INCITE computing program, and supported by the National Center for Atmospheric Research (NCAR), the U.S. National Science Foundation P2C2 program, and the DOE Abrupt Change and EaSM programs.



Geology, 2018, 46 (8), pp. 731-734 (4)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/School of Geography, Geology and the Environment/Physical Geography


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1 GSA Data Repository item 2018267, additional information on chronology, climate controls on annual band thicknesses, model/data comparison, and the links between climate variability and hominin evolution, is available online at, or on request from The annual band thickness datasets are archived at the British Geological Survey (BGS) National Geoscience Data Centre (NGDC):