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Forcing of wet phases in southeast Africa over the past 17,000 years

Abstract

Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000 years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established1,2,3,4,5. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing2,3, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes4,5. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000 years ago) and the Younger Dryas (around 12,000 years ago), or when local summer insolation was high in the late Holocene, that is, during the past 4,000 years.

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Figure 1: Modern atmospheric circulation over southern Africa during Southern Hemisphere summer, summer rainfall and vegetation types.
Figure 2: Records of environmental variability in southeastern Africa over the past 17,000 years.
Figure 3: Detailed comparison of Greenland climate changes with hydrologic variations in the Zambezi catchment during the last deglaciation.

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Acknowledgements

This work was supported by the DFG Research Center/Cluster of Excellence ‘The Ocean in the Earth System’ and DFG grant Sche903/8. Laboratory assistance was provided by K. Siedenberg, M. Segl, W. Bevern, B. Meyer-Schack and R. Kreutz. We thank R. Schneider for logistical support and S. Weldeab for sample preparation for radiocarbon analyses. Comments by Y. Huang and J. Russell improved the manuscript.

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Experimental work was carried out by E.S., H.K., G.M. and J.P.; data analysis and interpretation were carried out by E.S., H.K., G.M., M.P. and J.P.

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Correspondence to Enno Schefuß.

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The authors declare no competing financial interests.

Additional information

Data reported here are stored in the Pangaea database (http://www.pangaea.de/10.1594/PANGAEA.771396).

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Supplementary Information

This file contains Supplementary Text, Supplementary Figures 1-4 with legends, Supplementary Table 1 and additional references.The original file that appeared on line had corrupted and was replaced on 03 January 2012. (PDF 296 kb)

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Schefuß, E., Kuhlmann, H., Mollenhauer, G. et al. Forcing of wet phases in southeast Africa over the past 17,000 years. Nature 480, 509–512 (2011). https://doi.org/10.1038/nature10685

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