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Interhemispheric symmetry of the tropical African rainbelt over the past 23,000 years

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Abstract

The distribution of rainfall in tropical Africa is controlled by the African rainbelt1, which oscillates on a seasonal basis. The rainbelt has varied on centennial to millennial timescales along with changes in Northern Hemisphere high-latitude climate2,3,4,5, the Atlantic meridional overturning circulation6 and low-latitude insolation7 over the past glacial–interglacial cycle. However, the overall dynamics of the African rainbelt remain poorly constrained and are not always consistent with a latitudinal migration2,4,5,6, as has been proposed for other regions8,9. Here we use terrestrially derived organic and sedimentary markers from marine sediment cores to reconstruct the distribution of vegetation, and hence rainfall, in tropical Africa during extreme climate states over the past 23,000 years. Our data indicate that rather than migrating latitudinally, the rainbelt contracted and expanded symmetrically in both hemispheres in response to changes in climate. During the Last Glacial Maximum and Heinrich Stadial 1, the rainbelt contracted relative to the late Holocene, which we attribute to a latitudinal compression of atmospheric circulation associated with lower global mean temperatures10. Conversely, during the mid-Holocene climatic optimum, the rainbelt expanded across tropical Africa. In light of our findings, it is not clear whether the tropical rainbelt has migrated latitudinally on a global scale, as has been suggested8,9.

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Figure 1: Modern-day mean annual rainfall, wet season length, wet season intensity and vegetation type for tropical Africa.
Figure 2: Latitudinal distribution of vegetation type for modern and past climate states.

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Acknowledgements

We thank A. Govin, H. Renssen and C. Li for comments and discussion. This work was supported by ESF—EUROMARC project ‘RETRO’ and the DFG Research Centre/Cluster of Excellence ‘The Ocean in the Earth System’. AMS dating on the core GeoB9535-4 carried out in Peking University was supported by the NSFC (40776028) and the Fok Ying Tong Education Foundation (111016) and datings carried out in Kiel were supported by the Alexander von Humboldt Foundation.

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Experimental work was carried out by J.A.C., E.S., M.Z., R.T., E.H., J.T., A.M. and M.Z. Data analysis and interpretation were carried out by J.A.C., S.M., E.S., D.H., M.P., T.M.D., M.S. and G.W.

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Correspondence to James A. Collins.

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The authors declare no competing financial interests.

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Collins, J., Schefuß, E., Heslop, D. et al. Interhemispheric symmetry of the tropical African rainbelt over the past 23,000 years. Nature Geosci 4, 42–45 (2011). https://doi.org/10.1038/ngeo1039

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