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Increase in African dust flux at the onset of commercial agriculture in the Sahel region

Abstract

The Sahara Desert is the largest source of mineral dust in the world1. Emissions of African dust increased sharply in the early 1970s (ref. 2), a change that has been attributed mainly to drought in the Sahara/Sahel region2 caused by changes in the global distribution of sea surface temperature3,4. The human contribution to land degradation and dust mobilization in this region remains poorly understood5,6,7,8,9,10,11, owing to the paucity of data that would allow the identification of long-term trends in desertification12. Direct measurements of airborne African dust concentrations only became available in the mid-1960s from a station on Barbados2 and subsequently from satellite imagery since the late 1970s: they do not cover the onset of commercial agriculture in the Sahel region 170 years ago11,13,14. Here we construct a 3,200-year record of dust deposition off northwest Africa by investigating the chemistry and grain-size distribution of terrigenous sediments deposited at a marine site located directly under the West African dust plume. With the help of our dust record and a proxy record for West African precipitation15 we find that, on the century scale, dust deposition is related to precipitation in tropical West Africa until the seventeenth century. At the beginning of the nineteenth century, a sharp increase in dust deposition parallels the advent of commercial agriculture in the Sahel region. Our findings suggest that human-induced dust emissions from the Sahel region have contributed to the atmospheric dust load for about 200 years.

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Figure 1: Locations of site GeoB9501 and Lake Bosumtwi.
Figure 2: Comparison of dust deposition and precipitation records for the late Holocene.
Figure 3: Relationship between δ 18 O of authigenic carbonates from Lake Bosumtwi 15 and dust deposition flux at site GeoB9501.

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Acknowledgements

Radiocarbon datings were performed at the Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research in Kiel and at the Poznan Radiocarbon Laboratory. This work was funded through the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System”. We thank M. Prange for plotting the TOMS data in Fig. 1 and U. Röhl, K. Enneking, V. Lukies and M. Klann for technical support.

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Contributions

S.M. designed the study, took the cores, measured XRF data and wrote the manuscript. D.H. calibrated the data, and calculated the end-member model. D.P. and H.W.F. performed 210Pb and 137Cs dating, aligned the multicore and the gravity core and provided part of the age model. J.-B.S. and I.M. performed grain-size analyses. M.Z. performed the EDP-XRF analyses for calibration. M.S. and D.H. performed the statistical analyses. G.M. calculated the reservoir age and provided the age model for the gravity core. All authors contributed to the interpretation of the data.

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Correspondence to Stefan Mulitza.

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The authors declare no competing financial interests.

Additional information

Data have been submitted to the Publishing Network for Geoscientific & Environmental Data (PANGAEA, http://www.pangaea.de).

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Supplementary Information

This file contains Supplementary Methods, Supplementary Tables S1-S2, Supplementary Notes, References and Supplementary Figures S1- S5 with legends. (PDF 474 kb)

Supplementary Data

This file contains the Supplementary Data - see Contents list in file for details. (XLS 1579 kb)

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Mulitza, S., Heslop, D., Pittauerova, D. et al. Increase in African dust flux at the onset of commercial agriculture in the Sahel region. Nature 466, 226–228 (2010). https://doi.org/10.1038/nature09213

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