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 temperature^3,4. The human contribution to land degradation and dust mobilization in this region remains poorly understood^{5,6,7,8,9,10,11}, 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 ago^11,13,14. 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.