Increasing late Holocene dust deposition in West Africa is amplified by land use change

Abstract

Changes in dust deposition in West Africa over the mid- to late Holocene have traditionally been attributed to orbital forcing affecting the West African Monsoon. However, land use change also occurred throughout this period, and the relative importance of human activities is poorly constrained. Here we challenge a purely climatic explanation by showing that anthropogenic activities could have led to increasing dust emissions in late-Holocene West Africa. To characterize land use effects on dust, we developed a dust mobilization potential index that represents the intensity of land use and landscape modification based on archaeological evidence and contemporary observations of land use effects on dust mobilization. Our analysis reveals that the locus of human-induced dust emissions shifted over time, with initial increases in the southern Sahara and Sahel coinciding with early agricultural and pastoral intensification, followed by gradual southward expansion into more humid regions alongside the spread and diversification of farming and herding practices. Notably, human-induced dust emissions continued to increase even during periods of relative climate humidity, including 3500–2500 BP and the Medieval Climate Anomaly (1150–650 BP), a trend inconsistent with purely climatic forcing but consistent with a concurrent rise in in the intensity of human activities. Our results suggest that while large-scale climate change established the overarching aridification trend in Holocene West Africa, progressive land use amplified the landscape's sensitivity to erosion, leading to a dust response disproportionate to climatic forcing alone.