The Sahara experienced several humid episodes during the late Quaternary, associated with the development of vast fluvial networks and enhanced freshwater delivery to the surrounding ocean margins. In particular, marine sediment records off Western Sahara indicate deposition of river-borne material at those times, implying sustained fluvial discharges along the West African margin. Today, however, no major river exists in this area; therefore, the origin of these sediments remains unclear. Here, using orbital radar satellite imagery, we present geomorphological data that reveal the existence of a large buried paleodrainage network on the Mauritanian coast. On the basis of evidence from the literature, we propose that reactivation of this major paleoriver during past humid periods contributed to the delivery of sediments to the Tropical Atlantic margin. This finding provides new insights for the interpretation of terrigenous sediment records off Western Africa, with important implications for our understanding of the paleohydrological history of the Sahara.

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During an environmental survey, living (stained) benthic foraminiferal faunas were investigated at 14 stations within the Cassidaigne Canyon (NW Mediterranean Sea) and the surrounding area. For many decades, industrial bauxite residues (namely red mud) have drained into this canyon via a submarine pipe. Stations investigated in this paper are located between water depths of 288 and 2,432 m from the shelf break to the deeper basin and at a distance ranging between~5 and 70 km from the pipe outlet. At almost every site, surface sediment is characterized by red mud deposits and their geochemical imprints. Our ecological observations show that foraminiferal standing stocks and simple diversity (S) decrease across the margin in response to the decreasing food input to the seafloor with increasing water depth. The foraminiferal composition echoes the overall mesooligotrophic patterns of our study area. The contribution of opportunistic and stress-tolerant species, commonly identified as recolonizers of freshly disturbed areas, is minor at the 14 stations. This clearly shows that red mud dispersal in the Cassidaigne Canyon and the surrounding area has no major ecological impact on foraminiferal diversity.

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