Climate-induced variability of fluvial and aeolian sediment supply and gravity-driven sediment transport off Northwest Africa

Abstract

This study focuses on climate-induced variability in terrigenous sediment supply and gravity-driven sediment transport off NW-Africa during the past 13 kyr. Sediment texture, mainly based on detailed grain-size analysis of the terrigenous silt and fine fraction and modelled end members for aeolian and fluvial supply, was studied on seabed samples recovered from the NW-African continental margin between 17° and 33°N as well as on a high-resolution Holocene sediment record off Morocco to display spatial and temporal variations in dominant sediment transport processes to the Atlantic Ocean and to obtain an overview of the evolution in continental aridity since the last deglaciation. Additional information on the evolution in Holocene NW-African climate and its implications for sediment transport processes is obtained from a high-resolution record of a submarine meandering channel system, the Cap Timiris Canyon, off presently hyperarid Mauritania.Under modern conditions terrigenous sediment supply along the NW-African continental margin north of 29°-30°N is characterized by fluvial discharge to the Atlantic Ocean, whereas further south, sediments are dominantly transported offshore by large dust plumes. During the Early to Mid Holocene relatively humid conditions were prevalent, although (sub-)millennial recurring dry phases are superimposed on this aridity record throughout the Holocene. Further south, off the Sahara desert, gravity-driven sediment transport is also controlled by climate variability during the past 13 kyr. We distinguish two phases of turbidity current activity and relate them to deglacial sea-level rise and Holocene climate variability, respectively. A climate-related coupling to be active for this depositional system during the Holocene is inferred by a (quasi-)periodic turbidity flow pattern and by excluding usually resorted triggers for turbidity current activity within this submarine channel system.