Climate-induced discharge variations of the Nile during the Holocene: Evidence from the sediment provenance of Faiyum Basin, north Egypt

The Faiyum Basin of northern Egypt occupies a key location on the source-to-sink pathway of the Nile. High-resolution grain size, organic carbon and carbonates, as well as geochemical and magnetic analyses, were conducted on a sediment core retrieved from the basin to infer changes in sediment provenance in association with climate-induced variations in Nile River discharge during the Holocene. A high Si/Al ratio in the coarse sediment with weak magnetic properties prior to ca. 9.7 cal ka BP indicated prevalent aeolian activities in the lake basin, revealing no Nile discharge inputs and thus a dry Nile. Initial high values of the mobile elements (CaO, MgO and Sr) after ca. 9.7 cal ka BP with well-sorted finer sediment marked the establishment of a flow connection between the basin and the Nile since then. This establishment was followed by a durative hydrological connection to the Nile until ca. 5.0 cal ka BP inferred from high organic matter and stable magnetic and geochemical properties of the finer sediment, implying a humid climate phase of the Nile between ca. 9.7–5.0 cal ka BP. Afterwards, an increasing Ti/Al ratio and magnetism of the sediment indicated a brief change in sediment provenance, as material from the volcanic Ethiopian Uplands carried by the Blue Nile and the Atbara became dominant. A drying climate prevailed in the Nile Basin after ca. 5.0 cal ka BP. Although the Ti/Al ratio and sediment magnetic properties still showed a prominent sediment contribution from the volcanic Ethiopian Uplands, the natural discharge from the river Nile to the Faiyum Basin was weakened, especially when increasing water extraction by humans occurred after ca. 4.0 cal ka BP. The sediment provenance pattern of the Faiyum Basin was substantially influenced by climate-induced variations of the Nile discharge in response to the advance/retreat of the African Summer Monsoon (ASM) driven by the northward/southward migration of the Inter-Tropical Convergence Zone (ITCZ).