Abstract:

The Mediterranean Sea lies at the interface between the African monsoon and the European temperate climate zones while receives from the surrounding continents significant amounts of lithogenic detritus with very different rock compositions and weathering regimes, making it an ideal area to study the Earth’s hydrological cycle. Previous works mostly focused on the Saharan dust and Nile discharge, but might have underestimated the supplies from other sources, especially overlooked the potential impact of paleo-rivers in the wider North-African margin. Focusing on the sapropel S1 layer deposited in the African Humid Period, combined with the present-day/Late-Holocene sediments collected from core tops, 30 samples from 18 core sites across the eastern Mediterranean Sea (EMS) were selected for elemental geochemical analysis. Comparing between two time slices (~9.5-8.9 ka vs. ~1.7-0 ka) having different hydroclimate backgrounds, this study permits a basin-wide detailed investigation of the terrigenous detrital inputs to EMS in the Holocene. Particularly, we aim to distinguish and characterize geochemically the various dust and riverine contributions. The Ti/Al, Zr/Al, Ca/Al, Y/Al ratios all showed longitude and latitude gradient variations, making them reliable indicators for Saharan dust; the differences between detrital elements likely reflect changes in the dust source and delivery routes originated from North Africa. Consistent north-south pattern in the dust proxies suggests a persistent interacting boundary of 36°N between the subtropical high-pressure belt and the temperate westerlies in the Holocene. Contrary to dust proxies, the riverine indicators were not only significantly higher in value for the Early Holocene than the present-day, but also exhibited different geographical patterns. The P/Al ratio showed west-east and north-south decreasing trends indicative of riverine inputs from the numerous small rivers along the coast of the northern Mediterranean Sea. Potential supply of North African paleo-rivers that were reactivated by intensified monsoon precipitation could be discerned based on the differences between the Ti/Al or K/Al and (Cr+Ni)/Al ratios. Taken together, the riverine inputs should have largely increased during the Early Holocene, while the delivery extents differed between the river systems, affected by specific hydroclimate mechanisms and the delivery of the surface currents.

Key words: Mediterranean, Holocene, African Humid Period, sapropel S1, elemental geochemistry, Saharan dust, paleo-river