Nd isotopic compositions of Eastern Mediterranean sediments: tracers of the Nile influence during sapropel S1 formation?

Nd isotopic composition of Eastern Mediterranean sediments are used to inve stigate the influence of Nile flux variations during the formation of the y oungest sapropel S1. Four box cores located on an east-west transect (aroun d 35 degreesN) at increasing distance from the Nile source were studied. is an element of (Nd(0)) signatures were measured in the lithogenic (alumino- silicate residue) fraction and the authigenic/biogenic (carbonates, organic matter and Fe, Mn oxyhydroxides) fraction of the sediment after 1 M HCl le aching. The is an element of (Nd(0)) profiles of the residual fraction show more radiogenic values in the sapropel layers than in the adjacent sedimen ts. These profiles follow the Gaussian-shaped Ba/Al profile shape which def ines S1. The is an element of (Nd(0)) variations can be related to changes in the proportions of two continental sources of particulate material: Nile particles and Saharan aerosols. A simple mixing model reveals that the con tribution of Nile particulates to the sediments increases relative to Sahar an aerosols during sapropel formation, indicating a higher Nile discharge a nd a decrease in eolian input at that time. For the cores located closest t o the Nile fan, the is an element of (Nd(0)) signatures of the leachable fr action are always higher in the sapropel layer (-5 to -4) than in the adjac ent sediments (similar to - 6). The sapropel layer is an element of (Nd(0)) values increase with decreasing distance to the Nile towards values close to the Nile particulates. All the results obtained on the leachable fractio n point towards a massive input of Nile freshwater during S1 deposition. (C ) 2001 Elsevier Science B.V. All rights reserved.