A geochemical record of precession-induced cyclic eastern Mediterranean sedimentation: Implications for northern Sahara humidity during the Pliocene

The chemical composition of lithogenic components in Pliocene sediments fro m the eastern Mediterranean displays periodic variations that are related t o earths orbital parameters owing to changes in insolation of the northern hemisphere. This can be explained by two different paleoclimatic/palaeocean ographic scenarios. During oligotrophic periods. similar to those persistin g in the modern Mediterranean, sedimentation is rather uniform, and sedimen ts receive high proportions of eolian material from the surrounding deserts . During more humid intervals sedimentation is dominated by fluviatile mate rial that has been introduced by the Nile and northern borderland rivers. H igher nutrient loads associated with enhanced riverine input and a change i n water circulation led to eutrophication, water column anoxia, and saprope l deposition in the eastern Mediterranean. Our investigations confirm earli er works claiming that in large parts of the northern Sahara palaeoclimatic conditions changed frequently from arid to more humid. Our results suggest that these changes in the Pliocene match with the approximately 22-ka inso lation cyclicity.