Provenance of the various grain-size fractions in the Negev loess and potential changes in major dust sources to the Eastern Mediterranean

Abstract

The isotopic composition of Sr and Nd and elemental concentrations (e.g., Na, K, Ca, Mg, Al) of three primary Negev loess sequences trace the relative contributions of desert dust sources over the past ~180,000 yr to the southeastern Mediterranean. We focused on the geochemical signature of the fine (<20. μm) and coarse (>20. μm) grain-size modes of the loess to identify their respective provenances.The isotopic composition of the coarse fraction falls on a mixing line of sources feeding the Nile and its delta. The chemical compositions of the coarse fraction and the Sinai-Negev sand dunes are similar, indicating that this fraction is the product of aeolian abrasion of the adjacent Sinai-Negev sands. In turn, these sands are derived from the Nile delta and transported inland. The fine fraction has less negative εNd values and slightly deviates from the mixing line, indicating an additional end-member. The higher εNd values and Mg/Al ratios of the fine fraction are relatively well correlated (R2=0.64) and point to Arabian dust as an additional source. Temporal changes in the geochemical composition of loess over time reflect changes in climates of source areas and the Eastern Mediterranean. Shifts from Saharan to Arabian fine dust-dominated intervals indicate wetter conditions in the southern Sahara that weaken dust fluxes from this source relative to the Arabian fluxes.