The uranium-isotopic composition of Saharan dust collected over the central Atlantic Ocean

Uranium isotopic compositions, (U-234/U-238)(activity), are utilized by earth surface disciplines as chronometers and source tracers, including in soil science where aeolian dust is a significant source to the total nutrient pool. However, the (U-234/U-238)(activity) composition of dust is under characterized due to material and analytical constraints. Here we present new uranium isotope data measured by high precision MC-ICP-MS on ten airborne dust samples collected on the M55 trans-Atlantic cruise in 2002. Two pairs of samples are presented with different size fractions, coarse (1-30 mu m) and fine (<1 mu m), and all samples were processed to separate the water soluble component in order to assess the controls on the (U-234/U-238)(activity) of mineral aerosols transported from the Sahara across the Atlantic. Our results indicate (U-234/U-238)(activity) above one for both the water soluble (1.13-1.17) and the residual solid (1.06-1.18) fractions of the dust; no significant correlation is found between isotopic composition and travel distance. Residual solids indicate a slight dependance of (U-234/U-238)(activity) on particle size. Future modeling work that incorporates dust isotopic compositions into mixing or isotopic fractionation models will need to account for the wide variability in dust (U-234/U-238)(activity). (C) 2015 Elsevier B.V. All rights reserved.