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

•Sahara dust is a source of nutrients and fertilizes soils.•Mineral dust collected in a transect across the Atlantic was analyzed for uranium isotopic composition.•Saharan dust has a wide variability of ratios in the insoluble fraction, driven by differences in dust source.•Uranium in the water soluble fraction of the dust is dominantly derived from sea salt.

Uranium isotopic compositions, (234U/238U)activity234U/238Uactivity, 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 (234U/238U)activity234U/238Uactivity 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 μm) and fine (<1 μm), and all samples were processed to separate the water soluble component in order to assess the controls on the (234U/238U)activity234U/238Uactivity of mineral aerosols transported from the Sahara across the Atlantic. Our results indicate (234U/238U)activity234U/238Uactivity 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 (234U/238U)activity234U/238Uactivity 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 (234U/238U)activity234U/238Uactivity.