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.