Dust deposition is extremely variable over all timescales. Yet the impact of this variability on ocean biogeochemistry is currently not known, at least on the global scale. Here, we force a global model of ocean biogeochemistry over 1996 to 2001 with daily fields of dust deposition simulated by an atmospheric aerosol model. Our model results suggest that dust deposition explains a large part of the temporal variability of surface iron in the tropical regions and in part of the subarctic Pacific. However, while dust deposition is dominated by daily events, its impact on surface iron is maximal on interannual timescales. The largest fluctuations of surface iron produced by dust occur in oligotrophic regions where phytoplankton growth is not primarily controlled by iron availability. Consequently, the variability of surface chlorophyll induced by aerosol iron is predicted to be very small everywhere, especially relative to the impact of the ocean dynamics.