Fig. 2.

Nutrient and trace metal contribution from aerosols of different origin. Enrichment of trace element and nutrient concentrations from the addition of African (Sahara Desert) aerosols (black bars) and European aerosols (white bars) collected locally at the Gulf of Aqaba. These amounts (micrograms or micromoles) were released to the incubation bottles from the addition of 6 mg of African aerosols (AD), or 6 mg of European aerosols (ED). Note that each incubation received a distinct aerosol filter collected simultaneously (triplicate treatments were not homogenized), resulting in some variability between triplicates. The top of the wide bar for each component represent the replicate with the lowest measured concentration, and the top of the thin line represents the highest concentration measured (e.g., the full range is represented not errors). Concentrations were measured as described in ref. 19. We use the lower value of Cu in the African dust (top of the broad black bar) for calculating the threshold concentration that corresponds to the chlorophyll levels in the Gulf. The lowest Cu concentration in the African aerosols is ≈3 times higher than the highest in the European aerosols. The amount of Cu added from the aerosol resulted in a 2-fold increase compared with the ambient Cu concentrations in Gulf of Aqaba surface water (which are similar to Atlantic surface water concentrations).