Fig. 2a plots the calculated flux of total aerosol iron (aerosol FeT) along the P02 cruise track. The flux of aerosol FeT varied between 37.3 and 5690 nmol/m2d (median = 226 nmol/m2d). In general, the flux of aerosol FeT decreased as sampling moved eastward; however, two periods of high atmospheric dust were observed. For our purposes, a dust event is broadly defined as a
SAR131675 of elevated aerosol Fe concentrations relative to the samples collected immediately before and after. The greatest aerosol FeT fluxes were measured during dust events occurring on 21–24 June (30°N, ~ 136°E; 415–5690 nmol/m2d) and 10–11 July (30°N, ~ 172°E; 4380 nmol/m2d). The AMBT for the highest aerosol FeT sample collected during the first dust event showed transport from mainland Asia (Z1) while the AMBTs for the others were from Z4 (Indonesia) and Z5 (Central Pacific). The aerosol FeT/AlT ratio in a sample can assist in identifying the predominant aerosol source and in the case of the first dusty
period the ratios are consistent with crustal sources. Five of the six samples had FeT/AlT molar ratios within the range reported for average upper continental crust (Fe/Al = 0.26; Wedepohl, 1995) and for both Chinese desert dust and loess specifically (desert: Fe/Al = 0.4 and loess plateau: Fe/Al = 0.37; Zhang et al., 1993 and Zhang et al., 199
cool while the other's FeT/AlT ratio was 0.13. During the second dusty period, FeT/AlT ratios were consistent with Asian dust even though the corresponding AMBTs suggest transport from the central Pacific. Data from size fractionated samples collected contemporaneously (data not shown here) suggest that the aerosol populations of these samples were dominated by > 1.0 μm particles, consistent with the size spectrum of mineral dust particles (Jickells et al., 2005).
