Summary
The distribution of dissolved (D) and acid-dissolvable (AD) Fe, Ni, Cu and Pb in upper water (0-300 m depth) was determined along a transect in the Australia sector (140E) of the Southern Ocean during three cruises conducted from November 2001 to March 2002. There was no significant difference in the concentration between dissolved and acid-dissolvable species for Ni and Cu. D Ni and D Cu showed moderately strong positive correlations (r > 0.7) with silicate, phosphate and nitrate. For Fe and Pb, the acid-dissolvable concentration mostly exceeded the dissolved concentration. D Pb considerably decreased from January to February in the Polar Frontal Zone and in the continental shelf water. AD Pb maxima occurred in the Antarctic Zone, resulting in the maximum AD/D ratio of 7. D Fe concentration in the surface mixed layer was less than 0.7 nM in the Polar Frontal Zone and the Antarctic Zone and increased southward beyond the Antarctic Divergence. The horizontal distribution of D Fe did not show a clear temporal change, which was contrast to the other nutrients and trace metals. AD Fe substantially increased in the continental shelf water and the AD/D ratio reached to 11. The following conclusions can be drawn from these data. (1) Ni and Cu exclusively exist as dissolved species and their circulation is controlled by biogeochemical cycles similar to those of the nutrients. (2) Pb is dominated by particulate species. The distribution of D Pb is highly variable in terms of both time and space due to a sporadic source and strong scavenging. (3) D Fe is rather a minor fraction of total Fe. Shelf sediments appear to be a strong source for Fe and there is a substantial variation in the supply to the upper water. D Fe in the mixed layer of the Antarctic Zone is maintained at a low concentration thorough summer probably because of rapid uptake by organisms.