DISSOLVED TRACE-METALS IN THE SOUTHWESTERN INDIAN-OCEAN

Dissolved trace met concentrations are reported for a section in the s outhwestern Indian Ocean, extending from 7 to 27-degrees-S around the 56-degrees-E meridian. Overall distributions conform to those found in other oceans, with Cd, Cu, Ni and Zn showing recycled, or nutrient-li ke, behaviour, whereas Mn is enriched in the mixed layer relative to d eep water. Deep-water concentrations of the recycled elements are inte rmediate between those for the North Atlantic and North Pacific Oceans , as would be expected from known patterns of deep-ocean circulation. For Cd and Zn, depletion in the surface layer approaches detection lim its while for Cu and Ni significant near-surface concentrations (0.9 a nd 2.1 nM, respectively) are found. Relationships between the concentr ations of metals and nutrients are similar to those described in the l iterature for the recycled metals for other regions, although signific ant variations exist from ocean to ocean. Maximum manganese concentrat ions in the upper water column are about or below 1 nM, as expected fo r a region remote from continental sources of airborne particulate mat erial. Minor variations in maximum concentration with latitude are evi dent as a result of the complex geochemistry of this element. Deep wat er manganese concentrations are uniformly low, showing no evidence for benthic or hydrothermal sources.