Dissolved trace metals in the southwestern Indian Ocean

Abstract

Dissolved trace metal concentrations are reported for a section in the southwestern Indian Ocean, extending from 7 to 27°S around the 56°E meridian. Overall distributions conform to those found in other oceans, with Cd, Cu, Ni and Zn showing recycled, or nutrient-like, behaviour, whereas Mn is enriched in the mixed layer relative to deep water. Deep-water concentrations of the recycled elements are intermediate 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 limits while for Cu and Ni significant near-surface concentrations (0.9 and 2.1 nM, respectively) are found. Relationships between the concentrations of metals and nutrients are similar to those described in the literature for the recycled metals for other regions, although significant variations exist from ocean to ocean. Maximum manganese concentrations in the upper water column are about or below 1 nM, as expected for a region remote from continental sources of airborne particulaet material. Minor variations in maximum concentration with latitude are evident as a result of the complex geochemistry of this element. Deep water manganese concentrations are uniformly low, showing no evidence for benthic or hydrothermal sources.