TRACE-METAL DISTRIBUTIONS ACROSS THE CONTINENTAL-SHELF NEAR OTAGO PENINSULA, NEW-ZEALAND

The distributions of the trace metals iron (Fe), copper (Cu) and cadmi um (Cd) along with hydrological parameters (salinity, temperature and reactive phosphate) across the New Zealand continental shelf near Otag o Peninsula have been studied. This is a region in which the Subtropic al Convergence (STC), a major oceanic front separating subtropical and subantarctic waters, is uniquely located close to land, permitting an examination of the influence of terrestrial sources of Fe and Cu on o ceanic waters containing excess micronutrients. Acid-soluble (110 nmol kg(-1)) and dissolved (6.3 nmol kg(-1)) Fe concentrations were highes t over the central shelf, and decreased rapidly across the mixing zone of the STC to about 5 nmol kg(-1) for both forms. The distribution of acid-soluble and dissolved Cu were similar to their counterparts for Fe. Depth-concentration profiles for acid-soluble Fe and Cu suggest re suspension of shelf sediments is the main source. The ratio of oxine-l abile to acid-soluble Fe varied from 0.03 to 0.26, with the highest va lues found in the near surface waters. Oxine-labile Fe and Cu also dec reased in concentration in a seawards direction, and with depth, indic ating the influence of near surface processes on the reactivity of the se elements. Cd concentrations across the continental shelf were very low (< 200 pmol kg(-1)) and exhibited no clear spatial trend and no co rrelation with phosphate. Comparison of the Cd/P ratio across the shel f indicated that the waters in this region were strongly depleted in C d relative to P. Phosphate concentrations were lowest in neritic water and increased in the seawards direction because of mixing with nutrie nt-rich Subantarctic Surface Water. (C) 1998 Elsevier Science B.V. All rights reserved.