Cadmium, Lead and Copper Complexation in Antarctic Coastal Seawater. Evolution during the Austral Summer

Abstract

The evolution of cadmium, lead and copper complexation by organic ligands was studied along the water column during the 1990/91 summer in the Gerlache Inlet (Antarctica). The complexation was estimated by determination of the total dissolved concentration of metals, the labile concentration, the ligand concentrations and the relative conditional stability constants. The mean value of the total dissolved cadmium concentration was 0.83 nM until mid-December; the concentration was gradually depleted initially in the subsurface layer then down to the bottom. The mean concentration along the water column in February was 0.15 nM. The labile fraction represented 90% of the total until December, and it was reduced to about 20% in the upper 50 m by February. The cadmium was complexed by one class of ligands detectable after mid-December. Initially it was present only in the surface layers and later was extended to the bottom. The ligand concentration reached a maximum (2.2 nM) during the phytoplankton bloom in December. The mean total dissolved concentration for lead ranged from 0.083 nM until December to 0, 030 nM in the upper 100m at the end of the summer. The labile fraction did not change during the season and meanly represented 39% of the total dissolved concentration. The lead was complexed by one class of ligands, its mean concentration ranges between 0.60 nM at the beginning of the summer to 1.2 nM at the end of the season. The total dissolved copper concentration ranged between 1.6 to 3.8 nM. The labile fraction was strongly dependent on depth and time, ranging from values lower than 1% in surface water to a maximum value of 40% in deep water. The copper was complexed by two classes of ligand, the first present only in surface layers and the second homogeneously distributed along the water column. The results for the three metals are compared to those obtained for surface samples collected in the whole of Terra Nova Bay between summer 1987/88 and summer 1989/90.