Apparent copper complexation capacity and conditional stability constants in north atlantic waters

Abstract

Surface water samples were collected in the north Atlantic Ocean in July–August 1983. Their apparent complexation capacity for copper (CC Cu) was determined on board, using differential pulse anodic stripping voltammetry under clean room conditions. Measurements were carried out by direct titrations as well as after equilibration of copper spikes. CC Cu and conditional stability constants ( K′) were calculated, by means of three different methods, which are compared. On the basis of salinity, temperature, silicate and phosphate concentrations the following surface waters could be distinguished: North Atlantic Drift (I), East Greenland Current (II), Labrador Current (III) and Gulf Stream waters (IV, V). CC Cu and K′ were found to differ between these waters. The range of values for CC Cu and their mean values given in parentheses, as calculated from van den Berg plots for waters I–IV are: I, 53–65 (59); II, 47–66 (55); III, 37–53 (45); IV, 20–42 (33) nM Cu. The range and mean values for log K′ are: I, 8.23–8.33 (8.28); II, 7.89–8.11 (7.98); III, 8.40–8.41 (8.41); IV, 7.90–8.21 (8.06). Information on complexation kinetics extracted from the titration curve revealed that k f ′ is area-specific. The complexation rate constant in the northern part (Area I) is about two times larger than that in the southern area IV, (3.6 ± 0.3) and (2.2 ± 0.2) × 10 4 s −1 M −1 Cu, respectively. Preliminary results for deep water samples suggest smaller but still existent CC Cu and higher K′ than those found for surface waters.