The chemical mass balance of the amazon plume—II. Copper, nickel, and cadmium

Abstract

Trace element samples spanning the salinity range were collected in the Amazon plume in June 1974 and 1976. In 1976, laboratory mixing experiments using unfiltered river water and seawater were undertaken. The studies show that copper and nickel are unreactive in the Amazon plume on a time scale of a few days: in both field and laboratory studies the elements are related linearly to salinity, so that neither adsorption and precipitation not desorption reactions significantly alter the net flux of these elements. The 1974 field data indicate there may be up to 25% removal of copper, probably biologically, although a conservative interpretation could be entertained if systematic deviations from the resulting copper-salinity plot are ignored. Cadmium behavior was not clearly defined. There is some indication of desorption, and the estuarine data can be used to set an upper limit on the net flux. The net effective contribution of the elements to the ocean from the Amazon is copper, 24 nmol kg−1; nickel, 4 to 5 nmol kg−1; and cadmium, <0.1 nmol kg−1.