On the distribution of copper, nickel, and cadmium in the surface waters of the North Atlantic and North Pacific Ocean

Abstract

Concentrations of copper, nickel, and cadmium have been determined for about 250 surface water samples. Nonupwelling open‐ocean concentrations of these metals are Cu, 0.5–1.4 nmol/kg; Ni, 1–2 nmol/kg; and Cd, less than 10 pmol/kg. In the equatorial Pacific upwelling zone, concentrations of Ni (3 nmol/kg) and Cd (80 pmol/kg) are higher than in the open ocean, but Cu (0.9 nmol/kg) is not significantly enriched. Metal concentrations are higher in cool, nutrient‐rich eastern boundary currents: Cu, 1.5 nmol/kg; Ni, 3.5 nmol/kg, and Cd, 30–50 pmol/kg. Copper is distinctly higher in the coastal waters of the Gulf of Panama (3–4 nmol/kg) and also higher in the shelf waters north of the Gulf Stream (2.5 nmol/kg); these copper enrichments may be caused by copper remobilized from mildly reducing shelf sediments and maintained by a coastal nutrient trap. In the open ocean, events of high‐Cu water (1.5–3.5 nmol/kg) are seen on scales up to 60 km; presumably, these are due to the advection of coastal water into the oceanic interior. The lowest copper concentrations in the North Pacific central gyre (0.5 nmol/kg; (Bruland, 1980)) are lower than in the Sargasso Sea (1.3 nmol/kg), while for nickel the lowest concentrations are 2 nmol/kg in both the North Pacific and the North Atlantic. Nickel and cadmium, while generally correlated with the nutrients in surface waters, show distinct regional changes in their element‐nutrient correlations. The residual concentrations of trace metals in the surface waters of the ocean can be explained if biological discrimination against trace metals relative to phosphorus increases as productivity decreases.