CONTINUOUS TRANSECTS OF CADMIUM, COPPER, AND ALUMINUM IN SURFACE WATERS OF THE ATLANTIC-OCEAN, 50-DEGREES-N TO 50-DEGREES-S - CORRESPONDENCE AND CONTRAST WITH NUTRIENT-LIKE BEHAVIOR

On three north-south transects across the Atlantic Ocean continuous pr ofiles of Cd, Cu, and Al were measured in surface waters with ultra cl ean sampling and analytical procedures. Salinity, nutrients, and Al se rved as tracers to identify the characteristic oceanographic regimes s ampled under the different circumstances encountered during three diff erent seasons. The behaviour of the biodepleted element Cd and of the biointermediate element Cu was then investigated in relation to hydrog raphy and nutrient cycling. Trace metals and nutrients are generally u ncoupled in surface waters. A Cd/PO4 relationship only exists at high concentration levels, which were reached in winter under continental i nfluence and in the immediate proximity to intense upwelling. The pref erential removal of Cd over phosphate downstream of upwelling regions was confirmed. The reverse situation was observed in the northeastern Atlantic, where Cd depletion occurred after that for phosphate. The di fference is tentatively attributed to continental sources of Zn for wh ich Cd substitutes. The continent and the shelves are the major source for Cu. Except in proximity to these sources, the latitudinal Cu dist ribution is very smooth with open-ocean values around 0.65 to 1 nmol/k g as a result of slow scavenging, probably related to organic complexa tion. The tropical Atlantic Ocean shows very distinct signatures of di ssolved Al and silicate in low-salinity waters. These signatures can b e used to trace the origin of freshwater to atmospheric or river/shelf inputs, which have very different Al/Si ratios. The Amazon River was identified as the probable source of a low-salinity zone sampled in Oc tober 1990 at 5-9 degrees N, 28 degrees W, with elevated nutrients, pa rticulate organic C, Cu, and Cd values. Copyright (C) 1997 Elsevier Sc ience Ltd