Copper-complexing capacity of South Pacific waters

Abstract

The strong copper-complexing capacity of seawater from the western tropical Pacific Ocean and the Coral Sea has been measured by a method based on competition between naturally occurring ligands and Chelex-100 ion-exchange resin. In the nutrient-depleted surface waters, the values ranged from 4 to 72 nM. For deeper waters there were larger variations with values ranging from 2 to 136 nM in the region of the salinity minimum at approximately 800-1000 m. There was no evidence for increased complexing capacity due to the sediment-water interface. Since changes in complexing capacity are ultimately of biological origin, the variability must have arisen when the waters were in the euphotic zone at polar latitudes. The samples were unfiltered and the complexing capacity could be due to either dissolved organic compounds or to particles so small that their settling velocities are negligible compared with the time elapsed since the water parcel was last in the euphotic zone. There is no direct correlation between complexing capacity and water density or concentration of nutrients. The results suggest that parcels of water up to 100 km wide can travel distances up to 10 000 km and maintain a chemical signature different from the surrounding water.