Cobalt and copper distributions in the waters of Santa Monica Basin, California

Abstract

The trace metals cobalt and copper are removed from the oceans interior by scavenging on to particle surfaces1, but the mechanisms for removal of these two metals are probably quite different. Cobalt appears to be scavenged by manganese oxide particles1,2, whereas organic compounds are the main carrier phase for copper3,4. Remobilization of these metals in marine sediments therefore proceeds by different pathways. The differences in the pathways of remobilization are accentuated in oxygen-deficient environments: manganese oxide reduction is accelerated at low oxygen levels5 and organic carbon is preserved6. Cobalt fluxes from sediments underlying oxygen-deficient waters should be enhanced and copper fluxes reduced. We report here measurements of the cobalt and copper distributions in the waters of an oxygen-deficient marine basin in the Southern California Bight. Cobalt concentrations near the bottom are raised four times above the background level, whereas copper concentrations show no increase. These measurements confirm features of existing models for the oceanic cycles of these metals.