Cobalt (Co)

Atomic number:	27
Atomic weight:	58.9332
Average concentration in ocean:	20 pmol/kg
Residence time:	340 years

Distribution in ocean
Dissolved cobalt has a scavenged profile. Its concentration is high at the surface due to a major input from the atmosphere and its concentration decreases with depth as dissolved cobalt is sorbed onto sinking particles and removed to the ocean sediments (scavenging). (data). Cobalt is an essential nutrient. However, surface depletions are not usually seen unless dissolved Zn concentrations are low, leading to the suggestion that Co may substitute for Zn.

Speciation
Cobalt exists as the +2 ion in seawater.

Residence time
The cobalt residence time is from Tracers in the Sea (Broecker, W. S. and Peng, T.-H., 1982. Eldigo Press, Palisades, NY). It was calculated from the global average river input.

Analysis
Cobalt is usually determined by complexing the metal with an insoluble organic ligand and extracting the complex into an organic phase, followed by graphite furnace atomic absorption spectrometry. It can also be determined by flow injection analysis with chemiluminescence detection (Sakamoto et al., 1986). Cathodic stripping voltammetry

References