Copper (Cu)
| Atomic number: |
29 |
| Atomic weight: |
63.546 |
| Average concentration in ocean: |
2.4 nmol/kg |
| Residence time: |
5000 years |
Distribution in ocean
Dissolved Cu has a modified, nutrient-like vertical profile.
It is depleted at the surface and it's concentration increases with depth (data).
It does not reach a mid-depth maximum, as do most other nutrients. Its
concentrations increase continuously with depth. This behavior is believed
to result from remineralization of particulate copper from sinking particles
back into the dissolved phase, as occurs for other nutrient elements.
However, the Cu(+II) is sufficiently reactive to readsorb back onto sinking
particles (scavenging) and a mid-depth maximum does not accumulate.
Speciation
Inorganic copper exists primarily as the +II oxidation state in seawater as CuCO30
although photochemical processes can produce some Cu(+I) in surface
waters. The Cu(+II) is strongly bound by organic molecules that appear to
be produced by phytoplankton. Most (>99%) of the copper is bound
by these ligands. In surface waters, less than 0.1% of the Cu is present
as the Cu2+ aquo ion. The remainder is bound primarily to
organic molecules, called ligands. The ligand concentration
decreases with depth and the aquo ion concentration increases with depth.
Residence time
The copper residence time was calculated from the river and atmospheric inputs
(Boyle, et al., 1977).
Analysis
Copper is determined by graphite furnace, atomic absorption spectrometry after
preconcentration with an organic extraction. Copper can also be determined
by anodic stripping voltammetry or by flow injection analysis with
chemiluminescence detection.
References