Gallium (Ga)
| Atomic number: |
31 |
| Atomic weight: |
69.723 |
| Average concentration in ocean: |
17 pmol/L |
| Residence time: |
100 - 750 yr |
Distribution in ocean
Dissolved Ga has a complex vertical profile
with the major features of a scavenged element such as aluminum.
Concentrations are relatively high at the surface (data).
A shallow maximum occurs in many profiles just below the surface, perhaps due to
remineralization from sinking particles. A minimum occurs in
intermediate water due to scavenging onto particles. A large increase
occurs towards the bottom due to diffusion from pore waters or remineralization
at the sediment-water interface.
Speciation
Gallium is present in seawater as the strongly hyrolyzed +III ion, Ga(OH)30
and Ga(OH)4-.
Residence time
The residence time was estimated using a 1-D advection/diffusion/reaction model
to range from 750 yr in the deep Central Pacific to 100 yr in the deep SubArctic
(Orians and Bruland, 1988).
Analysis
Gallium is determined by graphite furnace, atomic absorption spectrometry after
preconcentration by organic extraction.
References