Lanthanum (La)

Atomic number:	57
Atomic weight:	138.9055
Average concentration in ocean:	40 pmol/kg
Residence time:	650-1600 years

Distribution in ocean
La has a modified, nutrient-like vertical profile similar to that of copper. Low concentrations are found at the surface and values increase continuously with depth (data).

Speciation
The rare earth elements are present in seawater in the +III oxidation state, except Ce, which can also be oxidized to the +IV state. Complexation with carbonate ion dominates the speciation of REE's, e.g., LaCO₃⁺.

Residence time
The residence time was estimated from the Y and Ho residence times and the ratio of the particulate fraction of the metals (Alibo and Nozaki, 1999). This assumes reversible scavenging onto sinking particles.

Analysis
Rare earth elements are determined by mass spectrometry. The measurements shown here were determined using Inductively Coupled Plasms-Mass Spectrometry in shore based laboratories.

References