Phosphorus (P)

Atomic number:	15
Atomic weight:	30.9737
Average concentration in ocean:	2.0 ľmol/kg
Residence time:	69,000 yrs

Distribution in ocean
Dissolve P has a nutrient like vertical profile with low concentrations at the surface and increasing values at depth due to remineralization of P from sinking particulate organic matter (data). These profiles do not do real justice to the complexity of P distributions in the ocean. A north-south section of dissolved PO₄^3- through the Atlantic Ocean shows the large variability that can occur. The concentrations of PO₄^3- in the ocean are very highly correlated with NO₃^- concentations, except at low oxygen values when NO₃^- may be lost by dissimilatory nitrate reduction.

Speciation
Dissolved P is present in seawater primarily as HPO₄^2- and H₂PO₄^-, which are base ions of orthophosphoric acid (H₃PO₄). The sum of these ions are typically called phosphate.

Residence time
The phosphorus 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
Phosphate is determined colorimetrically by forming a blue colored reduced, phosphomolybdate complex.

References & Notes