Phosphorus (P)

Atomic number: 15
Atomic weight: 30.9737
Average concentration in ocean: 2.0 Ámol/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 PO43- through the Atlantic Ocean shows the large variability that can occur.  The concentrations of PO43- 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 HPO42- 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