1. The biogeochemical cycling of phosphorus in marine systems Introduction Sources of P Sinks of P Residence times P cycling within the ocean P distribution P composition P bioavailabity P turnover time conclusions

2. Sources of P Riverine Atmospheric Volcanic

3. P Sinks Organic matter burial P sorption and iron coprecipitation Phosphorite burial Hydrothermal processes

4. Residence times The global marine inventory of dissolved P is close to 3.2*10 15 mol P.The residence time of P relative to the known P sources ranges from 20000 to 8000 years.But based on the P sinks the residence time has dropped from 80000 to 10000 years.

5. P cycling within the ocean Dissolved inorganic P Total dissolved and dissolved organic P

6. Dissolved inorganic P In most studies the dissolved inorganic P is characterized using phosphomolybdate under acidic conditions. A more appropriate term for the fraction measured with this technique is the Soluble reactive phosphorus.

7. Total dissolved and dissolved organic P TDP is generally quantified by using high temperature and pressure in the presence of a strong oxidizing reagent in this manner all of the P within the sample is converted to inorganic P.

8. P Distributions The average global concentration of SRP in the oceans is 2.3 micromole and is by far the largest reservoir of dissolved P.

9. P composition The composition of P within marine systems has been difficult to constrain.

10. P bioavailability In the inorganic form P is most bioavailable

11. P turn overtime They are studding nutrients turn over times in the ocean now a days.

12. Conclusions It is clear that elucidating the cycling of all nutrients in marine systems is extremely important if we are to understand current controls on primary production. P sinks could be much larger then current estimates as more information concerning the distribution and magnitude of phosphoritic deposits is known.

13. Conclusions The intensity of upper ocean P cycling, in particular, can have a direct impact on the magnitude of particulate matter exported from the euphotic zone to underlying sediments. Hence long term changes in P cycling will effect the residence time of P over geological time scales.

14. Future outlook There is still a lot of work to be done.

15. Articles used. The biogeochemical cycling of phosphorus in marine systems by Claudia R. Benitez-nelson. Marine nitrogen: Phosphorus stoichiometry and the global N:P cycle by John A.Downing. The relative influences of nitrogen and phosphorus on oceanic primary production.