The isotopic cycle of oceanic phosphate. I

Steady-state conditions seem to exist in the Atlantic and Pacific Oceans in the case of the 18O content of dissolved phosphate. The measured delta 18O(PO43-) values are fairly constant at all latitudes and depths. A constant difference of about 1% exists between average Atlantic and Pacific results. Oxygen isotope measurements carried out on phosphate in the organic matter of fish, showed an average difference of about 3% when compared with dissolved oceanic phosphate. Such a difference can be attributed to biological fractionation effects in the metabolism of phosphate. However, the equilibrium fractionation factors in the phosphate-water system are poorly known and consequently it is not known whether this difference represents an approach to, or a deviation from, isotopic equilibrium conditions. (Auth.)