Concentrations of phosphate plotted versus nitrate and colored by the amount of oxygen present in each sample.  Note that samples with low oxygen concentrations (<20 µmol/kg) lie above and left of the main trend.  This is indicative of nitrate loss at low oxygen concentration as bacteria use nitrate as a terminal electron acceptor when oxidizing organic carbon.  The data indicate that approximately 0.3 µmol/kg PO₄^3-  remain when NO₃^- is completely depleted.  The graph was prepared using the Electronic WOCE Atlas and Ocean Data View.