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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.