text: The balance of dissimilatory nitrate reduction to ammonium and denitrification alters the accuracy of f-ratio calculations. The f-ratio is used to quantify the efficiency of the biological pump, which reflects sequestering of carbon from the atmosphere to the deep sea. The f-ratio is calculated using estimates of new production (primary productivity stimulated by nutrients entering the photic zone from outside the photic zone, for example from the deep ocean) and regenerated production (primary productivity stimulated by nutrients already in the photic zone, released by remineralisation). Calculations of the f-ratio use the nitrogen species stimulating primary productivity as a proxy for the type of production occurring; productivity stimulated by NH rather than NO is regenerated production. DNRA also produces NH (in addition to remineralisation) but from organic matter which has been exported from the photic zone; this may be subsequently reintroduced by mixing or upwelling of deeper water back to the surface, thereby, stimulating primary productivity; thus, in areas where high amounts of DNRA is occurring, f-ratio calculations will not be accurate.