A new quasi-conservative tracer, N*, is introduced to study nitrogen fixation and denitrification in the world oceans. N* is defined as a linear combination of nitrate and phosphate, accounting for the stoichiometric ratio of remineralization. This tracer helps eliminate the effects of nitrification on nitrate and phosphate, allowing for the identification of denitrification and nitrogen fixation. The distribution of N* reveals that the Arabian Sea, eastern tropical North and South Pacific, and parts of the Bering Sea and continental shelves have low N* values, indicating denitrification. In contrast, the North Atlantic and Mediterranean show high N* values, suggesting nitrogen fixation. The study estimates nitrogen fixation in the North Atlantic at 28 Tg N yr⁻¹, three times higher than previous estimates. This suggests that nitrogen fixation may be underestimated. The results indicate that the oceanic nitrogen budget may be in balance, with the North Atlantic acting as a source and the Indian Ocean and parts of the Pacific as sinks. The study highlights the importance of N* in understanding global nitrogen cycles and their implications for the marine carbon cycle and atmospheric CO₂ concentrations.A new quasi-conservative tracer, N*, is introduced to study nitrogen fixation and denitrification in the world oceans. N* is defined as a linear combination of nitrate and phosphate, accounting for the stoichiometric ratio of remineralization. This tracer helps eliminate the effects of nitrification on nitrate and phosphate, allowing for the identification of denitrification and nitrogen fixation. The distribution of N* reveals that the Arabian Sea, eastern tropical North and South Pacific, and parts of the Bering Sea and continental shelves have low N* values, indicating denitrification. In contrast, the North Atlantic and Mediterranean show high N* values, suggesting nitrogen fixation. The study estimates nitrogen fixation in the North Atlantic at 28 Tg N yr⁻¹, three times higher than previous estimates. This suggests that nitrogen fixation may be underestimated. The results indicate that the oceanic nitrogen budget may be in balance, with the North Atlantic acting as a source and the Indian Ocean and parts of the Pacific as sinks. The study highlights the importance of N* in understanding global nitrogen cycles and their implications for the marine carbon cycle and atmospheric CO₂ concentrations.