Reorganization of the Southern Ocean circulation at the end of the last ice age was proposed to have reduced deep ocean CO₂ storage, yet a mechanistic understanding is still lacking. Here, we reconstruct nitrate consumption patterns across the Antarctic Circumpolar Current during the last deglaciation with two nitrogen isotope archives: fossil diatom frustules and deep-sea corals from cores and sites more than 120° longitude apart at the Kerguelen Plateau and Drake Passage. Both archives indicate an equatorward ACC and widespread surface nitrate depletion during the Last Glacial Maximum, followed by two southward ACC migrations during Heinrich Stadial 1 and the Younger Dryas–early Holocene. These southward migrations caused a focused increase in nitrate supply to the Antarctic Zone, steepening the nitrate gradient across the Antarctic Polar Front. Their timing coincides with rises in atmospheric CO₂ and the concentrations of oxygen and unused nutrients in the deep ocean, implicating ACC migration as central to the deglacial CO₂ release.