The glacial/interglacial rise in atmospheric CO2 is one of thebest known changes in paleoclimate research - yet the cause for it is still unknown.Forcing a coupled ocean--atmosphere--biosphere box model of the global carbon cycle with proxy data over the last glacial termination we are able to quantitatively reproduce transient variations in pCO2 and its isotopic signatures (d13c, D14c) observed in natural climate archives.According to our model, a reduction of aeolian iron fertilization in the Southern Ocean together with a breakdown in Southern Ocean stratification, the latter caused by rapid sea ice retreat, trigger the onset of the pCO2 increase.After these events the reduced North Atlantic Deep Water (NADW) formation during the Heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the Boelling-Alleroed warm interval are the main processes determining the atmospheric carbon records in the subsequent time periodof Termination I.We further deduce that a complete shutdown of the NADW formation during the Younger Dryas was very unlikely.Changes in ocean temperature and the terrestrial carbon storage together with carbonate compensation are the dominant processes explaining atmospheric d13C after the Boelling-Alleroed warm interval.