The global carbon cycle plays a significant role in glacial/interglacial transitions. On one hand because carbon reservoirs and exchange rates are subject to external climate conditions, on the other hand because changes in carbon dioxide concentrations lead to amplification and mediation of regional climate variations.Time slice experiments so far were unable to unambiguously explain the driving forces of the glacial/interglacial change in atmospheric CO2 of about 100 ppmv. Additional information can be gained from the temporal evolution of the carbon cycle using transient model runs, which have to be in line with pronounced variations in ice core CO2 concentrations over the last glacial/interglacial transition.Using a coupled atmosphere/biosphere/ocean box model of the global carbon cycle it is possible to quantify changes in CO2 and d13C observed in Antarctic ice core records. To this end the model is transiently driven by various proxy records over the last 25,000 years. The results show that marine productivity, a breakdown in Southern Ocean stratification triggered by sea ice retreat, the terrestrial biosphere as well as carbonate compensation add at specific intervals to the overall change in CO2 and d13C.