Polar ice represents the most direct archive for information about the composition of the palaeoatmosphere. From ice cores in Greenland and Antarctica it is known that the concentration of the greenhouse gas CO2 shows a remarkable correlation with temperature.Several mechanisms and models have been proposed to explain the glacial/interglacial CO2 shift and its close resemblance with the temperature curve but also the prominent leads and lags in the phase relation of CO2 with temperature. Currently, models describing the global carbon cycle at these time scales are not able to satisfactory explain the 100 ppm shift from glacial to interglacial. The isotopic signature of CO2 offers a valuable tool to constrain the sources and sinks of pCO2 changes. Physico-chemically dissolved CO2 in the ocean, peat and soils, and terrestrial biomass constitute the mayor active carbon pools affecting the CO2 budget of the atmosphere. Since fluxes from one pool to another are characterized by specific isotopic fractionation factors, it is possible to calculate these fluxes with d13CO2 data. Although pCO2 data is available up to four glacial cycles, isotopic information is sparse and restricted to the last approx. 25 ka due to methodological constraints.Below a depth of about 700 m, pressure forces gases into the crystal lattice and formation of gas-clathrats starts. Since the metastable clathrats prevent using the established mechanic extraction for d13CO2 analysis, sublimation of the entire ice matrix is necessary to extract its CO2 completely and without fractionation. Therefore, a new technique is presented aimed to measure d13C CO2 of air from ice below the clathrath forming depth. By using continuous-flow IRMS coupled with GC, simultaneous separation of CO2 from N2O and organic ice impurities is achieved with a marked reduction of the sample amount to about 5 g. The small sample requirement combined with a short analysis time for GC-IRMS will enable us to measure replicates and thus to increase precision. Here we present the preliminary set-up of the new method with first results concerning overall precision and reproducibility.