The interpretation of water isotope records in Antarctic ice cores is crucial for our understanding of past climate changes. Here we use novel water tracers in an ECHAM6‐wiso simulation to investigate moisture source controls on deuterium excess in Antarctic precipitation, particularly the logarithmic variant . The simulation captures the amplitude of seasonal changes in observed and of precipitation. There are, however, some model biases that cannot be resolved through adjustments to kinetic fractionation parameters or the model resolution. These may reflect issues in the hydrological cycle representation or the representation of isotope processes. The simulated in Antarctic precipitation reliably reflects moisture source sea surface temperature (SST): shows a higher correlation than traditionally defined deuterium excess. Ocean surface relative humidity with respect to SST (RHsst) influences during evaporation, however, this influence weakens above the ocean surface. 79% of the variance in of annual precipitation at Dome C is due to changes in moisture source SST. is more sensitive to source SST in inland Antarctica than in coastal regions, making it a robust proxy for reconstructing past SST at the inland ice core sites. The explained variance of by source SST for daily precipitation at Dome C is lower at 28%, which increases to 59% after excluding very low precipitation days (0.02 mm). Finally, we find reversed relationships between source SST and in the vapor above the Southern Ocean, potentially driven by cold air outbreaks or precipitation processes.