Moisture Source Controls on Water Isotopes in Antarctic Precipitation—Insights From Water Tracers in ECHAM6-Wiso

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

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