Caveats of the Isotopic Paleothermometer: Spatial and Temporal Isotope – Temperature Relationships

Abstract Water isotopes are a tracer of hydrological processes and a paleoclimate proxy from ice core records. The isotopic signal is acquired throughout the hydrological cycle, from evaporation over the ocean, during each precipitation event, and during post-depositional processes such as isotopic exchange between snow and atmospheric moisture. Due to these multiple contributions, the isotopic paleothermometer (i.e., the relationship between isotope ratios in ice and local temperature, on which past climatic reconstructions are based) is only empirically calibrated. Yet, different isotope-to-temperature relationships are obtained spatially in surface snow and temporally in precipitation. Here, we report the vapour isotopic composition monitored on a traverse across East Antarctica as well as at two fixed locations: the coastal site of Dumont D’Urville and the inland station of Concordia. We show that the isotope-to-temperature relationship is inherently different using vapour isotopic composition temporally and spatially across the East Antarctic Plateau due to fundamental differences in the variations of the rainout fraction across time and space. Since the Rayleigh distillation predicts parallel evolution of vapour and precipitation isotopic composition, our results can be directly transferred to the interpretation of the isotopic signal in ice core records.