Air Mass Origin Effects on Antarctic Snow Isotopic Composition: An Observation and Modelling Study

Abstract. Water stable isotopes (δ¹⁸O and δD) from ice cores are commonly used to reconstruct past temperature variations because of their well-established relationship with local air temperature. However, depositional and post-depositional effects lead to large uncertainties to use this proxy in Antarctica. Depositional effects are largely influenced by the origin of precipitation moisture, which exhibits asymmetries shaped by the continent’s geographical and topographical features. Additionally, precipitation intermittency – especially in low-accumulation areas – introduce aliasing in the recorded signal, significantly limiting the temperature signal that can be retrieved. Post-depositional processes, such as sublimation and firn-atmosphere exchange, can further alter the isotopic composition of snow before its transformation into ice, potentially modifying the correlation between δ¹⁸O and air temperature for snow samples. Here, we present new water isotope measurements from surface snow collected during the East Antarctic International Ice Sheet Traverse (EAIIST) across a remote region of the East Antarctic plateau. The traverse – crossing a transitional zone between predominately Indian and Pacific moisture sources – provides direct insights into the key role of air mass origin in shaping the δ¹⁸O-temperature relationship. A comparison between snow isotopic values and precipitation simulations from the atmospheric general circulation model LMDZ6iso shows that the model accurately captures the spatial variation of the δ¹⁸O–temperature relationship observed in snow. This result also supports the model’s ability to predict the temporal slope required to calibrate isotopic ice core records for past temperature reconstructions, even in regions where precipitation events originate from different sources. Finally, the impact of sublimation on δ¹⁸O and d-excess (an effect that must be considered for accurate paleoclimatic reconstructions) is evidenced for the region covered by EAIIST.