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Water stable isotopes recorded in Antarctic ice cores have traditionally been used to infer past surface air temperatures (SAT). During the historical period (1850 onward), observational data and good quality ice core records overlap, yielding an opportunity to investigate key relationships between ice core stable water isotope (δ18O) measurements and the Antarctic climate. We present a new ensemble of climate model simulations covering 1851-2004 using the UK Met Office HadCM3 general circulation model equipped with water stable isotopes. Our ensemble captures observed historical SAT and precipitation trends, and weak δ18O trends. The weak δ18O trends mean there is no significant relationship between SAT and δ18O over one third of Antarctica, and also half of our considered ice core sites, though relationships are stronger when using regional averages. The strongest regional relationships occur in the West Antarctic Ice Sheet (WAIS) region. This decoupling between SAT and δ18O occurs primarily because of the impact of autumnal sea ice loss during the simulated warming. The warming and sea ice loss is associated with: (i) changes in near-coastal air mass intrusions (synoptic effects) induced by changes in the large-scale circulation and/or sea ice; (ii) direct sea ice driven changes in moisture pathways (especially lengths) to Antarctica; and (iii) precipitation seasonality changes, again mostly driven by sea ice changes. Consequently when reconstructing temperatures over these timescales, changes in sea ice need to be considered; both to determine the most appropriate SAT and δ18O relationship, and to understand how uncertainties affect the inference of past temperature from ice cores δ18O measurements. [ABSTRACT FROM AUTHOR]

Stable water isotopic observations in surface snow over Antarctica provide a foundation for validating isotopic models and interpreting Antarctic ice core records. Here, we present a new compilation of Antarctic surface snow isotopic dataset with strict quality control from published and unpublished sources including measurements from snow pits, snow cores, ice cores, deep surface snow, and precipitation (multi-year average values). The dataset contains a total of 1867 data points, including 1604 locations for oxygen isotope ratio (d18O) and 1278 locations for deuterium isotope ratio (d2H). 1204 locations have both d18O and d2H, from which d-excess (d-excess = d2H - 8 × d18O) can be calculated. The dataset also contains geographic and climate information. The database has a wide range of potential applications, such as the study of the spatial distribution of water isotopes in Antarctica, the evaluation of climate models, and the reconstruction and interpretation of Antarctic ice core records. As an example of model evaluation, the compiled isotopic dataset is used to assess the performance of isotope-enabled atmospheric general circulation models (AGCMs) on simulating the spatial distribution of water isotopes over Antarctica. This dataset is the most comprehensive compilation so far of observed water isotope records at multi-year average scale from multiple sources for Antarctica. It is available for download at https://doi.org/10.5281/zenodo.7294183 (Wang et al., 2022). [ABSTRACT FROM AUTHOR]