Water stable isotopes spatio-temporal variability in Antarctica in
1960–2013: observations and simulations from the ECHAM5-wiso
atmospheric general circulation model
Authors: Goursaud Sentia , Masson-Delmotte Valérie , Favier Vincent , Orsi Anaïs , Werner Martin 
Published: December 2017

Abstract. Polar ice core water isotope records are commonly used to infer past changes in Antarctic temperature, motivating an improved understanding and quantification of the temporal relationship between δ18O and temperature. This can be achieved using simulations performed by atmospheric general circulation models equipped with water stable isotopes. Here, we evaluate the skills of the high resolution water-isotope-enabled atmospheric general circulation model ECHAM5-wiso (the European Centre Hamburg Model), nudged to European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis using simulations covering the period 1960–2013 over the Antarctic continent. We compare model outputs with field data, first with a focus on regional climate variables and, second on water stable isotopes, using our updated dataset of water stable isotope measurements from precipitation, snow and firn/ice core samples. ECHAM5-wiso simulates a large increase in temperature from 1978 to 1979, possibly caused by a discontinuity in the European Reanalyses (ERA) linked to the assimilation of remote sensing data starting in 1979. The comparison with accumulation and water stable isotope data is thus restricted to the period 1979–2013, for accumulation and water stable isotope data from snow and firn/ice core. Such a restriction was not decided for the isotopic composition from precipitation data that consist in a few number of points. For this comparison, we used outputs corresponding to the same exact days of observations, even if it was before 1979. Although some model-data mismatches are observed, the (precipitation minus evaporation) outputs are found to be realistic products for surface mass balance. A warm model bias over Central East Antarctica and a cold model bias over coastal regions explain first-order δ18O model biases by too strong isotopic depletion on coastal areas and underestimated depletion inland. At the second order, despite these biases, ECHAM5-wiso correctly captures the observed spatial and seasonal patterns of δ18O. The results of model-data comparisons for the inter-annual δ18O standard deviation differ when using precipitation or ice core data. Further studies should explore the importance of deposition and post-deposition processes affecting ice core signals and not resolved in the model. Despite systematic offsets, the increase of deuterium excess from coastal to inland regions is well simulated by the model. These results build trust in the use of ECHAM5-wiso outputs to investigate the spatial, seasonal and inter-annual δ18O-temperature relationships. We show that local spatial or seasonal slopes are not a correct surrogate for inter-annual temporal slopes, leading to the conclusion that a stationary isotope-temperature slope cannot be applied for the climatic interpretation of Antarctic ice core. We finally explore the phasing between the seasonal cycles of deuterium excess and δ18O, as a source of information on changes in moisture sources affecting the δ18O-temperature relationship. The few available records and ECHAM5-wiso show different phase relationships in coastal, intermediate and central regions. This work valuates the use of the ECHAM5-wiso model as a tool for the investigation of water stable isotopes in Antarctic precipitation, and calls for extended studies to improve our understanding of such proxies.