Water stable isotope 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: June 2018

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. 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 patterns of deuterium excess. 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. These results build trust in the use of ECHAM5-wiso outputs to investigate
the spatial, seasonal, and inter-annual δ18O–temperature
relationships. We thus make the first Antarctica-wide synthesis of prior
results. First, we show that local spatial or seasonal slopes are not a
correct surrogate for inter-annual temporal slopes, leading to the conclusion
that the same isotope–temperature slope cannot be applied for the climatic
interpretation of Antarctic ice core for all timescales. Finally, we 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 evaluates 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.