Water isotopic composition along Antarctic transects (blue: Zhongshan-Dome A transect; green: Syowa-Dome F transect; red: Terra Nova Bay-Dome C transect) and comparison with modeling outputs (black and grey line: MCIM with S=1-0.004T and S=1-0.002T respectively, from Landais et al., 2012a; dotted line: LMDZ-iso with S=1-0.004T (Risi et al., 2013))Water isotopic composition along Antarctic transects (blue: Zhongshan-Dome A transect; green: Syowa-Dome F transect; red: Terra Nova Bay-Dome C transect) and comparison with modeling outputs (black and grey line: MCIM with S=1-0.004T and S=1-0.002T respectively, from Landais et al., 2012a; dotted line: LMDZ-iso with S=1-0.004T (Risi et al., 2013))
The isotopic composition of oxygen and deuterium in surface snow from East Antarctica varies primarily as a function of the local temperature. The snow that is deposited undergoes metamorphism (modification of grain shapes), as well as densification under the weight of overlying layers. These two processes ultimately lead to ice layers where the isotopic compositions are preserved over hundreds of millennia and can be used to reconstruct past climate variations. However, concerns have been raised about the impact of metamorphism on the snow (and therefore the ice) isotopic compositions. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. Surface snow samples collected along traverses were analyzed for δ18O, d-excess and 17O-excess. The results show that the distillation process controls the coast-to-dome evolution of δ18O as well as d-excess. For 17O-excess, the coastal values are modified only in very remote areas, where kinetic fractionation at condensation becomes significant. Precipitation samples collected one-year round at Dome C and Vostok show the same relationship between parameters as the surface snow samples, indicating that the same processes are active. However, the slope of the δ18O/T relationship is lower in the precipitation compared to the surface snow from traverses, suggesting that using either geographical or temporal slopes could lead to significant differences in the temperature reconstructed from ice cores. We also present results from year-round measurement of surface snow samples at Dome C (same processes) and from snow pits (possible stratospheric influence on 17O-excess at Vostok and S2).
Reference: A.Touzeau, A. Landais, B. Stenni, R. Uemura, K. Fukui, S. Fujita, S. Guilbaud, A. Ekaykin, M. Casado, E. Barkan, B. Luz, O. Magand, G. Teste, E. Lemeur, M. Baroni, J. Savarino, I. Bourgeois, C. Risi, 2016. Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters, The Cryosphere, 10, 1–16, 2016, doi:10.5194/tc-10-1-2016
a) Isotopic composition of the precipitation at Vostok over one year. A: samples from the upper trap (pure precipitation); B: samples from the lower trap (precipitation mixed with blowing snow). For the 17O-excess, dark green points were measured at LSCE whereas light green points were measured at HUJI. (b) Isotopic composition of the precipitation at Dome C over one year.