Résumé
Water stable isotopes are currently measured in polar ice cores. The long records of $δ_{18}O$ and δD provide unique information on the past polar temperature while the combination of $δ_{18}O$ and δD constrains the evolution of the oceanic evaporative regions. Recently, new analytical developments have made it possible to measure with high precision a new isotopic ratio in water, $δ_{17}O$. As for δD and $δ_{18}0$, the combination of $δ_{17}0$ and $δ_{18}0$ shows a high dependence with the climatic conditions during evaporation. Based on measurements of the different isotopic ratios in Antarctica surface snow, we show that while the combination of $δ_{18}0$ and δD in the so-called d-excess displays variation with local climatic conditions in the polar regions in addition to the influence of the evaporative regions, the combination of $δ_{17}0$ and $δ_{18}0$ in the so-called $^{17}O_{excess}$ is not modified during the air mass transportation above the polar regions. This makes $^{17}O_{excess}$ a simpler parameter than d-excess to constrain the evolution of the oceanic evaporative regions. Finally, records of d-excess and $^{17}O_{excess}$ over the deglaciation in the Vostok ice core suggest significant changes in the evaporative regions. Our interpretation is that the relative humidity over the ocean was higher during the glacial period than today and that reevaporation increased over the deglaciation.