Stable isotopes of water (δD and δ¹⁸O) have been performed for more than 50 years with the aim to understand the links between water cycle and climate. On the one hand, records of δD and δ¹⁸O provide information on temperature changes at high latitudes (e.g. ice core records) and on precipitation intensity along the trajectory at low latitudes. On the other hand, combination of δ¹⁸O and δD in the so-called d-excess constrains the climatic conditions (temperature, relative humidity) over the oceanic evaporative regions albeit in a complex manner (difficulty to disentangle the different parameters). Recently, the possibility to measure with high precision δ¹⁷O in water has enabled one to introduce a new parameter, ¹⁷Oexcess, resulting from the combination or δ¹⁸O and δ¹⁷O. When measured in ice core, this parameter is expected to be a more direct tracer of relative humidity of the oceanic evaporative regions than d-excess.
In order to better understand this new parameter as well as to extract the maximum climatic information from the combination of ¹⁷Oexcess and d-excess, we present different original studies combining the two parameters in several key regions. First, we study how local processes (precipitation, sublimation) in polar region can affect ¹⁷Oexcess archived in ice core with respect to d-excess records through two studies at the NEEM station (Greenland): (1) isotopic measurements of vapor versus precipitation and (2) seasonal cycle isotopic measurements from a shallow core. Second, we present ¹⁷Oexcess measurements on different Antarctic ice cores over the last deglaciation in order to constrain the change in source relative humidity for different parts of Antarctica over this period.