Geographic variations in the slope of the delta (super 2) H-delta (super 18) O meteoric water line over Europe; a record of increasing continentality

delta (super 2) H and delta (super 18) O values of precipitations follow an empirical linear relationship at the global scale that is called the Global Meteoric Water Line (GMWL) and characterized by a slope of 8. However, Local Meteoric Water Lines (LMWL) may have different slopes S depending on their geographic situation. Monthly delta (super 2) H and delta (super 18) O of precipitation have been compiled from European IAEA stations. Those data allowed the calculation of the slopes S of the delta (super 2) H-delta (super 18) O LMWL determined for each station. S increases with longitude f from approximately 5 (Portugal) to approximately 9 (Russia), they are positively correlated with relative humidity (RH), negatively with temperature, and positively with the mean intra-annual amplitude of temperatures, which is a proxy of continentality. Slopes of 5 to 6, recorded in southwest Europe, reflect mean RH (70 to 75%) and sea surface temperatures ( approximately 25 degrees C) of the Central Atlantic Ocean where the main flux of moisture is formed before being transported by the westerlies. In addition, falling water droplets within an air column with a high RH (>80%) and low temperature are expected to escape sub-cloud evaporation. Therefore, slopes with values close to 9 are considered to reflect isotopic equilibrium conditions during the condensation of water vapour in clouds.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5040647