Geographical variations in the slope of the δ2H–δ18O meteoric water line over Europe: a record of increasing continentality

δ2H and δ1820 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 depending on their geographic situation. Monthly δ2H and δ1823 O of precipitation have been revised manuscript with corrections in blue compiled from European IAEA stations. Those data allowed the calculation of the slopes S of the δ2H–δ1825 O LMWL determined for each station. S increases with longitude δ from c.5 (Portugal) to c.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 (c.25^oC) of the Central Atlantic Ocean where the main flux of moisture is formed before being transported by the westerlies. The observed logarithmic growth of S with increasing continentality is interpreted as a temperature effect during the progressive distillation of the humid air mass over Europe. 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.