ANALYSIS OF DEW 17O-EXCESS VARIATIONS AND FORMATION CHARACTERISTICS IN THREE DIFFERENT CLIMATIC ENVIRONMENTS

With increased aridity in many regions under global climate change, dew plays an increasingly important role in the hydrological input of many ecosystems especially in the arid and semiarid regions. Few studies investigate the sources and formation mechanisms of dew under different climatic conditions. ¹⁷O-excess, as a new tracer, is reported to preserve information about water sources and precipitation formation mechanism. Therefore, to fill the knowledge gap in dew sources and formation mechanisms, we investigated the dew and rainfall isotope variations including ¹⁷O-excess in three different climate regions (i.e., Gobabeb in the central Namib Desert, Nice in France with Mediterranean climate, and Indianapolis in the central United States). The preliminary results showed that the vapor of dew formation in the Gobabeb were from the Atlantic Ocean, through comparing the local dew water line with local meteoric water line (LMWL) and global meteoric water line (GMWL). While dew in Nice and Indianapolis were both from the continental recycling moisture. In addition, informed by the δ′¹⁸O-δ′¹⁷O relationship and the positive correlation between ¹⁷O-excess and d-excess, dew in the Gobabeb (0.5189) experienced kinetic fractionation associated with evaporation at the moisture source, while the dew in the other two sites, were mainly affected by equilibrium fractionation. The ¹⁷O-excess of dew in all sites were not affected by local meteorological factors. This study provides a practical method to distinguish dew sources and provides mechanistic understanding of dew formation mechanisms in different ecosystems.