Environmental drivers of precipitation stable isotopes and moisture sources in the Mongolian Plateau

Abstract

Τhe absence of precipitation-isotope stations in the wide flatland of the Mongolian Plateau (MP) hinders the analysis of precipitation processes. For this reason, a precipitation-isotope station was established in Erenhot in 2015. Based on precipitation samples collected during all precipitation events between January 2015 and December 2019, we analyzed the temporal variations of stable isotopes (δ2H, δ18O) in precipitation and their influencing factors, including meteorological factors, sub-cloud evaporation, and moisture sources. Oxygen and hydrogen isotopes in precipitation in Erenhot are richer than those in Ulaanbaatar, which is situated close to the mountains and depleted compared to, e.g., Baotou. In Erenhot, oxygen and hydrogen isotopes in precipitation are controlled by the temperature effect, similarly to Ulaanbaatar, but also by the amount effect in summer. The low slope of the local meteoric water line indicates that raindrops have undergone sub-cloud evaporation. The annual mean sub-cloud evaporation fraction was 5.2% from 2015 to 2019, while sub-cloud evaporation fraction was highest in summer (7.5%). Sub-cloud evaporation is mainly correlated by relative humidity, precipitation amount, regional (pan) evaporation, and air temperature. Relative humidity has the greatest effect and masks the effect of air temperature. The study area is mainly controlled by the west wind and winter monsoon, which brought 75.6% of the total precipitation with −7.75‰ δ18O. During summer, the Pacific monsoon resulted in 13.5% precipitation with −10.34‰ δ18O in the study area, while the Indian monsoon had negligible impact. Except for moisture advection, the moisture recycling fraction accounted for 11.1% of local precipitation, with −10.32‰ δ18O. This study compensates for the lack of global network of isotopes in precipitation (GNIP) stations in the MP, reveals the MP precipitation-isotope signatures and their influencing factors, and provides basic precipitation-isotope information for researching the distribution of precipitation-isotope signatures in Asia and the water cycle in the MP.