δ18O characteristics of meteoric precipitation and its water vapor sources in the Guilin area of China

Abstract

The stable isotopic composition of meteoric precipitation is an important component of global and regional water cycle research. Stable isotope data can help reconstruct paleoclimate related to ice cores, lake sediments, and stalagmites. We investigated the daily variation in isotopic composition of meteoric precipitation from 2008 to 2012 in the Guilin region of China. δ18O of meteoric precipitation ranged from −14.21 to +2.38 ‰, with an average value of −5.78 ‰ (Vienna Standard Mean Ocean Water; VSMOW). Meteoric precipitation in the summer half-year (May through October) increased, with a relatively low δ18O value of −8.04 ‰ (VSMOW; average of 261 groups) and −56.03 ‰ (VSMOW) of average δD, accounting for 67.6 % of the total annual meteoric precipitation. Meteoric precipitation in the winter half-year (November through April) decreased, with a relatively high δ18O value of −2.89 ‰ (average of 210 groups) and −9.23 ‰ of average δD, accounting for 32.4 % of total meteoric precipitation. The local meteoric water line (LMWL) equation in Guilin area has local climate characteristics. By combining environmental isotope data of precipitation using a backwards trajectory, water vapor sources of the meteoric precipitation in Guilin area are inferred and traced. Our results show that the isotopic composition of meteoric water vapor sources in Guilin area are related to monsoon type, source of precipitation cloud masses, and precipitation properties. The isotopic composition of meteoric precipitation in the summer half-year (May through October) was mainly affected by the summer monsoon or summer typhoons, namely controlled by water vapor source from the Bay of Bengal and the South China sea, and the second the West Pacific, and the δ18O value of meteoric precipitation was strongly negative. There was a significant negative correlation between the δ18O values of meteoric precipitation and the amount of precipitation and temperature in the summer half-year. The amount effect of the meteoric precipitation often concealed the temperature effect. The isotopic composition of meteoric precipitation in the winter season or winter half-year was affected by the water vapor source of the warm moist air masses from the West Pacific and continental cold air masses from the Siberia–Mongolia/winter monsoon or local evaporation vapor circulation, and the δ18O value of meteoric precipitation was relatively positive, and indicated that the water vapor of meteoric precipitation along the water vapor trajectory was affected by the evaporation as well as the local water vapor evaporation. The research results have showed that different sources of water vapor has a significant influence on the δ18O variation of meteoric precipitation, therefore, analysis of δ18O in the meteoric precipitation, especially its seasonal variation characteristics of analysis, can conversely reveal the water vapor sources of local meteoric precipitation.