Stable isotopic compositions of waters in the karst environments of China: Climatic implications

Abstract

A total of 117 water samples, including cave water, ground water, spring water and river water, collected from the monsoonal area of China have been analyzed for their H- and O-isotope composition. Overall, a δ 18O– δD correlation is observed of δD = −4.45 + 6.6 δ 18O ( R 2 = 0.90) and a significant evaporation effect observed for the southern sites. Average δ 18O and δD site values generally correspond to those of precipitation in nearby cities, with correlations of δD = 2.18 + 7.23 δ 18O ( R 2 = 0.95) for the sample sites and δD = 11.05 + 7.95 δ 18O ( R 2 = 0.95) for the cities. The effects of rainfall amount and temperature on precipitation δ 18O were calculated using a simplified theoretical model derived from the Rayleigh distillation equation, which demonstrated that the sign of δ 18O p vs. T correlation is dependent on precipitation intensity. The mean δ 18O value of cave waters exhibit decreasing trends with increasing latitude and reveal a spatial pattern of positive correlation with annual mean temperature and precipitation, mainly reflecting isotopic fractionations in the moisture source traveling from the ocean side to the inland continent. This spatial pattern implies that the δ 18O values recorded in the proxy climate records derived from speleothems might be influenced by shifts in monsoon boundary during the past, especially between glacial and interglacial intervals.