VARIATIONS OF THE STABLE ISOTOPIC COMPOSITION OF PRECIPITATION AND CAVE DRIP WATER AT ZHENZHU CAVE, NORTH CHINA: A TWO-YEAR MONITORING STUDY

摘要

We investigated potential factors influencing variations in isotopic composition of external precipitation and internal drip water at Zhenzhu Cave, Hebei Province, north China. Two meteoric precipitation sites and three cave drip sites were monitored monthly during April 2012-April 2014. The results of meteoric precipitation present: on monthly timescale, delta O-18(p) and delta D-p showed a significant seasonal double peak characterized by depleted isotopic values in both dry and wet seasons (but a significant seasonal variation in d-excess). There is a weakly negative correlation with monthly mean precipitation amount but no significant correlation with surface air temperature. Based on GNIP data, there are no significant correlations on an interannual scale between annual weighted mean delta O-18(p) (and delta D-p) and annual precipitation or annual mean temperature. This implies the variation of delta O-18(p) (and delta D-p) in the area cannot be interpreted solely as reflecting an "amount effect" or "temperature effect" on either seasonal or interannual scale, and may be affected by moisture sources. There isn't any significant change in delta O-18(d) and delta D-d values of cave drip water during monitoring period, demonstrating that cave drip water comprise a mixture of precipitation integrated over a long period rather than seasonal timescale. There were significant seasonal changes in cave air CO2 concentration, with higher concentrations in summer and lower concentrations in winter that is well correlated with environmental variables such as surface temperature and precipitation, which may help improve the interpretation of stable carbon isotope records from speleothems (delta C-13(s)) in relation to cave air CO2.