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 dripwater at Zhenzhu Cave, Hebei Province, north China. Two meteoric precipitation sites and three cave drip sites weremonitored monthly during April 2012–April 2014. The results of meteoric precipitation present: on monthly timescale,δ18Op and δDp showed a significant seasonal double peak characterized by depleted isotopic values in both dry and wetseasons (but a significant seasonal variation in d-excess). There is a weakly negative correlation with monthly meanprecipitation amount but no significant correlation with surface air temperature. Based on GNIP data, there are no significantcorrelations on an interannual scale between annual weighted mean δ18Op (and δDp) and annual precipitationor annual mean temperature. This implies the variation of δ18Op (and δDp) in the area cannot be interpreted solely asreflecting an “amount effect” or “temperature effect” on either seasonal or interannual scale, and may be affected bymoisture sources. There isn’t any significant change in δ18Od and δDd values of cave drip water during monitoring period,demonstrating that cave drip water comprise a mixture of precipitation integrated over a long period rather thanseasonal timescale. There were significant seasonal changes in cave air CO2 concentration, with higher concentrationsin summer and lower concentrations in winter that is well correlated with environmental variables such as surfacetemperature and precipitation, which may help improve the interpretation of stable carbon isotope records from speleothems(δ13Cs) in relation to cave air CO2.

[学科分类] 地质学