Hydrogeochemical and climatic interpretations of isotopic signals from precipitation to drip waters in Liangfeng Cave, Guizhou Province, China

Abstract

Oxygen isotope is a commonly used proxy for paleoclimatic studies on stalagmites. In order to understand the transmission of isotopic signals from precipitation to stalagmites, meteorological indexes of exterior and interior cave and hydrogeochemical proxies of drip waters in Liangfeng Cave have been monitored from April, 2011 to April, 2013. Samples of rain and drip waters from three drip sites (designated as 1#, 5#, and 6#) are collected for hydrogen and oxygen isotopes testing. Results show that the amount-weighted mean δ18O value of rain in the first year (May 9, 2011 to May 1, 2012) is lighter than that in the second (May 30, 2012 to May 2, 2013). This may result from different proportions of the Pacific/Indian Ocean source moistures. The arithmetic mean δ18O values of 1#, 5#, and 6# are similar to the multi-year amount-weighted mean δ18O value of precipitation. Hydrogeochemical analyses of drip waters reveal that the discharge rates increase in the order of 6# < 1# < 5# and that water/rock reaction, fresh/old water mixing and CO2 degassing exert dominant controls on seepage waters in aquifers. Hard infiltration of rain during dry season (with heavier δ18O value) due to its small amount may cause lower mean drip water δ18O values (e.g., 1#). Evaporation during the dripping and exuding processes in dry season may result in heavier mean drip water δ18O values (e.g., 6#). Considering calcite depositing mostly during dry season, we compare the mean δ18O values of drip waters during dry season between the first and second years. Differences exist and share the same trend with rain. The results indicate that drip waters can inherit oxygen isotopic signals of rain. But it is critical to have a “Replication Test” on δ18O records of stalagmites from the same cave for paleoclimatic studies. What’s more, δ18O values in stalagmites feeding by drip waters that have no/little annual δ18O variations may be useful to paleotemperature reconstructions.