| Cave Secondary Sediment as an important carrier for the research of climatic evolution has made series of remarkable achievements. Stalagmites and other secondary sediments have a lot of substitution indexes, such as δ18O, δ13C, trace element, growth rate and so on. These offers a variety of information on temperature, precipitation, vegetation, hydrological condition for paleoclimate reconstruction. However, the cave water was affected by the calcite precipitation prior, location, hydrodynamic type, hydrogeochemical process during the process of transmitting and recording the environmental signal. These lead to the uncertainty and multiple solutions about indicators’ environmental implications. Therefore, in order to reconstruct a high resolution time sequence of paleoclimatic change by secondary sediments, it’s important to strengthen the monitoring work and understanding the hydrological and chemical processes of karst caves.Six cave water sites have been selected for a long term monitoring in Naduo Cave, Guanling county of Guizhou Province, China. The monitoring indicators include temperature, humidity, concentration of CO2, dripping speed, electrical conductivity, p H, δ13CDIC, and the ionic concentration of K+, Na+, Ca2+,Mg2+, SO42-, HCO3-. The goal of this paper is to analysis the hydro-geochemical variation characteristics and its driving mechanism of cave water, understanding the geochemical processes of Naduo cave, Meanwhile, exploring the hydro-geochemistry indicators’ feedbacks to climate events through the research of field sampling, experimental analysis and combining with local climate data. The result showed that:(1) The geochemistry characteristics of cave water are controlled by bedrock dissolution and soil leaching. There are some discrepancies of main ions’ concentration among six cave water sites due to the difference of its migration pathways and migration time.(2) The water in Naduo Cave can respond perfectly to the external climate environment, which inherited the characteristics of precipitation. There was distinctive seasonal variation of cave water p H, conductivity and HCO3-, due to the change of temperature, precipitation, concentration of CO2 and other physical conditions. The diluting effect of cave water caused by anomalous ascent of precipitation was reflected in its p H and HCO3- concentration during the rainy season in 2014.(3)Since the enhancement of bedrock dissolution and soil leaching, the concentrations of Ca2+, Mg2+, Sr2+ and SO42- showed seasonal variation characteristics that the rainy season is higher than dry season.The concentration of four ions’ sensitive to the response of the annual precipitation change caused by extremely climate events. During the rainy season, the concentration of Ca2+、Mg2+ and SO42- occurred in 2013 is relatively higher and more stable than it appeared in 2014.The anomalous ascent of precipitation in 2014 leads to the dilution effect has greater influence on geochemical characteristics of cave water than bedrock dissolution and soil leaching,The response time and susceptivity of each monitoring site is inconsistent. The specific response process is related to precipitation intensity, rock strata characteristics and fracture development degree.(4) The SIc of cave water during rainy season is lower than that in dry season while its PCO2 is higher. Both of them are mainly controlled by p H. Under the circumstances of suitable temperature, the precipitation had a important influence on the deposition of speleothem.(5) The water in Naduo cave can respond perfectly to the external climate environment, which inherited the characteristics of precipitation. The ratios of Mg/Ca and Sr/Ca could indicate the change of precipitation. But the influence mechanism and environmental significance of different sites is inconsistency, due to the effect of PCP, migration pathways, extreme climate and environmental change at the same time. We’d better be cautious when using it as an environmental indicators.(6) Influenced by the increase of precipitation, the concentration of dissolved CO2 in soil and activity of plants and microorganism, the δ13CDIC values possess extraordinary seasonal characteristics: summer is lighter, winter is heavier. There is remarkable difference among δ13C DIC of cave waters at 6 sampling sites, due to the effect of different hydrogeochemical processes.Therefore, the interpretation of δ13CDIC recorded in speleothems can be more accurate if we make a long term monitoring of the cave system and considering the effects of the hydrogeochemical processes mentioned above. |
PDF Full Text Request