| Global warming has been the common concern of the world, so the research on global climate change attracts more and more attention in various fields, paleoclimate research which has become an important way to understand the law of climate and environment evolution. As one of the cave deposits, stalagmite is one of the important archives in the research of paleoclimate which has abundant proxies can extract many signals like temperature, precipitation, vegetation, hydro logical, paleoenvironment and so on. But from the perspective of the forming process of stalagmite, the transmission process of information is more complicated and subject to many factors, there are still many uncertainties and controversies about these proxies to interpretation the environment, therefore need cave monitoring of drip water and modern deposits to adjust and provide an important basis for the forming mechanism of stalagmite and the correct interpretation of recorded paleoclimate information.A monthly cave monitoring work has been conducted in Penglaixian Cave, Shitai County, Anhui Province from April2011to October2013. We chose four drip-sites in this cave (PLXD-1, PLXD-2, PLXD-3and PLXD-4) and obtained a lot of hydrogeochemical indices, such as the temperature and humidity inside the cave, the CO2concentration of the cave air, the drip rate, temperature, pH values, EC, concentration of anion and cation (HCO3-、SO42-、Ca2-、Mg2-、Sr24-、Ba2+) of drip water. Meanwhile, we also discussed the changes of characteristics which can indicate environmental significance and control factors of modern deposits’growth rate. The primary conclusions as follows:(1) The concentration of cave air CO2had seasonal variations. From winter to next spring, the concentration was gradually reduced, the opposite trendency from summer to autumn and there was a relationship with rainfall and temperature. Additionally, in the tourist season of Penglaixian Cave, CO2concentration increased significantly in tourists’concentrated area. Hence, the influence of the cave to tourists have a certain sensitivity. (2) There were many factors that impacted pH values of drip water, included temperature, precipitation, cave air CO2, temperature inside cave, the fractured bedrock aquifer and the concentration of CO2in overlaying soil which produced by vegetation breathing and biological activities. By comparing the variation of CO2concentration and drip water pH values, we found the former was not the main factor that impacted on pH values but the concentration of CO2in overlaying soil was.(3) The concentration of Ca2+was influenced by precipitation and piston effect and reached peak values in spring and early summer. However, the typhoon "Haikui" led to continuous torrential rains in the district of Penglaixian Cave in August2012and the dilution effect of rainfall resulted Ca2+concentration decreased. Hence we inferred that adequate rainfall conducive to increasing ion concentration, once the intensity increased, and the dilution effect of rainfall led to ion concentration decreased. On the other hand, the peak value of Mg2+concentration was later than Ca2+concentration, the main reason was affected by karst water transport processes, the intensity of rainfall and leaching of soil.(4) PCP process led to higher Mg/CaN Sr/Ca%Ba/Ca ratios,δ13C of drip water and modern deposits in site PLXD-2. The intuitionistic character above this drip site had proven PCP and the drip rate of PLXD-2was too slow that strengthened the PCP process. But the intensity of PCP cannot inhibit the deposition of calcite (the mole ratio of Mg/Ca was less than1.5). Therefore the crystal structure of speleothems in site PLXD-2was still calcite.(5) The growth rate of modern deposits was influenced by Sic, pH values, the concentration of HCO3-、SO42-、Ca2+of drip water and degassing of CO2from drip water. Firstly, the concentration of Ca2+and Slc of drip water were necessary but not sufficient condition for the occurrence of deposition. Additionally, the more pH values of drip water higher, the more growth rate faster, the modern deposit was less. Moreover, the high concentration of HCO3-、SO42-may inhibit the carbonate deposition. Fourthly, when the cave air CO2concentration was low and would drive CO2degassing from drip water quickly. And there was inexistence extreme discontinuous flow, the growth rate was the slowest when the drip rate was the lowest.(6) There are three cycles on SIc of drip water within a year and they maybe the evidence of sub-layer of stalagmite that reflect annually laminated stalagmite. |
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