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石笋由于分布广泛、定年准确,并且具有丰富的气候和环境代用指标(如氧碳稳定同位素~([1,2])、微层厚度~([3])、微量元素~([4~6])等),因而受到古气候学家广泛关注。其中,微量元素和稳定碳同位素常被用来间接地反映局地干湿变化。当降水减少时,洞穴滴水在洞顶储存时间较长,使岩溶水在补给石笋之前已经发生了方解石沉积作用。由于Mg,Sr和Ba在方解石和溶液中的分配系数远小于1~([7,8]),从而使Ca优先于Mg,Sr和Ba沉积出来,使得溶液(渗流水及其所形成的滴水)和现代次生碳酸盐沉积物中的Mg,Sr和Ba富集,进而导致Mg/Ca,Sr/Ca和Ba/Ca比值增大~([4,5,9]),这种现象被称为方解石前期沉积作用(Prior Calcite Precipitation,简称PCP)。此外,当降水减少,洞穴滴水滴率变慢(即PCP作用增强)时,CO_2脱气时间增长也会导致石笋碳同位素偏
Stalagmites are widely distributed and accurate in age. They have rich climatic and environmental proxy indicators (such as stable isotopes of oxygen and carbon (1,2), microlayer thickness (3) and trace elements (4 to 6 ]), Etc.), which pays close attention to by paleoclimate scientists. Among them, trace elements and stable carbon isotopes are often used to indirectly reflect local wet and dry changes. When the precipitation decreases, the drip of caves is stored for a long time in the top of the cave, so that the karst water has taken place before the stalagmite supply. Since the distribution coefficients of Mg, Sr and Ba in calcite and solution are far less than 1 to 7 (7,8), Ca is preferentially deposited over Mg, Sr and Ba such that the solution (seepage water and the drip ) And the enrichment of Mg, Sr and Ba in modern secondary carbonate sediments, resulting in an increase in Mg / Ca, Sr / Ca and Ba / Ca ratios [4,5,9] It is called Prior Calcite Precipitation (PCP). In addition, when the precipitation decreases and the rate of drip drip in the cave becomes slow (ie, the effect of PCP is enhanced), the increase of degassing time of CO 2 will lead to the carbon isotope deviation of stalagmite