武都万象洞方解石现代沉积体系δ^(18)O值月变化特征  

Monthly isotopic variations of calcite deposition system in Wanxiang Cave, Wudu County, Gansu

作　　者：白晓[1] 桑文翠[1,2] 李丰山[1] 张德忠[3] 

机构地区：[1]兰州大学西部环境与气候变化研究院,甘肃兰州730000 [2]甘肃省地质环境监测院,甘肃兰州730020 [3]兰州大学资源环境学院,甘肃兰州730000

出　　处：《地球化学》2015年第3期245-253,共9页Geochimica

基　　金：教育部高等学校博士学科点专项科研基金(20120211120024);国家自然科学基金(41201197);中央高校基本科研业务费专项基金(lzujbky-2014-211)

摘　　要：万象洞所在地大气降水同位素值年内波动较大,变化起止时间存在显著的年际差异。观测期内,武都降水同位素δD-δ18O组合特征与周边城市降水同位素多年平均值重建的区域降水雨水线基本重合,洞穴所在地区降水同位素具有很好的区域代表性。洞穴滴水同位素值年内变化幅度较小,基本反映了当地大气降水同位素值的月加权平均水平。洞穴次生碳酸盐与洞穴滴水之间符合同位素平衡分馏基本规律。季节尺度上,不同监测点滴水及次生碳酸盐δ18O值因受地下水混合作用强弱差异及洞穴温度的小幅变化等影响而略有差异;年际变化上,夏季风爆发前后降雨量的权重及爆发时间的早晚对洞穴滴水-碳酸盐体系同位素水平存在一定的影响。万象洞洞穴滴水、石笋氧同位素信号在年代际尺度上可以很好地指示区域内大气降水的同位素变化特征。Significant isotopic variations in precipitation were observed in Wudu, Gansu, where Wanxiang Cave is located. There a notable inter-annual difference exists in saltation times for δ^18O variation in precipitation, and it was found that the inter-annual δD-δ^18O characteristics coincide with the local meteoric water line, so the regional precipitation isotope value can be well represented by the isotope value for Wudu precipitation. However, the intra-annual δ^18O variations for drip water in Wanxiang Cave were found to be insignificant, as they basically reflect the weighted average isotope value of the local precipitation. An equilibrium fractionation was observed between secondary calcite and cave drip water. On seasonal timescale, slight difference δ^18O value exists between drip water and secondary calcite, which we believe is caused by difference in underground water mix-intensity and slight variations in cave temperature. δ^18O for cave water and stalagmite from Wanxiang Cave may have been influenced by the weight of the precipitation before and after the Asian Summer Monsoon onset and the monsoon onset time. On decadal timescale, the isotope characheristics of regional precipitation can be well indicated by the oxygen isotope values for drip water and secondary calcite from Wanxiang Cave.

关 键 词：大气降水 洞穴滴水 Δ^18O 石笋 万象洞 

分 类 号：P597[天文地球—地球化学]