Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication
Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication
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DOI：
10.3389/feart.2021.794762
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发表时间：
2021-12
期刊：
影响因子：
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通讯作者：
Ye Tian;Haiwei Zhang;Rui Zhang;Fan Zhang;Zeyuan Liang;Yanjun Cai;Hai Cheng
中科院分区：
文献类型：
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作者：
Ye Tian;Haiwei Zhang;Rui Zhang;Fan Zhang;Zeyuan Liang;Yanjun Cai;Hai Cheng
洞穴藻方解石稳定氧同位素(δ18OC)是古气候研究中应用最广泛的指标之一，了解其季节-年际变化对古气候重建具有重要意义。对江西中国东南部神农洞2016-2021年的五年降水量和岩溶洞穴水进行了监测。局地大气水线为δD=8.2 0×δ18O+13.34，与全球大气水线相似。研究了降水和洞穴水的稳定氢氧同位素(δD和δ18O)特征。降水和洞穴水的δ18O和δD具有明显的季节变化。夏季和秋季降水δ18O和δD值普遍偏低，而冬春季δ18O和δD值较高。同时，降水δ_(18O)值偏低不仅出现在年降水量最大的6~7月，也出现在降水量有限的8~9月。季风降水水汽来源的回溯轨迹分析表明，年际尺度上吸湿区域变化不大，6-7月降水的水汽主要来自南中国海和孟加拉湾，而8-9月的水汽主要来自西太平洋和局地。厄尔尼诺-南方涛动通过调节夏季风降水在年降水量和水汽来源中的百分比，是影响δ18O值的重要因素。月平均降水量δ18O与NI3.4指数的关系表明，东亚夏季风在拉尼娜阶段加强，导致季风季(5~9月)降水较多，δ18O值较低，而厄尔尼诺阶段则相反。
Speleothem calcite stable oxygen isotope (δ18OC) is one of the most widely used proxies in paleoclimate research, and understanding its seasonal-annual variability is very significant for palaeoclimate reconstruction. Five-year precipitation and karst cave water from 2016 to 2021 were monitored in Shennong cave, Jiangxi Province, Southeast China. The local meteoric water line (LMWL) is δD = 8.20 × δ18O + 13.34, which is similar to the global meteoric water line. The stable hydrogen and oxygen isotope (δD and δ18O) characteristics of precipitation and cave water were studied. δ18O and δD of precipitation and cave water show obvious seasonal variations. Lower precipitation δ18O and δD generally occur during summer and autumn compared with higher δ18O and δD values during winter and spring. Meanwhile, low precipitation δ18O values do not only appear in June–July when precipitation is the highest of the year but also appear in August–September when precipitation is limited. The back-trajectory analysis of monsoon precipitation moisture sources shows that the moisture uptake regions vary little on inter-annual scales; the water vapor of rainfall in June–July comes from the South China Sea and the Bay of Bengal, while the moisture source in August–September is mainly from the West Pacific and local area. The El Niño-Southern Oscillation is an important factor affecting the value of δ18O by modulating the percentage of summer monsoon precipitation in the annual precipitation and moisture source. The relationship between amount-weighted monthly mean precipitation δ18O and Niño-3.4 index shows that the East Asian summer monsoon (EASM) intensifies during La Niña phases, resulting in more precipitation in monsoon season (May to September, MJJAS) and lower δ18O values, and vice versa during El Niño phases.