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Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication

2021; Frontiers Media; Volume: 9; Linguagem: Inglês

10.3389/feart.2021.794762

2296-6463

Ye Tian, Haiwei Zhang, Rui Zhang, Fan Zhang, Zeyuan Liang, Yanjun Cai, Hai Cheng,

Geology and Paleoclimatology Research

Speleothem calcite stable oxygen isotope (δ 18 O C ) 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 × δ 18 O + 13.34, which is similar to the global meteoric water line. The stable hydrogen and oxygen isotope (δD and δ 18 O) characteristics of precipitation and cave water were studied. δ 18 O and δD of precipitation and cave water show obvious seasonal variations. Lower precipitation δ 18 O and δD generally occur during summer and autumn compared with higher δ 18 O and δD values during winter and spring. Meanwhile, low precipitation δ 18 O 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 δ 18 O by modulating the percentage of summer monsoon precipitation in the annual precipitation and moisture source. The relationship between amount-weighted monthly mean precipitation δ 18 O 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 δ 18 O values, and vice versa during El Niño phases.