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| Titel |
Controls on oxygen isotope variability in precipitation and drip water at eight caves in the monsoon regions of China |
| VerfasserIn |
Wuhui Duan, Jiaoyang Ruan, Weijun Luo, Tingyong Li, Lijun Tian, Guangneng Zeng, Dezhong Zhang, Yijun Bai, Jilong Li, Tao Tao, pingzhong zhang, Ming Tan |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104905
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| Publikation (Nr.) |
 EGU/EGU2015-4347.pdf |
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| Zusammenfassung |
| Cave monitoring is important to fully understand the climatic significance of stalagmite δ18O
records. Most previous studies focus on one cave, or several caves in one area. A large
regional-scale investigation on the isotopic composition of precipitation and drip water is
scarce. To investigate the regional-scale climate forcing on the oxygen isotopic composition
of precipitation in the monsoon regions of China (MRC) and how the isotopic signals are
transmitted to various drip sites, a three-year-long (2011-2014) on-site rainfall and drip water
monitoring program has been carried out with approximately monthly sampling at 37 drip
sites in eight caves in the MRC.
Neither rainfall amount nor air temperature are the predominant controls on the oxygen
isotopic composition of monthly precipitation. The rain in the wet season (May to October),
with relatively low δ18O values, is sourced from tropical air masses, whereas the
rainfall in the dry season (November to April), with relatively high δ18O values, is
mostly sourced from continental air masses. Additionally, the weighted summer
rainwater δ18O values decrease from coastal southwest China to inland northeast
China, which suggests that the moisture of monsoon rainfall in China originates
mainly from Indian Ocean, and transports to the north along the southwest-northeast
path.
28 of the 37 drip sites are constant drips with little discernable variation in drip
water δ18O through the whole study period. For most of the constant drips, the
mean value of each drip water δ18O is nearly identical to or slightly higher than the
three-year weighted mean value of the corresponding local rainwater δ18O, indicating
these drips may be mainly recharged by none-evaporated or slightly evaporated,
well-mixed older water stored in the vadose zone. 7 of all the 37 drip sites are seasonal
drips, for which, although the amplitude of drip water δ18O is narrower than that
of rainfall, the monthly response of drip water δ18O to local precipitation is not
completely dampened. Specially, there are 3 sites in Shihua cave which can be classified
not only as a seasonal drip but also as a constant drip. 2 of all the 37 drip sites are
medium-variability drips, with constant and relatively negative drip water δ18O
values in the wet season but with variable and relatively positive drip water δ18O
values in the dry season. However, their essential recharge mode is different. For
these drips, the drip water δ18O is not only unable to inherit the seasonal signals
but also unable to inherit the long-term signals of the precipitation. Consequently,
the factors controlling the oxygen isotopic composition of drip water and then the
stalagmite is site-specific. In principle, though, for most of the stalagmites, the δ18O
profile may record the annual or longer time-scale climatic signals of rainfall δ18O. |
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