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Precipitation Seasonality in Central China over Last Century Reconstructed
author: source: Time:2021-06-24 font< big medium small >

In recent decades, extreme events become more intense and frequent in the context of global warming, and the Asian monsoon region has become one of the most affected areas.

The study of the seasonal precipitation variation is particularly important to the social and economic development. However, little is known about the decadal to longer timescale variability of seasonal precipitation due to the lack of instrumental records in the past few centuries. 
Recently, a joint research group led by Prof. TAN Liangcheng from Institute of Earth Environment of the Chinese Academy of Sciences constructed a seasonally resolved (~0.16yr) δ18O series of an annually laminated stalagmite from Xianglong Cave, central China. 
The researchers found that the stalagmite δ18O values revealed significant annual cycles (Fig. 1), with lower δ18O values occurring in summer monsoon (SM) season, whereas higher values occurring in non-summer monsoon (NSM) season. Thus, the seasonal amplitude of δ18O (Δ18O) was a measure of the climate seasonality in this area.  

Fig. 1 The section and δ18O record of stalagmite XL21. (Image by LIN, et al)
Comparisons indicated a significantly negative correlation between the Δ18O series and the observed SM/NSM rainfall ratios (Fig. 2), which may be explained by the cave recharge model. 
In this model, the main recharge was from SM rainfall. During the SM period, the δ18Os inherited the composition of δ18O-depleted SM rainwater and became negative gradually. Whereas during the NSM period, SM rainfall together with the NSM rainfall, maintained drips during the NSM season. Therefore, δ18Omax and δ18Omin were smaller with increased SM rainfall amount. But δ18Omax values would be larger with the increased proportion of NSM rainfall, which would induce a larger Δ18O value. The Δ18O value thereby was negatively related to the SM/NSM rainfall ratio.

Fig. 2 Comparison of Δ18O (B) and other instrumental record. (Image by LIN, et al)
Moreover, Δ18O correlated well with the Pacific Decadal Oscillation (PDO) on a decadal scale (Fig. 2). Increased SM/NSM rainfall ratio was observed during the warm phase of PDO, and decreased SM/NSM rainfall ratio was observed during the cold phase of PDO. 
This work, published in Palaeogeography, Palaeoclimatology, Palaeoecology as invited research article, was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB40000000) and the National Natural Science Foundation of China (41991252).
Contact: Bai Jie, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China. Email: baijie@ieecas.cn
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