川东北石笋记录的600 a前干旱事件

A drought event recorded by a stalagmite from northeastern Sichuan in central China

关键词:  石笋  氧同位素  方解石沉淀  干旱事件  El Niño  华中

Key words:  stalagmite  stable oxygen isotope  calcite precipitation  drought event  El Niño  central China

摘要:

通过分析川东北狮子洞石笋SI2高分辨率稳定氧同位素组成（ δ¹⁸O），重建了该地区过去~2 ka降水变化历史。SI2的 δ¹⁸O记录显示川东北地区在~600 a前出现过一次干旱事件，该事件在SI2的生长发育和碳酸盐沉积中也有显示。在川东北地区这一事件表现为三幕结构。该事件在我国中部地区的一些石笋记录中也有显示，也与历史文献记载一致；但在我国南方地区的古水文记录中没有明显显示。这一事件的成因还有待今后更加深入的研究。

Abstract:

Background, aim, and scope With global warming, climatic extremes such as flood, drought and heat wave are becoming increasingly serious and exert more and more threats to human society. Investigations of past climatic extremes help us to understand the variations and controlling mechanisms and to contribute to prediction of these events. In this paper, a drought event which happened ~600 a ago in central China was reported to be recorded by a stalagmite (SI2) collected from NE Sichuan, and its evolution and controlling mechanisms were investigated. Materials and methods The stalagmite SI2 was collected from Shizi Cave (32°24′N, 107°10′E). U-²³⁰Th dates and ²¹⁰Pb dating results indicate that SI2 developed during the last ~2100 years. The stable oxygen isotope ( δ¹⁸O) of SI2 was determined with a Thermo-Fisher MAT 253 mass spectrometer with analytical errors better than 0.1 ‰. Results The SI2 δ¹⁸O record varied from −7.42‰ to −9.27‰ with an average of −8.67‰. A general decreasing trend was observed in the δ¹⁸O record prior to AD 200, followed by an apparent and long-lasting increasing trend until AD 1400 when the heaviest δ¹⁸O ratio of the whole record, −7.42‰ occurred. From AD 1400 to ~AD 1800, an overall negative shift was displayed with the lightest value of the whole record, −9.27 ‰ appeared at the end of this stage. The SI2 δ¹⁸O record showed a gradual increasing trend again during the last 200 years. The SI2 δ¹⁸O record indicated a drought event happened ~600 a ago, which was supported by the growth of stalagmite SI2. Calcite precipitation in SI2 was relatively more concentrated on the growth center when the event happened, suggesting lower dripping rates under a relatively dryer climate. The SI2 δ¹⁸O record suggested that the drought event was episodic, consisting of three dry episodes. Discussion This drought event was also recorded by other stalagmites in central China as well as historical documents. However, changes in hydroclimate in South China did not illustrate an apparent manifestation of this event. The spatial distribution of this event in monsoonal China suggested a possible origin from sea surface temperature in the tropical Pacific Ocean which might be in an El Niño-analogue state. However, this explanation was in contradiction with the recent work of Tan et al (2019) and more investigations were warranted. Conclusions The δ¹⁸O ratio and growth of stalagmite SI2 recorded a drought event happened ~600 a ago in NE Sichuan in central China. This event consisted of three dry episodes. Recommendations and perspectives The spatial distribution of this event in monsoonal China suggested a possible tropical origin but further investigations were warranted in future.