| 引用本文: | 栗若馨,蔡演军,黄守毅,王海波,薛刚,卫莹莹,贺梅,宁有丰,贾雪雪,王婷,程海.2025.青藏高原中南部天门洞倒三冰消期石笋沉积及其环境意义【封面文章】[J].地球环境学报,16(1):31-42 |
| LI Ruoxin,CAI Yanjun,HUANG Shouyi,WANG Haibo,XUE Gang,WEI Yingying,HE Mei,NING Youfeng,JIA Xuexue,WANG Ting,CHENG Hai.2025.Stalagmite deposition and its environmental significance during the antepenultimate deglaciation in Tianmen Cave, south-central Qinghai-Xizang Plateau 【Cover】[J].Journal of Earth Environment,16(1):31-42 |
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| 青藏高原中南部天门洞倒三冰消期石笋沉积及其环境意义【封面文章】 |
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栗若馨1，蔡演军1*，黄守毅1，王海波1，薛刚 2，卫莹莹3，贺梅1，宁有丰1，贾雪雪1，王婷1，程海1
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1.西安交通大学 全球环境变化研究院，西安 710049
2.西安地球环境创新研究院，西安 710061
3.西华师范大学，南充 637009
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| 摘要: |
| 通过对青藏高原中南部天门洞石笋TM-18b进行230Th测年和稳定同位素测试，建立了倒三冰消期249.89—240.32 ka BP的石笋碳氧同位素记录。结合已发表的、发育在同一洞穴石笋的年代和同位素数据，对倒三冰消期石笋生长记录和同位素序列进行分析，发现天门洞石笋TM-18b和19TM-3在倒三冰消期弱季风区间分别沉积28.5 mm和13.9 mm，持续时间约6.5 ka和5.2 ka，表明倒三冰消期弱季风区间青藏高原气候较为温暖湿润。南极冰芯记录的大气CO2、CH4浓度及δD的上升和δ18Oatm的下降，以及全球海平面的上升支持倒三冰消期弱季风区间青藏高原气候的回暖。弱季风区间石笋δ18O记录显示季风降水贡献减少，说明冰川融水和/或西风水汽可能为区域降水增多、气候变湿提供了大量水汽。 |
| 关键词: 石笋 δ18O 倒三冰消期 印度夏季风 青藏高原 |
| DOI：10.7515/JEE232033 |
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| 基金项目:第二次青藏高原综合科学考察研究（2019QZKK010102）；中国科学院战略性先导科技专项（B类）（XDB40010200）；西安交通大学青年拔尖人才（A类）项目 |
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| Stalagmite deposition and its environmental significance during the antepenultimate deglaciation in Tianmen Cave, south-central Qinghai-Xizang Plateau 【Cover】 |
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LI Ruoxin1, CAI Yanjun1*, HUANG Shouyi1, WANG Haibo1, XUE Gang2, WEI Yingying3, HE Mei1, NING Youfeng1, JIA Xuexue1, WANG Ting1, CHENG Hai1
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1. Institute of Global Environmental Change, Xi’an Jiaotong University, Xi’an 710049, China
2. Xi’an Institute for Innovative Earth Environment Research, Xi’an 710061, China
3. China West Normal University, Nanchong 637009, China
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| Abstract: |
| Background, aim, and scope Among the seven most recent deglaciations, the Antarctic ice core temperature record shows the least but fastest temperature rise during the antepenultimate deglaciation. Additionally, three North Atlantic Ice Rafted Debris (IRD) peaks occurred at T-Ⅲ, while only one or two IRD peaks were present at Termination Ⅰ, Ⅱ, and Ⅳ. This particularity makes the study of the antepenultimate deglaciation one of the entry points for a deeper understanding of the processes and mechanisms behind rapid climate change. However, there are few studies on paleoclimatic reconstruction that span the antepenultimate deglaciation. In this study, we examine the growth and stable isotope records of stalagmites from Tianmen Cave in the south-central Qinghai-Xizang Plateau during the antepenultimate deglaciation and endeavor to understand the climatic and environmental changes and their implications. Materials and methods Stalagmite TM-18b was collected in a cave chamber approximately 200 m from the entrance of Tianmen Cave, measuring 13 cm in height and 4 cm in diameter. At various depths from the top of the stalagmite, seven powder subsamples (around 80 mg) were taken along the growth layer using a hand drill for U-Th dating. The powdered samples were dated using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). A total of 73 subsamples were extracted with a hand drill at 0.5 mm intervals along the stalagmite growth axis for stable isotope analysis, which was carried out using a DeltaⅤstable isotope mass spectrometer, equipped with a Kiel Ⅳ Carbonate Device. All of these experiments were conducted in the Isotope Laboratory at Xi’an Jiaotong University, China. Results TM-18b began to grow at about 493 ka BP, and after growing 8 cm, there was a growth hiatus. Then, a growth of 3.6 cm occurred between 248 ka BP and 243 ka BP, followed by a depositional hiatus. Around 0.91 ka BP, with the change of depocenter, the stalagmite was redeposited by 1—2 mm. In this study, we focus on the antepenultimate deglaciation recorded by stalagmite TM-18b. The δ18O values of stalagmite TM-18b ranged from −20.1‰ to −12.2‰, covering a range of 8‰. It fluctuates between −15‰ and −12.2‰ at 39.5—11 mm from the top, and there is an interval of high δ18O value at about 27 mm. At 11 mm from the top, the δ18O value drops rapidly to about −20‰. At 3.5 mm from the top, the δ18O record of the antepenultimate deglaciation was interrupted by a depositional hiatus. The δ13C record exhibited a downward trend until it reached about −6.5‰, and there is an interval of relatively high δ13C values at 20 mm during the decline. Discussion Based on previous studies of the stalagmites from Tianmen Cave, along with simulations and observations of water vapor transport over the Qinghai-Xizang Plateau, we further confirm that δ18O in the south-central Qinghai-Xizang Plateau largely reflects the variation in the intensity of the Indian summer monsoon, i.e., the more depleted the δ18O value, the stronger the Indian summer monsoon, and vice versa. Since stalagmites were deposited under near-isotopic equilibrium conditions, we propose that the variation in stalagmite δ13C in Tianmen Cave is mainly related to changes in the overlying vegetation and soil biological activities; specifically, a more depleted δ13C value indicates a wetter and/or warmer climate. According to extrapolations from previous studies, stalagmites would cease growing due to low temperatures and/or reduced precipitation during the antepenultimate deglaciation. However, stalagmites TM-18b and 19TM-3 deposited 28.5 mm and 13.9 mm (where the carbonate δ18O values are greater than −15‰) and lasted 6.5 ka and 5.2 ka, respectively, during a period of low insolation. This implies that both temperature and humidity were favorable for stalagmite growth during this interval. This phenomenon suggests that the climate of the Qinghai-Xizang Plateau during this time may have been relatively warm and humid. Global climatic events, such as the increases in CO2, CH4, and δD, the decrease in δ18Oatm, and the rise in sea level, supported the warming of the Qinghai-Xizang Plateau during the WMI of the antepenultimate deglaciation. The δ18O record indicates that monsoon precipitation decreased, while the δ13C record shows a significant improvement in climate and increased humidity within the WMI. During this time, meltwater from glaciers and/or water vapor transported by westerlies may have contributed moisture to local precipitation, combined with elevated temperatures, creating favorable environmental conditions for stalagmite deposition. Conclusions The phenomenon of stalagmites TM-18b and 19TM-3 in Tianmen Cave deposited tens of millimeters and grew for thousands of years during the antepenultimate deglaciation has certain uniqueness. To some extent, it suggests that the climate of south-central Qinghai-Xizang Plateau may have been warm and humid during the WMI of antepenultimate deglaciation. Recommendations and perspectives The paleoclimatic study of antepenultimate deglaciation is still scarce, and the detailed causes of speleothem deposition events in the south-central Qinghai-Xizang Plateau warrants further investigation. |
| Key words: stalagmite δ18O antepenultimate deglaciation ISM Qinghai-Xizang Plateau |
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