Climatic and environmental changes during Heinrich 6 recorded by δ13C in stalagmites from Jinfo Cave, Chongqing
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摘要: 在末次冰期发生的6次海因里希事件(Heinrich事件,简称H事件)中,H6事件发生年代最早,对其研究较少,利用高分辨率石笋记录研究H6事件期间的气候环境变化,有助于理解高低纬度气候变化对H事件的响应过程。本文基于重庆市金佛洞石笋JF2017铀系测年数据和碳同位素数据,重建H6事件期间中国西南地区季风气候环境的演化过程。结果显示:石笋JF2017的δ13C值在61 811±204 a B.P.~59 716±159 a B.P.时段显著偏重,持续大约2 095 a,暗示该时段季风减弱和生态植被退化,对应北大西洋H6事件。H6事件期间,石笋JF2017的δ13C记录在61 811~60 848 a B.P.期间开始先逐渐偏重至最大值,随后发生短时间尺度的波动变化;最后在60 848~59 716 a B.P.期间缓慢偏轻至H6事件结束,整体呈现先逐渐偏重后又缓慢偏轻的趋势,内部存在百年际尺度的气候震荡,表明H6事件期间当地气候不稳定。石笋JF2017记录的百年际尺度的季风气候变化可能与热带辐合带和北大西洋经向翻转环流密切相关。
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关键词:
- 亚洲季风 /
- Heinrich 6 /
- 石笋δ13C /
- 金佛洞 /
- 中国西南
Abstract:Of the six Heinrich events (H event for short) occurring during the last glacial period, H6 event has been less studied due to its earliest occurrence time. However, using high-resolution stalagmite records to study climate and environmental changes during H6 event can help people understand the response of climate change at high and low latitudes to the H events. In recent years, much progress has been made in terms of studies on paleoclimate and environmental changes with use of stalagmite δ13C records. Besides, some stalagmite δ13C records have been used to study the climate change of the events on a millennium scale during the last glacial period, but there is no detailed record of the high-resolution climate change in Southwest China during the H6 event. In this case, the JF2017 stalagmite δ13C may provide an excellent proxy for exploring the climate and environmental change during H6 event. Based on the dating data of uranium series and carbon isotope data of JF2017 stalagmite in Jinfo Cave, we analyzed the climate significance indicated by stalagmite δ13C, and reconstructed the evolution process of the monsoon climate environment in Southwest China during H6 event. Developed from the Jinfo-Yangzi Cave system, Jinfo Cave is located in Jinfo Mountain, Nanchuan district, Chongqing, Southwest China, with an altitude of 2,080 m. The Jinfo Mountain area belongs to subtropical humid monsoon climate, which is jointly affected by the Indian Summer Monsoon and the East Asian Summer Monsoon (ASM). In this study, the age samples of stalagmites were tested by Neptune Plus Multi-receiver Plasma Inductively Coupled Mass Spectrometry (MC-ICP-MS), and the carbon isotopes of stalagmites were tested by Delta-V-Plus gas isotope ratio mass spectrometer and carbonate automatic sampling device Kiel-IV online. The experimental results are based on Vienna Pee Dee Belemnite (V-PDB) with δ13C experimental analysis error<0.06 ‰(2σ). According to data analysis, the variation range of stalagmite JF2017 δ13C is from -1.44 ‰ to -4.92 ‰, with an average value of -3.40 ‰. JF2017 stalagmite δ13C fluctuates significantly, and change amplitude is -3.48 ‰. JF2017 stalagmite δ13C records show that the value mainly presents a negative-positive-negative-positive trend during the period of 63,000-58,000 a B.P. Due to the complex influence factors of stalagmite δ13C, we compared JF2017 stalagmite δ13C records with JFYK7 stalagmite δ18O records in Yangkou Cave which belongs to the same cave system as Jinfo Cave in order to further analyze the climate significance of stalagmite JF2017 δ13C. The comparison indicates a similar variation between the stalagmite stable isotope records of Yangkou Cave and JF2017 stalagmite δ13C records. Through previous research, JFYK7 stalagmite δ18O is indicative of variations in ASM intensity, and the positive shift in stalagmite δ18O corresponds to weakened ASM. In this study, we observed that the stalagmite JF2017 δ13C value was slightly positive, corresponding to the positive JFYK7 stalagmite δ18O. Therefore, under the background of weakening ASM, JF2017 stalagmite δ13C records can reflect the change of ecological environment caused by the change of regional hydrological climate. In addition, the comparison between JF2017 stalagmite and the stalagmites from other caves indicate that JF2017 stalagmite δ13C records were comparable with other climate records during H6 event. From 61,811 a B.P.to 60,848 a B.P., the values gradually became heavier, reaching to the maximum, and then fluctuated on a short-time scale. Finally, from 60,848 a B.P. to 59,716 a B.P., they became slightly lighter to the end of H6 event. The comparison between JF2017 stalagmite δ13C and other relevant records in the rest of the world shows fluctuations in the stalagmite δ13C record, so do the corresponding ITCZ and AMOC. This study shows that the stalagmite JF2017 δ13C value was significantly heavier during the 61,811 ± 204 a B.P.-59,716 ± 159 a B.P. period, lasting for about 2,095 a, which may suggest that the monsoon weakened and the ecological vegetation degraded during this period. This result corresponds to the North Atlantic H6 event. During H6 event, stalagmite JF2017 δ13C records became heavy to the maximum value during the period of 61,811-60,848 a B.P., followed by the fluctuation change on the short-time scale. During the period of 60,848-59,716 a B.P., the values slowly became lighter to the end of the H6 event. The trend of becoming light after a gradual increase of weight and a climate shock inside on a centennial scale indicate that the local climate was unstable during H6 event. The monsoon climate change on a centennial scale recorded by stalagmite JF2017 may be closely related to the Intertropical Convergence Zone (ITCZ) and the North Atlantic meridional overturning circulation (AMOC). -
Key words:
- Asian monsoon /
- Heinrich 6 /
- stalagmite δ13C /
- Jinfo Cave /
- Southwest China
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图 3 石笋JF2017年代模型图
注:深蓝色圆点表示U-Th测年点的年代及深度,深蓝色误差棒表示测年误差(±2σ);红色实线表示年代模型曲线,蓝色实线表示95%的置信界限。
Figure 3. Chronological model of stalagmite JF2017
Note: Dark blue dots indicate the age and depth of the U-Th dating points; error bars in dark blue indicate the dating error (±2σ); solid line in red indicates the chronological model curve; solid line in blue indicates the 95% confidence limit.
图 4 石笋JF2017 δ13C记录
注:深蓝色曲线为该数据20点滑动平滑,黑色虚线为数据平均值,红色误差棒表示测年误差(±2σ)。
Figure 4. δ13C records of stalagmite JF2017
Note: Dark blue curve indicates that the record is smoothed using a 20-point running mean; the black dotted line indicates the average value of the data; the error bars in red represent dating errors (±2σ).
图 5 石笋JF2017的平衡分馏检验
注:(a)深度为70 mm处生长层的δ13C和δ18O;(b) 深度为81 mm处生长层的δ13C和δ18O (红色点线图为δ13C;深蓝色点线图为δ18O)。
Figure 5. Equilibrium fractionation tests of stalagmite JF2017.
Note: (a) δ13C and δ18O values with a depth of 70 mm; (b) δ13C and δ18O values with a depth of 81 mm (red dotted line: δ13C; dark blue dotted line: δ18O.
图 6 JF2017石笋δ13C记录与其他石笋记录对比
注:(a) 金佛洞石笋JF2017 δ13C(本研究);(b) 和(c)羊口洞石笋JFYK7 δ18O和 δ13C[9];(d)和(e) 羊子洞石笋YZ1 δ18O和δ13C[21];(f)和(g) 永兴洞石笋YX55 δ18O和δ13C[23];黄色阴影部分表示H6发生的时间段。
Figure 6. Comparison of JF2017 stalagmite δ13C record with other stalagmite records
Note: (a) JF2017 stalagmite δ13C in Jinfo Cave; (b) and (c) JFYK7 stalagmites δ18O and δ13C[9] in Yangkou Cave; (d) and (e) YZ1 stalagmites δ18O and δ13C[21] in Yangzi Cave; (f) and (g) YX55 stalagmites δ18O and δ13C[23] in Yongxing Cave; yellow shadow: the time when H6 occurred.
图 7 JF2017石笋δ13C记录与全球其他气候记录对比
注:(a)金佛洞JF2017石笋δ13C记录(本研究); (b)羊口洞JFYK7石笋δ18O记录[9] ;(c)65°N夏季太阳辐射[53];(d)格陵兰冰芯δ18O记录[54]; (e) 北大西洋MD95-2040沉积岩芯SST记录[55];(f) 北大西洋KNR191-CDH19沉积岩芯231Pa/230Th记录(误差棒表示年代误差)[56];(g)卡里亚科盆地MD03-2621沉积岩芯反射率记录[57];橙色虚线表示H6的开始和结束。
Figure 7. Comparison of JF2017 stalagmite δ13C record with other climate records in the rest of world
Note: (a) JF2017 stalagmite δ13C in Jinfo Cave; (b) JFYK7 stalagmite δ18O in Yangkou Cave[9]; (c) summer solar radiation at 65°N[53]; (d) ice core δ18O record in Greenland[54]; (e) SST record of MD95-2040 sediment core in North Atlantic Ocean[55] ; (f) 231Pa/230Th record of KNR191-CDH19 sediment core in North Atlantic Ocean (error bar: age error)[56]; (g) reflectivity of MD03-2621 sediment core in Cariaco Basin[57]; dotted line in orange: the beginning and the end of H6.
表 1 金佛洞石笋JF2017 230Th测年结果
Table 1. 230Th dating results of stalagmite JF2017
样品
编号深度
/mm238U
/ppb232Th
/pptd234U*
(measured)230Th/238U
(activity)230Th Age (a B.P.)
(corrected)JF2017-1 23.0 50 639±100 42±39 −118.1±1.1 0.361 7±0.0010 58 368±235 JF2017-2 28.5 35 390±71 163±41 −120.6±1.1 0.363 7±0.0010 59 050±248 JF2017-3 42.0 52 946±106 2±39 −118.6±1.2 0.365 9±0.0010 59 345±244 JF2017-4 49.0 50 680±59 98±15 −116.1±1.0 0.368 8±0.0006 59 728±159 JF2017-5 61.5 39 643±67 61±33 −113.5±1.1 0.371 6±0.0009 60 076±217 JF2017-6 71.5 38 075±48 182±19 −109.8±1.1 0.376 1±0.0006 60 681±177 JF2017-7 73.5 27 942±57 610±47 −110.5±0.8 0.377 3±0.0011 61 018±261 JF2017-8 88.5 57 510±98 32±31 −119.4±1.1 0.374 6±0.0008 61 339±219 JF2017-9 93.0 34 514±51 383±26 −116.1±1.1 0.378 1±0.0007 61 769±204 JF2017-10 107.5 49 708±94 91±36 −119.5±1.1 0.379 0±0.0010 62 332±248 注:衰变常数取值为λ230Th=9.157 7×10−6a−1;λ234U=2.826 3×10−6a−1;λ238U=1.551 25×10−10a−1;δ234U = ([234U/238U]$_ {\rm{activity}}^{-1}$)×103,δ234U初始值是根据230Th 年龄获得,即δ234U初始值=δ234U测量值×eλ234×T;初始230Th年龄校正采用地壳230Th/232Th平均比值: 4.4×10−6±2.2×10−6。
Note: The value of the decay constant is λ230Th=9.1577×10−6a−1; λ234U=2.8263×10−6a−1; λ238U=1.55125×10−10a−1; δ234U = ([234U/238U]$_ {\rm{activity}}^{-1}$) x 103, δ234Uinitial value is obtained based on 230Th age, i.e. δ234Uinitial value = δ234Umeasured value×eλ234×T; The initial 230Th age adjustment was based on the average ratio of 230Th/232Th in the earth's crust: 4.4×10−6±2.2×10−6. -
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