| 中晚全新世湘西莲花洞石笋灰度变化特征
及其古气候意义 |
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| 引用本文： | 张会领,殷建军,林玉石.中晚全新世湘西莲花洞石笋灰度变化特征
及其古气候意义[J].热带地理,2018,38(6):810-818. |
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| 作者姓名： | 张会领 殷建军 林玉石 |
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| 作者单位： | （1．中国地质科学院岩溶地质研究所自然资源部//广西岩溶动力学重点实验室，广西 桂林，541004；
2．广东海洋大学 海洋工程学院海洋工程系，广东 湛江 524088） |
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| 基金项目： | 中国地质科学院岩溶地质研究所岩溶动力学重点实验室开放基金（KDL201501）；中国科学院边缘海地质重点实验室开放基金（MSGL15- 09）；国家重大研究计划（2018YFA0605601） |
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| 摘 要： | 以湖南湘西莲花洞LH2石笋为研究对象，在高精度铀系定年的基础上，构建了湘西地区中晚全新世文石石笋灰度序列。中晚全新世，LH2石笋灰度值与δ18O值呈负相关同步变化，与旋回沉积速率呈正相关关系。LH2石笋的剖面灰度与文石的结晶形态有关，受降雨量和温度的控制。LH2石笋灰度显示，中晚全新世（8.6—0.03 ka B.P.）湘西地区气候变化可以划分为3个阶段：8.6—5.7 ka B.P.期间，夏季风强盛，气候暖湿，灰度值整体偏高；5.7—2.8 ka B.P.期间，灰度值逐渐降低，指示夏季风持续减弱，气候从暖湿向冷干过渡；2.8—0.03 ka B.P.期间，灰度值整体偏低，且存在较大幅度的波动，表明该时段气候整体偏冷干，但其间存在明显的温湿波动。在轨道尺度上，LH2石笋灰度值主要受北半球夏季太阳辐射量和热带辐合带（ITCZ）位置的控制。在百年尺度上LH2石笋灰度值的突变可能与北大西洋冰筏事件存在关联；年代际尺度上，LH2石笋灰度的变化受太阳活动和太平洋年代际涛动（PDO）的调控。在年际尺度上LH2石笋灰度的波动可能受厄尔尼诺—南方涛动（ENSO）活动驱动。
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| 关 键 词： | 中晚全新世 灰度 古气候 莲花洞 石笋 湘西 |
Variations in Grey Scale of a Stalagmite from Lianhua Cave,Hunan and
Its Paleoclimatic Implications during the Mid-late Holocene |
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| ZHANG Huiling,YIN Jianjun,LIN Yushi.Variations in Grey Scale of a Stalagmite from Lianhua Cave,Hunan and
Its Paleoclimatic Implications during the Mid-late Holocene[J].Tropical Geography,2018,38(6):810-818. |
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| Authors: | ZHANG Huiling YIN Jianjun LIN Yushi |
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| Institution: | (1. Key Laboratory of Karst Dynamics, NLR&GZAR , Institute of Karst Geology, CAGS, Guilin 541004,China; 2. Department of Ocean Engineering,
College of Ocean Engineering, Guandong Ocean University, Zhangjiang 524088, China) |
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| Abstract: | Based on 42 230Th ages, the results of X-ray diffraction analysis and the grey values of the polishing profile of an aragonite stalagmite, named LH2, which was collected from Lianhua Cave, this paper established the grey scale time series of aragonite stalagmites during the mid-late Holocene in western Hunan. During the mid-late Holocene, the average grey scale value of stalagmite LH2 was 185.7, the maximum was 218 and the minimum was 116. The average grey scale resolution of stalagmite LH2 was 4a and the resolution of grey scale could reach 2a in some time intervals. In general, the change pattern of grey scale of stalagmite LH2 imitated the change of solar radiation at 30°N in summer during the mid-late Holocene. Since 8.6 ka B.P., the amount of summer solar radiation in north Hemisphere has decreased gradually and the grey scale values of stalagmite LH2 decreased synchronously. During the mid-late Holocene, the grey scale of stalagmite LH2 significantly inversely correlated with its 18O values, but positively correlated with its growth rate. Although the grey scale of stalagmite LH2 followed that of summer insolation, it was punctuated by eight low grey scale events lasting about 1~5 centuries occurred at 8.1, 7.2, 5.7, 5.0, 3.7, 2.8, 2.1 and 1.4 ka B.P.. Some research suggest that the cause of the grey scale change of stalagmites was different in different cave. As for Lianghua Cave, Gray values of stalagmite LH2’s polishing profile might relate to crystalline forms of aragonite which were controlled by rainfall and temperature in western Hunan province. During the mid-late Holocene (8.6-0.03 ka B.P.), the history of climate in western Hunan could be divided into three stages. From 8.6 ka B.P. to 5.7 ka B.P., the overall level of gray value was higher, the oxygen isotope value was more negative and the growth rate of stalagmite was higher. The climate was characterized by high temperature and heavy rain, the summer monsoon was strong. From 5.7 ka B.P. to 2.8 ka B.P., the gray values decreased gradually, the oxygen stable isotope values became heavier and the growth rate of stalagmite reduced progressively, which indicated the summer monsoon weakened continuously and the climate turned from warm-wet to cold-dry gradually. From 2.8 ka B.P. to 0.03 ka B.P., the overall level of gray value was lower and fluctuated violently. Meanwhile, the oxygen stable isotope value was heavier and the growth rate of stalagmite was lower and fluctuated strongly. It indicated the climate was cold and dry and existed warm-wet fluctuations. On orbital timescale, variations of gray values of stalagmite LH2 were controlled by the summer insolation in Northern Hemisphere and the location of ITCZ. On centennial timescale, abrupt change of gray values of stalagmite LH2 might relate to ice raft events occurred in the North Atlantic Ocean. When North Atlantic ice raft events occurred, the East Asian summer monsoon weakened, the climate was cold and dry in the western Hunan, and the grey scale of stalagmite LH2 decreased. On inter-decadal scale, solar activity and PDO might regulate gray values of stalagmite LH2. On inter-annual timescale, fluctuations of gray values might be driven by ENSO. |
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| Keywords: | mid-late Holocene gray value western Hunan Paleoclimate |
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