新疆中部巴鲁克洞石笋记录的全新世和MIS5c-5a阶段气候和环境变化

发布时间：2018-06-19 01:08

本文选题：新疆地区 + 洞穴石笋　；参考：《兰州大学》2017年博士论文

【摘要】：在当前全球气候变化背景下,利用地质载体(如极地冰芯、海洋钻孔沉积物、陆生黄土、湖泊沉积物及洞穴沉积物等)进行地表过去气候和环境变迁规律和特征的研究,可以为未来气候和环境变化提供参照,也是气候变化领域的研究重点之一。近二十年来,国内外学者利用石灰岩地层中广泛发育的岩溶洞穴沉积物(主要为石笋),在高精度同位素地质年代测试技术(铀系测年)的支持下,高分辨率地分析和检测了石笋碳酸盐中的稳定同位素(氧和碳)、微量元素含量和比值、微量元素同位素、微层厚度和灰度、磁学信号、有机化合物含量等指标,从中提取了能够重建区域气候和环境变迁的信息,同时也将石笋古气候记录发展为气候变化研究的重要标尺之一。本论文在采集我国新疆中部天山南麓巴鲁克洞的石笋样品并在建立其铀系绝对定年结果的基础上,检测了石笋的氧碳同位素(δ18O、δ13C)和微量元素比值(Mg/Ca、Sr/Ca、Ba/Ca、U/Ca)指标,重建了新疆中部地区近两千年、全新世和MIS5c-5a阶段的不同时间尺度上(百年、千年和轨道)的环境演化和气候变迁历史,探讨了区域气候变化的可能驱动机制及环境变化对区域社会发展的可能影响。本论文得到的主要结论如下:(1)在分析研究区现代大气降水观测数据基础上,发现年内尺度上以乌鲁木齐站为代表的新疆天山地区,月均降水氧同位素(δ18Op)值与月均温度之间存在显著正相关关系,表现为“温度效应”影响;月均δ18Op值与月均降雨量之间为弱正相关。年际尺度上,年均加权平均δ18Op值与年均温度之间显示了弱的负相关,表明了年际尺度上“温度效应”的失效;结合天山中部乌源一号冰川和天山东部庙儿沟冰川的近50年冰芯氧同位素(δ18Oi)序列,发现冰芯δ18Oi值的偏负趋势与近50年乌鲁木齐站及新疆地区温度的上升趋势相反,说明年代际尺度上“温度效应”也并非主导作用。进一步分析了研究区在特殊年份的水汽来源差异,发现在较温暖的1997年,可能有相对较多的来自高纬度区域的δ18Op值偏负的水汽,而在较冷的1988年则增加了来自中低纬度区域的δ18Op值偏正的水汽。新疆中部地区大气降水δ18Op值及石笋δ18O值的偏负或偏正变化,不仅与水汽输送有关,还与输送通道的水汽再蒸发、局地水汽循环以及冰雪融水(其δ18O值非常偏负,~-20‰)的贡献等有关。(2)近两千年来,巴鲁克洞的一支87mm的石笋BLK12C的13个铀系绝对定年结果显示其方解石沉积覆盖了过去2457年,该石笋δ18O和δ13C值显著的十年际-百年尺度的周期性波动叠加在长时间的同位素值偏正的趋势上,且在中世纪气候异常期(Medieval Climate Anomaly,MCA,950-1250AD)同位素值整体偏负,同时也存在十年际尺度的偏正事件。这种突变和整体较低的同位素值特征也体现了在了石笋的Mg/Ca比值序列中,其与稳定同位素序列显示相似的变化模式。在MCA期间,石笋氧碳同位素的突然变化反应了这一时期研究区气候环境的不稳定性和较大幅度的快速变化,相比而言,小冰期(Little Ice Age,LIA,1300-1900AD)时,石笋氧碳同位素的变化幅度不如MCA期间,整体上同位素值偏正,尤其是1300-1400AD期间的显著偏正。此外,石笋微量元素指标(Sr/Ca、Ba/Ca、U/Ca)在MCA期间的变化很小,这可能反映了该时期地表土壤和大气粉尘的活动比较弱;在LIA时,Sr/Ca、Ba/Ca、U/Ca的高频波动比较显著,可能说明该时期土壤有机质含量的增加和微生物活动的加强等。巴鲁克洞石笋氧碳同位素序列中的近200年周期波动,可能反映了太阳活动周期对研究区的百年尺度气候和环境演化的驱动作用。此外,巴鲁克洞石笋记录中显示的公元14世纪期间显著的气候突变能够较好地对应于蒙古帝国的兴盛和衰落时间,其他一些历史朝代更替和区域文化发展和衰落的时间节点亦能在巴鲁克洞石笋代用指标波动中找到对应关系,可能说明了区域环境变化对社会文明演替的影响。(3)全新世期间,巴鲁克洞两支石笋BLK12A与BLK12B/C的38个高精度的铀系年龄覆盖了过去9500年,其高分辨率(~20年)的氧碳同位素序列显示石笋的δ18O序列在轨道尺度上的变化模式与北半球高纬度夏季太阳辐射变化相似,同时叠加了诸多千年-百年尺度的气候事件(如8.2ka事件、~3ka事件)。巴鲁克洞全新世石笋δ18O值记录整体上为早-中全新世(9.5~3ka)时偏负(-6.5~-9‰),其中7~6ka时石笋δ18O值有一个偏正的谷段(以6.4ka为中心)。在~3ka时,石笋δ18O值突然偏正(幅度约2‰),之后在大约500年时间里,石笋δ18O值显示较大的波动,但其范围在-5~-6.5‰之间。其中,BLK12A石笋在2.5~1.3ka为一个显著的沉积间断,在石笋横切面上亦能观察到一个具有石花状方解石沉积的条带。此外,石笋微量元素比值(Sr/Ca、Ba/Ca、U/Ca)序列显示在早中全新世时比值较高,而晚全新世比值较低,在~3ka左右发生了显著的微量元素比值增大的事件,可以认为巴鲁克洞所在区域全新世期间的局地湿度为早全新世较干而中晚全新世逐渐变湿,与湖泊沉积物重建的区域湿度序列一致。同时,巴鲁克洞代用指标反映的~3ka左右的气候突变事件可能与天山地区高山冰川的前进及西风环流的调整有关。(4)在MIS5c-5a期间,巴鲁克洞的2支石笋(BLK12E和BLK12F)的24个高精度铀系年龄显示其碳酸盐沉积发育时段为78.5~101.6ka(~23.1ka),所对应的是MIS5c的晚期至MIS5a的结束(late-MIS5c to MIS5a)。两支石笋具有高度重复性变化的氧碳同位素序列(~100年分辨率)显示了间冰段(5c和5a)时δ18O值偏负和冰段(5b)时δ18O值偏正的特征(幅度达到~3‰),低分辨率的微量元素指标也有类似的变化模式。巴鲁克洞MIS5c-5a期间的石笋记录反映了轨道尺度上岁差周期对该区域环境和气候的主导作用。与南北半球具有全球气候意义的代用指标对比后,可以推测巴鲁克洞所反映的新疆中部地区气候变迁响应于轨道尺度的北半球高纬度气候(格陵兰冰芯记录)与南半球气候(南极冰芯记录)的波动。值得注意的是,格陵兰冰芯所记录的北半球温度的上升(~85.5ka)要早于南极冰芯所记录的全球温度的上升(~84.5ka),也领先于亚洲东部季风气候(中国三宝洞石笋记录)和亚洲中部干旱区(新疆巴鲁克洞、科桑洞及乌兹别克斯坦Ton洞石笋)气候的转型。
[Abstract]:Under the background of global climate change, the study on the laws and characteristics of the climate and environment changes of the earth's surface by using geological carriers (such as polar ice core, marine drilled sediment, terrestrial loess, lake sediments and cave sediments) can provide reference for climate and environment change in the future, and it is also the focus of research in the field of climate change. First, in the past twenty years, scholars at home and abroad have used the widely developed karst cave sediments (mainly stalagmite) in the limestone strata. Under the support of high precision isotope geochronology Test Technology (uranium dating year), the stable isotopes (oxygen and carbon), trace elements content and ratio of trace elements in the carbonates of stalagmite are analyzed and detected with high resolution. Isotopes of quantitative elements, thickness and gray level of microlayers, magnetic signals, and organic compounds content have been used to extract information that can reconstruct regional climate and environmental changes. At the same time, the paleoclimate records of stalagmite are also developed as one of the important scales for the study of climate change. This paper is a collection of the Baruch cave in the southern foot of Tianshan, central Xinjiang, China. On the basis of the absolute dating results of the uranium system, the oxygen carbon isotopes of the stalagmite (delta 18O, Delta 13C) and the ratio of trace elements (Mg/Ca, Sr/Ca, Ba/Ca, U/Ca) were measured, and the environmental evolution and climate on the different time scales (100 years, thousand years and orbits) in the middle of Xinjiang were rebuilt for nearly two thousand years. The possible driving mechanism of regional climate change and the possible influence of environmental changes on regional social development are discussed. The main conclusions of this paper are as follows: (1) on the basis of the analysis of the observational data of Modern Atmospheric Precipitation in the study area, it is found that the monthly average precipitation of the Xinjiang Tianshan area, represented by the Urumchi Railway Station, is the same as the monthly precipitation. There is a significant positive correlation between the value of the position element (delta 18Op) and the monthly mean temperature, which shows the effect of "temperature effect", and the monthly mean Delta 18Op value is weakly positively correlated with the monthly average rainfall. The annual average weighted average Delta 18Op value shows a weak negative correlation with the annual average temperature, indicating the failure of the "temperature effect" on the interannual scale. The ice core oxygen isotope (delta 18Oi) sequence of the glacier of Wu Yuan 1 in the middle part of the Tianshan Mountain and the mioer gully glacier in the east of Tianshan Mountain found that the negative trend of the ice core Delta 18Oi value is contrary to the rising trend of the temperature in the Urumchi Railway Station and Xinjiang region in recent years, indicating that the "temperature effect" is not the leading role in the interdecadal scale. Further analysis of the research is made. The difference in the source of water vapor in the special year is found in the warmer 1997. It is found that in the warmer 1997, there may be a relatively large amount of water vapor with a negative Delta 18Op value from the high latitudes, while in the cold 1988, the delta 18Op value from the middle and low latitudes is more positive. The delta 18Op value of the atmospheric precipitation and the delta 18O value of the Stalagmite in the middle of Xinjiang are negative or negative. The partial positive change is related not only to the water vapor transport, but also to the water vapor re evaporation of the transport channel, the local water vapor cycle and the contribution of the ice and snow melt water (its delta 18O value is very negative, ~-20 per thousand). (2) in the last two thousand years, the absolute dating of 13 uranium systems of a 87mm stalagmite BLK12C in the 87mm cave shows that the calcite deposits covered the past 245 years. In the 7 year, the periodic fluctuation of the ten annual scale of the stalagmite Delta 18O and delta 13C value is superimposed on the tendency of long time isotopic values, and the isotopic values of the medieval climatic anomaly (Medieval Climate Anomaly, MCA, 950-1250AD) are overall negative, but also in the ten interannual scale. The characteristics of low isotopic values also reflect a similar pattern of variation in the Mg/Ca ratio sequence of stalagmite, which is similar to that of stable isotopes. During the period of MCA, the sudden changes in oxygen and carbon isotopes of stalagmite reacted to the instability and rapid changes of the climate and environment in this period, compared to the small ice period (Little Ice A). When GE, LIA, 1300-1900AD), the oxygen and carbon isotopes of stalagmite are less than that of MCA, and the isotopic values are very positive on the whole, especially in the period of 1300-1400AD. In addition, the trace elements (Sr/Ca, Ba/Ca, U/Ca) of the stalagmite (Sr/Ca, Ba/Ca, U/Ca) change very little during MCA, which may reflect the weak activity of soil and atmospheric dust in this period; in L. At IA, the high frequency fluctuations of Sr/Ca, Ba/Ca and U/Ca are more significant, which may explain the increase of soil organic matter content and the enhancement of microbial activity during this period. The recent 200 years' periodic fluctuation in the oxygen carbon isotope sequence of Baruch's Cave Stalagmite may reflect the driving effect of the solar activity cycle on the Centennial climate and environmental evolution of the study area. In addition, the remarkable climate change during the fourteenth Century ad of the Baruch cave can correspond to the prosperity and decline time of the Mongolia Empire, and the time nodes of other historical dynasties and regional cultural development and decline can also find the corresponding relationship in the fluctuation of the Baruch Cave Stalagmite substitution index, which may be explained. The influence of regional environmental changes on the succession of social civilization. (3) during the Holocene, the 38 high precision uranium system ages of two stalagmite BLK12A and BLK12B/C in the Baruch cave covered the past 9500 years. The high resolution (~20) oxygen carbon isotope sequence showed the variation pattern of the stalagmite Delta 18O sequence on the rail scale and the high latitudes in the northern hemisphere in summer The variation of the solar radiation is similar, and a number of millennial - Centennial climate events (such as the 8.2ka event, ~3ka event) are superimposed. The Baruch cave Holocene stalagmite Delta 18O records are generally negative (-6.5~-9 per 1000) at the time of the early Middle Holocene (9.5~3ka), of which the delta 18O value of the Stalagmite in 7~6ka has a positive Valley (centered on 6.4ka). At ~3ka, the stalagmite [delta]. The 18O value is abrupt (about 2 per thousand), and after about 500 years, the value of the stalagmite Delta 18O shows a larger fluctuation, but its range is between -5~-6.5 per thousand. Among them, the BLK12A stalagmite is a significant sedimentary discontinuity at 2.5~1.3ka. In the cross section of the stalagmite, a strip with stone calcite deposits can also be observed. Besides, the trace element of the stalagmite is in the trace element. The Sr/Ca (Ba/Ca, U/Ca) sequence shows that the ratio of the early Holocene is higher, while the late Holocene ratio is low, and a significant increase in the ratio of trace elements has occurred around ~3ka. It is considered that the local humidity during the Holocene period of the Baruch cave is gradually wetted by the early Miocene and the middle and late Holocene, and the lake deposition. The regional humidity sequence of the reconstruction is consistent. At the same time, the climatic catastrophe around ~3ka reflected by the Baruch Tung substitution index may be related to the advance of the alpine glaciers and the adjustment of the westerly circulation in the Tianshan region. (4) during the period of MIS5c-5a, the 24 high precision uranium system ages of 2 stalagmite (BLK12E and BLK12F) in the cave of the cave show their carbonate deposits The development period is 78.5~101.6ka (~23.1ka), which corresponds to the end of the late MIS5c to the end of MIS5a (late-MIS5c to MIS5a). The oxygen carbon isotope sequence of two stalagmite with high repeatability (~100 year resolution) shows that the delta 18O value of the interglacial segment (5C and 5a) is negative and the Delta (5b) value is positive when the delta 18O value is negative and the ice section (5b) is low. The trace element index of the rate also has a similar change pattern. The stalagmite records during the Baruch cave MIS5c-5a reflect the leading role of the precession cycle on the environment and climate in the orbital scale. Compared with the alternative indicators of the global climate in the northern and southern hemispheres, the climate change in the central Xinjiang region reflected by the Baruch cave can be speculated. The high latitude climate (Greenland ice core record) and the Southern Hemisphere climate change in response to the orbital scale. It is noteworthy that the rise of the Northern Hemisphere temperature recorded by the Greenland ice core (~85.5ka) is earlier than the global temperature rise recorded by the Antarctic ice core (~84.5ka), as well as the Eastern Asian climate. Climate change in the arid region of Central Asia (Baruch hole, Xinjiang, Ton cave and stalagmites in Uzbekistan).
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P532

【参考文献】