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罗布泊湖相沉积物记录的全新世以来区域环境变化
林永崇
学位类型博士
导师穆桂金
2017-05-01
学位授予单位中国科学院大学
学位授予地点新疆乌鲁木齐
学位专业理学博士
关键词罗布泊 全新世 风沙活动 气候变化 Lop Nur Holocene Wind-sand Activity Climatic Change
摘要过去全球变化(PAGES)研究是全球变化研究的重要内容,对过去全球变化深入研究能够有效揭示其变化历史、演变规律及其成因机制,为预测未来环境变化提供科学依据。湖相沉积物是古环境信息的重要载体之一,蕴含大量的环境信息,具有较好的连续性和较高的分辨率。湖相沉积物被广泛用于重建不同时间尺度的古环境变化序列,探讨环境演变驱动机制,解析区域环境对全球变化的响应等。罗布泊地处塔里木盆地东端,地势低平,是整个塔里木盆地的汇流中心,沉积着以万年计的湖相沉积物,是区域古环境变化研究的理想场所。在历史上,罗布泊地区曾孕育出光辉灿烂的“楼兰文明”,为古丝绸之路重要的交通枢纽。本研究以罗布泊湖相沉积为研究对象,在“大耳朵”湖湖心位置以 1cm 分辨率连续采集了一个厚度为 378cm 的 LB 剖面(顶部 20cm 盐壳,以 10cm 间隔采样),并采集了 10 个 14C 年代学样品。首先通过加速器质谱仪(AMS)进行 14C 年代测试,建立了较高分辨率的年代–深度模型。然后对 LB 剖面样品进行粒度、磁化率、TOC、烧失量等各种环境代用指标测试分析,结合各代用指标的环境意义,重建了全新世以来罗布泊地区环境变化序列。最后与周边地区全新世环境变化特征比较,讨论罗布泊地区环境变化的驱动机制。获得以下主要结论和初步认识:(1)LB 剖面层理发育完善,层理清晰;剖面发育连续,韵律组合良好。各种环境代用指标之间如粒度、TOC、有机质烧失量、碳酸盐烧失量、磁化率等都发生同步变化,并与剖面现场观察记录有很好的对应关系。通过 14C 测年方法进行多层定年,基于沉积年代学理论建立了 LB 剖面年代–深度模型。罗布泊 14C 年代存在明显的碳库效应,LB 剖面碳库效应约为 3075 年,剖面各时期沉积速率较为接近,底部 378cm深度年代约为 9.1cal. ka BP。(2)罗布泊全新世以来主要表现为逐渐湿润的趋势。前人 C/N 比值数据显示全新世罗布泊湖相沉积有机质主要为外源成因的,因此代表流域的植被状况。TOC 和有机质指标在 9.1– 4.2 cal. ka BP 时段含量相对较低,流域环境较为干旱,并在 7.2 – 5.2cal. ka BP 期间最干旱;4.2 cal. ka BP – 1.1 cal. ka BP TOC 和有机质含量相对较高,处于全新世最湿润的阶段。1.1 cal. ka BP 以来转变为较干旱气候。(3)罗布泊全新世以来湖泊碳酸盐含量反映了湖泊盐度变化特征。9.1 – 8.5 cal. cal.ka BP 湖泊碳酸盐相对较低,矿化度低;8.5 – 4.2 cal. ka BP 期间,碳酸盐总体处于较高水平,湖水盐度较前期有所增加;4.2 cal. ka BP 以来,湖泊进入硫酸盐沉积阶段,盐度在 4.2 – 3.0 cal. ka BP;3.0 – 2.2 cal. ka BP;2.2 – 1.1 cal. ka BP 三个阶段出现旋回式升高,湖泊盐度波动式增加。1.1 cal. ka BP 以来,湖泊盐度有所降低,并在 0.6 cal.ka BP 出现低值,湖泊水量出现丰枯波动;0.4 cal. ka BP 以来为氯化物沉积阶段,湖泊处于最高盐度。(4)罗布泊地区全新世以来长期存在风沙活动,并发生多次风沙活动事件。罗布泊地区在 9.0 – 8.5 cal. ka BP,6.0 – 5.5 cal. ka BP, 4.4 – 3.9 cal. ka BP,3.1 – 2.7 cal. kaBP,2.3 – 1.7 cal. ka BP 和 1.1 ka BP 以来出现风沙活动较强烈时期,尤其是 9.0 –8.5cal. ka BP,4.4 – 3.9 cal. ka BP 和 1.1ka 以来风沙活动最强烈。罗布泊风沙活动响应北大西洋冷事件,在约 4.2 cal. ka BP、3.0 cal. ka BP、 2.2 cal. ka BP、1.1 cal. ka BP表现为冷干的气候特点。(5)罗布泊地区全新世气候主要受太阳辐射强度变化及其引起的西风环流强度、位置南北移动和流域山地冰雪补给量变化共同作用的结果。早、中全新世太阳辐射较强烈,西风带北移,流域降水较少,地表有效湿度较低,流域较为干旱,而冰雪融水补给较多,湖水矿化度较低。中、晚全新世太阳辐射强度减弱,地表有效湿度增加,西风带南移,降水增加,地表有效湿度较高,流域较为湿润;而冰川显著退缩,湖泊补给减少,湖水矿化度升高。另外,全新世北大西洋冷事件通过西风环流影响亚洲中部环流系统。冷事件爆发时增强了中纬西风环流和西伯利亚高压,促使区域风场加强,并通过塔里木盆地东灌气流影响罗布泊地区风沙活动。
其他摘要Past Global Changes (PAGES) is an important part of the Global Change Research Program (GRCP). Further studying the PAGES can effectively reveals the history of past global changes, evolvement rule and genetic mechanism, and provides the scientific basis for predicting future climate change scenarios. The lake sediments with better continuity and higher resolution content plenty of palaeoenvironment information. It is one of the important materials to study the palaeoenvirnonment change and widely used to rebuild the environment evolutionary sequence, and discuss the driving mechanism of environmental evolution and the response of regional environment to the global climatic change. Lop Nur lake is situated at the east of the Tarim Basn. The dried lake with very flat terrain was confluence center of the whole basin and deposited tens of thousands lacustrine sediments. It is a perfect place for regional ancient environment study. Lop Nur has spawned the “Loulan civilization” and was an important transportation junction for ancient Silk Road in history. In this study we sampled a 378 cm profile (name LB profile) with 1 cm resolution (10 cm resolution on the top 20 cm) and 10 radiocarbon chronology samples in the center of the “Great Ear” lake. We firstly dated 10 chronology samples using the AMS (accelerator mass spectroscopy) and builded the age-depth model of profile LB. Then we tested various environmental proxies including grain size, magnetic susceptibility, TOC, loss of organic matter and carbonate content. Basing on the change characteristics of these proxies, we rebuilded the Holocene environment change sequence. We lastly discuss the driving mechanism of the regional environment change. The main conclusions are as follow:(1) The profile LB develops continuous stratification which with good rhythm. There are good correspondence among the environmental proxies of grain size, TOC, loss of organic matter, carbonate and magnetic susceptibility, and which even correspond to the record of field observation. We builded a depth – age model based on the 14C chronology and the sedimentology. There is apparently reservoir effect of radiocarbon of the 14C chronology in Lop Nur lake. The profile LB has a uniform deposition which with a reservoir effect of ~3075 years and an age of ~ 9.1 cal. ka BP at 378cm depth. (2) The reconstruction supports that the climate in Lop Nur region was gradually wetting during Holocene. The C/N data from other researchers indicate the organic matter of the lake sedimentary is mainly exogenous and their contents represent the state of watershed vegetation. The results suggest Lop Nur has experienced three paleoclimatic stages: it was in relative dry climate during 9.1 – 4.2 cal. ka BP especially during 7.4–4.2 cal. ka BP which with low TOC and organic matter. The climate was in a wet environment between 4.2 cal. ka BP and 1.1 cal. ka BP. Since 1.1 cal. ka BP it returned to dried climate. (3) The changing lake carbonate reflects its salinity variation in Lop Nur lake during Holocene. The low carbonate content indicates lake salinity was in a little low level between 9.1 – 8.5 cal. cal. ka BP. The rising carbonate content show the salinity is in a high and stable level between 8.5 – 4.2 cal. ka BP. During 4.2 and 1.1 cal. ka BP the lake are in sulfate deposition stage which with three cyclic and increased lake salinity. Since 1.1 cal. ka BP the lake was in chloride deposition stage which with the highest salinity. (4) Aeolian activity was long-existed in the Lop Nur region in the Holocene. They were stronger during the stages of 9.0 – 8.5 cal. ka BP,6.0 – 5.5 cal. ka BP, 4.4 – 3.9 cal. ka BP, 3.1 – 2.7 cal. ka BP, 2.3 – 1.7 cal. ka BP and the last 1.1 ka BP, especially during 9.0 – 8.5 cal. ka BP,4.4 – 3.9 cal. ka BP and the last 1.1 cal. ka BP the aeolian activity are strongest. The climate in Lop Nur region respond to the north Atlantic cold event, and cold and dry climate happened at 4.2 cal. ka BP, 3.0 cal. ka BP, 2.3 cal. ka BP and 1.1 cal. ka BP (5) The regional climate in Lop Nur was dominated by solar radiation, westlies and mountain glaciers around Tarim Basin. During the early- and middle- Holocene (9.1 – 4.2 cal. ka BP) the solar radiation were stronger and the westlies northward moved, which caused relative low effective humidity of the earth’s surface and dry climate. However the lake obtained vast glacial melt runoff supply causing low lake salinity. During middle- and late- Holocene (since 4.2 cal. ka BP) the solar radiation weaken and the westlies southward moved, which caused relative high effective humidity of the earth’s surface and wetter climate. But the remarkable receding glaciers reduced glacial melt runoff supply and caused the lake cyclic cyclical retreated. In addition, aeolian activities in Lop Nur region were mainly controlled by the Northern Atlantic cold events during Holocene. The westerlies and the Siberian High strengthen once northern Atlantic cold event outburst, and enhance the region wind field. This influences the aeolian activity of Lop Nur region.
学科领域自然地理学
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14785
专题研究系统_荒漠环境研究室
作者单位中国科学院新疆生态与地理研究所
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林永崇. 罗布泊湖相沉积物记录的全新世以来区域环境变化[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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