【作者】 陶士臣；

【导师】 陈发虎； 安成邦； Kam-biu Liu（廖淦标）；

【作者基本信息】 兰州大学 ， 自然地理学， 2011， 博士

【摘要】 目前,全球气候变化已成为国际社会关注的焦点,只有客观的理解过去气候历史及其变化特征才能为应对未来气候变化提供正确的决策依据。我国西北地区是亚洲中部干旱区的重要组成部分,该地区气候干旱、生态脆弱,更容易遭受气候变化的影响。因此,本文选择位于新疆东部的两个临近湖泊开展全新世植被与环境变化研究。巴里坤湖和托勒库勒湖位于天山东端山间凹陷盆地内,属于封闭性湖泊,是开展该区域过去植被与环境变化研究的理想载体。2006年3月课题组在两个湖泊采集到一系列沉积岩芯。2010年6月在托勒库勒湖靠近湖泊中心位置获取一套81 cm长的短岩芯(TLKL10)。本文只详细介绍沉积岩芯所记录的全新世植被与环境。选用地层中的陆生植物残体、沉积物全样以及提取花粉浓缩物进行AMS和常规14C测年,共计获得21个(巴里坤湖14个,托勒库勒湖7个)年代数据。本文对巴里坤湖(205个样品,理论分辨率为55年每样品)以及托勒库勒湖的沉积样品进行花粉分析(74个样品,理论分辨率160年每样品),结合两个湖泊的现代表土花粉数据(巴里坤湖46个,托勒库勒湖23个),定性重建了新疆东部全新世植被与环境。巴里坤湖花粉谱显示,湖泊周围11600cal yr BP以来主要是以蒿属、藜科、禾本科以及菊科为代表的荒漠、荒漠草原或草原,部分时段出现片状桦木林地。其中,11600-9400 cal yr BP期间是以藜科和菊科为代表的荒漠,植被盖度和沉积率低；属于干旱的气候环境。9400-7900 cal yr BP期间,荒漠逐渐向以蒿属、禾本科以及藜科为代表的荒漠草原过渡,该时期湖泊周围的降水或有效湿度逐渐增加、气温升高,属于干旱环境向温暖湿润的过渡期。7900-4200 cal yr BP期间,草原类植物进一步增多,以藜科为代表的荒漠进一步退缩,以桦木属为代表的乔灌木植物扩张。湖泊周围是以蒿属、藜科以及禾本科为主的典型草原/荒漠草原,并出现了片状桦木林地。这一时期湖泊周围出现了全新世最温暖湿润的气候环境。4200-3800 cal yr BP期间,蒿属和桦木花粉快速下降而藜科则显著增加,植被演化为荒漠,气候明显干旱。3800 cal yr BP以来,以蒿属为代表的草原成分扩张,指示地方性草甸的莎草科以及唐松草属也明显增多,以藜科为代表的荒漠迅速下降,桦木植物的分布依然没有明显的变化。这一时期湖泊周围为荒漠草原/草甸草原；环境较为适宜,但与温暖湿润的中全新世相比,环境有所恶化。在相对温暖湿润的气候背景下,在2500-2300 cal yr BP期间再次出现短暂的气候恶化事件,这期间蒿属减少,代表干旱环境的菊科有所增多。现代的植被与环境从3800 cal yr BP开始,特别是2300 cal yr BP以来逐渐形成。托勒库勒湖花粉谱显示,该湖花粉主要由菊科、麻黄属、蒿属、禾本科、藜科以及石竹科等组成。11600 cal yr BP以来,湖泊周围主要为砾漠、荒漠草原或草原,气候整体干旱,总体上不如同期巴里坤湖周边的植被与环境状况。全新世植被与环境存在两个明显不同的阶段：11600-8000 cal yr BP期间,以耐旱的菊科、麻黄属以及石竹科为代表的砾漠；湖泊沉积速率明显偏低,这一时期湖泊周围土壤风化作用弱、湖泊自身生产力低下,整体为干旱气候。大约从8000 cal yr BP开始,植被组成发生明显变化,由上一阶段干旱的砾漠演变为以蒿属、藜科以及禾本科为代表的典型草原或荒漠草原,气候相对温暖湿润；但较高的藜科指示这一时期依然较为干旱。在8000 cal yr BP以来相对湿润的环境背景下,出现了4500-3800 cal yr BP期间的明显干旱环境。记录显示,藜科快速增加,蒿属、禾本科以及莎草科所占比例降低,与巴里坤湖的记录基本一致。3800 cal yr BP以来,禾本科以及藜科逐渐下降且趋于稳定,蒿属逐渐上升,气候环境改善。现代植被与环境大约从3800 cal yr BP开始逐渐形成,特别是2650cal yr BP以来植被组成与环境变化整体稳定。两个湖泊在整个全新世可以大体划分四个明显的阶段：即①干旱的早全新世(11600-8000 cal yr BP);②温暖湿润的中全新世(8000-4200/4500 cal yr BP);③中全新世向晚全新世过渡期间(4200/4500-3800 cal yr BP)的干旱事件；④相对湿润的晚全新世(3800 cal yr BP以来)。两个湖泊周围在早全新世为砾莫或荒漠,中全新世为典型草原或荒漠草原,干旱事件期间为荒漠植被,晚全新世为荒漠草原、草甸有所发育。两个湖泊记录的新疆东部地区全新世气候变化的总体特征与亚洲中部干旱区其他研究点、甚至北大西洋地区的记录具有良好的可比性；而早全新世植被与环境演化明显滞后于东亚季风影响区、青藏高原北部边缘区以及临近的阿尔泰山地区的记录约2000-3000年。更多还原

【Abstract】 Presently, global climatic change is a hot topic around the world. Paleoclimatic studies are greatly important to understand the potential characteristics and trends of further climatic change. Chinese northwestern region is a key part of the arid central Asia. The climate there is dry, with a frangible ecology which is easy influenced by climatic change. Hence, I selected both lakes Balikun and Tuolekule which are located in eastern Xinjiang, to carry out the studies of vegetation and environmental changes during the Holocene. Both lakes are typical inland salt lakes without an outlet, and are ideal study sites to understand vegetation and environmental changes in this area.In March 2006, we collected several parallel sediment cores from both lakes. In June 2010, we extracted another 81-cm (TLKL10) sediment core, located near the center of Tuolekule Lake. The sedimentary record from both lakes covers the late Quaternary. This dissertation, however, solely focuses on the records during the Holocene.We selected terrestrial plant remains, bulk sediment, and pollen concentrate as the materials for 14C dating by conventional and accelerator mass spectrometry (AMS). As a result, we have21 age dates (14 in BLK06 core, seven in TLKL06 and TLKL10 cores) from both lakes. I analyzed fossil pollen samples from both lakes Balikun (205 samples, ca.55 years/sample) and Tuolekule (74 samples, ca.160 years/sample), as well as the modern pollen samples from both lakes (Balikun-46 samples; Tuolekule-23 samples). The overall purpose of this study is to reconstruct the vegetation and environmental changes in eastern Xinjiang, China, during the Holocene.It was a relatively dry environment, with the typical vegetation types of desert, steppe or desert steppe mainly consisting of Artemisia, Chenopodiaceae, Gramineae. and Compositae, as well as patches of birch forest in certain periods over the Balikun Lake region during the Holocene.The desert consists of Chenopodiaceae and Compositae. with low sedimentation rate indicating it was a dry environment between 11600-9400 cal yr BP over the lake region. The vegetation type changed from desert to desert steppe with main vegetation plants of Artemisia, Gramineae, and Chenopodiaceae between 9400-7900 cal yr BP. It was an interim period that the climate changed from dry, possibly cold to warm-wet.Since about 7900 cal yr BP, the steppe composition was further increasing, while the desert vegetation, such as Chenopodiaceae was abruptly decreasing, and Betula was quickly rising. The vegetation type was typical steppe with patches of birth forest. It was a warm and humid environment between 7900-4200 cal yr BP around the lake.However, percentages of Artemisia and Betula pollen were quickly decreasing. Conversely, proportion of Chenopodiaceae pollen was markedly increasing, indicating that the vegetation changed from typical steppe to desert. It was a typical centennial-scale climatic event between 4200-3800 cal yr BP.Since 3800 cal yr BP, the steppe vegetation, such as Artemisia, was quickly expanding and the local meadow pollen, such as the percentages of Cyperaceae and Thalictrum were also increasing. However, the percentage of Chenopodiaceae pollen was markedly decreasing during this period, while percentage of Betula pollen was still low. All of these signifying that it was a desert steppe or meadow steppe around the lake in the late Holocene, and the environment was also relatively warm and wet. However, comparing with the middle Holocene (7900-4200 cal yr BP), the environment had some deterioration.During the relatively warm and wet phase, there was a deterioration period of 2500-2300 cal yr BP. Artemisia pollen was reducing, but Compositae pollen, indicating the dry environment was increasing.The pollen diagram for Tuolekule Lake mainly consists of Compositae, Ephedra, Artemisia, Chenopodiaceae, and Caryophyllaceae. All of these major pollen types indicate a relatively dry environment around the lake during the Holocene. According to the pollen assemblages, the vegetation and environmental changes can be dividing into two main stages in the Holocene.In the early Holocene (11600-8000 cal yr BP), the pollen assemblages mainly consist of Compositae, Ephedra, and Caryophyllaceae, indicating a gravel desert over the lake region. At the same time, the low sedimentation rate indicates the weak weathering around the lake’s catchment, as well as the low productivity of the lake due to the extremely dry and perhaps cold climate during this period.However, since 8000 cal yr BP, the vegetation composition had greatly changed. The gravel desert was markedly decreasing, while desert steppe or steppe plants, such as Artemisia, Chenopodiaceae, and Gramineae were quickly expanding around the lake. These changes denote that the climate became warm and wet in comparison to the early Holocene (11600-8000 cal yr BP). Similar to Balikun Lake, it also records a centennial-scale dry event between 4500-3800 cal yr BP. During this short period, the percentage of Chenopodiaceae pollen was quickly increasing, while percentages of Gramineae, Artemisia, and Cyperaceae pollen were apparently decreasing.Since 3800 cal yr BP, percentages of Gramineae, and Chenopodiaceae pollen were gradually decreasing, with their proportions eventually stabilizing. At the same time, Artemisia pollen was gradually increasing. All of these indicate that the climate was recovering, and became warm comparing with last stage (4500-3800 cal yr BP). The modern environment gradually formed since that time, especially since 2650 cal yr BP, when the vegetation and environment were relatively stable.The vegetation and environmental changes by pollen records from both lakes are coincident with each other in the Holocene. Dividing it into four major stages, it was dry and perhaps cold in the early Holocene (11600-8000 cal yr BP); warm and humid in the middle Holocene (8000-4500/4200 cal yr BP); and relatively warm and wet climate since 3800 cal yr BP, with a typical centennial-scale climatic event during 4500/4200-3800 cal yr BP in both lakes. Correspondingly, gravel desert or desert were the main types around both lakes in the early Holocene, and the typical steppe appeared in the middle Holocene, as well as the desert steppe with some local meadow in the late Holocene in this region.The characters of vegetation and environmental changes from the records in both lakes are consistent with the other records in Xinjiang and arid central Asia, even with records around the North Atlantic during the Holocene. However, the pollen results in both lakes are markedly different from the records in the Asian summer monsoon region, north margin of the Tibetan Plateau, and even the Altai Mountains region especially in the early Holocene, and pollen records in both lakes existing 2000-3000 years lag compared with the records in above region during the early Holocene.更多还原