【作者】 张欣佳；

【导师】 周爱锋；

【作者基本信息】 兰州大学 ， 自然地理学， 2013， 硕士

【摘要】 六盘山天池(35°15,N,106°18’E),位于六盘山南部,甘肃庄浪县境内,湖面海拔2430m,湖泊面积约0.02Km2,湖盆最深处达8.2m,主要补给方式为降水补给。该区年均气温3.4℃,年均降水量615mm(50年平均资料),其中7-9月的降水量占全年总量的50%-60%。目前该地区的主要植被类型为灌丛及草甸,植被覆盖率较高。六盘山天池位于黄土高原中部,属于我国东南季风区与西北干旱区之间的过渡地区,对气候及环境变化敏感,是研究全新世气候变化的理想区域。本文选择从六盘山天池湖心处获取的GS07A、GS07B两根平行岩芯为研究对象,通过14C测年、环境磁学参数测试及XRF岩芯元素扫描,重建了中全新世以来六盘山天池地区的环境变化记录,通过对比甘肃省历史时期人口数据、九仙洞及董哥洞的石笋氧同位素数据、总太阳辐射数据(△TSI),得出了以下结论：1.六盘山天池沉积物中的磁性颗粒以亚铁磁性和反铁磁性矿物为主。样品SIRM/x比值的平均值为22kA/m,且GS07A孔岩芯从底部到顶部均匀分布了大量的完整冷杉叶片,表明六盘山天池沉积物中磁性矿物并未受到早期成岩作用改造,湖泊沉积物磁学特征记录了研究区内过去6200年的气候环境信息。在6200-1300CalyrBP阶段,磁性矿物来源于流域成壤作用,夏季风强(弱),降水量多(少),土壤发育强(弱),进入六盘山天池的磁性矿物增加(减少),χ值升高(降低)。1300Cal yr BP-今,受人类活动的影响,磁性矿物来源方式发生了变化,χ高值主要指示了在人类活动影响下,植被破坏、土地利用状况发生改变导致黄土高原磁性较高的物质进入湖泊沉积。同时晚全新世以来气候干旱,夏季风弱也有可能是导致磁化率升高的原因之一。2.XRF岩芯扫描获得的结果表明,六盘山天池沉积物中的Al、Si、K、Ti、 S、Ca六种元素以及相关的主成分分析(PCA)结果显示出PCAl与Al、Si、K、Ti四种元素高度正相关,其正值指示流域内外源碎屑输入量大,间接指示研究区气候湿润,降水量高。PCA2主要与S、Ca两种元素相关,在6055-380Cal yrBP期间,其负值指示沉积物中富硫酸盐类沉积物,间接指示低湖面及干旱气候；380Cal yr BP-现在,异常的高值可能指示来源于黄土高原的富含钙元素的风成沉积物增多。六盘山天池自中全新世以来湖面变化不明显,基本保持稳定。3.中全新世以来,六盘山天池地区气候可大致划分为两个阶段：6200-1300CalyrBP,六盘山天池沉积物磁性矿物来源于流域内径流输入,PCA1偏正,指示研究区内夏季降水量较高,水动力加强,气候较湿润；1300Cal yrBP-今,六盘山天池沉积物磁性矿物受人类活动强烈影响,来源方式发生了改变,PCA1偏负,指示研究区气候趋于干旱,夏季风强度减弱。但是结合该地区历史人口数据及同一岩芯的孢粉数据进行对比后认为,这一时期内湖泊沉积物的各项指标均受到了人类活动的强烈影响,不能完全反映研究区内的自然气候变化。更多还原

【Abstract】 Liupan Mountains is located at the South-West of the Ningxia Hui Autonomous Region, and the east of the Gansu Province, is the transitional zone between arid and semi-arid climate ofChina. Liupan Mountains Tianchi Lake, also known as Guanshan Tianchi Lake (35°15’N.106°18’E), is located in the Zhuanglang County, lake surface elevation is2430m, lake area is about20,000m2, the deepest point is8.2m, and the lake is mainly feed by rainfall. The mean annual temperature of Liupan Mountains Tianchi Lake area is3.4℃, the mean annual precipitation is615mm, the precipitation in July, August and September constitute around50%-60%of this area’s annual precipitation. The main vegetation types in this area are bush and meadow, the vegetation coverage is high. Liupan Mountains Tianchi Lake is located at the center of Loess Plateau, where is the transitional zone between South-East monsoon region and North-Wesr arid region, is sensitive to the changes of climate and environment, this area is the ideal area to research the Holocene climate changes. In this paper, we choose two parallel cores which got from the center of Liupan Mountains Tianchi Lake to research. Using AMS14C dating, environmental magnetic parameters and XRF(X-Ray Fluorescence) core scanning, to reconstruct the climate changes since Middle-Holocene in Liupan Mountains Tianchi Lake region. Compared with Population of Gansu Province during historical periods,δ18O records of Jiuxian cave and Dongge cave, Total Solar Irradiance (△TSI), we can draw several conclusions below:1. Magnetic minerals of Liupan Mountains Tianchi Lake’s core sediment is mainly consisted of ferromagnetic and anti-ferromagnetism magnetic minerals. The average value of SIRM/x is22kA/m, and from bottom to the top of core GS07A, there are a mass of fir needles, these shows magnetic minerals in the Liupan Mountains Tianchi Lake wasn’t transformed by early diagenesis, these magnetic minerals record climate changes in the past6200years truly.6200-1300Cal yr BP, summer monsoon strong (weak), the development degree of soil of lake drainage basin strong (weak), more (less) magnetic minerals entered the Liupan Mountains Tianchi Lake,Xhigh (low).1300Cal yr-present, the sources of magnetic minerals changed to exogenous dust, the main source region is the Loess Plateau, the high value of Xindicate weak summon monsoon and arid climate. But a series of researches shown that in this period,Xmainly reflect human activities, not the nature climate change.2. Element dates of Al, Si, K, Ti, S, Ca in the sediment of Liupan Mountains Tianchi Lake and the Principal Component Analysis (PCA) result shows:PCA1is high-positive correlate with Al, Si, K, Ti, positive value of PCA1indicate high input of exogenous clastics in watershed, and indicate moist climate, high precipitation indirectly.PCA2is correlate with S and Ca, in6055-382Cal yr BP, negative value of PCA2indicate the presence of gypsum-rich and carbonate-rich facies, and indicate low lake level, arid climate indirectly;380Cal yr BP-present, the positive value of PCA2indicate more exogenous dust from the Loess Plateau. The lake level remains stable in the past6200years.3. since the mid-Holocene, the climate history of Liupan Mountains Tianchi Lake can be divided into two stages:6200-1300Cal yr BP, the sources of magnetic minerals of Liupan Mountains Tianchi Lake was contacted with pedogenesis in the watershed, the positive value of PCA1indicate moist climate and high summer precipitation;1300Cal yr BP-present, the sources of magnetic minerals of Liupan Mountains Tianchi Lake changed to exogenous dust from the Loess Plateau, the negative value of PCA1indicate arid climate and weak summer monsoon. But compared with the Population of Gansu Province during historical periods and pollen date from the same core, the result shows that in this period all the indexes influenced by human activities heavily can’t reflect nature climate changes in the study area.更多还原