| 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. |
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