昆仑山北坡近5000年以来黄土堆积的环境信息*

根据昆仑山北坡克里雅河上游海拔2750m的一处台地的风尘沉积剖面KMA,利用沉积物粒度、总有机质含量(TOM)、碳酸盐含量和部分孢粉记录重建了当地近5000年的环境变化历史。研究认为,研究剖面所在地区在4300cal.aB.P.前和3000~2600cal.aB.P.之间相对湿润,其余时段均表现为干旱状态; 塔克拉玛干沙漠南缘风沙活动在3400cal.aB.P. , 3000~2600cal.aB.P. ,1800cal.aB.P. , 1200cal.aB.P. , 900~650cal.aB.P.表现活跃,沙漠向南扩张,表明在KMA剖面古环境记录中塔里木盆地南部沙漠边缘和山地的降水存在着显著分异。红色噪声谱分析还显示,KMA剖面的环境记录存在多种与太阳辐射或者太阳活动相关的显著周期,可能表明研究区环境变化的主要驱动因素与太阳辐射强迫有关。

EOLIAN DEPOSITS IN NORTHERN SLOPE OF KUNLUN Mts AND THEIR PALAEOENVIRONMENTAL IMPLICATIONS DURING THE PAST 5000 YEARS

A less than 5000 years environmental change has been recorded in the eolian deposit section KMA from the upper reaches of the Keriya River, Southern Xinjiang. The temporal framework was made by three ¹⁴ C ages, which makes it possible to establish a time series for the continuous sequence. The proxy indicators of grain sizes, total organic matter, and pollen records are applied to reconstruct the palaeoenvironment, and to probe into the changes of the southern margin of the Talimakan Desert. Coarser particles, especially sand contents were used to indicate the distance from the section to the desert, and the A/C (Artemisia/Chenopodiaceae) ratio as was used as the moisture parameter. Comparison between the coarser particle contents and the A/C ratio in the KMA section suggests differences between the environmental processes of the section locality and those of southern margin of the Tarim Basin. Our data shows that in an arid background it was relatively moist during the periods both prior to 4300cal.aB.P. and between 3000cal.aB.P. to 2600cal.aB.P. On the contrary, some sand activity phases in southern margin of the Talimakan Desert are recorded around 3400cal.aB.P. ,3000~2600cal.aB.P. 1800cal.aB.P. , 1200cal.aB.P. and 900~650cal.aB.P. , accompanied by the southward-extending desert. Referred to modern reanalysis data from NCEP/NCAR, this relatively moisture pattern, existed in the upper and lower northern slope of the Kunlun Mountain, should have been resulted from the vertical variation of precipitation along the slope.Spectral analysis for sand content and TOM was performed using the program REDFIT 3.5. The spectral amplitudes of sand content and TOM peak at 204.8a, 92.7a, 80.0a that exceed the 95 ％ chi-squared limit of confidence, with other minor peaks seen at 117a and 111.7a. The cycles of higher frequencies have not been tested due to the lack of temporal resolution. These periodicities of some 204.8a, 92.7a and 80.0a are dominant in the KMA record and correspond to the cycles of solar activity, suggesting a possible driving force of solar activity, although the mechanism behind is still unclear. In a summary, our data may have suggested that there existed a climatic tele-connection in century time scale between central Eurasia and the North Atlantic, supporting the hypothesis that solar activity may have been an important factor in driving the climate system on our planet.