北大西洋地区的末次冰期气候波动在全球具有广泛记录.伊犁地区作为西风区向季风区过渡的边缘带,对气候变化响应敏感,千年尺度气候波动如何影响该区域有待进一步解答.黄土作为恢复古气候的重要地质记录,有利于上述问题的研究.通过对伊犁则克台剖面黄土沉积进行粒度端元分析,结果表明:则克台黄土粒度可分为四个端元,分别为EM1(0.8 m)、EM2(8 m)、EM3 (25.1 m)和EM4(51.6 m).EM1代表成壤组分;EM2代表高空西风组分;EM3和EM4代表尘暴组分,但EM4组分更能够反映末次冰期西伯利亚高压在伊犁地区的扩张.EM2和EM4都能记录千年尺度气候的波动,但响应程度却不同:51.3 ~20 ka, EM4含量变化曲线记录的千年尺度气候事件更为明显;然而20 ka之后,千年尺度事件在EM2含量变化曲线中更为突出.这表明西风和西伯利亚高压都是千年尺度气候信号的重要扩散机制,且造成上述差异的原因很可能是太阳辐射驱动下的北半球冰量变化.
英文摘要:
Millennium-scale climate changes such as Heinrich events and Dansgaard-Oeschger cycles,occurred in North Atlantic region in the last glacial period have a wide range of records around the world,which included,for example, the marine deposit in the Arabian Sea and the loess and stalagmite in East Asian monsoon region. As a transitional westerly-edge-zone to monsoon region,Ili area located in Xinjiang Province, China,is sensitive to climate change. Relevant studies show that millennial-scale climate events are recorded in Ili loess, but how millennial-scale fluctuations affected this region needs a further answer. As an important geological record restoring the paleoclimate information, the loess in this area is beneficial to the study of the above problems. This study selected Zeketai section in the Ili Basin as the research object. The section has 20.35 m thickness and was sampled at 5 cm interval. Finally 407 samples were obtained. The end member analysis was processed for the grain size of loess above 12 m in this profile. The result showed that the grain size distribution in this profile suited to yield four Gen. Weibull endmembers with modal size of 0.8 m(EMl), 8 m(EM2), 25.1 m(EM3) and 51.6 m(EM4) respectively,representing pedogenic component (EM1),upper-level westerly wind (EM2) and dust storm (EM3 and EM4). However, EM4 is more capable of reflecting the expansion of the Siberian high pressure in Ili area during the last glacial period. Both EM2 and EM4 can record the fluctuations of the Millennium-scale climate, but the response degrees of the two EMs are different. When H events occur, EM4 content gets increased and EM2 content gets decreased. When the cold events occurred, the ice volume in the northern hemisphere was increased,and the increased cold air in the Arctic region strengthened the Siberian high pressure, and then expanded into the Ili area, resulting in a large dust storm weather. Under the westerly wind transport,the dust was accumulated on the north bank of the Goness River. However, the blocking of the Qinghai-Tibet Plateau divided the westerly belt into two branches in winter, and the main axis lies on the southern side of the Himalayas, so the influence of Westerlies on the region is weakened. During the whole glacial period,the Westerlies belt moved southward for a long time and the main axis was southward. When the cold event occurred, the Westerlies belt remained in the south. During 51.3 ~ 20 ka, millennial-scale events are more obvious in EM4 content change curve; After 20 ka,YD and H1 events are more outstanding in EM2 content change curve. This suggests that both Siberian high pressure and Westerlies are the important spread mechanisms of millennial-scale climate changes. The cause of the above difference is likely to be the change of global ice volume driven by solar insolation on the orbital time-scale. In addition, regional factors also influence the grain size change in Zeketai.