关键词: 沙漠/黄土过渡带;MIS3阶段;花粉记录;植被演替;增温响应

Abstract: Human culture was profoundly influenced by climate change. The increasing warmth of the anathermal in the Last Deglaciation and the Megathermal Period of the Holocene are two important periods for cultural evolution. Sensitive vegetation responses to climate change can be traced by fossil pollen records. The loess-paleosol sections of Caijiagou(CJG), Yulin (38.1°N, 109.8°E) and Hanjialiang(HJL), Fugu(39.5°N, 111.1°E), located in the desert-loess transition zone, northern Loess Plateau, were selected to conduct high-resolution pollen analysis. Based on a field survey, as well as the comparison of magnetic susceptibility curves, grain size curves and the δ18O record of stalagmite from Sanbao/Hulu caves during the last 50 ka, we established a depth-age mode of these profiles. Forty-four pollen samples were palynologically identified to rebuild the vegetation succession in the region, and to explore its response to climate changes since the LGM. At least 300 pollen grains were counted for most samples. Forty-seven families and 20 genera of pollen were identified. Four to five pollen assemblage zones were divided according to the variations of major pollen percentages, pollen concentrations and modern surface pollen research for the CJG and HJL profiles, respectively. A detailed history of vegetation succession and its response to climate changes since the LGM was reconstructed. For the CJG section, the pollen assemblage consisting mainly of Artemisia seems to represent a desert steppe during the LGM. During the Last Deglaciation, the pollen assemblage mainly consisting of Rununculaceae and Poaceae might reflect the appearance of a sparse steppe environment. In the Younger Dryas, the Artemisia and Poaceae assemblage might suggest the development of a meadow steppe. During the Holocene Optimum, the meadow-steppe dominated by Artemisia appeared. For the HJL section, steppe dominated by Artemisia lasted from the LGM to the Holocene Optimum, but the pollen concentration of the Last Deglaciation and Holocene Optimum was significantly higher than that of MIS-3 and the LGM. Moreover, accompanying drought-resistant plants such as Chenopodiaceae and Taraxacum-type appeared during the LGM, but suffurticosa plants of Zygophyllaceae appeared during the Last Deglaciation due to the improvement of water availability. Our results showed that the vegetation succession of the Desert/Loess transitional zone was mainly controlled by the changes of temperature and water availability since the LGM. During the cold/dry period of the LGM, local vegetation was dominated by drought-resistant species with low vegetation coverage and monotonous community. During the anathermal of the Last Deglaciation and Megathermal Period of the Holocene, vegetation coverage increased with some magaphanerophytes. Our research provides a valuable modern analogue for the study of vegetation in response to global warming.

Key words: Desert-loess transition zone; LGM; Pollen record; Vegetation succession; Response to climate warming