Vegetation And Climate Changes In The Middle And Northern Loess Plateau Over The Past 26000 Years

The global climate system has experienced the Last Glacial Maximum (LGM) to the early Holocene, the mid-Holocene Optimum, and the late Holocene with the huge fluctuation of temperature over the past 26000 years. The process should include the various possible scenarios of climate change in the future. It is the basis for the study of the response of the future environment and the ecosystem to the climate change.In China, the loess-paleosol sequence of the Loess Plateau is continuous and has complete records of the paleoclimate change, meanwhile, the Loess Plateau is located in the arid and semi arid areas, whose northern and western parts are adjacent to the Asian inland desert, so it has a higher sensitivity to the climate change. Therefore, the Loess Plateau is an ideal region to study the paleovegetation and paleoclimate change.Most studies have suggested that grassland dominated the Loess plateau during the Holocene Optimum, and just a few regions such as the Weihe Basin and other areas with the better water condition grow some forests. However, the existing paleovegetation records in the LGM in the Loess Plateau are relatively small and low resolution. Therefore, we need to obtain more records to understand the impact of the glacial-interglacial cycles on the vegetation.This paper selects two sections for the study, which are Jingbian section and Fuxian section with the lower ages being c.26000 years. The paper aims to reconstruct the vegetation during the past 26000 years on the basis of pollen analysis, and compares the response characteristics of the vegetation at Jingbian and Fuxian to the climate change.Pollen results show that the studied area was dominated by steppe vegetation (mainly Artemisia) over the past 26000 years. Except for Artemisia, other major vegetation composition varied both temporally and spatially. Plants were much more abundant, with less desert vegetation and more deciduous trees, during the early-middle Holocene than in the Last Glacial Maximum (LGM), indicating a wetter and warmer climate.During the LGM, desert steppe prevailed at Jingbian, mainly composed of Artemisia, Chenopodiaceae and Asteraceae, while at Fuxian, Chenopodiaceae and Asteraceae decreased and Poaceae increased, indicating the vegetation similar to arid-steppe-type Artemisia frigida steppe. During the early-middle Holocene, the vegetation at Jingbian was close to Artemisia frigida-desert steppe, with decreased Chenopodiaceae and Asteraceae. At Fuxian, Corylus increased, and Chenopodiaceae and Asteraceae nearly disappeared in the early-middle Holocene, suggesting the vegetation similar to Artemisia-type meadow steppe.Comparison of two pollen records shows a north-south climate gradient in both glacial and interglacial periods, i.e. the farther north, the colder and drier it becomes, exhibiting a climate pattern similar to the present over the Loess Plateau. Furthermore, the spatial difference of vegetation is much more evident in the Holocene Optimum than in the LGM, indicating a much steeper climate gradient in warm period than in cold stage.