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FOSSIL RECORDS OF LIPID MOLECULES FROM HOLOCENE PEAT ON ZOIGê|PLATEAU
若尔盖高原全新世气候序列的类脂分子化石记录*

Keywords: the Zoige Plateau,the Holocene,lipid molecular fossil,climatic series
若尔盖高原
,全新世,类脂分子化石,气候序列

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Abstract:

The research area is located on a gradually rising plateau (the Zoigê-Hongyuan Plateau) facing the north slope of the Tibetan Plateau. The peat swamp sampling site is in Hongyuan County, 2km southeast of the township, with an altitude of 3505m(a.s.l.). The core is 4.5m long and sampled at 1cm intervals. This peat sedimentary sequence was systematically investigated by lipid molecular stratigraphy by gas chromatography-mass spectrometer (GC-MS). A variety of molecular fossils are found in this peat profile, including n-alkanes, n-alkanols, n-fatty acids and so on. The n-alkanes are ranged from C15~C35, having a maximum at C31. A bimodal distribution of n-fatty acids from C10 to C26 was observed, maximizing at C16 and C22 or C24, The alkanols from C12 to C28 also display a bimodal distribution, maximizing at C16 and C22 or C28. Higher plants are the predominant source of the n-alkane compositions. The distribution patterns of n-fatty acids and n-alkanols indicate a mixed input from higher plants, algae, and microorganisms. Based on the establishment of a reliable AMS dating of the high resolution peat core, we have been able to establish climate and environment change series of the Zoigê Plateau using the distribution patterns of n-alkanes, n-alkanols, and n-fatty acids during the Holocene, together with the use of total organic carbon content, pollen assemblages and so on in the peat sequence. The results confirm that n-alkanes, n-fatty acids and n-alkanols proxies bear significant climate information. Of importance in paleoclimate reconstruction are the ratios of low molecular numbered and high molecular numbered molecule fossils (L/H) and average carbon chain length (ACL) representative of the relative abundance between microorganisms and higher plants. The higher L/H, the lower ACL, the warmer-wetter the climate; while on the contrary, the lower L/H, the higher ACL, the colder-drier the climate. These molecular fossil proxies together with total organic carbon content reveal a succession of several paleoclimate intervals. The Younger Dryas in this record is a cold and dry period. After this period, all proxies have shown a significant change, reflecting the abrupt arrival of the warm and humid Holocene period. The interval of 10~4kaB.P. is the Early Holocene warm-wet period. The Late Holocene cold-dry period occurred about after 4kaB.P. Although the above results are in agreement with other results in general sense, this study also shows somewhat difference in the detailed paleoclimate signals extracted from molecular fossils. The discrepancy might be resulted from the changed biogeochemical impact on different lipid fractions, the varied organism populations in different ecosystems as well as various reflects on climatic factors such as temperature and humidity. The results reveal that lipid molecular fossils have more sensitivity compared with total organic carbon content in recording the detailed climatic information.

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