【作者】 夏忠欢；

【导师】 徐柏青； 易朝路；

【作者基本信息】 中国科学院研究生院（青藏高原研究所） ， 自然地理学， 2008， 博士

【摘要】 本文分别在青藏高原南部的大枪勇错、空姆错,中部的纳木错以及东北部的克鲁克湖和小柴达木湖钻取了浅岩芯,通过对沉积物中正构烷烃的提取分析和单体氢同位素比值的测定来探讨该类生物标志物单体δD值的气候指示意义。通过将青藏高原南北断面湖泊表层沉积物中陆源正构烷烃(n-C25、n-C27、n-C29、n-C31)的δD值与当地生长季节大气降水的δD值进行比较,发现两者有很好的相关性,说明陆源沉积正构烷烃主要记录了生长季节降水的同位素信号。正构烷烃n-C25、n-C27与大气降水间氢同位素表观分馏在-45‰至-70‰之间,平均分馏值是-57‰;正构烷烃n-C29、n-C31与大气降水间氢同位素表观分馏在-70‰至-95‰之间,平均分馏值是-82‰。这四种陆源生物标志物与降水间的氢同位素表观分馏沿断面都稳定。通过对比欧洲南北断面的-130‰表观分馏值,可以看出青藏高原南北断面陆源沉积正构烷烃与大气降水间的表观氢同位素分馏小很多。通过将青藏高原南北断面湖泊表层沉积物中水生生物来源的正构烷烃(n-C17、n-C19、n-C21、n-C23)的δD值与当地湖水的δD值进行比较,发现两者不具有相关性,说明沉积物中水生生物来源的正构烷烃没有记录源水的同位素信号。藻类来源的正构烷烃n-C17、n-C19与湖水间的氢同位素分馏在-30‰至-170‰之间,沉水/浮游植物来源的正构烷烃n-C21、n-C23与湖水间的氢同位素分馏在-40‰至-160‰之间,沿断面分馏均不稳定。通过对比欧洲南北断面稳定的-157‰分馏值,可以看出不同地区源水与沉积物中水生生物来源的正构烷烃间的氢同位素分馏可能不一定稳定在-157‰。通过将青藏高原南部空姆错的时间跨度约50年、7年间隔的岩芯剖面中陆源正构烷烃(n-C25、n-C27、n-C29、n-C31)的δD值与当地浪卡子气象站和拉萨气象站的气候要素进行比较,发现这些生物标志物单体的δD值与年平均气温相关,与生长季节平均气温显著相关,说明陆源沉积正构烷烃单体δD值主要记录了生长季节的气温信号,具有作为古温度代用指标的潜力。更多还原

【Abstract】 To explore the climatic implication of compound-specific hydrogen isotope ratios of sedimentary n-alkanes, the author sampled shallow sediment cores respectively from the climatically and environmentally distinct basins Qiangyong Glacier Lake,Kongmu Co Lake,Nam Co Lake, Keluke Lake and Xiao Qaidam Lake along a S-N transect on the Tibetan Plateau for the extraction and analysis of these biomarkers.δD values of terrigenous n-alkanes (n-C25, n-C27, n-C29 and n-C31) extracted from recent lake surface sediments from the five lakes along the S-N transect are compared to that of precipitation spanning a wide range from -167‰to -51‰and clearly correlate withδD values of meteoric water during the growth, indicating that terrigenous n-alkanes record the precipitation signal during the growth. The fractionation between precipitation and alkanes of n-C25 and n-C27 cover a range from -45‰to -70‰whilst that between precipitation and alkanes of n-C29 and n-C31 vary from -70‰to -95‰, both being fairly constant along the S–N Tibetan transect with the mean at -57‰and -82‰, respectively. By comparison with the fractionation of -130‰along the S–N European transect, it implies that the hydrogen isotopic fractionation between meteoric water and terrestrial n-alkanes along the Tibetan transect represent distinct character.δD values of aquatic derived n-alkanes (n-C17, n-C19, n-C21 and n-C23) extracted from recent lake surface sediments from the five lakes along the S-N transect are compared to that of lake water spanning a wide range from -135‰to -22‰and the results show that these biomarkers do not record lake water signal. The fractionation between lake water and algae derived alkanes of n-C17 and n-C19 cover a range from -30‰to -170‰whereas that between lake water and submerged/floating plants derived alkanes of n-C21 and n-C23 varies from -40‰to -160‰, both covering a wide range along the S–N Tibetan transect with the mean at -94‰and -93‰, respectively. By comparison with the constant fractionation of -157‰along the S–N European transect, it implies that the hydrogen isotope fractionation between source water and sedimentary aquatic n-alkanes may not be necessarily constant at -157‰in different regions.δD values of terrigenous n-alkanes (n-C25, n-C27, n-C29 and n-C31) extracted from a short sediment profile spanning the past near-50 years at 7-year resolution from Kongmu Co Lake on the southern Tibetan Plateau are compared to the climate elements of Langkazi and Lhasa weather stations and clearly correlate with mean annual air temperature and significantly correlate with mean growing season air temperature, indicating that these biomarkers record the air temperature signal during the growth and have the potential to be used as a paleotemperature proxy.更多还原