为探究青藏高原全新世夏季风最强、气候最湿润阶段这一争论议题,本文应用气相色谱仪(GC-FID)和气相色谱-高温热转变-同位素比值质谱仪(GC-TC-IRMS), 分析了兹格塘错沉积岩心正构烷烃及其氢同位素特征。结果表明,兹格塘错岩心中主要以n-C_(15 /16 /17)为主峰碳的短链正构烷烃占据主导地位,指示了湖泊自生浮游藻类与菌类等低等生物对湖泊沉积岩心中的有机质贡献高于大型水生植物和陆生高等植物表皮蜡质所产生的有机质。基于正构烷烃参数(如:碳优势指数CPI值和平均碳链长度ACL值)及单体氢同位素比值在时间序列上的变化特征,指出兹格塘错流域的气候湿润期处于中全新世(5.8 ~ 2.7 cal ka BP), 明显滞后于早全新世的太阳辐射最强期,这主要归结于该流域冰川融水补给的匮乏及局地环流的影响。
英文摘要:
In order to discuss which period was the strongest summer monsoon and the wetter conditions observed during the Holocene on the Tibetan Plateau,n-Alkanes and compound-specific hydrogen isotopes in sediments of Lake Zigetang Co were analyzed using gas chromatography(GC-FID) and gas chromatography-thermal conversion-isotope ratio mass spectrometry(GC-TC-IRMS). The results indicated that short chain n-alkanes C_(15),C_(16) and C_(17),which probably derived from aquatic algae,plankton and photosynthetic bacteria,dominated the n-alkane composition in lacustrine sediments of Lake Zigetang Co. The variation of n-alkane indicator ratios(e. g. ACL and CPI values) and deltaD values revealed that higher effective moisture availability at Lake Zigetang Co occurred in the middle Holocene(5.8 - 2.7 cal ka BP) that much later after the insolation maximum. This might be attributed to the absence of glacial meltwaters and local recycling of air masses in the catchment of Lake Zigetang Co.