可可西里古湖泊沉积物有机碳δ^(13)C变化特征及其影响因素

Variation Characteristics and Influencing Factors of Organic Carbon Isotope from Palaeolake Sediments in Hoh Xil Area

文章选择青藏高原腹地可可西里边缘地区古湖泊为研究对象,通过对湖泊沉积物有机碳、氮和粒度等分析,对中更新世以来BDQ06孔湖泊沉积物有机碳同位素的波动特征及其影响因素进行了分析。结果表明:湖泊沉积物有机质以湖泊自生植物为主,有机碳同位素的大小主要指示挺水植物与沉水植物的比例,进而指示湖泊水体大小的变化。沉积物C/N值较低时;碳同位素偏重阶段,湖泊沉积物以沉水植物为主,植物主要利用水中溶解的CO2进行光合作用,因此有机碳同位素偏正,指示湖泊水体较大,环境条件较好;碳同位素偏负阶段,湖泊沉积物以挺水植物和浮游生物为主,植物主要利用大气中CO2作为碳源,类似于C3植物,碳同位素偏轻,指示湖泊水体较小,气候偏干。其中在岩芯的部分层位有机碳δ13C曲线出现几个明显偏低的位置,对应的C/N>10,说明此时段有大量陆源高等植物进入湖泊,并不是由挺水植物和浮游植物所造成的。

A multiproxy record,including grain size,organic carbon and nitrogen,and the stable isotope compositions of organic carbon（ δ13C） obtained from Core BDQ06 in the marginal Hoh Xil area,Tibet Plateau,provided evidence for climate change since mid-Pleistocene. The influencing factors and variation characteristics of organic carbon isotope were reviewed. The organic carbon content is controlled by autophyte from lake. The variation of organic carbon isotope is mainly related to the ratio of emergent plant to submerged plant,indicating fluctuation of lake level.Variations of the δ13C can be used to estimate various sources of organic matter in the aquatic environment. The higherδ13C values and lower C / N ratios show the dominance of the submerged plant in the lake,and may reflect higher lake level and more moderate climate. The lower δ13C values is attributed to contributor of emergent aquatic plant and planktont,which used atmospheric CO2 for photosynthesis,indicating lower lake level and drier climate. Additionally,in certain phases,lower δ13C values corresponding to the C / N ratios of more than 10 may be related to the input of terrestrial higher plant.