新疆罗北洼地湖相沉积物有机碳同位素的变化序列及其古环境意义  

STABLE CARBON ISOTOPE RECORD OF ORGANIC MATTER FROM THE LOP-NUR LACUSTRINE SEDIMENT IN XINJIANG,NORTHWEST CHINA

作　　者：罗超[1] 刘卫国[2] 彭子成[1] 杨东[3] 贺剑峰[1] 刘桂建[1] 张彭熹[4] 

机构地区：[1]中国科学技术大学地球和空间科学学院,合肥230026 [2]中国科学院地球环境研究所黄土与第四纪国家重点实验室,西安710075 [3]西北师范大学地理与环境科学学院,兰州730070 [4]中国科学院青海盐湖研究所二部,西安710043

出　　处：《第四纪研究》2008年第4期621-628,共8页Quaternary Sciences

基　　金：国家重点基础研究发展规划项目(批准号:2004CB720208);国家自然科学基金项目(批准号:40473006和40599424);高校博士学科点基金项目(批准号:20050358006)资助

摘　　要：测定了新疆罗布泊地区湖相沉积物CK-2钻孔样品的总有机碳含量(TOC)及其同位素组成、碳酸盐含量和C/N比值等环境代用指标,以及石膏矿物的质谱-铀系年龄。测试结果表明,20~9kaB.P.期间沉积物δ13Corg.在-23.4‰^-16.1‰之间波动且阶段性明显,与TOC呈现良好的相关关系,整体变化趋势同南极Dome C冰芯中记录的全球大气CO2浓度一致;C/N比值表明有机碳来源主要是陆生高等植物。因此大气CO2浓度变化是影响20~9kaB.P.期间罗布泊湖相沉积物δ13Corg.值变化的主导因素,周围山体上C3/C4植物相对生物量的变化则是另一重要因素。依据δ13Corg.的变化序列将此时间段湖区古环境的演化分成6个阶段:20.0~14.1kaB.P.期间受到末次盛冰期的影响,气温偏低,湖水丰沛;14.1~13.3kaB.P.是一个气候不稳定期,冷暖波动较频繁,但以暖为趋势;13.3~12.8kaB.P.期间经历了一段冷期,于12.8kaB.P.结束了末次冰期,随后气候开始转暖至11.8kaB.P.;其后气温再次变冷并维持到10kaB.P.;最后从10kaB.P.进入全新世暖期。δ13Corg.序列明显向偏负方向变化,表明该地区变暖的趋势相当明显。罗布泊地区日益干旱化是全球气候变化的结果,尤其是受到全球CO2浓度的不断升高所制约。A δ13 record of the organic matter （δ13Corg） in lacustrine sediment of CK-2 core, deposited during 20 ~ 9kaB. P., taken from the Luobei depression （40°47′N,91°03′E） , Lop-Nur Lake, Xinjiang, NW China is presented in this paper. The chronology is provided by the uranium/thorium disequilibrium dates. The results show that the δ13Corg. values varies from -23.4‰ to -16. 1‰ and have obvious correlation with the contents of organic matter. The C/N values indicate that the contents of organic matter in the sediment are mainly controlled by plants in the mountains around the district. The general synchronization between the δ13Corg. in the CK-2 core and the atmospheric CO2 concentration suggests that the change of the latter was the control factor to the variation of δ13Corg. values, but not the only one. It is generally accepted that the carbon isotope composition of plant material is correlated with C3/C4 pathways of carbon fixation in photosynthesis. Climate change influenced the ratios of C3 and C4 plants, which can be reflected in δ13Corg. variation in sediments. The balance between C3 and C4 plants depends on temperature and humidity. Results of this study confirm that the lowδ13Corg. values are corresponding to higher mean temperature,which caused a wetter environment on the mountains because of the more thawy snow. The δ13Corg. record of CK-2 core showed six stages during 20 ~ 9kaB. P. ： 1 ）A period of extreme cold, attributed to the last glacial maximum （LGM） , occurred at 20.0 ~ 14. lkaB. P. ; 2） An instable stage between 14. 1 ~ 13.3kaB. P. is suggested by the dramatic variation of all proxies; 3 ） A short cold stage occurred at 13.3 ~ 12.8kaB. P. ; 4） The last glacial ended at 12. 8kaB. P. and the climate became warmer; 5 ） The period of a Younger-Dryas-like cold event between 11.8 ~ 10.0kaB. P. ; 6） The beginning of the Holocene at 10.0kaB. P. Based on comprehensive research, it can be concluded that the extent of arid process was certainly the result of natural m

关 键 词：罗布泊地区 有机碳同位素 古气候 大气CO2浓度 C3 /C4植物 

分 类 号：P532[天文地球—古生物学与地层学] P534.622[天文地球—地质学]