新疆罗布泊地区近3.2万年沉积物的气候环境记录

CLIMATIC AND ENVIRONMENTAL RECORDS IN THE SEDIMENT OF THE LUOBEI BILLABONG IN LOP-NUR,XINJIANG IN RECENT 32ka

文章对新疆罗布泊地区罗北洼地CK-2钻孔自顶部到10.35m的岩芯,按5cm间隔取样,进行了磁化率、粒度、色度、碳酸盐、有机质含量和pH值的12项环境代用指标的测定,以及相关样品的质谱-铀系法定年,得出了近32000年以来在该地区经历的4个冷湿和暖干变化的气候-环境序列:阶段Ⅰ(31.98～19.26kaB.P.),处于晚韦克萨尔冰期的早期,经历了全球变化的未次盛冰期(23～19kaB.P.),12项环境指标的统计平均值为-0.8773,是本序列的最低值,对应为最强的冷湿期;阶段Ⅱ(19.26～13.53kaB.P.)为继后的间冰期,相应环境指标的统计平均值为+0.5233,环境转为暖干期;阶段Ⅲ(13.53～12.73kaB.P.)为晚韦克萨尔冰期的晚期和得里亚斯冰期,也是全球未次冰期的晚期,其环境指标统计平均值为-0.1075,环境转冷湿;阶段Ⅳ(12.73kaB.P.～近代)为全新世温暖期,其环境指标统计平均值为+1.275,是本序列的最高值,气候转为强暖干期。在阶段Ⅳ,12.08～11.80kaB.P.处出现了新仙女木(YD)的冷事件,10～9kaB.P.为全新世期内最早出现暖事件的时间。从冰期与间冰期的旋回分析,本区的气候-环境变化与全球同步,反映出受到全球变化的主旋律制约。从区域的特征分析,由于受到青藏高原的隆升、西风的加强,而西南和东亚季风的减弱,出现了冷/湿和暖/干的气候-环境变化的大格局,其不同于我国东部季风气候区的冷/干、暖/湿变化的大趋势。从环境代用指标的统计值(从-0.8773到+1.275)表明,本地区的干旱化进程是自然变率的必然结果,到全新世温暖期间更为突出。而近数千年或近数十年的人类活动营力只起到了叠加或促成的作用。

A borehole of 50.14m depth （CK -2） was drilled in the Luobei billabong, which is located at 40°47′N, 91°03′E, in the district of Lop-Nur in Xinjiang Province. The current study was on the sample from the top to 10. 35m of the core. An environmental sequence in Lop-Nur, Xinjiang since 3.2kaB. P. has been reconstructed by using environmental proxies of the susceptibility, particle size, color, carbonate, organic carbon, and pH values of the sediments and mass spectrometry-uranium series dating. The environmental history could be divided into four stages. Stage Ⅰ （31.98 - 19.26kaB. P. ） corresponds to the early of late Weichsel Glacial Period including Last Glacial Maximum （LGM, 23 - 19kaB. P. ）. The statistical average of 12 environmental proxies of this stage is -0. 8773, which is the lowest value in this sequence, indicating the coldest-wettest weather of this area in this stage. Stage Ⅱ （ 19. 26 - 13. 53kaB. P. ） corresponds to an interglacial period. The Statistical average of 12 environmental proxies is ＋ 0. 5233, which shows that the weather became warmer-dryer. Stage Ⅲ （ 13.53 - 12.73kaB. P. ） corresponds to the late of late Weichsel Glacial Period. The statistical average of 12 environmental proxies of this stage is -0. 1075 and the weather became colder-weter again. Stage Ⅳ （ 12.73kaB. P. - present） corresponds to the Holocene warm period. The statistical average of 12 environmental proxies of this stage is ＋ 1. 275, which is the highest value in the sequence. The environmental change of this district is thus highly consistent with global change, suggested by the clear glacial-interglacial cycles, but different from the mutative trend of monsoon region in east China by its own cold-wet and warm-dry characteristics. The statistical values of the 12 proxies provide us the information that the extent of arid process is certainly the result of natural movement instead of human activity. The implementation of the ＂Development of Western Region＂ strategy must take the account of the background of arid environment in this region.