西藏纳木错末次盛冰期以来的古植被、古气候和湖面变化

Paleovegetation,paleoclimate and lake-level change since the last glacial maximum in Nam Co ,Tibet

西藏纳木错湖相沉积的U系、14C年龄和孢粉分析结果表明,纳木错沿岸的拔湖约1.5～8.3m和8.3～15.6m的T1和T2分别形成于末次盛冰期以来约(11.81±0.10)～(4.22±0.09)kaB.P.期间和(28.2±2.8)kaB.P.左右。该套湖相层的孢粉组合、地层和湖岸堤的分布表明,在末次盛冰期期间,纳木错湖面主要波动于拔湖12～20m之间,但湖面最低可达拔湖约8m。区域植被主要为以蒿和莎草科为主、含松和桦的草原。在约11.8～4.2kaB.P.期间,湖面波动于拔湖2～9m之间,区域气候整体较为暖湿。其中全新世大暖期出现在约8.4～4.2kaB.P.期间,气候温暖湿润,区域出现针叶林或针阔叶混交林,气温可能比现今高约5℃,降水量可能比现今多100～200mm,湖面扩张并升高,最高可达拔湖约10m。

Nam Co is the biggest and highest(4718m a.s.l.)lake in the central Tibetan Plateau.The U-series and 14 C dating and sporopollen analysis of lacustrine deposits in Nam Co ,Tibet,indicate that ter-races T 1 and T 2 distributed at1.5～8.3m and8.3～15.6m above lake level around Nam Co respectively were formed at11.81±0.10～4.22±0.09ka BP and28.2±2.8ka BP respectively since the last glacial maxi-mum.The sporopollen assemblage,strata and lake levee distribution indicate that during the last glacial maximum the lake level of Nam Co mainly fluctuated between12and20m above lake level but that the lowest lake level may have reached～8m above lake level.Regional vegetation was grassland containing dominantly Artemisia and Cyperaceae with minor pinus and betula.During the period from11.8to4.2ka BP,the lake level fluctuated from2to9m above lake level.The climate was generally warm and wet.The Holocene Megathermal took place about 8.4～4.2ka BP.Then in the area coniferous and deciduous broad-leaf mixed forest occurred and the climate was much warmer and wetter,with the temperatures be-ing～5℃higher and the precipitation being100～200mm more than the present ,and the lake volume increased and the lake level rose and might reach a maximum of ～10m above lake level.