CLIMATIC CHANGE IN THE NORTHEAST QINGHAI-TIBET PLATEAU DURING THE LATE GLACIAL/HOLOCENE TRANSITION
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摘要: 我国最大的内陆封闭湖泊青海湖的沉积岩芯为研究末次冰期/全新世过渡期间青藏高原东北部的环境变化和季风降水演变提供了连续高分辨率环境档案。对两孔岩芯的多学科研究结果表明:大约14000～11600aB.P.期间气候干冷,湖泊的自生碳酸盐和有机质生产率远低于全新世;季节性入湖径流量在11600aB.P.突然增大;从10700aB.P.起,夏季蒸发量突然增大,干旱化作用导致碳酸盐滩湖环境;区域降水量在10000aB.P.的增大结束了滩湖环境,标志了早全新世温暖较湿气候的开始。全新世早期的青海湖水深比现在要浅20m左右,表明那时的有效湿度显然比现在要低很多。14000～10000aB.P.期间青海湖水深不超过6m,说明在末次冰消期的这一时段中,青藏高原东北部没有形成大规模冰融水。在10700～10000aB.P.期间突发的干旱事件与西欧的新仙女木事件(YoungerDryas)年代相当,但没有气候变冷的证据。青藏高原东北部末次冰消期的气候变化表现了明显的阶段性特征和有效湿度的突然改变。区域季风降水量和夏季温度的变化决定了该过渡期的这种变化格局。Abstract: Sediment cores from Lake Qinghai, the largest closed inland lake in China, can provide continuous environmental records with a higher resolution for studying climatic change in the northeast Qinghai-Tibet Plateau during the late glacial/Holocene transition. Two of such sediment cores were studied in a multidisciplinary way. The climate there was cold and dry in about 14000～11600 a B.P. ( 14C dating), resulting in a shallow lake with carbonate and organic productivity much lower than those in Holocene. Seasonal catchment inflow abruptly increased in 11600 a B.P. A sudden enhancement of summer evaporation in 10700 a B.P. led to a negative P-E balance and eventually the formation of carbonate playa lakes. The termination of the playa lake environment in 10000 a B.P. marked the abrupt onset of a warm and relatively wet climate regime of Holocene. The effective moisture was much lower during early Holocene than today, which is supported by the reconstructed depth of lake water being some 20 m shallower than that today. The water depth of the paleo-lake was about 6 m in 14000～10000 a B.P. Therefore it is concluded that there has been no large meltwater inflow into Lake Qinghai since at least 14000 a B.P. The arid event in 10700～10000 a B.P. was coeval with the European Younger Dryas, but there is no evidence to indicate cooling. All of these suggest a step-wise climatic pattern with three abrupt shifts during the late glacial/Holocene transition. It is the change of summer temperature and monsoon precipitation that determined this climatic pattern in the northeast Tibet-Qinghai Plateau.
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Key words:
- Tibet-Qinghai Plateau /
- Lake Qinghai /
- paleoclimate /
- Younger Dryas
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