柴达木盆地克鲁克湖全新世气候变化的正构烷烃分子记录

PLANT WAX n-ALKANES RECORD OF THE HOLOCENE PALEOCLIMATIC CHANGES FROM A CORE SEDIMENT OF HURLEG LAKE IN THE QAIDAM BASIN

对位于青藏高原北部柴达木盆地内的克鲁克湖钻孔沉积物中的正构烷烃进行了详细定量分析。根据正构烷烃P_(aq)指数和叶蜡烷烃平均链长(ACL_(27～33))等参数的变化特征,探讨了湖区过去12kaB.P.以来的古气候变化特征。结果表明:该区域在9kaB.P.之前的早全新世气候干旱,9～6kaB.P.是整个全新世相对最湿的阶段,6kaB.P.之后气候又逐渐趋向于干旱,但干旱程度要弱于早全新世。这一全新世气候变化样式与受西风影响的亚洲内陆干旱区全新世以来的气候变化样式基本一致,但与同一钻孔沉积物中CaCO_3含量和孢粉A/C值所重建的古气候变化过程存在一定差别。这种差别主要体现在6kaB.P.以后的重建结果。我们推测,6kaB.P.后,禾本科植物在湖盆周围植被中的比例显著增加可能是导致上述差别的一个重要原因。本工作表明,在古环境重建中,采用多指标相,互相验证,互相补充,会有利于获得更准确、更详细的古植被及古气候变化历史。

Plant wax-derived n-alkanes have been successfully applied to paleoenvironmental studies. However researches on the comparison between n-alkanes and pollen assemblage, a powerful tool for reconstructing the regional paleoecological history, are scarce, despite the fact that significant information could be obtained by such comparisons. In this study,plant wax-derived n-alkanes were extracted from a sediment core at Hurleg Lake in the Qaidam Basin, North West China and analyzed for paleoclimatic reconstructions in the lake region, n-alkane parameters of the average chain length （ ACL27-33 ） and the Paq index were used to infer the regional effective moisture and the lake-level status,respectively. The data indicate a dry condition during the early Holocene（prior to 9kaB. P. ）, a wet condition during the interval of 9 -6kaB. P., and a slightly drying trend but a still wet condition after 6kaB. P. This pattern is generally consistent with that of climate changes in the Asian interior influenced by the westerlies. However there are some discrepancies between the n-alkane record and data of the pollen assemblage and carbonate concentration. We infer that the discrepancies might result from a great increase of Poaceae plants in the lake basin because these discrepancies mainly occurred after 6kaB. P. The present study demonstrates the validity of application of plant wax n-alkanes to paleoenvironmental reconstructions and highlights the importance of multiproxy interpretations in paleoclimatic researches.