小冰期新疆楼兰地区绿洲生态环境变迁事件

Environmental change of the ancient oasis in Loulan, Xinjiang during the Little Ice Age

干旱区绿洲水分主要来自河流补给,而河流水源主要是冰雪融水或山地降水。本研究通过对楼兰地区古绿洲植物残体AMS 14C年代学测试并结合前人研究成果,分析楼兰地区古绿洲生态环境恶化时间并探讨其原因。结果显示楼兰地区小冰期前(1460AD之前)发育了最近一期古绿洲,进入小冰期后生态环境恶化并导致绿洲消亡。楼兰地区生态环境恶化与前人的研究结论亚洲中部小冰期相对湿润的大环境"相悖"。结合流域古河道变迁地层和历史文献记录分析表明,楼兰地区小冰期期间生态环境恶化主要是古塔里木河迁移、改道造成的。虽然小冰期流域获得较多的水分补给,但是河流迁移、改道导致楼兰地区水分补给显著减少,生态环境恶化,绿洲最终消亡。这不同于前人研究显示的楼兰文明发展后期绿洲生态环境恶化是由于河流补给显著减少造成的。因此,干旱区局地生态环境变迁不一定是区域气候变化直接造成的。

The oasis water source in the arid area mainly comes from river recharge,while the river water source mainly comes from snow and ice melt or mountain precipitation.Based on the AMS 14C chronology test of ancient oasis plant residues in Loulan area and the previous research results,we analyzed the deterioration time of the ancient oasis ecological environment in Loulan area and discussed its causes.The results show that the last period of the ancient oasis was developed before the Little Ice Age in Loulan area(before 1460 AD).After entering the Little Ice Age,the ecological environment of the oasis deteriorated and died.The cold and humid environment in the Little Ice Age in central Asia is incompatible with the dry ecological environment in Loulan.Combined with the stratigraphic and historical documents of the paleochannel changes in the basin,it indicates that environmental change of the ancient oasis in Loulan area during the Little Ice Age was mainly caused by the migration and diversion of the Tarim River.Although the basin received more water supply during the Little Ice Age,the river migration and diversion caused a significant reduction in water supply in the Loulan area,and the ecological environment deteriorated,and the oasis eventually disappeared.This is different from the previous study that the deterioration of the oasis environment in the late stage of Loulan civilization was caused by a significant reduction in river recharge.In addition,the demise of the oasis in the Loulan area suggests that climate change was not necessarily the direct cause of the local ecological environment changes in the arid region.