从腾冲和香格里拉沉积记录看60ka BP以来的印度季风活动特征

The characteristics of the Indian monsoon:Evidences from the sedimentary records of Tengchong and Shangri-La over the past 60 ka

通过腾冲北海与香格里拉纳帕海有机碳含量、δ^13C、粒度等沉积指标和若干孢粉指标的对比,参照60ka BP以来孟加拉湾的沉积韵律互层与δ^18O记录,发现它们同与印度季风系统存在密切关联。然而由于经纬与海陆分布的差异,夏季风和冬季风对各处的影响亦有很大差别。大约发生于37-32ka BP的强大的暖湿型气候事件在北海与纳帕海盆地的沉积序列之中反映突出,成为过去60ka间最引人瞩目的现象,但是却缺乏海域记录的有力呼应。海陆记录对比结果表明,MIS3后期区域气候事件的控制因素来自陆地而非海洋,青藏高原在此期间的特别升温导致印度冬季风的衰退及其他大气环流型式的改变有可能是重大气候事件形成的主因。此外,陆地地貌对于季风的降水效应也有不可忽视的影响。

On the basis of correlating some significant proxies,such as TOC,δ13C,grain-size and pollen data,from the Napahai lake,Shangri-la and the Beihai wetland,Tengchong,and referring the sedimentary rhythm and δ18O record since 60 ka BP from the Bay of Bengal,we found that all of them have been closely affected by the Indian monsoon system.Because of the difference in their latitudinal,longitudinal and sea-land situations,however,the climatic records clearly show a differential affinity to the summer monsoon or to the winter one.The most impressive climatic shock over the past 60 ka was a great thermal and wet event that happened roughly from 37 ka BP to 32 ka BP and was evidently manifested within both the Beihai＇s and the Napahai＇s sedimentary sequences.Discordantly,that event cannot be recognized in the marine records.We deduced from the correlation between the continental deposit and marine deposit that the control of the regional climatic event originated from the land side rather than the sea side during the late MIS3.It is likely that an extreme warming up at that phase at the Tibetan Plateau,which resulted in the decline of the Indian winter monsoon and other changes of the atmospheric circulation,was responsible for the event.The geomorphologic configuration played an important role in the monsoonal precipitation as well.