云南宣威4.6万年以来洞穴石笋古气候变化记录

石笋是高分辨地记录古气候环境变化的主要信息载体之一。本文通过对宣威下水龙洞 1号石笋进行α能谱铀系测年及碳、氧同位素分析,获得了距今 46.1ka至 2.75ka高分辨率的古气候演变信息。其年龄与δ18O值的记录在纵向上的变化具有明显的韵律性特征,可与深海岩芯V2 8～ 2 3 8同位素记录所揭示的第 3阶段、2阶段和 1阶段进行对比。反映 46.1ka以来宣威地区的气候波动与全球的气候变化具有明显的一致性。但是,区内是气候变化的敏感区,是东亚季风与印度洋季风交互作用的特殊区域,存在有明显的地区性气候变化特征,在整个末次冰期时段 (4 6.1～8.1ka)气候总体偏温暖,10.2 5ka为新仙女木冷事件的最冷终止点。在全新世大暖期时段的 7.1～ 3.7ka间显示气候温暖湿润,而在 3.7～ 2.75ka间伴随太阳辐射和印度洋西南季风强度的减弱,气候有明显的降温趋势。此外,石笋的碳、氧同位素显示的气候冷暖变化是,主沉积旋回以万年级、千年级和百年级为周期性变化;亚旋回以千年级和百年级为周期性变化。

The Record of Climatic Change from Stalagmite in Xiashuilong Cave of Xuanwei City Since 46ka

Stalagmites in karst caves are the main carrier of paleoclimatic and paleoenvironmental records with the high resolution.The high resolution information on paleoclimatic change from 46.1ka B.P. to 2.75ka B.P. has been obtained through α-counting U-series dating and carbon and oxygen isotopic analysis of No.1 stalagmite in Xiashuilong cave of Xuanwei city. The record of its ages and δ 18 O value in the change of the vertical section have obvious rhythm characteristics and can be compared with the oxygen isotopic records of deep-sea cores at Ⅲ,ⅡandⅠ stages. It reflects that the climatic changes in Xuanwei area coincides with the fluctuation of global paleoclimatic change.But here is the sensitive area of the climatic change and also the specific region of the reciprocity between East Asian monsoon and Southwest monsoon,and the feature of the climatic change caused by them was obvious in this region.The overall last glaciation from 46.1ka B.P. to 8.1 ka B.P. show warm climate trend in the mass,and 10.25 ka B.P. is the coldest of the end point of Younger Dryas event.The Holocene Megathermal period during 7.1 ka B.P. and 3.7 ka B.P. are the climate of temperate (warm)-wet.The climate during 3.7 ka B.P. and 2.75 ka B.P. has obvious trend of decreasing temperature to follow the weakness of the sun radiation and the Southwest monsoon intension.Furthermore,the cold and warm change of the climate indicate that the main sediment cycles in stalagmite take the periodicity change as ten thousand years, thousand years and hundred years, and sub-cycles in stalagmite show the periodicity change as thousand years and hundred years.