云南寻甸中全新世降温事件的石笋同位素记录

通过对寻甸仙人洞X1石笋进行高精度的TIMS-U系测年和碳、氧同位素分析,建立了寻甸地区8000aB.P.以来高分辨率的古气候变化时间序列。研究结果表明,寻甸地区8000aB.P.以来石笋记录的古气候环境变化,大致可分为3个气候期:中全新世8000—5560aB.P.为气候适宜期,显示印度季风由强盛逐渐减弱的趋势,气候温暖湿润期,与太阳辐射增强引起的北半球季风环流加强有关;中全新世中晚期5560—4400aB.P.为季风转变期,显示印度季风减弱并快速退出、萎缩,东亚冬季风加强并快速推进,太阳辐射强度减弱,气候为干冷期;中全新世晚期4400—2000aB.P.,显示东亚冬季风逐渐减弱,东亚夏季风有所增加,气温有所回升,但气候变化的波动大。研究还表明,全新世以来石笋记录的气候变化非常不稳定,在千年尺度上表现为台阶状,在短尺度———百年尺度上呈锯齿状波动。石笋记录的突发性气候波动事件,与冰芯记录极为相似,反映低纬度地区石笋记录的季风气候与高纬度及北极地区的气候具有极好的相关性,这对于认识现代气候系统变化以及对未来十年、百年尺度的气候预测具有重要的科学意义。

COOLING EVENTS IN ISOTOPE RECORDS FROM A STALAGMITE DURING THE MIDDLE HOLOCENE IN XUNDIAN AREA, YUNNAN

The time sequence of paleo-climatic change in the Xunding region since 8 000 a B. P. has been reconstructed by TIMS-U series dates and the analysis of oxygen isotopes from a stalagmite in the Xianren Cave in Xunding, Yunnan. Our research results have shown that the paleoclimatic environment change from a stalagmite record in the Xunding area since 8 000 a B.P. can be divided three stages of climate change: (1) The Middle Holocene Epoch-climate optimum time from 8 000 a B.P. to 5 560 a B.P. showed a trend of India summer monsoon from strong to weak gradually, and presents a warm and humid climate environment. It is related to the strengthen of monsoon circumfluence in Northern Hemisphere aroused by the intensification of the solar radiation. (2) The middle stage of the Middle Holocene Epoch from 5 560 a B.P. to 4 400 a B.P. is an abrupt change stage of climate cold events or altering period of monsoon. The period showed that the India summer monsoon became weak and quitted rapidly or declined, the East-Asian winter monsoon became strong and moved forward rapidly, the strength of solar radiation became weak, the air temperature dropped down and the climate indicated a dry and cold period. (3) The late stage of the Middle Holocene Epoch from 4 400 a B.P. to 2 000 aB.P. showed that the East- Asian winter monsoon became weak and summer monsoon became strong, the air temperature rose slowly. There is a big vibration of climate change. Our studies indicated that the climate change from X1 stalagmite record since the Holocene is relatively unstable, representing a sidestep shape on a thousand years scale and a sawtooth shape on a short time scale-the centenary time scale. The abrupt climate change events on a centenary and thousand years scale from X1 stalagmite records similar to the ice core records, indicated that the monsoon climate from stalagmite records in the low-latitude region is in good agreement with the climate records in the high-latitude region and the arctic pole. It is of important scientific significance in understanding the change of the modern climate system, for climate forecasting on a decade-centenary time scale, discussing the change of climate environment in the Holocene and the rise and fall of human civilization and evolution history.