Climate And Environment Change In The Past 1500a At Baishuitai , Yunnan

The information of climatic and environmental change in the past 2000a is very important in international programs such as PAGES , WCRP and CLIVA .The programes require higher time resolution so as to find out how climate and environment change ,revealing the regulation of the climate evolution , the direction of the future climate change could be forecast This thesis reviewed the achievements of paleoenvironment reconstruction obtained carbon and oxygen stable isotopes, and raised the problems existing within this field. On the basis of former research, The meanings of oxygen-carbon isotope and organic carbon climate proxy indexes in Southwest China were discussed . Travertine or tufa has its own advantage in the reconstruction of paleoclimatic change: 1) it has higher deposition rate up to 1～20mm per year.which increase the resolution to be seasonal and annual; 2) The information of paleoclimate recorded by carbon and oxygen isotopes in travertine reflects the changes of related environment of the earth's surface ,whereas cave stalagmite reflects the average information of local area. The deposition rate of travertine reachs 1 ～20mm per year ,consisting of abundant micro-banding layers ,The thickness and the width of the micro-banding of single band are enough for analyzing stable isotopes and trace elements so that we can achieve the higher resolution of season or month in paleoclimate reconstruction with travertine . We used a travertine sample in 7cm thickness from Baishuitai,Yunnan Province,SW China to get isotope data of carbon and oxygen, from which discovered a periodic change of δ18O was found ,moreover points of low δ18O value in travertine are in khaki color and loose stratum, moreover high δ18O points in travertine are in gray compact layer. The khaki and loose layer was deposited in summer and the gray compact layer in winter time . So, the past between two adjacent high δ18O represent a complete annual layer. The time sequence of high resolution paleoclimatic change since the 1500a B.P. has been reconstructed by the high precision TIMS-U series datings and the analysis of carbon and oxygen isotopes of the travertine deposites at Baishuitai. It revealed that the paleoclimatic changes since 1500 a B.P. at Baishuitai can be divided into four climate periods approximately: 1)in the first period from 1570aBP to 1052aBP, temperature decreased quickly followed by sudden temperature rising 2)from 1052aBP to the time of first clay layer formation , it is the second climate period, when temperature decreased again but slowly. 3)in the third period from the first clay layer formation to the second clay layer formation , temperature increased slowly 4)in the forth period, from the second clay layer formation to 400a BP, it seemed something happened to reduce CO2 release from deep earth, which made carbon isotope be much lighter(>4‰).