In Holocene The Shennongjia High Resolution Stalagmite Climate Records

The high-resolution palaeoclimate records of cave secondary carbonate have been broadly used to explore the detail structures of the paiaeoclimatic millennial oscillations and then to interpret the driving mechanism for the decadal or centennial climate variability. One stalagmite (named QT9) collected from Qingtian Cave, Shennongjia, Hubei Province with a total length of 199mm is confirmed developing during the Holocene Megathermal Maximum, between 6700 to 6100a BP, by ²³⁰Th dates and counting data of annual layer-thickness. During its formation, the circumstance conditions of the cave were relatively stable and the annual layers were continuously developing with the average thickness of 304μm, so we can perform high-resolution measurements for it by multi-proxies such as the grey level, annual layers' thickness and the stable isotope composition, etc.This thesis discusses some basic problems related to those proxies with modem climatic conditions in situ and which climate those proxies reflected. The analyses methods include three aspects as following. Firstly, we observed and imaged the profile sections of QT9 stalagmite by the microscope, BX51 system of OLYMPUS Company and then surveyed the laminar thickness with image manipulation software. Secondly, we scanned the profile polished by HP Scanner and then surveyed the gray grade with ENVI software. Here, author matched the grey data with the annual thickness data according to depth, and calculated the total grey value in every annual layer. Thirdly, for oxygen and carbon stable isotope ratio determinations, a total of 186 powder samples were taken using a hand-held dental drill. Samples were analyzed with an on-line, automated, measuring system connected to Finnigan MAT253 ratio mass spectrometer.Author statistically checked out the correlation between annual layer thickness curve and annual total grey grade (ATG for short) curve and then found that the both proxies exist positive correlation (n=582,r=0.49 in annual scale and r=0.77 after 7 point running average). Besides, Schulz's red noise spectrum analysis shows that the two proxies have the same cycles. From the above author draws a conclusion that both the layer thickness and ATG probably reflect the same climatic factor. ExotericaJly the annual thickness indicates the accumulation rate of cave secondary carbonate and has the positive relations with precipitation, so they are both used as precipitation proxy. In fact, ATG indicates annual TOC output of soil above the cave, while it is conformed to microbe activity, which is more depended on precipitation than temperature. So it is rational that ATG could be regarded as another proxy of precipitation.In Shennongjia Range region, the δ¹⁸O values of modern precipitation don't obviously reflect well-defined isotope "effect" such as precipitation amount effect or temperature effect. The δ¹⁸O profile of QT9 is positively correlated with that of GISP2 during the period from 6700a BP to 6100a BP, demonstrating that our δ¹⁸O curve of stalagmite probably indicates the palaeo-temperature fluctuate. As the previous studies, the δ¹⁸C values can reflect vegetation types classified by photosynthesis. According to the δ¹⁸C curve of QT9, the vegetation coverage expanded to higher altitude range after 6330a BP, which indicated that the climate became warmer and wetter. The Dajiuhu Lake in the southwest of Shennongjia, is a 23km distance from Qingtian Cave, and has well-developed sediments since the last glacial maximum. The pollen paiaeoclimatic records of lake drilling supported the conclusion about the vegetation 's alteration.Wavelet analysis is a widely used tool in climatic research. In this paper author used the 'Morlet' wavelet transform to perform statistic analysis for the proxies. The result shows that it is...