Preliminary Reconstruction of the Temperature Curve of the Last Major Climatic Cycle in North China
Sun Jianzhong (Xian Geology College)
Vegetation is a very sensitive climatic indicator, and the curve of xylophyta pollen content can basically give an analog simulation of the paleo-temperature curve. By using other different climatic indicators for temperature values of every crest and trough of the pollen curve, we reconstruct the paleo-temperature curve. In recent years, large amount of materials have been accumulated in this region, such as permafrost,, periglacial structures (involutions, ice wedges), periglacial flora (pollen-spore complex of dark coniferous forest and birch forest), periglacial fauna (Mammuthus-Coelodonta fauna) and C14 and U-series datings, making us possible to reconstruct the temperature curve of the Last major climatic cycle in this region. The south boundary of the distribution of the Mammuthus fossils had reached down to Kaifeng, Henan Province. Mammuthus is one of the indicators of permafrost, so the mean temperature of Kaifeng in last glacial stage should be 0 ℃ or lower. Whereas at present, the mean temperature there is 13 C. It means that, the lowest temperature of the glacial stage was at least 13 C lower than that at present, the coldest period 23,000-13,000 y. B. P. in the last glacial stage. During 32, 000-23, 000 y. B. P. dark coniferous forest went down from high mo-untains to the low plains in large-scale with temperature 6 - 8 ℃ lower than that at present. During 36,000-32,000 y. B. P. temperature dropped down for a short duration. In the period of 53,000-36,000 y. B. P., birch forest developed in the Northeast, temperature went up a little, but still 4℃ lower than that at present. The periods of 32,000-23,000 and 53,000 -36,000 y. B. P. were two relatively warm and humid periods in the last glacial stage (70,000 - 12,000 y. B. P. ) During 70,000-53,000 y. B. P.. desert and steppe developed, it was very cold but better than the period of 23,000-13.000 y. R P., 10℃ lower than that at present. The period of 88,000-114,000 y. B. P. was the period of Xujiayao man, and the temperature was 4 ℃ lower than that at present with fluctuation, a transitional period from last interglacial to last glacial stage. In this way, we reconstructed the temperature curve of the last major climatic cycle, similar to the oxygen isotopic curves of the ocean deposits. But some links are still missing, awaiting supplementary material. Accompanying the change of climate, transgressions and regressions took place at the Yellow Sea region. Transgressions happened in the relative warmer periglacial inter-stages, whereas regressions happened in the colder periglacial stages.