| 其他摘要 | Special attentions have been focused on the stable isotopic climatology because of its well-developed theoretical basis. The isotopic signals in plant cellulose have been addressed to be precision records of the climate changes. In the past 30 years or so, a large number of investigations have been performed to explore the mechanisms in carbon, oxygen and hydrogen isotopic fractionations in plant physiological process, which is particularly important to the global climate study. The study of palaeoclimate brings us unprecedented chances and challenges. Much work needs to be done to explore the climatic rules and to constrain the climatic mechanisms. To study the climate systematically with different timescales and high time-resolutions, the author selected tree rings and peat profiles as climate archives and chose stable isotopic techniques to extract climatic signals from them,, My study illustrates that stable isotopic compositions in plant cellulose are sensitive indicators of regional climate. Integrated high-resolution climatic information has been extracted on annual scales, decade scales, centurial scales, as well as millennial scales, which contributes greatly to recognizing the climate rules and to shedding light on the dynamic mechanisms of the climate system. 1. Climate information inferred from stable isotopic compositions in Pinus Koraiensis tree rings in Antu Area (1) Isotopic compositions in PK {Pinus Koraiensis) tree rings are influenced by many climatic factors synthetically, which results in low correlation coefficients between single isotopic proxy and single climatic factor. In this study, the author designed a new combined climatic factor, named "temperature-relative humidity" factor (TH for short), and got perfect result. Our study reveals that both δ13C and δ18O are well correlated to TH factor from May to August. Climates reconstructed from TH factor are synchronous with those recorded in "Antu chorography)} , suggesting that the new approach is reliable and should be strengthened in the following work. Low cloud information from May to July was significantly recorded in 5 13C in PK tree ring. Correlation analysis between different climatic factors and δ13C indicates that influence of low cloud to δ13C is through an indirect way. Low cloud leaves its footprints by influencing climatic factors such as relative humidity, solar irradiance, which transfer low cloud signals to δ13C directly through the photosynthesis process. Quasi-2-yr, quasi-4-yr and quasi- 10~8-yr periodicities are discovered both in 813C time series and in 5 18O time series. These periodicities are recognized to be the response of Quasi Biennial Oscillations (QBO) of the East Asia summer monsoon, the quasi-4-yr oscillations of ENSO and the quasi-11-yr cycles of solar activities, respectively. (4) The author improves the conventional oxygen, hydrogen isotopic fraotionation models by integrating "exchanging-factor"(fexch) and "evaporating- factor-1 (fevap) (see the text for details). Well performance of the improved model has been verified by comparisons with the conventional models. The improved1 model characterizes by "self-adapting" when simulating, which is expected to be conducive to the simulation of isotopic compositions in precipitation from peat cellulose isotopic compositions. 2. Climates inferred from 8 18O in peat cellulose, Hongyuan (1) General temperature trends of Hongyuan, Jinchuan and Dunde are synchronous, suggesting coherency of temperature variations in China. In general, temperature varies on a low level during 6000-4000 aBP, on a high level during 4000-1500 aBP, and recurs to a relatively low level during 1500-0 aBP. 4000 aBP and 1500 aBP are two striking temperature transitions in the past 6000 years. A series of low temperature events are identified in Hongyuan, which synchronize well with those in North Hemisphere such as Jinchuan, Dunde, Greenland, North Atlantic region, etc. In particular, during each low temperature period, there concur strong social reorganizations, social collapse, or culture decline, which demonstrates that climate changes, especially abrupt changes, can influence social economy and social structure strongly. Strong coherency was discovered between the general temperature trends in Hongyuan., Jinchuan and trend in atmospheric A14C, suggesting that solar activities may be the main driving forcing of temperature variations in China. Power spectrum analysis gives further evidence for the assumption. Significant 88-yr and 123-127-yr periodicities are extracted, indicating a typical centurial-scale temperature variability. 3. Discussion (1) Mean temperature variations in China in the last millennium synchronize well with the classical solar minimum, such as the Darton minimum, the Maunder minimum, the Sporer minimum and the Oort minimum, suggesting a strong linkage between temperature variations and solar variability in the last millennium. During 1050-1250 a AD or so, temperature varied on a relatively high level, corresponding to the Medieval Warm Period. Solar irradiance is also strong during this period of time inferred from atmospheric A14C, 10Be series in ice core, and the simulated Total Solar Irradiance (TSI). Temperatures reconstructed from considerable Chinese tree rings also indicate that there is really no abnormal global warming in China in the last several centuries. These evidences suggest that temperature in China in the last several centuries may not go beyond the natural variability. (2) An ideal model is brought forward related to the thermohaline circulations (THC) and the Australian-Asian summer monsoon. This model can explain the observed phenomena, such as the coherency between Indian summer monsoon and the North Atlantic temperature variability, the opposite long-term precipitation trends between northeast China and southwest China, the "seesaw effect" of temperature variations between North Pacific and North Atlantic, etc. THC has been recognized to play a key role in controlling the long-term trends of dry/humid climate in Indian summer monsoon regions and in East Asia summer monsoon regions. |
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