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首页> 外文学位 >Hydrocarbon biomarkers as paleoenvironmental proxies: Recorders of vegetational changes in China during the last glacial to Holocene transition.
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Hydrocarbon biomarkers as paleoenvironmental proxies: Recorders of vegetational changes in China during the last glacial to Holocene transition.

机译：碳氢化合物生物标志物作为古环境的代名词：记录了最后一次冰川到全新世过渡时期中国植被变化的记录。

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It is essential to understand how C4 vs. C3 vegetation changes have responded to the climate variations during the last glacial to the Holocene transition. Despite many previous researches, so far it is still difficult to isolate whether pCO2 or one of the other climate parameters alone is the factor mainly responsible for C 3 vs. C4 vegetation changes during the transition.; I have conducted a detailed delta13C analysis of n-alkanes extracted from lake and loess sediments in China along a broad southeast-northwest transect across the country. Two lakes (Toushe and Tianyang) and two loess deposits (Xunyi and Luochuan) were chosen from the SE and NW end of the transect, respectively. Analysis on one core from Heqing Basin in southwestern monsoon area was also performed. Total lipids were extracted by soxhlet or sonication. n-Alkanes were isolated by silica gel column chromatography, measured for concentrations on a GC and confirmed for structure on a GCMS, and then analyzed for the carbon isotope ratios on a GCIRMS.; During the LGM, the southeast experienced a C4 expansion, presumably due to the increasing aridity and/or lower pCO 2, together with a growing-season temperature still high enough to support C4 plant growth. However to its northwest end, the Chinese Loess Plateau witnessed a significant decrease in C4 plant cover because of lower growing-season temperatures, despite lower pCO 2 and higher aridity. A growth-season temperature below a turnover point of about 14°C appears to be deleterious for C4 vegetation. By contrast, in the Holocene, C4 plant coverage increased on the CLP as growth-season temperatures rose. However, far to the southeast on the Leizhou Peninsula, the dramatically increased precipitation offset the advantages of increasing temperature, leading to a decrease in C4 coverage.; The two-dimension model of pCO2 and growing-season temperature constructed by Cerling et al. (1997) is not adequate to reconstruct vegetation changes over the continent of China during the LGM to the Holocene transition. I have therefore constructed a three-dimension diagram for predicting C4/C3 dominance of grasses, which contains temperature, aridity (precipitation) and partial pressure of CO2.
机译：必须了解在上一次冰川期至全新世过渡期间，C4与C3的植被变化如何响应气候变化。尽管有许多先前的研究，到目前为止，仍然很难分离出pCO2还是其他气候参数中的一个是导致过渡期间C 3与C4植被变化的主要因素。我已经对从中国湖泊和黄土沉积物中提取的正构烷烃进行了详细的delta13C分析，沿着中国东南部和西北部广泛的样带。从样带的东南端和西北端分别选择了两个湖泊（头社和天阳）和两个黄土矿床（旬邑和洛川）。还对西南季风区鹤庆盆地的一个岩心进行了分析。通过索氏提取或超声提取总脂质。通过硅胶柱色谱法分离正构烷烃，在GC上测量浓度，在GCMS上确认结构，然后在GCIRMS上分析碳同位素比。在LGM期间，东南部经历了C4膨胀，这可能是由于干旱增加和/或pCO 2降低，加上生长季节的温度仍然足够高以支持C4植物的生长。然而，到西北端，尽管pCO 2较低且干旱较高，但由于生长季节温度降低，中国黄土高原的C4植物覆盖率显着下降。生长季节温度低于转换点（约14°C）似乎对C4植被有害。相反，在全新世，随着生长季节温度的升高，CLP的C4植物覆盖率增加。然而，在雷州半岛的东南部，降水的急剧增加抵消了温度升高的优势，导致C4覆盖率下降。 Cerling等人构建的pCO2二维模型和生长季节温度。 （1997年）不足以重建从LGM到全新世过渡期间中国大陆的植被变化。因此，我构建了一个三维图来预测草的C4 / C3优势，其中包含温度，干旱度（降水）和CO2分压。

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