Palaeoenvironmental Evolution Deduced from Organic Carbon Stable Isotope Compositions of Napahai Lake Sediments, Northwestern Yunnan, China
Palaeoenvironmental Evolution Deduced from Organic Carbon Stable Isotope Compositions of Napahai Lake Sediments, Northwestern Yunnan, China
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DOI：
10.18307/20010402
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
Y. Yong;Fang Nian-qiao;Hu Chaoyong;Nie Haogang;Qi Zun-li
中科院分区：
文献类型：
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作者：
Y. Yong;Fang Nian-qiao;Hu Chaoyong;Nie Haogang;Qi Zun-li
纳帕海湖位于横断山脉腹地，是一个碳酸盐岩侵蚀盆地。湖泊水位在低水位和高水位阶段之间波动较大。湖平面的变化直接影响的数量和分布的水生植物群落，利用不同的碳源进行光合作用，从而印记的有机沉积物的特征13 C组成。影响有机质沉积物13 C组成的另一个原因是交替阶段还原氧化条件的变化。另外，在潮湿寒冷的环境下，碳酸盐岩地层的强烈溶解作用，可以利用HI、TOC和δ 13 C来重建湖平面波动和气候变化。结果表明，总有机碳和氢指数的增加与δ 13 C值的降低基本相关，这可能是由于新兴和漂浮水生植物的繁荣以及与暖干或温带干燥气候相关的低湖水位环境的相对还原。在高湖平面阶段，气候凉爽湿润，TOC和HI的降低往往与δ 13 C值的升高有较好的相关性，这可能是由于水生植物生产力低下、有机质氧化分解和碳酸盐岩地层在潮湿凉爽条件下强烈溶解所致。古环境重建表明，主要的环境变化分别发生在32 kaBP和15 kaBP。湖泊水位在57 - 43 kaBP之间波动频繁，43 kaBP ~ 37 kaBP之间略有上升。之后，当气候变得温暖和干燥时，湖面急剧下降。从约32 kaBP开始，由于气候凉爽潮湿，湖平面有明显的上升，并一直维持到末次盛冰期末期。温暖干燥的气候再次回到该地区，湖泊水位在全新世期间继续下降。湖平面在约3 -2kaBP小幅上升后，现代气候主导着纳帕海湖。
The Napahai Lake, situated in the hinterland of the Hengduan Mountains, is a basin by the erosion of carbonate rocks. The lake levels have experienced great fluctuation between low stand and high stand stages. The lake level changes directly influences the amount and distribution of aquatic plant communities that used different sources of carbon for photosynthesis, thereby imprinting the organic sediments with a characteristic 13 C composition. Another reason influencing the 13 C composition for bulk organic sediment, in this case, is the change of reduction oxidation condition in the alternative stages. In addition with the strong dissolution of carbonate strata in humid cool conditions, the lake level fluctuations and climatic changes could be reconstructed using HI, TOC and δ 13 C. The results show that increase in total organic carbon and hydrogen index correlates in general, with decrease in δ 13 C values, which could be attributed to the flourishing of emerging and floating aquatic plants as well as a relative reduction environment in a low lake level associated with a warm dry or temperate dry climate. The decreases of TOC and HI often correlate well with δ 13 C value increasing in a high lake level stage accompanied with a cool humid climate, which might be attributed to low productivity of aquatic plants, oxidation that triggers decomposition of organic matters and strong dissolution of carbonate strata in humid cool conditions. The palaeo environmental reconstruction shows that major environmental changes took place at 32kaBP and 15kaBP respectively. The lake levels exhibited frequent fluctuations between ca.57-43kaBP, and then the lake level slightly rose from ca.43kaBP to ca.37kaBP. After then, the lake level dropped dramatically when the climate became warm and dry. From ca.32kaBP, the lake level had a distinct rise due to cool humid climate and kept high until the end of the Last Glacial Maximum. A warm dry climate returned to the areas again and the lake level remained lowering during the Holocene. After the lake level rose in a minor amplitude from ca.3-2kaBP., modern climate dominates the Napahai lake.