| Summary: | 碩士 === 國立中山大學 === 海洋科學系研究所 === 103 === Toushe Basin is a semi-enclosed basin, where locates in central Taiwan and situates at an elevation of 650 m with a cover area of 1.75 km2. According to the recent 20 years meteorological data from the nearby Sun-Moon Lake Station, the local mean annual temperature is 21.2˚C and the average precipitation is 2401 mm. The annual rainfall pattern shows distinct wet and dry season types. Summer (July-September) is the main precipitation season in this region. Based on meteorological data, we consider that the East-Asian monsoon system and Typhoon are two controlling factors on determining the climate conditions of this district. Sediments of this basin are enriched with peats, which are mainly formed in anoxic environment, and are great archives for preserving paleo-climatic and -environmental changes. Previous studies are mainly focus on elementary and pollen analysis and are less focus on organic biomarkers, which are useful proxy for paleo-studies.
In this research, sediment samples derived from a cross-sectional sedimentary profile are used for organic geochemistry analysis, which include measurements of n-alkyls and alkane-derived 13C. Age model was constructed based on 14C AMS dating. The time scale of the record covers the interval between 6240 yr BP to 1385 yr BP, corresponding to geological time scale since middle Holocene to late Holocene. Preserved n-alkanes in peats are mainly produced by higher plants, thus the derived biomarkers can reflect the changes in vegetation and further provide evidences for climate changes. As claimed by n-alkanes carbon preference index (CPIalk), the local environment is less affected by degradation and oxidation. Thus the derived biomarkers variations are mainly reflect the changes of paleo-vegetation and the inferred paleoclimatic changes. On the basis of the analytical results of biomarker, the regional environment achieved the most humid period during 5800~5100 yr BP. Then the condition gradually shifted to drier type and reached the driest period between 4500~2500 yr BP. After that, the climate conditions gradually turned into stable and continuing developed into the present mode since then on.
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