利用有機物物地球化學指標重建臺灣西部海岸平原晚第四紀以來環境變遷

Environmental Changes of Western Coast in Taiwan Since Late Pleistocene: Using Multiple Proxies of Sedimentary Organic Matter

顧惠禕(Huei-wei Ku)

指導教授 ： 陳于高

國立臺灣大學/理學院/地質科學研究所/博士(2006年)

https://doi.org/10.6342/NTU.2006.00641

摘要

本研究選擇台北盆地五股岩心以及西南地區宅港、義竹、三寮灣岩心沈積物，分析其中有機物質的碳氮比以及碳與氮同位素，在西南岩心部分更增加木質素的分析，以期能對臺灣海岸地區自晚第四紀以來的環境變化有更全面的瞭解。在分析結果方面，由碳氮比與有機碳同位素的良好對比看來，臺灣西南沿海地區與台北盆地在深海氧同位素地層stage2時，有機物由以C3植物與水中藻類來源（平均約-25‰）轉變為以陸生的C4植物（平均約-14.3‰）為主，顯示這一段時期為較乾燥的氣候環境，台北盆地岩心於深海氧同位素地層stage6時也有相同的變化，均與全球的氣候變遷及海水面升降趨勢相符。在植被的變化方面，可由上述三岩心之結果看出，自stage5的C3被子植物為主，演變為stage3-4的C3與C4混合的過渡時期，進一步進入stage2變為乾燥的環境，以C4被子植物為主。最後在stage1時氣候轉變為溫暖潮濕，C3植物又成為此沈積環境中主要的有機物來源。此外，由沈積物氮同位素分析的結果得知，台北盆地與宅港地區沈積環境周圍生長的大型水生植物族群與數量消長與現今潟湖環境所得的分析結果相近，認為在stage1時期南北兩處岩心皆是有海水入侵的半封閉的潟湖環境。在台北盆地的stage7時期則因水深較深，水體中營養鹽可能以再循環的來源為主，同位素值較重，與宅港岩心stage5的變化亦相近。

關鍵字

台灣海岸平原 ； 有機物 ； 穩定碳同位素 ； 穩定氮同位素 ； 碳氮比 ； 木質素 ； 古環境變遷

並列摘要

A molecular and isotopic geochemical study on core sediments from San-liao-wan, Zai-kang and Yihju, southwestern coastal plain of Taiwan, and Wu-ku, Taipei Basin, was conducted in order to identify changes in the terrestrial vegetation over the past 50K years. Variation of the organic source in the sediments, as determined by the molecular study, correspond with stable delta-13C values of bulk organic matter and elemental C/N ratios. This evolution trend also coincides the general climatic changes defined by palynological studies. The delta-13C values of bulk organic carbon shows a shift from C3 terrestrial and aqatic sources (average -25‰) to a C4 dominated terrestrial source (up to -14.3‰) at Marine Isotopic Stage (MIS) 2. Thereafter decreased into to -25‰ during MIS 1. A comparison between the delta-13C values and the biomarker from vascular plants (CuO lignin oxidation products) indicates that the vegetation transition of the coastal area was from mainly C3 angiosperm in MIS 5 to a mixture of C3 and C4 in MIS 3-4. The C4 angiosperm increase in arid MIS 2 is marked by increasing lignin proxies C/V, S/V, Ad/Al(v), high bulk organic C/N ratio and delta-13C. Periods of high and various delta-15N in MIS 1 and MIS 7 represent different nutrient condition. In MIS 1, various delta-15N along with increasing TOC could be possibly the record of the unstable trend of aquatic productivity due to the dynamic mixing ratios of seawater and fresh water. In Taipei Basin, the 15N-enriched nitrate from denitrification might become the main source of nitrogen for the primary producer and led to heavy delta-15N in the sediment in MIS 7.

並列關鍵字

coastal plain of Taiwan ； organic matter ； stable carbon isotope ； stable nitrogen isotope ； C/N ratios ； lignin parameter ； paleoenvironmental change

參考文獻

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