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標題: | 以石筍與現代器測紀錄重建廣西2000年來的氣候變化 Reconstruction of paleoclimate during the past 2000 years in Guangxi based on stalagmite and instrumental records |
作者: | Wan-Yin Lien 連婉吟 |
指導教授: | 李紅春 |
關鍵字: | 石筍,古氣候,氧同位素,碳同位素,AMS 14C定年, stalagmite,paleoclimate,18O,13C,AMS 14C dating, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | 東亞夏季風為主導東亞地區氣候的主要因素之一,而古氣候重建有助於我們對於東亞夏季風的理解,能夠更了解其如何影響各地降雨及其控制因素,且可以預測未來的氣候變化。本研究針對三個採自廣西壯族自治區的石筍做分析以重建當地古氣候,JL10和JL12採自金倫洞,YLY12則位於伊嶺岩。金倫洞 (23.553oN,108.265oE) 位於中國廣西省南寧市馬山縣,洞長約9公里;其南方60 km處的伊嶺岩 (23.041oN, 108.297oE) 則是位於南寧市武鳴縣內,洞長約1.1 km,兩者皆在同一氣候帶且有相似地形及植被情況。石筍JL10約有10 cm長,AMS 14C定年結果顯示具有大氣核爆碳十四曲線,透過和大氣核爆曲線的對比及數紋層的結果得出此石筍約有60年的紀錄,生長速率約為1.5 mm / yr。JL12和YLY12分別有35 cm、10 cm長,由於石筍年輕且鈾含量太低,導致鈾系定年結果無法使用,因此以AMS 14C定年,分別為1500年和2000年。雖然JL12和YLY12的14C年齡有死碳的影響,但可用死碳影響最小的年代點來建立年代模式。這三個石筍都有進行碳氧同位素的分析,作為解釋古氣候的指標。JL10年代近且生長快速,可以得到高解析度的氣候指標紀錄,因此能和現代的器測紀錄做比對,發現此研究區域的石筍18O值在夏季降雨量高時變低,迴歸分析及小波相關分析也指出兩者存在顯著的負相關。另外,YLY12的18O紀錄和桂林乾濕指數也有相同的負相關。因此得知,此研究區域的石筍18O值在十年尺度-百年尺度上以雨量效應主導,且EOF結果顯示,廣西地區的夏季降雨雖然受到西北太平洋季風及印度季風影響,但金倫洞和伊嶺岩的石筍最主要還是反映整個廣西地區在東亞季風影響下的降雨變化。在中世紀暖期 (AD 900-1200),石筍18O值低於2000年來的平均值,指示廣西為濕潤時期,小冰期 (AD 1300-1760) 時,18O值比整體平均值高,指示比較乾燥的時期,石筍的高死碳比例同樣說明此時期雨量少。另外,可將小冰期分為兩期,第一期 (AD 1300-1560) 雨量變化劇烈,第二期 (AD 1560-1760) 的降雨則是相對穩定的變化。值得注意的是,廣西的小冰期並非在持續的乾燥氣候狀態,僅於初期、一二期交界、末期處於乾燥時期,其他時段雨量並沒有明顯偏低。此重建結果與附近地區的紀錄相符,本研究的古氣候重建資料有助於建立更詳細的乾濕分佈。 Paleoclimate reconstructions help us to understand the role of the East Asian Summer Monsoon (EASM) on local precipitation and controlling factor of EASM variability, and to improve our climatic prediction. This study presents three stalagmite records, JL10 and JL12 from Jinlun Cave (23.553oN, 108.265oE) and YLY12 from Yilingyan Cave (23.041oN, 108.297oE) which are only 60 km apart in Guangxi, China. AMS 14C dating has been applied to all three stalagmites for chronology construction, and stable oxygen and carbon isotopes analyses for paleoclimate proxies. The 10-cm long stalagmite JL10 shows a “nuclear bomb carbon curve”, which allows comparison with the atmospheric 14C curve to build up the age model. Through the comparison, we obtained the age of JL10 spanning the past 60 years with a growth rate of 1.5 mm / yr, which is confirmed by lamination counting. The 35-cm long stalagmite JL12 from Jinlun Cave and 10-cm long stalagmite YLY12 from Yilingyan Cave reveal 1500-year and 2000-year continuous growth respectively. Although dead carbons influence the 14C dating results, it is a feasible dating method for the stalagmites as 230Th/U dating on both stalagmites was not successful due to low U contents. The 18O record of JL10 has a negative correlation with the summer rainfall confirmed by multiple regression analysis and wavelet coherence, showing so-called “amount effect”. The Empirical Orthoganl Function (EOF) results demonstrate that rainfall variability around Jinlun Cave can represent the rainfall trend in Guangxi. The relatively lower 18O values of the JL12 and YLY12 records during the Medieval Warm Period (MWP, AD900-1200) indicate wetter climate. Higher 18O values, exhibiting dry conditions, only occurred in the beginning, middle and the end of Little Ice Age (LIA) in Guangxi. In the first phase of LIA, from AD1300 to AD1560, the 18O fluctuated drastically, while the 18O was stable in the second phase of LIA (AD1560-AD1760). Furthermore, the dead carbon fraction (DCF) varying throughout the stalagmite JL12 and YLY12 records, ascending during the LIA, descending during the MWP, reflected dry condition during the LIA and a moist climate in the MWP. The paleoclimate of Guangxi reconstructed by the stalagmite records is comparable to other paleoclimatic records in this region, and is favorable for building up a fine dry-wet pattern under the influence of the EASM. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/69920 |
DOI: | 10.6342/NTU201800507 |
全文授權: | 有償授權 |
顯示於系所單位: | 地質科學系 |
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