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標題: | 石筍指示三萬六千年至兩萬五千年間東熱帶印度洋氣候紀錄 Stalagmite-inferred paleoclimate records in the eastern tropical Indian Ocean during 36-25 thousand years ago |
作者: | 林益增 Yi-Zeng Lin |
指導教授: | 沈川洲 Chuan-Chou Shen |
關鍵字: | 石筍,東熱帶印度洋,間熱帶輻和帶,印度洋偶極震盪, Stalagmite,eastern tropical Indian Ocean,ITCZ,IOD, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 在數年至數十年時間尺度上,印度洋區域尤其是東熱帶印度洋地區的水文氣候,被印度洋偶極震盪(Indian Ocean Dipole, IOD)現象影響;於軌道尺度下的變化,則是受到間熱帶輻和帶(Inter Tropical Convergence Zone, ITCZ)位移所主導。然而在百年至千年尺度的氣候變化中,IOD及ITCZ對此區域降水的影響迄今尚未明瞭。本研究利用取自聖誕島Upper Daniel Roux Cave(南緯十度二十六分,東經一百零五度三十九分)的石筍為材料,利用鈾釷定年技術建立年代模式,並以碳氧同位素分析,重建過去三萬六千年至兩萬五千年間的數十年至百年解析度的降水紀錄變化。石筍同位素資料通過Hendy Test測試,表明應可以記錄區域主要的水文氣候變化。結果顯示氧同位素(δ18O)介於-5.1至-2.8‰之間,受到雨量效應的影響;碳同位素與氧同位素有一定的相關性,反映出受降雨影響了生物活動力與植被的覆蓋率;而碳氧同位素紀錄可以反應該區域的水文氣候狀況。δ18O紀錄顯示從36.0 ka (千年) 的-3‰劇烈下降到35.2 ka的-5‰並保持穩定狀態,直到34.2 ka時急劇增加到-3.7‰。隨後自33.8 ka的-3.0‰減少到32.5 ka的-5.1‰,緊接著保持-5到-4‰之間的震盪到29.3 ka為止。在29.3-26.3 ka從-4‰緩增到-3‰的期間,於28 ka夾雜一段約400年的-3‰高峰值,最終δ18O從26.3 ka的-2.8‰轉變為25.6 ka的-4.5‰。其中有2個降水量較高的區域在35.8-34.2和28.1-27.6 ka (δ18O:-5‰),3個乾燥區域在34.1-33.5、28.7-28.1和26.8-26.1 ka (δ18O:-3‰) 。此石筍δ18O指示的降水變化與位於赤道東印度洋北部,且同樣受到ITCZ影響降雨的蘇門答臘島外的海洋沉積物岩心SO189-119KL (3°31’N)和SO189-39KL (0°47’S) (Mohtadi et al., 2014),有著千年尺度上的反相關。這種現象表明,末次冰期東印度洋千年尺度的降水變化主要受ITCZ位移控制,而非受到類似IOD事件影響。 Indian Ocean Dipole (IOD) oscillation affects the hydroclimatic condition in the Pan-Indian Ocean territory, especially precipitation in the eastern tropical Indian Ocean realm, on annual-decadal scales, even the variation of Inter Tropical Convergence Zone (ITCZ) shift is the dominant factor over the orbital scale. However, the effects of IOD and ITCZ on the regional precipitation on the centennial-millennial scale in the glacial time are obscure. Here we present the replicate stalagmite carbon and oxygen isotope records covering 36-25 thousand years ago (ka, relative to AD 1950), anchored with 30 U-Th ages, from Upper Daniel Roux Cave on Christmas Island (10°26′S, 105°39′E), eastern Indian Ocean, to provide a multidecadal-to-centennial-resolved precipitation evolution. Isotopic data pass the “Hendy Test” and can preserve the original hydroclimatic signals. Stalagmite δ18O records, ranging from -5.1 to -2.8‰, were mainly controlled by the “amount effect”. δ13C data agree with δ18O records and this agreement reflects the variation of precipitation-triggered bioactivity and vegetation cover associated with changes in hydroclimatic conditions. The δ18O record shows a sharp decrease from -3‰ at 36.0 ka to -5‰ at 35.2 ka and keeps this plateau of -5‰ until a sharp increase to -3.7‰ at 34.2 ka. It then decreases from -3.0‰ at 33.8 ka to -5.1‰ at 32.5 ka, followed by stable values hovering around -5 to -4‰ from 32.5 to 29.3 ka, an abrupt increase to -3‰ during 29.3 -26.3 ka with an 18O-depletion 400-yr peak centered at 28.0 ka, and a final 18O-depletion shift from -2.8‰ at 26.3 ka to -4.5‰ at 25.6 ka. Two intervals with relatively high precipitation (δ18O: -5‰) are observed at 35.8-34.2 ka and 28.1-27.6 ka, and three drought intervals (δ18O: -3‰) at 34.1-33.5, 28.7-28.1 and 26.8-26.1 ka. The stalagmite δ18O-inferred precipitation-variation shows a general millennial-scale anti-phase symmetrical relationship of this southern tropical ITCZ sector with the planktonic foraminiferal proxy-inferred seawater δ18O records of marine sediment cores SO189-119KL (3°31′N) and SO189-39KL (0°47′S) (Mohtadi et al., 2014), located in the northern sector of the eastern equatorial Indian Ocean, off Sumatra Island. This general anti-phase concurrency suggests that the eastern Indian Ocean millennial precipitation change in the last glacial time could be mainly controlled by the ITCZ shift, instead of IOD-like variability, on the sub-orbital scale. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/88453 |
DOI: | 10.6342/NTU202302356 |
全文授權: | 同意授權(限校園內公開) |
顯示於系所單位: | 地質科學系 |
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