國際海洋古全球變遷研究─(總計畫及子計畫一)過去三十萬年以來的南海及西菲律賓海的古季風與古海洋變遷(I)

• Main Author: 黃奇瑜
• Format: Report
• Language: Chinese
• Published: 臺北市：國立臺灣大學地質科學系暨研究所 1998
• Subjects: 南中國海; 千年尺度; 長鏈碳不 飽和指標; South China Sea; millennial-scale; Greenland; Sunda; GISP; Greenland ice cores
• Online Access: http://ntur.lib.ntu.edu.tw/handle/246246/11712; http://ntur.lib.ntu.edu.tw/bitstream/246246/11712/1/872611M002004.pdf

國際海洋古全球變遷研究計劃 IMAGES (International Marine Past Global Change Study) 第三航次在1997 年6 月於 南中國海採得八支高品質深海長岩心 (平 均每支岩心34 公尺長)。本計劃分析其中 一支位於越南東南外海岩心MD972151 （8 o 43.73’N, 109 o 52.17’E ；水深1589 公尺） 的古季風/古海洋記錄，並探討引起南中國 海古氣候變遷的最主要機制。 高解析度碳酸鈣含量與長鏈碳不飽 和脂肪酸分析，顯示位在北半球低緯度南 中國海高頻率的古海洋變遷現象，不但與 高緯度格陵蘭GISP II 冰岩心的氧同位素 值（反應岩心位置的地面溫度）千年尺度 變化現象是相同，且變化時間幾乎是同時 可相對比的。當南海岩心中有孔蟲化石殼 體氧同位素值越負值時，碳酸鈣含量越 高，Uk37 SST 也越高，此時GISP II 冰岩 心的氧同位素值越正值。如果比較低緯度 南中國海岩心古季風/古海洋指標變化曲線 與位於中緯度中國黃土層序顆粒變化曲線 （冬季風強度指標）時，也可以發現兩者 間的正相關。這種北半球低、中、高緯度 海洋、大陸、冰帽古氣候的同時性遙相關 性，顯示千年至萬年尺度南中國海氣候變 化主要受控於冰川體積大小的改變。而後 者除了受控於地球—太陽行星軌道因素 外，可能尚有地球內部氣候回饋作用的影 響。 High resolution records of an IMAGES deep-sea core (MD 972151; 8 o 43.73’N, 109 o 52.17’E at water depth of 1,598 m) from the semi-closed South China Sea (SCS) reveal a millennial-scale paleoclimatic fluctuations with D-O cycles and Heinrich events reported from the high latitude regions in the Northern Hemisphere. In a long-term Milankovitch orbital time scale, carbonate contents and alkenone stratigraphy are parallel to planktic oxygen isotope stratigraphy. In a short-term millennial scale, both carbonate content and U k’ 37 SST are rapidly fluctuated in a high frequency like Greenland ice cores. In interglacial and the warm interstadial events in the last glacial time, U k’ 37 SST (27-28.5 ℃ in Stages 1 and 5; 25.5-26.5 ℃ in interstadial events) and carbonate contents (20-25 % in Stages 1 and 5; 10-15 % in interstadial events) are relatively high. In contrast, in the last glaciation (Stages 2-3-4), U k’ 37 SST and carbonate contents are relatively low, especially in the stadial events (SST: 24-24.5 ℃, CaCO3 : 3-5 %). Both carbonate contents and U k’ 37 SST in the SCS are primarily controlled by ice volume fluctuations and paleomonsoon conditions. Increase of ice volume in the last glacial time enhanced the atmospheric Siberian high pressure to intensify winter monsoon, thus decreased U k’ 37 SST in the SCS. Meantime, increase of ice volume also resulted in a low standing of sea level, thus exposed the Sunda Shelf to contribute much continental materials to dilute carbonate contents in the SCS marine sediments. The South China Sea paleoceanography is also correlated with paleomonsoon records in the Chinese Loess Plateau, the lower U k’ 37 SST (the stronger winter paleomonsoon) in the SCS the coarser grain sizes in the Chinese loess sequences. Both Milankovitch orbital forcing and the rapid earth internal interactions of ice-atmosphere-ocean climate systems are responsible for millennial-scale paleoclimatic tele-connections among Greenland ice cores, Chinese loess sequences and South China Sea deep-sea core.