臺灣博碩士論文加值系統

西北太平洋位於冷暖洋流交會的副極區，受到氣候事件、海冰、漂冰、洋流的影響甚大，因此在末次冰期以來，形成特殊且複雜的古海洋環境。本研究為了解西北太平洋古海洋變化，利用探取自北太平洋與白令海水團交會處的岩心LV 63-41-2（52˚34.1’ N, 160˚00.6’ E；水深1924公尺），分析烯酮類(alkenone)不飽和有機物重建末次冰期以來的海表溫度(Sea Surface Temperature, SST)變化，藉此來揭示洋流，海冰、漂冰、生物生產力與海冰覆蓋範圍的相互關係。結果顯示於16~27 ka BP，鈣板藻生產力較低及烯酮類之淡水指標(C37:4 %）較高，這可能代表此時有大量的淡水注入，與海冰融化和洋流帶來白令海海冰融水在海表面形成低溫且低鹽的水層層化現象。淡水形成良好的海水分層，並阻擋表層水的垂直混合作用，使得較深層的營養鹽無法上湧，故導致鈣板藻生產力降低。依本研就究的年代模式顯示，波令–阿勒羅德(Bølling-Allerød, B/A)暖期的SST上升可分為緩慢升溫的早期與快速升溫的晚期；而烯酮類之淡水指標(C37:4 %)顯示B/A暖期可能有大量淡水注入。本研究推論B/A暖期早期雖有大量淡水輸入，但海水分層狀況較末次冰期差且深度淺，較末次冰期海水可獲得較多的營養鹽上湧，使得鈣板藻生產力明顯增加。B/A暖期晚期海表溫快速上升，位於本岩心站位北方的勘察加半島沿岸海冰崩解成漂冰，融化的淡水降低表層水的垂直混合作用，使得自次表層水上湧的營養鹽降低，因而造成鈣質生物生產力由高轉低。在新仙女木事件(Younger Dryas, YD)時期，SST先上升再降低，烯酮類淡水指標(C37:4 %)顯示淡水注入較少，據此本研究推測西北太平洋於YD早期，海表溫為快速升高，鈣板藻生產力降低的狀態。

Sea surface temperature (SST) records from the subarctic Northwestern (NW) Pacific are ideal for reconstructing regional paleoceanographic changes sensitive to global climate change. In this study, used a core LV 63-41-2 (52.56˚ N, 160.00˚ E; water depth 1924 m) retrieved from a high sedimentation site, in which the interactions of the Bering Sea and the warm water mass from the NW Pacific are highly dynamic. I analyzed the alkenone of coccolithophorids secreted and preserved in the sediments of the core. Our results indicate that the alkenone concentrations are low prior to 16~27 ka BP, suggesting low productivity of coccolithophorids during the last glacial. High glacial C37:4 alkenone concentrations in the core imply large amount of fresh water influencing the surface water of the NW Pacific with a reaching to the Site LV 63-41-2. This study inferred that the low salinity water may be formed from the ice-melting water on site and/or brought by the surface current from the Bering Sea, and is efficient in producing strong water stratification condition. The stratification weakens vertical mixing of the upper water column, that in turn decreases the nutrients upwelled from deep to the surface therefores causes low productivity of coccolithophorids. The LV 63-41-2 alkenone-SST shows a gradual increase, associated with high C37:4 alkenone concentrations during the early Bølling-Allerød (B/A) period. It implies a weakened stratification and much stronger nutrient upwelling than the glacial. The late B/A period is characterized by an abrupt warming with possibly more melting sea ices in the Bering Sea and the coast near the Kamchatka Peninsula. The large amount of fresh water lens formed during the ice melting might have ceased vertical mixing and upwelling in the upper water column as evidenced by a decline of biological productivity of both calcerous and soliceous organism during late B/A. Based on the age model of LV 63-41-2, this study suggests an early warming and low productivity in the NW Pacific that is coincident with a rapid cooling in most of the Northern Hemisphere high latitudes during the Younger Dryas.

摘要…………………………………………………………………………………I
Abstract……………………………………………………………………………II
目次…………….…………….……….….………….….………………………..III
圖目次……………………………………………………………………………IV
表目次………………………………………………………………………IV
第壹章 緒論…...………………………………………………………….……1
1.1前人研究…...………………………………………………………….……1
1.2區域水文和環境背景…………..……………………………………….……2
1.3研究目的……………………………...……………………………….……2
第貳章 材料與方法……..…………………………………………………………4
2.1研究材料………………………………...………..……….…………………..4
2.2年代模式的建立………………………………...………..……….…………..4
2.3烯酮類不飽和有機物…………………………...………..……….…………..4
2.4分析方法………………………………...………..……….…………………..6
第參章 研究結果……..…………………………………………………………8
3.1年代模式與沉積速率…………………...………..……….…………………..8
3.2 鈣板藻生產力指標C37 alkenones……………...………..……….…………..8
3.3 烯酮類不飽和有機物西北太平洋U_37^k'- SST古海表溫度重建…..………….9
3.4 淡水指標C37:4…………………………………..……….…………………..9
第肆章 討論…………………………………………………………………………10
4.1 年代模式..………….……...………….....……..……….………………….10
4.2 淡水來源、海水分層與生物生產力的關係……….…..……….…………..11
4.3末次冰期以來亞北極西北太平洋的古海洋變遷….....…………………..11
第伍章 結論……………………………………………………………………16
參考文獻……………………………………………………………………………17
圖說…………………………………………………………………………………21
附錄…………………………………………………………………………………38

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