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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/15246

Title: 晚第四紀低緯度太平洋之古海洋學及氣候動力研究
Late Quaternary Paleoceanography and Climate Dynamics of the Low-latitude Pacific
Authors: Pai-Sen Yu
Contributors: NTOU:Institute of Applied Geosciences
Keywords: 低緯度太平洋;氧同位素第14階;浮游有孔蟲;海水表面溫度;反聖嬰
Low-latitude Pacific;MIS 14;planktic foraminifer;sea surface temperature;La Niña
Date: 2010
Issue Date: 2011-06-30T08:09:21Z
Abstract: 本論文選取南海與東赤道太平洋海域高解析度/高品質深海沉積物岩(MD972142、MD012394與ODP Site 1240),進行重建低緯度赤道太平洋古海洋的研究。本研究以低緯太平洋之古氣候動力觀點出發,探討南海、西太平洋、低緯度太平洋,甚至於全球性的晚第四紀氣候變遷格局。本論文獲得下列研究成果:1)穩定氧同位素第六階以來,東亞夏季與冬季季風表現於南海之海洋與氣候特徵;2)東亞夏季與冬季季風於軌道力週期上的表現以可能的氣候控制營力;3)過去十六萬年以來,東太平洋湧昇流之時空變化;4)穩定氧同位素第十四階在東亞與西太平洋季風盛行區所記錄之異常溫暖且潮溼氣候事件,及本事件與熱帶海洋之與全球氣候變遷的關連性,並尋求可能之解釋。 本研究以分析低緯度表層海洋之海水表面溫度變化為重心,嘗試由浮游有孔蟲化石群聚與水文梯度變化的觀點著手,首次於越南外海湧昇流區建立了過去十三萬五千年以來,MD012394浮游有孔蟲化石群聚與季風驅動之湧昇流記錄。浮游有孔蟲種屬Globorotalia inflata與Neogloboquadrina dutertrei(包括 Neogloboquadrina pachyderma–右旋種)的相對豐度應可分別作為越南外海湧昇流區之東亞夏季、冬季季風水文指標。此外,本研究嘗試比較位於南海東西兩側岩心MD972142與MD012394之有孔蟲群聚記錄並發現,冷水種屬(N. dutertrei與G. inflata)/暖水種屬(Globigerinoides ruber與Globigerinoides sacculifer)相對豐度之比例應可反映南海的區域水文梯度,可指示東亞冬季季風強弱的指標。 MD012394浮游有孔蟲化石群聚與海表溫估測顯示,最近十萬年以來,東亞夏季季風所驅動的湧昇流呈現明顯的歲差週期變化(~21-kyr),並於北緯13度的夏季太陽日照量達最大值時湧昇強度最高。夏季湧昇流指標種G. inflata豐度高值與低海表溫度與於當地夏季太陽日照量最大值呈現同相變化,相當於距今~11, 33, 59, 83千年前時達到最大值。本研究進一步推論夏季太陽日照量與東亞夏季季風強度可能為控制南海西側湧昇流的重要因素。另一方面,於整個時間序列上東西向海洋表層環境梯度的極值與歲差軌道力週期高值兩相吻合。梯度變化量的絕對值於距今22, 45, 71, 94與116千年前時達到最大,此結果顯示東亞夏季與冬季季風強度分別所造成的南海湧昇流強度與東西向水文梯度變化,似乎與歲差軌道力週期存在著某種關連性。此外,我們認為北半球東亞冬季季風之強弱變化可能和南半球澳洲夏季季風增強與否有關,而東亞冬季季風的強弱可能與穿越赤道氣流的強弱有關。 本研究完成的ODP Site 1240浮游有孔蟲群聚分析顯示,晚第四紀東赤道太平洋深受高緯度的祕魯–智利洋流與副極區洋流的影響。相較於上述西太平洋之南海古海洋記錄,歲差軌道力週期並未明顯地反映在東赤道太平洋的海表溫度記錄上。這可能與東赤道太平洋複雜的海洋與氣候特性有關。東赤道太平洋冷舌的時空變化重建顯示,於過去十六萬年以來,冷舌於東赤道太平洋海域遷移可能介於北緯3度至南緯6度。對於此區域之古海洋研究,我們建議除了探討熱帶地區的氣候動力機制外,高緯度的氣候營力亦須加以考量。 氧同位素第十四階時期的西太平洋與南海可能處於一異常溫暖且潮溼的環境。為了能充分認識低緯度太平洋區域對於穩定氧同位素地層第十四階特殊氣候事件之反應,並探討緯度向之東亞季風與西太平洋暖池區關係以及東–西向赤道太平洋區域氣候機制,本論文進行大陸黃土剖面、南北極冰心與赤道海洋岩心的氧同位素第十四階比較,並推論此時東西半球的大氣與海洋非對稱性逐漸增加,東–西低緯度太平洋呈現截然不同的氣候反應:東太平洋湧昇流強度增強,海表溫度大幅度降溫(~2oC);而東亞夏季季風強度增強,使得東亞/西太平洋則保持高溫且多降雨的氣候型態,此現象類似於現今太平洋常見的氣候現象–反聖嬰。
With respect to understandings of late Quaternary paleoclimatic changes and climate dynamics in the tropical oceans, high-resolution / high-quality marine sedimentary cores retrieved from South China Sea (SCS) and eastern equatorial Pacific (EEP) were used to reconstruct paleoceanography of low-latitude Pacific. For archieving detailed and in-deepth information on this issue, our research selected from regional areas SCS/EEP, western Pacific, low-latitude Pacific, and even the global scale. In this thesis, the main objectives include 1) reconstructing SCS oceanographic behaviours affected by the East Asian summer/winter monsoons variations since Marine Isotope Stage (MIS) 6; 2) understanding plausible climate mechanisms that drived orbital time-scales East Asian monsoons variations in the SCS; 3) spatial and temporal patterns of eastern equatorial cold tongue from the last 160 kyrs; and 4) understanding climatic evolution of low-latitude Pacific by comparing marine records with MIS 6-1 and MIS 15-13 time slices, and further investigating possible driving forcings for abnormally warm/humid glacial MIS 14 condition. Planktic foraminifer assemblages and temperature estimations on core MD012394 revealed that changes in monsoon-driven upwelling over the past 135 kyrs. Our results indicated that the relative abundance patterns of Globorotalia inflata and Neogloboquadrina dutertrei + Neogloboquadrina pachyderma R would regarded as hydrographic proxies for East Asian summer and winter monsoon, respectively. In addition, we established planktic foraminifer hydrographic index and SST estimates for these two records and demonstrated that these are useful for indicating the effects of the strength of the East Asain winter monsoons on the SCS surface ocean hydrography. The abundances of G. inflata with abruptly high values were appearred to coincide with Northern Hemisphere summer insolation maxima, particularly at ~11, 33, 59, and 83 kya. The results further supported the view that the strengths of both summer insolation and the East Asian summer monsoon have determined the relative abundance of planktic foraminifer fauna and the SSTs of the western SCS for the last 135 kyr. On the other hand, planktic foraminifer fauna and hydrographic gradient records were relatively high near ~22, 45, 71, 94, and 116 kya, when Northern Hemisphere summer insolation levels were low. The fauna assemblages were primarily indicative of East Asian winter monsoon strength, which was driven by a “cross-equator flow” mechanism. For the EEP region, our Site 1240 record reveals a significantly intensified cold SST condition that may result from enhanced influences from subpolar and/or Eastern Boundary Current (EBC) components into the EEP. However, SST records of ODP Site 1240 revealed no obvious precession cycles in comparison with precession-dominated low-latitudes / SCS-prevailed monsoon regions. This was due to those fairly complicated EEP environments. Thus, our results suggested that high latitude forcings should take into account while investigating climate dynamics of tropical oceans. Furthermore, spatial and temporal SST patterns across the EEP indicated that path of cold tongue possibly oscillated along a meridional variation within 3oN - 6oS over the past 160 kya. In particular, the apparently warm and wet glacial climate conditions of MIS 15-13 were well exemplified in many western Pacific sediment core and East Asian loess and lake records. In order to best understand the specific climate event, the paleoclimatic records reconstructed from this thesis could be compared comparing with other terrestrial records from Chinese loess, lakes in the East Asia, and further our understanding on the validity of the hypotheses on the tropical ocean origins of global climate changes in the late Quaternary. We observed a hemispheric asymetry pattern of the tropical Pacific climate, that is, warming in the west and cooling in the east at MIS 14. We further speculate that a large-scale climatic shifting that may have involved a migration of the Intertropical Convergence Zone and a change of trade wind patterns in the tropical Pacific, was probably responsible for the contrasting surface ocean hydrographies during MIS 14.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0D92860001
Appears in Collections:[應用地球科學研究所] 博碩士論文

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