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  • 學位論文

三十六萬年來印度-太平洋暖池海水表面溫度與水文動態

Indo-Pacific Warm Pool Sea Surface Temperature and Hydrological Dynamics during the Past 360,000 Years

指導教授 : 沈川洲
共同指導教授 : 魏國彥
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摘要


本研究利用位於巴布亞新幾內亞(Papua, New Guinea)東側所羅門海(Solomon Sea)之海洋沈積物岩芯MD05-2925 (9.3oS, 151.5oE, 水深1661米)重建了過去三十六萬年來高解析度(200-900年解析度)之海水表面溫度(sea surface temperature, SST), 降雨帶遷徙以及對溫室氣體(greenhouse gases)造成之輻射熱的非線性反應。 在過去50-60年以來,快速的氣候變遷已在低緯度的印度-太平洋暖池(Indo-Pacific Warm Pool, IPWP)區域造成急遽的溫度以及降雨帶的遷徙變化,環境所帶來的衝擊影響許多鄰近區域國家人民的安全。但是在缺乏長期的觀測紀錄,以及複雜的島嶼地形影響下,目前為止仍無法對於此區域的氣候模式有充分的瞭解。本研究嘗試利用古氣候/古海洋學研究方法釐清1. 快速氣候變遷事件時期低緯度地區與南北半球高緯度氣候系統之間的遙相關,2. 軌道力對於研究區域的主要降雨帶-間熱帶輻合帶(intertropical convergence zone, ITCZ)的南北遷徙影響,3. 溫室氣體濃度變化所造成的輻射熱對於本區域的海水表面溫度變化。為了達成以上目標,我們第一步利用了碳十四定年與底棲性有孔蟲氧同位素地層建立了過去36萬年來良好的年代模式,進一步利用了居住在海水表層的浮游性有孔蟲Globigerinoides ruber (white, s.s., 250-300 μm)的鎂/鈣與稀土元素/鈣 (Mg/Ca, and Rare Earth Element/Ca, REE/Ca)的比值重建了海水表面溫度與降雨變化,並與過去已發表在鄰近區域的紀錄做整合性的比較與討論。 以下整理本研究所重要結果:1. 在上次冰消期時,南印度太平洋暖池(S-IPWP)升溫早於北印度太平洋暖池區域(N-IPWP),並且在北半球冷卻事件(如Heinrich event 1與Younger dryas, H1 and YD)時,S-IPWP溫度上升較N-IPWP多。在降雨方面,整個印度太平洋暖池都在H1 and YD事件時有明顯的水體氧同位素增加增加,ITCZ的南移可以同時或是部份解釋為受到大氣的遙相關影響,或是來自於S-IPWP的暖化的海洋影響。2. 在軌道時間尺度下的ITCZ遷徙事件的研究,我們透過了浮游性有孔蟲的稀土元素/鈣比值成為所羅門海區域的新代用指標,REE/Ca可被解釋為PNG地區的降雨/化學風化代用指標。在過去28萬年來,ITCZ在PNG區域的降雨記錄正好與東亞夏季季風相反,但地軸傾角週期(obliquity)同時也在PNG地區的ITCZ降雨記錄上扮演重要的角色。如此顯著的obliquity週期可以藉擺盪在亞洲-澳洲大陸(Asia-Australia)之間的氣壓差所解釋,當地軸傾角改變時,因著亞洲與澳洲大陸的大小差異,會造成兩者陸地被加熱的程度差異,進一步影響到兩者之間的大氣壓力梯度。3. 我們發現在過去36萬年來的S-IPWP SST與溫室氣體所造成的輻射熱有非線性的關係,關鍵的閥值 (threshold) 位於二氧化碳濃度220 ± 10 (pCO2, ppmv),當大氣二氧化碳濃度低於220 ppmv時,S-IPWP對於輻射熱改變的敏感度(sensitivity)較小(0.5 oC/Wm-2), 但當二氧化碳濃度高於220 ppm時,敏感度將顯著改變(1.4 oC/Wm-2)。這樣的非線性關係在東赤道太平洋(eastern equatorial Pacific, EEP)地區的岩芯中也同樣被觀察到,但是在N-IPWP則區域缺乏類似的反應,這樣的現象暗示著南半球的影響。而根據 Jaccard 等人(2013)的研究顯示,當大氣二氧化碳濃度 220 ppmv, 過去一百萬年來同時也是南大洋海冰覆蓋以及相對應的中層水/模態水生產率改變的關鍵閥值。故此本研究推測S-IPWP SST的非線性變化是因為同時受到了直接來自於大氣的輻射熱改變,與海洋水團生產速率同時變化下的結果。 本研究建議未來在此區域仍須要更多高解析度的溫度與水文紀錄,特別是在重要的水文交界處,或是隨著經緯度分布的站位。更高空間解析度的大氣-海洋耦合模式的配合將更能幫助研究者瞭解此區域整合性的氣候動力學,最後至少涵蓋3-4個冰期間冰期的長時間尺度的研究對於瞭解低緯度地區與南北半球高緯度地區的遙相關也是非常重要的關鍵。

並列摘要


I In this study, we reconstructed the high resolution sea surface temperature (SST), and rain fall belt variations, and identified the non-linear relationship between low latitude Indo-Pacific warm pool (IPWP) and greenhouse gases radiative forcing during the past 360,000 years by using the marine sediment core, MD05-2925 (9.3oS, 151.5oE, water depth 1661 m), located in the Solomon Sea. For the past few decades, global climate changes have raised popular awareness of the fact that the air-sea thermal-hydrological conditions are crucial to large population’s lives and land management. However, the lack of long-term observation records and complex geography configuration hinder the understanding of the low latitude IPWP region. Here we attempt to reconcile the following: (1) teleconnections between both North and South Hemisphere (NH and SH) high latitude climate systems during the fast climate change period; (2) orbital configuration control to the rain fall belt, intertropical convergence zone (ITCZ) shifting; (3) greenhouses gases radiative forcing control to the IPWP surface thermal condition. To achieve these goals, we first reconstructed a well-constrained age model by using radiocarbon dates and composite benthic foraminiferal δ18O stratigraphy. Surface dweller planktonic foraminifera, Globigerinoides ruber (white, s.s., 250-300 μm), was used for measuring Mg, and REE/Ca ratios were applied to SST and precipitation conditions, respectively. Compilations of the previous studies were also applied for supporting regional climate interpretations. The summary of the main results in this study are the following: first, during the last termination, South-IPWP SSTs were warmed earlier than those of North-IPWP, and during the NH cooling events (e.g. Heinrich event 1 and Younger Dryas, H1 and YD), S-IPWP SSTs also warmed faster than the N-IPWP. For the precipitation pattern, N- and S-IPWP both show decreases during the H1 and YD. Southward shifting of ITCZ in the IPWP regions could be interpreted by the atmospheric teleconnection and/or the oceanic forcing from the relative warmer S-IPWP. Second, the orbital timescales of ITCZ shifting histories were reconstructed based in the G. ruber REE/Ca ratios generated from the site MD05-2925. REE/Ca in the Solomon Sea could be used as a new proxy related to the Papua New Guinea (PNG) precipitation/chemical weathering conditions. The basic climatic pattern reflected by REE/Ca record during the past 284,000 years from this study is opposite to that of the speleothem records from the East Asian. However, the obliquity cycle also plays an important role. The obliquity pacing in the IPWP ITCZ shifting could be interpreted as the atmospheric “pressure push” between the Asian-Australian continental heat differences, caused by differentiated solar energy under different obliquity degrees. Third, the non-linearity of S-IPWP SST responses to the greenhouse gases radiative forcing (ΔRFGHG) has been identified for the past 360,000 years. By using the non-overlapping binned method, we proposed a threshold of the sensitive changes around pCO2 220 ±10 ppm. Below this threshold, the sensitive (0.5 oC/Wm-2) was lower than the pCO2 >220 ppmv (1.4 oC/Wm-2). Significant sensitivity changes around 220 ± 10 ppmv are also supported by the Eastern Equatorial Pacific sites, but not the N-IPWP sites. This suggests that the non-linearity may be affected by the SH forcing. According to the Jaccard et al. (2013), the threshold may relate to the re-organization of the sea-ice distribution and consequential intermediate/mode water masses production rate changes. Thus, the combination of atmospheric (radiative changes) and oceanic (intermediate/mode water masses) changes have caused the non-linear response in the S-IPWP and EEP regions. In sum, we suggest future research is needed to provide high resolution (<1-kyr) proxies-inferred thermal and hydrological records in the critical path through the latitudinal and longitudinal site distributions. Further fully coupled and geographic resolution climate models are also required to reconcile the climate dynamics in IPWP. Finally, longer time span (cover at least 3-4 glacial/interglacial cycles) is also crucial to reconstruct the long term variability and teleconnection between high-low latitude and orbital configurations.

參考文獻


Bolliet, T., Holbourn, A., Kuhnt, W., Laj, C., Kissel, C., Beaufort, L., Kienast, M., Andersen, N., and Garbe-Schonberg, D., (2011), Mindanao Dome variability over the last 160 kyr: Episodic glacial cooling of the West Pacific Warm Pool. Paleoceanography 26, PA1208, doi: 10.1029/2010PA001966.
Cai, W., Lengaigne, M., Borlace, S., Collions, M., Cowan, T., McPhaden, M. J., Timmermann, a., Power, S., Brown, J., Menkes, C., Ngari, A., Vincent, E. M., and Widlansky, M. J., (2012), More extreme swings of the South Pacific convergence zone due to greenhouse warming. Nature 488, 365-369.
Carlson, A. E., and Winsor, K., (2012), Northern Hemisphere ice-sheet responses to past climate warming. Nature Geoscience 5, 607-613.
Chappell, N. A., Tych, W., Shearman, P., Lokes, B. & Chitoa, J. in Sediment Problems and Sediment Management in Asian River Basins (eds. Walling, D. E.) 92-102 (IAHS Press, Wallingford, 2011)
Cravatte, S., Delcroix, T., Zhang, D., McPhaden, M., and Leloup, J., (2009), Observed freshening and warming of the western Pacific Warm Pool. Climate Dynamics 33, 565 – 589.

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