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國立臺灣大學理學院地質科學系 博士論文
Department of Geosciences College of Science
National Taiwan University Ph.D. Dissertation
過去三十六萬年來印度-太平洋暖池 海水表面溫度與水文動態研究 Indo-Pacific Warm Pool Sea Surface
Temperature and Hydrological
Dynamics during the Past 360,000 Years
研究生：羅 立 (Li Lo) 撰
指導教授：
沈川洲
博士魏國彥
博士Advisors: Chuan-Chou Shen, Ph.D.
Kuo-Yen Wei, Ph.D.
民國一百零三年六月 June 2014
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ABSTRACT
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,
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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.
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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.
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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
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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。
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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。
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PUBLICATION LIST
1. Referred Papers
Min-Te Chen, Xiao-Pei Lin, Yuan-Pin Chang, Yi-Chi Chen, Li Lo, Chuan-Chou Shen, Yusuke Yokoyama, Delia W. Oppo, W. G. Thompson, Rong Zhang
Dynamic millennial-scale climate changes in the northwestern Pacific over the past 40,000 years
Geophysical Research Letters 2010, 37, 2010GL045202 (SCI IF: 3.792)
Chuan-Chou Shen, Chung-Che Wu, Yi Liu, Jimin Yu, Ching-Chih Chang, Doan Dinh Lam, Jain-Ru Jhou, Li Lo, Kuo-Yen Wei
Rapid and precise measurements of natural carbonate rare earth elements in fentogram quantities by inductive coupled plasma sector field mass spectrometry Analytical Chemistry 2011, 83, 6842-6848 (SCI IF: 5.856)
Li Lo, Yung-Hsiang Lai, Kuo-Yen Wei, Yu-Shih Lin, Horng-Sheng Mii, Chuan- Chou Shen
Persistent sea surface temperature and declined sea surface salinity of Kuroshio Current over the past 7,500 years
Journal of Asian Earth Sciences 2013, 66, 234-239 (SCI IF: 2.714, top ten hottest paper, 2013)
Li Lo, Chuan-Chou Shen, Chia-Jumg Lu, Yi-Chi Chen, Ching-Chih Chang, Kuo-Yen Wei, Dingchuang Qu, Michael K. Gagan.
Determination of element/Ca ratios in foraminiferal and coral using cold- and hot- plasma techniques on inductively coupled plasma sector field mass spectrometry Journal of Asian Earth Sciences 2014, 81, 115-122 (SCI IF: 2.379)
Liangcheng Tan, Chuan-Chou Shen, Yanjun Cai, Li Lo, Zhisheng An
Paleoclimatic and paleoenvironmental implications of trace element variations in an annually layered stalagmite from central China
Quaternary Research (accepted) (SCI IF: 2.204)
T. Li, C.-C. Shen, L.-J. Huang, X. Jiang, X. Yang, H.-S. Mii, S.-Y. Lee, Li Lo
Variability of Asian summer monsoon during the penultimate glacial/interglacial period inferred from stalagmite oxygen isotope records from Yangkou cave, Chongqing, southwestern China
Climate of the Past Discussion (accepted)
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2. Manuscripts Submitted
Yi Liu, Li Lo, Zhengguo Shi, Kuo-Yen Wei, Jain-Ru Jhou, Chung-Che Wu , Zicheng Peng, Chuan-Chou Shen
Evolution of Pacific Intertropical Convergence Zone over the past 280,000 years (submitted to Nature Geoscience, co-first author)
3. Manuscripts in preparation
Li Lo, Chuan-Chou Shen, Kuo-Yen Wei, George S. Burr, Horng-Sheng Mii, Min-Te Chen, Shih-Yu Lee, Meng-Chieh Tsai
Millennial meridional dynamics of Indo-Pacific Warm Pool during the last deglaciation
(to be submitted to Climate of the Past)
Li Lo, Kuo-Yen Wei, Sheng-Pu Chang, Horng-Sheng Mii, George S. Burr, Shih-Yu Lee, Min-Te Chen, Yi-Chi Chen, Chih-Kai Chuang, Chuan-Chou Shen
Non-linear response of South-IPWP SST to greenhouse gases radio-forcing during the past 360,000 years
(to be submitted to Nature)
4. OTHER PUBLICATION:
Kuo-Yen Wei, Yu-Shih Lin, Li Lo, Chuan-Chou Shen, In-Tien Lin, Horng-Sheng Mii Sea-surface temperature and hydrological variations in Okinawa Trough during the last 10,000 years
Interactions of Nature and Humans: Perspectives of Environmental History, Linking Publishing, 2008, 33-53, (in Chinese with English abstract).
Kuo-Yen Wei, Li Lo, Chih-Kai Chuang, Shao-Wei Huang, Jyh-Jaan Huang, Saul- Wood Lin
A short note on the extant Rhodoliths found on the continental shelf off Dong-He, eastern Taiwan
Western Pacific Earth Sciences 2009, (9), 99-118 (in Chinese with English abstract).
Li Lo, Yuan-Pin Chang, Chuan-Chou Shen, Min-Te Chen, Kuo-Yen Wei Invasion of warm, saline, and well ventilated intermediate water in cold stadials during the last 30,000 years? Evidence from the middle Okinawa Trough Site MD01- 2404
Minerlogical Magazine 2011, (75), 1352.
Li Lo
Footnote for the next generation’s geologists.
Evolution (演化) 2010, (16), 101-105 (in Chinese) Li Lo
Thermalhaline circulation and its importance to the Paleoceanography studies.
Science Monthly (科學月刊) 2014, April (in Chinese).
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5. CONFERENCE CONTRIBUTION:
Oral presentation:
Li Lo, Chung-Chou Shen, Kuo-Yen Wei, Meng-Yang Lee, Horng-Sheng Mii
High Resolution Sea Surface Temperature Records from the Southern Marginal Indo- Pacific Warm Pool: Deglaciation Timing and Inter-Basin Pattern Differences
2010 Western Pacific Geophysics Meeting Program
Li Lo, Yuan-Pin Chang, Chung-Chou Shen, Min-Te Chen, Kuo-Yen Wei
Invasion of Warm, Saline, and well Ventilated Intermediate Water in Cold Stadials during the Last 30,000 Years? Evidence from the Middle Okinawa Trough Site MD01-2404
2011 Goldschmidt Meeting
Li Lo, Yung-Hsiang Lai, Kuo-Yen Wei, Yu-Shih Lin, Horng-Sheng Mii, Chuan-Chou Shen
Persistent sea surface temperature and declined sea surface salinity in the northwestern tropical Pacific over the past 7,500 years
2013 The 13th symposium on Quaternary of Taiwan & 3rd International IMAGES/PAGES Workshop of PPP
Poster presentation:
Yin Lin, Yue-Gau Chen, Chuan-Chou Shen, Hong-Wei Chiang, Li Lo, Ching-Chih Chang, and Doan Dinh Lam.
Rainfall fluctuation over the past 4,000 years in Northern Vietnam inferred from stalagmite geochemical data
2007 American Geophysics Union Fall Meeting Program
Li Lo, Yi-Chun Lin, Meng-Yang Lee, Kuo-Yen Wei, Chuan-Chou Shen, and Horng- Sheng Mii
Changes in vertical hydrological profile at the southern margin of the Western Pacific Warlm Pool (WPWP) during the past 168,000 years
2008 American Geophysics Union Fall Meeting Program
Yung-Hsiang Lai, Kuo-Yen Wei, Chuan-Chou Shen, Horng-Sheng Mii, and Li Lo Hydrographic changes of the Kuroshio Current in the upper reach area during the past
6,000 years
2008 American Geophysics Union Fall Meeting Program
Meng-Yang Lee, Li Lo, Yi-Chun Lin, Horng-Sheng Mii, Kuo-Yen Wei, and Chuan- Chou Shen
Variability of thermocline hydrography at the southern margin of the Western PAcific Warm Pool during the last 170 ka
2009 General Assembly of European Geophysics Union Program
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Yi-Chi Chen, Yuan-Pin Chang, Min-Te Chen, Li Lo, Kuo-Yen Wei, and Chuan-Chou Shen
Intrusion of the Kuroshio Current to the Okinawa Trough during 40-100 thousand years before present?
2009 American Geophysics Union Fall Meeting Program
Li Lo, Kuo-Yen Wei, Chuan-Chou Shen, Meng-Yang Lee, Horng-Sheng Mii, and Chuan-Chou Shen
The formation of a permanent SST gradient at the Plio-Pleistocene boundary:
Highlights from the Western Pacific Warm Pool periphery area.
2009 American Geophysics Union Fall Meeting Program
Jyh-Jaan Huang, Kuo-Yen Wei, Chuan-Chou Shen, Li Lo, and Chi-Yu Huang Thermal and hydrological variability in the southern South China Sea over the past 11,600 years
2009 American Geophysics Union Fall Meeting Program
Chuan-Chou Shen, Kuo-Yen Wei, Yung-Hsiang Lai, Li Lo, Horng-Sheng Mii Intensification of the Kuroshio Current and orbit-driven southward shifts of Intertropical Convergence Zone and Western Pacific Warm Pool in the western Pacific since 8 thousand years ago
2010 Western Pacific Geophysics Meeting Program
Yuan-Pin Chang, Yi-Chi Chen, Li Lo, Chuan-Chou Shen, Min-Te Chen
The Last Interglacial-Glacial SST Records Derived from Foraminiferal Mg/Ca of the East China Sea (IMAGES core: MD012404) and the Implications on Hydrological Changes
2010 Western Pacific Geophysics Meeting Program
Yi-Chi Chen, Kuo-Yen Wei, Li Lo, Chuan-Chou Shen, Meng Yang Lee
Magnitude and timing of thermocline changes in the southwest Pacific warm pool during the last two terminations
2010 Western Pacific Geophysics Meeting Program
Chih-Kai Chuang, Kuo-Yen Wei, Huei-Chin Ke, Meng Yang Lee, Horng Sheng Mii, Li Lo
Upper Pliocene-Pleistocene Calcareous Nannofossil Biostratigraphy of ODP1115B in the Solomon Sea, Western Equatorial Pacific.
2010 Western Pacific Geophysics Meeting Program
Li Lo, Chung-Chou Shen, Kuo-Yen Wei, Meng-Yang Lee, Horng-Sheng Mii
High Resolution Sea Surface Temperature Records form the Southern Marginal Indo- Pacific Warm Pool: Deglacial Timing and Inter-Hemispheric Pattern Differences 2010 10th International Conference on Paleoceanography
Yi-Chi Chen, Kuo-Yen Wei, Li Lo, Chuan-Chou Shen, Meng Yang Lee
Magnitude and timing of thermocline changes in the southwest Pacific warm pool during the last two terminations
2010 10th International Conference on Paleoceanography
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Yin Lin, Li Lo, Yue-Gau Chen, Chuan-Chou Shen, Doan Dinh Lam
The Holocene Monsoon discrepancy between Southwest China and Northern Vietnam 2010 American Geophysics Union Fall Meeting Program
Chien-Ju Chou, Yi Liu, Li Lo, Kuo-Yen Wei, Chung-Chou Shen
Planktonic foraminifer rare earth elements as a potential new aeolian dust proxy 2012 American Geophysics Union Fall Meeting Program
Chih-Kai Chung, Kuo-Yen Wei, Li Lo, Yuan-Pin Chang, Huei-Chin Ke, Chuan-Chou Shen, Horng-Sheng Mii, Meng-Yang Lee, Pin-Chuan Lin
Quaternary high resolution paleoceanography records in the south marginal of Western Pacific Warm Pool
2013 The 13th symposium on Quaternary of Taiwan & 3rd International IMAGES/PAGES Workshop of PPP
Meng-Ting Chiang, Kuo-Yen Wei, Chih-Kai Chung, Li Lo
Pulleniatina coiling change events during early Pleistocene in ODP 1115B, western equatorial Pacific
2013 The 13th symposium on Quaternary of Taiwan & 3rd International IMAGES/PAGES Workshop of PPP
Li Lo, Kuo-Yen Wei, Sheng-Pu Chang, Horng-Sheng Mii, George S. Burr, Shih-Yu Lee, Min-Te Chen, Yi-Chi Chen, Chih-Kai Chuang, Chuan-Chou Shen
Non-linear response of S-IPWP SST to greenhouse gases radio-forcing during the past 360,000 years
2013 American Geophysics Union Fall Meeting Program
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TABLE OF CONTENTS
Abstract
...iAbstract in Chinese
...iiPublications List
...viiTable of Contents
...xiiChapter 1. Introduction
...1Chapter 2. Materials and methods summary
...19Chapter 3. Millennial meridional dynamics of Indo-Pacific Warm Pool during the last deglaciation
...38Chapter 4. Evolution of the Pacific Intertropical Convergence Zone over the past 284,000 years
...56Chapter 5. Non-linear response of South-IPWP SST to greenhouse gases radio-forcing during the past 360,000 years
...90Data tables
...120Table A. Globigerinoides ruber oxygen and carbon isotope...121
Table B. G. ruber Mg/Ca and inferred SST...128
Table C. Calculated surface water oxygen isotope, δ18OSW...133
Table D. G. ruber Nd/Ca...138
Table E. Composite benthic foraminifera δ18O...142
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TABLES AND FIGURES
Table 2-1...32
Table 2-2...33
Table 2-3...34
Table 2-4...35
Table 4-S1...80
Table 5-S1...114
Figure 1-1...11
Figure 1-2...12
Figure 1-3...13
Figure 1-4...14
Figure 1-5...15
Figure 1-6...16
Figure 1-7...17
Figure 1-8...18
Figure 2-1...36
Figure 2-2...37
Figure 3-1...50
Figure 3-2...51
Figure 3-3...52
Figure 3-S1...53
Figure 3-S2...54
Figure 3-S3...55
Figure 4-1...69
Figure 4-2...70
Figure 4-3...71
Figure 4-4...72
Figure 4-S1...81
Figure 4-S2...82
Figure 4-S3...83
Figure 4-S4...84
Figure 4-S5...85
Figure 4-S6...86
xiv
Figure 4-S7...87
Figure 4-S8...88
Figure 4-S9...89
Figure 5-1...102
Figure 5-2...103
Figure 5-3...104
Figure 5-4...105
Figure 5-S1...115
Figure 5-S2...116
Figure 5-S3...117
Figure 5-S4...118 Figure 5-S5...
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1
Chapter 1.
Introduction
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Chapter 1. Introduction
The Indo-Pacific Warm Pool (IPWP) is the largest marine warm water mass with an annual average sea surface temperature (SST) >28oC [Yan et al., 1992, Figure 1-1A, 1-1C]. Vigorous atmospheric circulation in the IPWP transports substantial latent heat and water moisture from the tropics to middle and high latitudes [Yan et al., 1992]. Global climate changes have shown significant impacts to the IPWP thermal variation and precipitation changes.
Over the past five decades, the IPWP has been responsible for regional surface water freshening and westward movements of precipitation zones that have caused regional drought in East Africa and storm track changes in East Australia [Cravatte et al., 2009; Williams and Funk, 2011].
The Intertropical Convergence Zone (ITCZ) migrates meridionally with the seasonal angle of the sun [Waliser and Gautier, 1993] and circles the globe in the tropics [Figure 1-1B, 1-1D]. The convergence of inter-hemispheric trade winds leads to strong convective clouds, heavy precipitation, and intense latent-heat transfer, altering rainfall patterns worldwide. Owing to its strong rainfall gradient, a small displacement in the position of the ITCZ can cause dramatic changes in hydrological conditions and the frequency of extreme weather events—like droughts, floods, and tropical cyclones [Cai et al., 2012].
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Furthermore, the rapid rise of anthropogenic CO2 emission in the past six decades has posted a threat to human sustainability. A doubled CO2 (560 ppmv) concentration of pre-industrial value is projected to occur in Years 2050-2100 and may cause global mean temperature warming for 2.0-4.5oC by the end of 21st century, which may be accompanied by large-scale ice sheet melts, rainfall belt shifts, and a rise in sea level [IPCC, 2007].
However, modern climatology studies could only provide short-term data to try to reconstruct present interactions between the air-sea system in the IPWP region.
Paleoclimatology studies are needed to test teleconnections between low and high latitude and radiative forcing variations to the sensitivity to the IPWP thermal and hydrological changes. To understand sea surface temperature (SST), ITCZ variations, and radiative forcing (RF) changes are crucial to make future predictions.
This study focuses on the reconstruction of the thermal and hydrological histories in the IPWP region, and further attempt to reveal the teleconnection between low and high latitudes, thermal variation accompanied with greenhouse gas concentrations, and precipitation belts shifting.
Since the early 2000s, intense paleoclimatology studies have been conducted to understand long-term thermal and hydrological changes in the IPWP during the glacial/interglacial (G/IG) cycles and to test the sensitivities of warm pool thermal and hydrological fluctuations to high latitude ice sheet coverage and greenhouse gas concentration variations through the late Pleistocene [e.g., Lea et al., 2000; Stott et al., 2002; Visser et al., 2003; Rosenthal et al., 2003; Stott et al., 2004; de Garidel-Thoron
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et al., 2005; Steinke et al., 2006; Levi et al., 2007; Xu et al., 2008; Linsley et al., 2010;
Bolliet et al., 2011, Figure 1-1, 1-2]. However, complicated ocean-island configuration and regional topography hinder the fidelity of detailed description of past climate changes [Griffiths et al., 2009; Mohtadi et al., 2011]. In particular, little is known about the meridional thermal-hydrological dynamics between the N-IPWP and S-IPWP during the last termination transition.
The lack of long-term records from the meteorological core of the ITCZ, in the low-latitude Pacific, severely hinders us from understanding its natural variability related to orbital forcings during the Quaternary. An understanding of ITCZ responses to orbital forcings has global significance because the region is the largest “heat engine” and moisture source in the world.
The sensitivity of tropical Pacific Ocean sea surface temperature to greenhouses gases radiative forcing (mainly contributed by CO2) changes during the past four to five G/IG cycles have been previously addressed by Lea, [2004] and Dyez and Ravelo, [2012]. They performed linear regression analyses to estimate SST responses to changes in pCO2. Based on the regression coefficients obtained from the paleoclimate records, they project a 33-36oC tropical Pacific SST for the future doubling CO2 scenario. Alternatively, the CO2 radiative effect on SST may not be linear and the climate may switch non-linearly as suggested by other studies [e.g., Paillard, 2001; Peacock et al., 2006; Carlson and Winsor, 2012]. Linear versus non- linear regression differences would not only affect the accuracy of the prediction to future climate evolution but also challenge our knowledge of the interactions between climate components within the system.
5
Motivation and the structure of this dissertation:
To obtain better understanding of the tropical Pacific response to greenhouse gases and ice volumes changes, we need high-resolution SST and hydrological records to address changes during the G/IG cycles and spatial recovery to identify possible climate teleconnections. This study of IPWP focuses on the teleconnection between low and high latitudes, thermal variation accompanied with atmospheric greenhouse gases concentration, and precipitation belts shifting.
Research region:
Papua New Guinea (PNG), a mountainous terrain located at the southern border of the ITCZ [Figure 1-1], delivers a large amount of suspended sediments and solutes to the adjacent oceans as a result of the prodigious precipitation in the region [Milliman et al., 1999; Nittouer et al., 1995]. This transport occurs mostly in the wet season (>90% annual load) when the ITCZ is located over PNG [Chappell et al., 2011]. Archives from nearby marine basins therefore reflect this sediment delivery and provide a direct record of precipitation influenced by the ITCZ position.
Solomon Sea, which is the passage of surface and subsurface water masses between low- and middle-latitude South Pacific Ocean gyre and cross equatorial currents [Grenier et al., 2011; Melet et al., 2010, Figure 1-2].
Structure of this dissertation and short summaries of results:
Material and methods are summarized in Chapter 2. We firstly present new oceanic proxy-inferred SST and ice volume-corrected surface seawater oxygen isotope δ18O (δ18OSW-IVC) records from the Solomon Sea near the Papua New Guinea (PNG) covering the past 23-10.5 thousand years ago (ka, before 1950 AD, Figure 1-3)
6
in Chapter 3. New SST and δ18OSW-IVC stacked records since the last termination are constructed for both N-IPWP and S-IPWP to understand regional thermal and hydrological changes and interhemispheric teleconnections [Figure 1-4]. Secondly, in chapter 4, we have established a 284-kyr record of rare earth elements (REEs) to Ca ratios in the planktonic foraminifer Globigerinoides ruber [Figure 1-5]. Furthermore, new calculations from a previous orbital-accelerated transient experiment using a coupled fast ocean-atmosphere model (FOAM, Kutzbach et al., 2008; Shi et al., 2011) forced by variations in orbital parameters is presented to clarify dynamical ITCZ migration processes in the western Pacific [Figure 1-6]. Thirdly, in chapter 5, we reconstruct a high resolution SST (200- to 900-yrs resolution) record from the Solomon Sea, on the S-IPWP, of the past four G/IG cycles during the past 360 thousand years (360 ka), and examine the non-linearity between the tropical Pacific SST and RF [Figure 1-7, 1-8].
We conclude that increasing IPWP thermal gradients during the Heinrich event 1 (H1) and Younger Dryas (YD) periods may alter the Hadley circulation and consequently reducing monsoon region precipitation. For the orbital timescale ITCZ shifting in the Solomon Sea region, obliquity can shift the position of the ITCZ and operates in tandem with precessional forcing. Given that the obliquity signal is stronger in the Nd/Ca-inferred precipitation record than in the simulation, our proposed obliquity-induced “pressure-push” mechanism might be more significant for both PNG and North Australia. We also propose that the SST is in fact nonlinear to RF and after a major threshold level at 220 ± 10 ppmv, which S-WPWP SST linearly increases ~1.9 ± 0.4 oC (by the sensitivity changes from 0.5 to 1.4 oC/Wm-2, when pCO2 ≥ 220 ± 10 ppmv). Potential mechanism to explain this non-linearity of S-
7
WPWP SST changes are the results of the combination of the Southern Ocean sea ice induced intermediate/mode water formations and the greenhouse gases changes.
8
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Figure 1-1. Climatological map of the Indo-Pacific Warm Pool (IPWP) sea surface temperature (SST, left) and precipitation (right) during 1950-2004 AD [Reynolds et al., 2002]. Upper panels are from the June-July-August (JJA), and lower panels are from December-January-February (DJF) averages of (A, C) SSTs and (B, D) precipitation distribution maps. SST and precipitation are at 0.5 oC and 2 mm/day intervals. Green star is the study site MD05-2925.
Orange and green dots are the previous study sites [Table 2-3] in IPWP region for reconstruction of meridional thermal and precipitation variations during the glacial/interglacial change [Chapter 3].
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Figure 1-2. Schematic circulation, water masses distribution, and site location map.
Purple triangle represents site MD05-2925 (9.3oS, 151.5oE) in this study, and red circles and blue squares are selected sites in the equatorial Pacific [Table 2-4]. Gray dashed lines show the Polar Front (PF), Subanatarctic Front (SAF), and Subtropical convergence zone (STC), respectively. Blue and green shadings indicate the formation region of Subanatarctic Mode Water (SAMW), and Antarctic Intermediate Water (AAIW), respectively. Dark red, orange, and blue shadings represent South Pacific Tropical Water (SPTW), Indo-Pacific Warm Pool (IPWP), and Eastern Equatorial Pacific (EEP) cold tongue regions, respectively. Blue dashed arrays represent the undercurrent pathways, (Equatorial Under Current, EUC, and orange solid ones represent surface current systems, South Equatorial Current (SEC) and North Equatorial Current (NEC). SAMW/AAIW transport Southern hemisphere (SH) high latitude to the SPTW, and then spread out the South Pacific Ocean through the EUC and EEP wind-driven upwelling [Pena et al., 2013] system and resurfacing process through water masses mixing [Qu et al., 2013]
within decades.
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Figure 1-3. Geochemical proxies from site MD05-2925. (A) δ18OSW-IVC (blue line) and (B) SST (red dots and line) were reconstructed with G. ruber Mg/Ca ratios and δ18OC. Gray line is the Greenland ice core NGRIP oxygen isotope record [Northern Greenland Ice Core Project Members, 2004]. Dark gray line denotes the Antarctica EPICA deuterium isotope record [Stenni et al., 2003]. The superimposed black lines are the 200-yr smoothed records. Black triangles are accelerator mass spectrometry (AMS) 14C dates [Table 2-1].
Vertical bars denote the H1 and YD periods.
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Figure 1-4. Four-hundred-year non-overlapping binned (A) SST and (C) δ18OSW-IVC
of N- (orange solid lines) and S-IPWP (green solid lines). Lower panel are the differences of (B) SST and (D) δ18OSW-IVC between N- and S-IPWP, respectively. The compilations of N- and S-IPWP surface water thermal and hydrological records were calculated with a non-overlapping binned method [Oppo et al., 2009; Linsley et al., 2010, Chapter 2]. All dashed lines represent 1-sigma uncertainty range. Gray bars represent the H1 and YD events.
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Figure 1-5. Time series of REE/Ca of planktonic foraminifera G. ruber. (a) La/Ca, Ce/Ca and Nd/Ca. (b) Pr/Ca, Sm/Ca, Gd/Ca and Dy/Ca. (c) Eu/Ca ,Tb/Ca and Lu/Ca. (d) Ho/Ca, Er/Ca and Yb/Ca. εNd values at ages of 49.5-50.1 and 58.8-60.6 kyr BP are given in panel (a).
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Figure 1-6. Spectral power analysis results. (a) MD 05-2925 planktonic foraminifer G. ruber Nd/Ca record. (b) Simulated PNG precipitation (5-12°S and 130- 160°E) over the past 284 kyr. We used REDFIT v 3.8 [Schulz and Mudelsee, 2002] to perform spectral analyses. Red and blue lines respectively denote 95% and 90% significance levels of coherence. Vertical bars are the significant precession and obliquity bands.
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Figure 1-7. Non-linear climate sensitivity. Past Solomon SST changes (ΔSST) to changes in greenhouse gas radiative forcing (ΔRFGHG). Both ΔRFGHG and ΔSST dataset has been interpolated to 1-kyr interval. Standard deviation of mean for every 10 ppmv equivalent pCO2 has been calculated by non- overlapping binned method (red triangles, Oppo et al., 2009; Linsley et al., 2010). The dark bar represents the significant difference threshold for the non-linear SST changes around 220 ± 10 ppmv.
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Figure 1-8. Tropical Pacific SST sensitivity. The SST sensitivity of (A) Solomon Sea (MD05-2925, purple triangles, this study), (B, C) eastern equatorial Pacific (TR163-19, and ODP 1240, blue squares, Lea et al., 2000; Pena et al., 2008, respectively), and (D-F) western Pacific (ODP 871, MD97-2140, and ODP 806, dark red circles, Dyez and Ravelo, 2012, de Garidel-Thoron et al., 2005;
and Lea et al., 2000, respectively). Only the MD05-2925 and ODP 1240 SST were resampled into 1-kyr resolution, the others were resampled into 4-kyr resolution. Gray circles, squares, and triangles represent the raw dataset for each site.
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Chapter 2.
Material and Methods
Summary
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Chapter 2. Material and Methods Summary
MD05-2925
Site MD05-2925 (9.3oS, 151.5oE, water depth 1661 m) was collected during the 2005 PECTEN (Past Equatorial Climate: Tracking El Niño) cruise which supported by International Marine and Climate Changes (IMAGES) Project on the research vessel Marion Dufresen. MD05-2925 is located at the northern slope of Woodlark Basin in the Solomon Sea, which is the passage of surface and subsurface water masses between low- and middle-latitude South Pacific Ocean gyre and cross equatorial currents. The New Guinea Counter Current and South Equatorial Current, as low-level western boundary currents, flow northwest through the Solomon Sea, transporting southern subtropical waters to the equatorial region via Vitiaz Strait [Melet et al., 2010a; Melet et al., 2010b; Cravatte et al., 2011; Grenier et al., 2011;
Melet et al., 2011]. The average sea surface temperature (SST) is 28.5 oC [Locarnini et al., 2010], with seasonally apart from the core region of the warm surface water mass in the Indo-Pacific warm pool (IPWP).
The precipitation sources are mainly comes from the south Indian Ocean and the Coral Sea [Gimeno et al., 2012], and are focused during the July-August- September (JAS). Intertropical convergence zone (ITCZ) and the South Pacific Convergence (SPCZ) are integrated here, which resulting as a bridging from the southwester equator to the middle latitude Pacific Ocean [Shiau et al., 2012, and references therein].
The total length of MD05-2925 is 2843 cm, and the upper 1882 cm was used in this study. The MD05-2925 core sediment is composed of a mixture of biogenic carbonate and silty clay [Beaufort et al., 2005]. The depth of core is well above the regional Carbonate Compensation Depth (CCD). The chlorophyll level of
21
0.2 mg/m3 [Radenac et al., 2012] for surrounding surface water in eastern Papua New Guinea (PNG) suggests low regional productivity. The dissolved-oxygen concentrations are high (>3 mL/L) through the whole water column including bottom waters of the eastern PNG [Garcia et al., 2010]. The local benthic oxygen flux, reflecting organic matter remineralization, is only 0.1 mol/m2/yr [Jahnke, 2003]. It is lower than the values of 0.8 mol/m2/yr for the reducing margins [notably in the eastern boundary upwelling systems (EUBS) and North Indian Ocean, Jahnke, 2003].
These data indicates an oxidative sea floor condition at this study site.
Oxygen isotope
Planktonic foraminifera, Globigerinoides ruber (white, s.s., 250-300 μm), were hand picked under microscope for the oxygen isotope measurement. Each samples contained 7-10 individuals and were immersed with methanol and ultrasonicated for 10 seconds, and rinsed with deionized water 5 times. Samples were immersed afterward in the hyperchloride sodium (NaOCl) for 24 hours, and then measured by an isotopic ratio mass spectrometer (IRMS), Micromass IsoPrime, housed in the National Taiwan Normal University. Long-term precision is 0.10‰
(2RSD, N = 701) with respect to Vienna Pee Dee Belemnite (VPDB) [Lo et al., 2013].
Trace elements/Ca (TE/Ca) measurements
For TE/Ca (mainly Mg and REEs) ratio measurements, 20-30 individuals were gently crushed and transported into 1.5 mL Teflon vial. The clean procedure is as follows: (1) Foraminiferal fragments were immersed with ethanol, ultrasonicated for 20 minutes, and then rinsed by Milli-Q ultra-pure water 3 times. (2) An aliquot of 0.45 mL 3% H2O2 was added for 2 hours to decompose organic material. (3) NH4Cl
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(0.45 mL, 1.0 N) was added for 20 minutes to adsorb cations on chamber surface. (4) NH2OH (0.45 mL, 0.01 N) was added for 3 hours to dissolve metallic oxides. (5) Diluted nitric acid (1 mL, 0.005 N) was added to polish the high-Mg content surface.
A sector field inductive coupled plasma mass spectrometer (SF-ICP-MS), Thermo Electron Element II, housed at the High-Precision Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, was used to determine trace element/Ca ratios following the methodology developed by Lo et al., [2014]. Two-year reproducibility for Mg/Ca analysis is
±0.21% (1 RSD).
We measured REE/Ca records of the planktonic foraminifer G. ruber (white, s.s. 250-300 μm). REE/Ca ratios were calculated using the ion beams of 46Ca, 139La,
140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 160Gd, 159Tb, 163Dy, 165Ho, 166Er, 172Yb and 175Lu, detected on an inductively coupled plasma sector field mass spectrometer (ICP-SF- MS), Thermo Fisher ELEMENT II, equipped with a dry introduction Cetac ARIDUS [Shen et al., 2011] system. Two-month 2-sigma reproducibility is ±1.9-6.5%. The detailed instrumental settings and analytical methodology are described in Shen et al.
[2001].
Nd isotope:
Planktonic foraminifer G. ruber and sediment (<63 m) samples were collected from two depths of 472-477 cm (49.5-50.1 kyr BP, 580 individuals, >250 μm) and 537-542 cm (58.8-60.6 kyr BP, 250 individuals, >250 μm) of core MD05- 2925. The picked planktonic foraminifer samples were cleaned with the same protocol for REE/Ca ratio analysis and then dissolved in 2 M HNO3. The sediment samples were first cleaned with 10% CH3COOH to remove carbonate, and
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subsequently cleaned with a reductive reagent (1 M NH2OH∙HCl in 25% CH3COOH) to remove Fe-Mn phases on the sample surface [Bayon et al., 2004]. The cleaned sediment samples were decomposed in a mixed solution of HF, HClO4, and HNO3, and then dissolved in 2 M HNO3.
Neodymium in the 2 M HNO3 dissolved samples was extracted by a two- stage column separation [Pin and Zalduegui, 1997]. The REE fraction in the solution was purified from the remaining major and trace elements using Eichrom RE resin.
Neodymium was subsequently separated from the other REE with Eichrom Ln resin.
Neodymium isotopic compositions were measured by a multi-collector ICP- MS (MC-ICP-MS), Thermo Fisher Neptune, in the HISPEC. The measured
143Nd/144Nd ratios were normalized to 146Nd/144Nd = 0.7219 using an exponential law.
La Jolla standard was measured at 0.511811±0.000014 (2, n = 13). All 143Nd/144Nd ratios were calibrated to the reported value relative to the La Jolla standard value of 0.511858 [Lugmair et al., 1983]. Sample 143Nd/144Nd ratios [(143Nd/144Nd)sample] are expressed as ε notation defined by an equation of εNd = [(143Nd/144Nd)sample/(143Nd/144Nd)CHUR-1]×104, where the 143Nd/144Nd ratio of CHUR standard for Chondritic Uniform Reservoir [(143Nd/144Nd)CHUR] is 0.512638 [Jacobsen and Wassergurg, 1980].
δ18OSW-IVC calculation
To extract seawater δ18O (δ18OSW) values, we used a cultural based equation, SST = 16.5 − 4.8 × (δ18OC − δ18OSW) [Bemis et al., 1998] and a constant offset of 0.27‰ between carbonate VPDB and Vienna Standard Ocean Water (VSMOW) scales. Ice volume corrected δ18OSW (δ18OSW-IVC) was calculated using the method proposed by Waelbroeck et al. [2002]. We only calculated δ18OSW-IVC for the last
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termination, because the complication of long-term sea level reconstruction.
Age model
A series of planktonic foraminiferal AMS 14C dates at 19 different depths, including 200 individuals of Globigerinoides sacculifer (>500 μm) each, from the upper 292 cm of the core were measured. Dates were calibrated to calendar ages (before 1950 AD) using CALIB 6.0.1 software [Stuiver et al., 2010] with a reservoir age difference (ΔR) estimated from the Marine Reservoir Correction Database (http://calib.qub.ac.uk/marine/). The calculated weighted mean ΔR value is 64 ± 23 years for the selected four sites around the Solomon Sea [Petchey et al., 2004].
The chronology was based on linear interpolation between calibrated 14C dates [Figure 2-1, Table 2-1].
Composite benthic foraminiferal oxygen isotope data are established with benthic foraminifera (>250 μm, 2-4 individuals each depth), including the Uvigerina spp. (171 samples), Cibicidoides wuellerstorfi (9 samples), and Bulimina spp. (6 samples) [Figure 2-2]. The δ18O offset calibration between Uvigerina spp. and C.
wuellerstorfi is +0.64‰ [Shackleton and Opdyke, 1973], and between Uvigerina spp.
and Bulimina spp. is -0.11‰ [Oba et al., 2006].
For core samples below 292 cm, the age model was constructed by correlating the composite benthic foraminiferal oxygen isotopic data of core MD05- 2925 to the LR04 stack record [Lisiecki and Raymo, 2005]. All age control points are summarized in Table 2-2 In addition, the age model is supported by two planktonic/nannofossil biostratigraphic events. The last occurrence (LO) of G. ruber (pink) occurred between the depth of 830 and 835 cm, average dated 126.8 kyr, which is consistent with the observation in the southern South China Sea [Lee et al., 1999].
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The first occurrence (FO) of Emiliania huxleyi was observed between the depth of 1550 and 1580 cm, with an age estimate of about 293-299 kyr and within Marine Isotope Stage (MIS) 8. The overall sedimentation rate is ~10 cm/kyr. The relatively high sedimentation rates ranged from 10-40 cm/kyr occurred at upper section of MD05-2925 from the depth of 0-300 cm which represents ~170 years per sample. For lower section, each sample represents ~906 years.
Radiative forcing calculation
Details of the ΔRFGHG calculation should consider all the major greenhouse gases, and calculate the differences between certain past time and the pre-industrial greenhouse gases level ([CO2]0 = 280 ppm, [CH4]0 = 700 ppb, and [N2O]0 = 720 ppb, Ramaswamy et al., 2001). The full equations to determine ΔRFGHG are listed below:
ΔRFCO2 = 4.841 ln ([CO2]/[CO2]0) + 0.0906 (√[CO2] – √[CO2]0)
EQ1 ΔRFCH4 = 0.036 (√[CH4] – √[CH4]0) –
[0.47 ln{1 + 2.01x10-5 ([CH4] [N2O]0)0.75 + 5.31x10-15 [CH4] ([CH4] [N2O]0)1.52}] – [0.47 ln{1 + 2.01x10-5 ([CH4]0 [N2O]0)0.75 + 5.31x10-15 [CH4]0 ([CH4]0 [N2O]0)1.52}]
EQ2
The contribution of N2O to CH4-induced radio forcing, however, is too small, and the EQ2 could be simplified as:
ΔRFCH4 = 0.036 (√[CH4] – √[CH4]0)
EQ3
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The sum of EQ1 and EQ3 is the total ΔRFGHG during the past 360 kyrs, however, the CH4 only contribute <5% of the RF. Thus in this study we only consider the RF contributed by CO2 (EQ1).
Non-overlapping binned method
To build stacked N- and S-IPWP records, we followed the suggestions by Leduc et al. [2010] and considered three criteria for this dataset: (1) sites location within 12oN to 15oS, which is the main IPWP range [Yan et al., 1992; Gagan et al., 2004], (2) little or no influence by coastal upwelling, and (3) usage of specific proxies, Mg/Ca-derived SST and δ18OC records, of planktonic foraminifer, G. ruber (white, s.
s.). We adopted the age model for sites, ODP 806, MD97-2140, MD97-2141, MD98- 2162, MD98-2170, MD98-2176, and MD98-2181. For records with available original radiocarbon ages from sites, including MD01-2378, MD01-2390, MD98-2165, and MD06-3067, we recalculated the age models using new CALIB 6.0.1 program [Stuvier et al., 2010]. The sea level change effect on δ18OSW was also corrected. The MATLAB code of a non-overlapping binned method was provided by Dr. D. W.
Oppo and Dr. B. K. Linsley [Oppo et al., 2009; Linsley et al., 2010]. We divided the total data into every 400-yr window and calculated the mean and standard error of mean for each time window.
ODP 806 (0.3oN, 159.4oE, water depth 2520 m, Lea et al., 2000), MD97- 2140 (2.0oN, 141.7oE, water depth 2547 m, de Garidel-Thoron et al., 2005), ODP 871 (5.6oN, 172.3oE, water depth 1255 m, Dyez and Ravelo, 2012), TR163-19 (2.3oN, 91oW, water depth 2348 m, Lea et al., 2000), and ODP 1240 (0.0oN, 86.5oE, water depth 2921 m, Pena et al., 2008) have also been collected to calculate the average climatic sensitivity [Table 2-4]. Due to the effect of time resolution, we resampled
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ODP 806, ODP 871, TR163-19, and MD97-2140 into 4-kyr, and ODP 1240 into 1- kyr time resolution and then compared to the same time resampled Antarctica ΔT and pCO2 records to calculated ΔRFGHG.
EOF analysis
We applied an empirical orthogonal function (EOF) analysis of modern SST dataset [1950-2004 AD, Reynolds et al., 2002] for a sector from 20oS – 20oN, and 100oE- 180oE to determine the boundary between North- and South-IPWP [Chapter 3].
EOF1 factor identified clearly different SST variation groups between equator. EOF2 shows minor (9.7%) but significant inter-annual zonal (ENSO) control on the SST patterns.
FOAM
The simulated precipitation and other climatological records [Chapter 4]
were calculated from an orbital-accelerated transient run using the coupled fast ocean- atmosphere model (FOAM, Kutzbach et al., 2008; Shi et al., 2011). With a factor of 100, the experiment was integrated for 2840 years under the orbital forcing only to obtain the climate evolution during the past 284 kyr. Changes in global ice volume/sea level and greenhouse gases were neglected. The spatial resolution was set to 4°×7.5° for atmosphere and 1.4°×2.8° for the ocean. A detailed description is available in Kutzbach et al. [2008], and Shi et al. [2011].
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