利用碳酸鹽元素和同位素比值重建過去的氣候與環境變化

Abstract

本論文旨在利用碳酸鹽元素和同位素比值來提高我們對過去氣候和環境變化的理解。論文分為四個不同研究主題，每個研究就一組不同的研究問題、方法和代理提供對過去氣候及環境條件的區域理解。第一個研究（第2章）利用中國西南部的石筍記錄調查人為活動對印度夏季季風降雨的影響。結果發現石筍氧同位素和印度夏季季風強度之間有強相關性，並揭示過去300年中六次顯著的季風減弱事件。這些事件可能受到自然氣候動態和人類活動的影響，其碳同位素記錄進一步闡明了工業化前後土地利用對印度夏季季風變化的影響。第二個研究（第3-1章）使用東沙環礁的珊瑚樣本來探討東亞冬季季風和厄爾尼諾-南方濤動變異對黑潮入侵南海的影響。結果顯示，黑潮入侵存在十年尺度的變化，主要受到東亞冬季季風變化的影響，而厄爾尼諾-南方濤動相位變化和太平洋十年波動的影響較弱。第三個研究（第3-2章）重建東沙環礁珊瑚中60年的鉛濃度變化記錄，結果揭示不同時期鉛污染的嚴重程度和在中國禁止含鉛汽油後過渡到工業排放的過程。中國的環境政策的有效性通過2005年後珊瑚Pb濃度的顯著下降得到證明。最後一個研究（第4章）利用南馬爾代夫的珊瑚記錄檢視熱帶印度洋海溫在過去四十年的變化。結果強調了海溫、海面鹽度、厄爾尼諾-南方濤動事件和印度尼西亚贯穿流之間複雜的相互作用。本論文對多個案例研究的全面分析為過去環境動態和人類對氣候系統的影響提供了寶貴的見解。從對中國西南部鐘乳石記錄的調查到對熱帶地區珊瑚樣本的檢驗，每個研究都有助於我們理解區域和全球氣候變化。研究結果強調在解釋古氣候記錄時需要考慮自然氣候驅動因素、人類活動和海洋過程。這些見解對於制定未來氣候預測以及氣候調適和減緩策略至關重要。

This dissertation comprises four case studies to enhance our understanding of past climate and environmental changes through the analysis of isotopic and elemental ratios in carbonates. The first case study examines speleothem records from southwestern China to investigate early anthropogenic impacts caused by changes of the Indian summer monsoon (ISM) rainfall. The correlation between oxygen isotopes (δ18O) and ISM intensity reveals six notable weakening events spanning the past 300 years. These events, potentially governed by a blend of natural climate dynamics and human activities, are further illuminated by insights gleaned from the carbon isotopes (δ13C) record, which underscores the impact of land-use and land-cover changes (LULC) during the pre-industrial era on ISM dynamics. The second case study explores the impact of East Asian winter monsoon (EAWM), El Niño–Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO) variabilities on the Kuroshio intrusion (KI) into South China Sea (SCS) using reconstructed sea surface temperature (SST) and sea surface salinity (SSS) variations in coral samples from Dongsha Atoll. Results indicate decadal variations from the KI, were primarily driven by changes in EAWM with weaker influence from ENSO phase shifts and the PDO. The third case study presents a 60-year record of atmospheric lead (Pb) deposition in Dongsha Atoll coral, revealing distinct phases of Pb pollution and the transition to industrial emissions post-Pb gasoline phase-out in China. The effectiveness of environmental policies implemented by China government is manifested by a decline in atmospheric Pb deposition post-2005. The final case study examines SST variations in the tropical Indian Ocean over four decades, utilizing coral records from the southern Maldives. The findings underscore the intricate interplay among SST, SSS, ENSO events, and the Indonesian Throughflow (ITF), giving the necessity to account for multiple factors in the interpretation of paleoclimate records. In conclusion, the multiple analysis of multiple case studies provides valuable insights into past environmental dynamics and human impacts on climate systems. From the investigation of speleothem records in southwestern China to the examination of coral samples in various locations, each study contributes to our understanding of regional and global climate variability. The findings emphasize the need to consider natural climate drivers, human activities, and oceanic processes when interpreting paleoclimate records. These insights are of value in further realizing climate projections and forming strategies for climate adaptation and mitigation.