2003-08-012024-05-18https://scholars.lib.ntu.edu.tw/handle/123456789/709000摘要：我們提出一個三年計劃，建立高精確度及高準確度珊瑚鈾釷定年方法，並將其應用在西太平洋古氣候及古水文的重建研究上。鈾釷濃度及同位素分析方法是利用過去一年半由國科會補助（NSC-91-2116-M-006-004, NSC-91-2116-M-002-034）開發成功的高精度磁場式電漿質譜技術（ICPMS）。本計劃於第二年及第三年擬利用台大地質系將添購之多頻電漿質譜儀（MC-ICPMS）發展微量鈾釷同位素分析，估計只要含10 ng的鈾足以提供1&#8240;（2σ）的精準度，以利小標本（10 mg）之測量。 明尼蘇達大學及澳洲國立大學是目前世界上擁有最好的珊瑚定年技術團隊，對於小於100年的標本，其定年精確度達2-3年。我們計劃應用與明尼蘇達大學共同研開成功的鈾釷分析技術，精確地將現生珊瑚及珊瑚化石標本做更好的年代控制。若考慮從鈾-234蛻變的釷-230量，儀器分析的精確度及各種誤差來源，理論上，對於3 g重的200年及400年標本定年精準度，分別小於6個月及一年。但在實際的方法建立過程中將會面臨三個重要問題：（1）正在成長的珊瑚霰石骨骼中所沉積的初始釷-230值必須要精確估計。（2）示蹤<br> Abstract: We propose a 3-year project to develop a high-precision and high-accuracy coral U-Th dating method, that will be applied to the reconstruction of paleoclimatic and paleo-hydrological conditions in the coastal waters of the Western Pacific Ocean. The instrumental technique employed is a high precision uranium and thorium analysis by magnetic sector inductively coupled plasma coupled mass spectrometry (ICP-MS). The development of this technique was supported by two National Science Council grants, (NSC91-2116-M-006-004, 01/2002-07/2002; NSC91-2116-M-002-034), over the past one and half years. In the 2nd and 3rd years, we propose to develop another new analytical technique by multi-collector inductively coupled plasma coupled mass spectrometry (MC-ICP-MS), which can provide a precision of 1&#8240; (2σ) for 10 mg coral with 10 ng U.. Research performed at the University of Minnesota (UMN) and Australian National University (ANU) have produced the best coral U-Th dating technique in the world with a precision of 2-3 years for corals younger than 100 years. We propose to modify the techniques that were developed at UMN for absolute age control of both living coral heads and fossil corals. If the number of 230Th atoms produced by the decay of 234U, an analytical precision of 1&#8240; (2) for 238U, 234U and 232Th isotopes, and a sample size of 3 g of coral are considered, then theoretically, an accuracy of better than 6 months and 1 year can be achieved for corals with an age < 200 and < 400 years, respectively. However, in practice, we will encounter three fundamental problems. First, the initial 230Th incorporated into growing aragonitic skeleton should be well constrained. Second, the isotopic composition in spike solution should be well quantified. Third, procedural blanks of 238U, 234U, 232Th, and 230Th should be reduced as much as possible and characterized at these low levels. After developing this technique, we will then apply it to paleoclimate studies, including paleo-Asian monsoon, precipitation, ENSO, and Kuroshio. Our high-precision coral chronology can also, for example, be applied to understanding the relationship between the frequency and magnitude of abrupt tectonic events (e.g., earthquakes in the subduction-zone settings), long-term variability in the occurrence of tropical cyclones (typhoons), and environmental pollution in coastal waters.珊瑚鈾釷定年法電漿質譜儀多頻電漿質譜儀古氣候變遷CoralU-Th dating techniqueICP-MSMC-ICP-MSPaleoclimate