本研究藉由無機沉澱碳酸鈣與珊瑚樣品來探討鈣(Ca)同位素在碳酸鈣形成過程中的質量分化效應；並以南中國海(South China Sea, SCS)海水剖面鈣同位素組成變化來初探海洋鈣的循環。本研究成功評估兩階段式化學純化技術應用於樣品中鈣的純化；並利用多接收器感應耦合電漿質譜儀(Neptune, Thermo-Fisher)搭配去溶劑進樣系統(APEX IR, ESI)發展了一套快速且高精確度的鈣同位素比值質譜分析技術，其δ44/42Ca 分析精確度可優於0.11‰ (2σ)，相當於國際水平。實驗室無機碳酸鈣沉澱實驗用於評估鈣同位素於碳酸鈣形成時所發生的同位素分化機制，從5-40°C 溫度控制實驗發現溫度影響鈣同位素的分化相當微小，在方解石與霰石結構的碳酸鈣樣品分別只有0.002 和 0.001‰/°C 的程度。同時，鈣同位素在沉澱母液與碳酸鈣產物間的差異程度(fractionation factor, α)與前人研究相差甚大，可歸咎於實驗過程中採用不同沉澱技術造成的結果，也突顯碳酸鈣結晶速率對於鈣同位素分化的重要性。從實驗室培育與自然生長的珊瑚樣本也觀察到類似的結果；溫度對於珊瑚骨骼中鈣同位素的分化影響相對於動力學所產生的效應顯得微小。綜觀不同型態的碳酸鈣樣品鈣同位素組成分析，結果顯示動力學效應較熱力學效應在鈣同位素分化的機制上扮演更為重要的角色。另一方面，本研究初探SCS 海水垂直剖面鈣同位素組成變化趨勢，藉以了解海洋碳酸鈣循環的機制。結果指出SCS 海水剖面的鈣同位素組成呈現微小但可分辨的系統性變化，底水呈現相對較輕的鈣同位素組成可部分解釋於與SCS 嚴重的碳酸鈣部分溶解(Partial dissolution)現象有關。未來研究將進一步提升鈣同位素組成的分析精度，並深入探討影響SCS 海水鈣同位素組成分化的主要機制。

The Ca isotope composition of synthetic carbonates and corals have been measured in order to evaluate the Ca isotope fractionation during the carbonate formation; and the δ44/42Ca of a seawater profile in South China Sea (SCS) has been performed as well to realize the oceanic Ca cycle in preliminary. A fast and high-precision analytical technique for the Ca isotopes has been developed using high-resolution multi-collector ICP-MS (Neptune, Thermo-Fisher) coupled with a desolvation system (APEX-IR, ESI). Two-steps separation technique has been successfully applied to separate matrix component from the analyzed compound to avoid potential spectral interferences. The external reproducibility for δ44/42Ca analysis is better than 0.11‰ (2σ) using a standard-sample-standard bracketing method. Calcium carbonates obtained from controlled inorganic precipitation were used for evaluating the Ca isotope fractionation during precipitation and display a rather small temperature-dependent fractionation at 5-40°C (0.002 and 0.001‰/°C for aragonite and calcite, respectively). The Ca isotope fractionation factor (α) in synthetic carbonates reveals a significant difference compared with previous studies, which was attributed to the difference in growth rate under various precipitation techniques. Furthermore, Ca isotopes in cultured and field corals, Porites sp., show also only minor temperature-dependent fractionation. Kinetic rather than the temperature effects would strongly affect the Ca isotope fractionation in carbonates. On the other hand, seawaters collected from SCS displays a small but significant δ44/42Ca vertical variation. The lowest value of δ44/42Ca in the SCS is detected in the bottom water which could be partly attributed to the intense partial dissolution on marine carbonates. Further studies are necessary to improve analytical precision and to understand the main controlling factors on seawater Ca isotopes.

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