珊瑚骨骼微量元素分析廣泛應用於重建過去氣候與海洋環境的變化，並通過測量珊瑚中鈾系同位素比值提供一個精確且可靠的定年方法。為增加微量元素或同位素應用於定年與重建古氣候/古環境的可信度，必須對這些元素/同位素在珊瑚骨骼形成時或形成後的遷徙行為有更深入的認識。因此，本研究採集臺灣南部墾丁沿海三處具代表性的微孔珊瑚（Porites sp.）樣品進行分析。其中靠近現代海岸線的萬里桐與龍坑地區，主要以較新鮮且外觀無明顯變質的珊瑚為採樣對象；與之對照較古老的龍磐公園珊瑚則是位於一處抬升約80公尺高的珊瑚礁臺地。珊瑚樣品中的放射性同位素（238U、 226Ra、210Pb、228Ra、224Ra、40K）以非破壞性的γ能譜儀進行分析，而微量元素（Mg、Sr、Ba、Mn、Fe、Al、Ti）則是使用感應耦合電漿發射光譜儀（ICP-OES）測量。

研究結果顯示，近海岸線的珊瑚樣品中238U活度落在1.209~1.291 dpm/g，與前人測量恆春西南沿海全新世珊瑚樣品的結果相近。龍磐公園珊瑚238U活度約只有近海岸線珊瑚的1/3，顯示成岩作用造成鈾同位素流失。鐳同位素及其子核種測量中發現，近海岸線珊瑚樣品中短半衰期的子核種214Pb、214Bi活度平均值較母核種226Ra活度低，推測可能是存在骨骼孔隙的222Rn經研磨而逸散至大氣；在已抬升的古老珊瑚中二者則頗為相近，間接證明珊瑚受到成岩作用可能發生重結晶而使孔洞封閉形成緻密的固體。釷同位素在珊瑚樣品中幾乎不存在顯示：（1）初始228Ra（半衰期為5.8年）在珊瑚中已衰變完畢，表明珊瑚死亡時間至少30年。（2）珊瑚中232Th的活度低於儀器的檢測限（≤ 0.003 dpm/g），而232Th主要是由陸源物質輸入，表示樣品中陸源碎屑物貢獻的232Th可忽略不計。龍磐公園珊瑚樣品中40K的流失同樣也可反映珊瑚受成岩作用的程度，唯近海岸線珊瑚樣品的40K變化似乎與珊瑚中的Ti含量有關，此相關性顯然無法歸因於成岩作用，確切原因目前未明。

珊瑚骨骼微量元素分析提供了包含元素的來源、行為或相關性上與環境變遷有關的重要信息。陸源碎屑來源的Al、Ti在珊瑚樣品中呈現良好相關性，反映著珊瑚過去生長時海洋環境中的陸源懸浮物含量。Fe、Mn與海水中的氧化還原電位有關，在珊瑚樣品中二者相關性高表示有溶解態的Fe2+、Mn2+結合到骨骼中；Fe、Mn也可能來自陸源懸浮物，由Fe、Ti相關性發現珊瑚中的Fe除了有溶解態的Fe2+，亦有來自陸源的碎屑顆粒物，而在Mn、Ti則呈現較無關係性。本研究結果也顯示Ba和Ti不具相關性，說明Ba和Ti雖都與陸源輸入有關，但實際是以不同形式進入珊瑚骨骼。Ba進入海水後自陸源顆粒物脫附並以溶解態形式被結合入珊瑚骨骼中，而Ti則是以懸浮顆粒的形式。Ba、Mn在此也顯示不具相關性，說明表層海水中的Ba受海水氧化還原電位的影響可能很小。

珊瑚中Sr/Ca和Mg/Ca比值常用以作為海水表面溫度（SST）指標。以前人文獻之珊瑚Sr/Ca-SST與Mg/Ca-SST關係式，分別帶入本研究珊瑚樣品的Sr/Ca、Mg/Ca比值，發現得到的海水表面溫度明顯不合理。本研究中測得的比值，尤其是Mg/Ca比值，變化幅度之大似乎不能單純用海水表面溫度變化來解釋。而龍磐公園受成岩作用影響的珊瑚樣品之外，即使樣品的Mg/Ca比值變化差距達一個數量級，仍可看出Sr/Ca和Mg/Ca彼此具有良好的相關性。這表示除了海水表面溫度和成岩作用，仍有未知的機制控制著珊瑚中的Sr/Ca、Mg/Ca比值，值得吾等進一步探究。

Reliable applications of the trace elements and isotopes for age dating and/or for paleoclimatic/paleoenvironmental reconstructions requires a better understanding of the behavior of such elements/isotopes during/after the formation of the corals. This study collected fossil Porites corals from three typical locations in the coastal areas of Kenting: two locations were at modern sea level while the other was an old coral from the uplifted reef plateau. For these corals, naturally-occurring radioisotopes were analyzed by γ-spectrometry and trace elements by ICP-OES. The results show that diagenesis might result in significant loss of uranium isotopes and 40K after its formation. While the activity of 226Ra is similar to its daughter nuclides 214Pb and 214Bi, it suggests that pores of coral were sealed due to the coral’s recrystallization by diagenesis. The initial 228Ra in all coral samples must have been decayed away, revealing that all samples must have been older than 30 years. Unrealistic SSTs were derived for the coral samples in this study. It seems that the measured ratios vary in a larger range to be accounted for by SST only and there must be unknown mechanism(s) except SST and diagenesis that control Sr/Ca and Mg/Ca in corals.

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