摘要
為了探討海洋中生物殼體之鈣同位素組成是否可以作為海洋中碳酸根離子濃度的代用指標，我們首先必需發展一套高精確性的鈣同位量測技術。因此我們
利用多接收器感應偶合電漿質譜儀搭配sample-standard bracketing 方式測量樣本的鈣同位素組成。但由於目前儀器所得到的精準度為0.2 ‰ (2σ)，並無法滿足我們的需求，因此我們轉而希望利用熱游離質譜儀搭配42Ca-48Ca 雙示蹤劑發展出一套新的空間幾何向量解法，以求得樣本鈣同位素組成。目前利用此套方法測量NIST SRM 915a CaCO3，所得結果精準度可以達到21 ppm (1σ)，已合乎我們實驗的要求。
目前世界各地海水的鈣同位素組成被研究的非常透徹。但是西太平洋海水的鈣同位素組成至今仍然是沒有數據公佈於世。我們希望利用趨於成熟的鈣同位素
量測技術，來詳細地了解現今西太平洋海水內鈣同位素分佈與均勻情形。本實驗中我們選取了位於南沖繩海槽(#1-10, 24°57'N-122°16'E, 水深10 m)與台灣東南方(FRI-SKII-S3, 22°10'N-121°10'E, 水深0 m)兩個位置的海洋表水樣本進行鈣同位素組成分析。兩個樣本的鈣同位素組成(δ40/44CaSRM915a)分別為-1.91 ± 0.16 (2σ)以及-1.89 ± 0.05 (2σ)，其所測量到的鈣同位素比值與其他研究學者結果相同，顯示現今全世界各大洋海水的鈣同位素的比值在分析誤差內是均勻相同。

Abstract
Calcium isotope ratio (δ40/44Ca) of marine foraminifera can be a new proxy for reconstructing the concentration of carbonate ion ([CO32-]) in paleo-oceans, provided that δ40/44Ca must be determined precisely to reach one sigma uncertainty (1σ) of < 30 ppm. In this study, we measured the δ40/44Ca of reference standard, NIST SRM 915, using multi-collector inductively-coupled-plasma mass-spectrometry (MC-ICP-MS) and thermal ionization mass-spectrometry (TIMS). The external precision of δ40/44Ca values determined by MC-ICP-MS was 0.2 ‰ (2σ), which is beyond that required for recognizing δ40/44Ca variations in marine foraminifera caused by the change of [CO32-] in paleo-oceans. In contrast, the data obtained from TIMS using 42Ca-48Ca double spike technique and a newly eveloped spatial vector calculation minimized the optimum external reproducibility to 21 ppm (1σ), which is well within the required precision. With this success, we used the TIMS techniques to measure the δ40/44Ca values of seawaters from south Okinawa trough (#1-10, 24°57'N-122°16'E, 10
m water depth) and southeast coast of Taiwan (FRI-SKII-S3, 22°10'N-121°10'E, 0 m water depth). These data are the first Ca isotope measurements for western Pacific seawaters. The δ40/44CaSRM915a values of these two seawater samples are -1.91 ± 0.16 (2σ) and -1.89 ± 0.05 (2σ). These results agree with the published global ocean data indicating the variation of seawater δ40/44Ca values is within 100 ppm (1σ).

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