海洋碳循環與氣候變遷之間存在錯綜複雜的關聯，顆粒有機碳輸出是碳封存的重要途徑，儘管利用沉積物收集器收集水層中特定深度的沉降顆粒是一種最直觀的測量方法，但由於時間與空間分佈限制，離散的觀測結果可能無法充分解釋序列變化。釷鈾不平衡法利用顆粒活性放射性核種—釷-234 (Th-234) 作為顆粒有機碳的示蹤劑，被廣泛運用於估算顆粒有機碳輸出通量 (particulate organic carbon flux，POC flux = [POC/Th-234] × Th-234 flux)，然而這個方法之主要參數 POC/Th-234存在很大的變異性，導致碳通量測量結果常偏離沉積物收集器測得的資料。本研究於臺灣西南沿海、南海北部及西北太平洋實際比較兩種方法得到的數據，並探討如何更有效利用Th-234作為顆粒態有機碳示蹤劑。漂浮式沉積物收集器測量POC flux實測值 (Mean ± SE) 為59.3 ± 2.8 (29.7–131.1)、56.1 ± 4.2 (33.4–99.8)、58.1 ± 7.2 (39.5–96.7) (mgC m-2 d-1)，而釷鈾不平衡法得到POC flux分別是64.8 ± 3.5 (22.5–144.2)、57.4 ± 4.1 (36.2–116.0)、60.2 ± 7.3 (31.8–99.0)，釷鈾不平衡法估算的碳通量約為實測值的1.1 ± 0.3倍，以兩種方法測得之平均POC flux在三個海域無顯著統計差異 (p > 0.05)，但實際上個別數值的最大差異達到1.7–2.4倍，顯示當Th-234 flux及POC/Th-234直接使用沉積物收集器的沉降顆粒測量時，此方法可用於大尺度估算碳通量。三個不同海洋環境的顆粒態有機碳與Th-234的比例具有顯著差異 (p < 0.001)，平均POC/Th-234 (μmolC dpm-1) 為1.95 ± 0.08、2.73 ± 0.16、3.47 ± 0.29，西北太平洋的比值高於南海北部，而當南海北部偏向黑潮水團性質時，也傾向於測得較高的POC/Th-234比值。不同海洋環境之間POC/Th-234比值的變異，主要是由於Th-234活度的差異所造成。

The ocean carbon cycle is intricately linked to climate change, with biological carbon pump (known as particulate organic carbon (POC) export) being a critical pathway for carbon sequestration. Sediment traps are the most straightforward method for collecting sinking particles at specific depths in the water column, but the limits of temporal and spatial coverage mean that discrete observational results may not fully capture sequential changes. The thorium-234/uranium-238 disequilibrium method, which uses the particle-reactive radionuclide thorium-234 as a tracer for POC, is widely used to estimate POC flux (= [POC/Th-234] × Th-234 flux). However, due to significant variability in the POC/Th-234 ratio, a key parameter in this method, leading to POC flux measurements often differ from sediment trap data.
In this study, we compare data obtained from both methods in the southwestern coast of Taiwan (SWCT), the northern South China Sea (NSCS), and the northwest Pacific Ocean (NWPO), to improve the utilization of thorium-234 as a tracer for POC flux estimation. Using sediment traps, POC flux (Mean ± SE) were 59.3 ± 2.8 (29.7–131.1), 56.1 ± 4.2 (33.4–99.8), 58.1 ± 7.2 (39.5–96.7) (mgC m-2 d-1) in SWCT, NSCS and NWPO, respectively, while the thorium-uranium disequilibrium method yielded POC flux values of 64.8 ± 3.5 (22.5–144.2), 57.4 ± 4.1 (36.2–116.0), 60.2 ± 7.3 (31.8–99.0). The POC flux estimated by the thorium-uranium disequilibrium method was approximately 1.1 ± 0.3 times the value obtained from sediment traps. While there was not statistically significant difference in mean POC flux between the three regions (p > 0.05), the distinct values could be as large as 1.7 to 2.4 times, indicating that the method can be used for large-scale POC flux estimation when Th-234 flux and POC/Th-234 are measured directly from sediment traps.
The ratio of POC to thorium-234 varies significantly among the three different marine environments (p < 0.001), with mean POC/Th-234 (μmolC dpm-1) of 1.95 ± 0.08, 2.73 ± 0.16 and 3.47 ± 0.29, respectively. The NWPO exhibits higher ratios than the NSCS, and the latter showing higher ratios when influenced by the Kuroshio intrusion into the South China Sea. These variations in POC/Th-234 ratios among different oceanic environments are primarily due to differences in thorium-234 activity.

論文審定書 i
摘要 ii
Abstract iii
目錄 v
圖目錄 vii
表目錄 vii
第一章 前言 1
1-1 藍碳 1
1-2 碳通量 2
1-3 研究現況 4
1-4 研究目的 7
第二章 材料與方法 8
2-1 研究區域 8
2-2 採樣方法 8
2-3 樣品分析 9
2-3-1 釷-234活度 (Thorium-234 Activity) 9
2-3-2 顆粒態有機碳 (Particulate Organic Carbon，POC) 9
2-4 資料處理 10
2-4-1 釷鈾不平衡法 10
2-4-2 Martin curve 10
2-4-3 海洋聖嬰指數 (Oceanic Niño Index，ONI) 11
2-5 統計敘述與檢定 11
第三章 結果與討論 13
3-1 不同海洋環境的顆粒態有機碳通量與釷-234通量 13
3-2 顆粒態有機碳通量估算 14
3-2-1 沉積物收集器與釷鈾不平衡法之比較 14
3-2-2 顆粒態有機碳通量垂直衰變率 16
3-3 顆粒態有機碳通量與釷-234通量隨收集時間之變化 17
3-4 海洋環境變化下顆粒態有機碳通量與釷-234通量之比例變化 18
3-4-1 季節至年間變異與氣候震盪之影響 18
3-4-2 顆粒有機碳通量估算之不確定性討論 21
第四章 結論 23

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