Particle Scavenging in the Nearshore Waters of Western Taiwan: 234 Th / 238 U Disequilibrium Elucidation

本研究利用海研二號（ORII-1248，2004年11月19日至23日），沿台灣西岸進行採樣工作，沿航跡使用表水監測系統觀測表水溫度、鹽度、透光度及螢光連續訊號。除基本水文資料外，採集水樣進行營養鹽、葉綠素a、顆粒態有機碳、初級生產力，以及細菌生產力等參數的分析。本研究目的為探討污染嚴重的台灣西部近岸水體顆粒動力機制。 由螢光和消光係數隨緯度的變化可知，南北海域顆粒組成差異大。以北緯23.67度為分界，台灣西南部近岸海域顆粒組成以生物性顆粒為主，西北部近岸海域顆粒組成則為無機性顆粒支配。高懸浮顆粒濃度導致溶解態234Th活度極低且變化大（0.1-0.75dpm/L），活度低值總出現在輸砂量高的台灣西部五大河口地區。與溶解態234Th活度相較，顆粒態234Th活度於台灣西南部近岸海域變化小，在台灣西北部近岸海域則與溶解態234Th活度呈鏡像分佈關係。本研究使用穩定狀態水平傳送清除模式估算清除現象強烈的台灣西部近岸水體，顆粒去除速率和停留時間，溶解態234Th與顆粒態234Th停留時間分別為<0-16天和<0-10天。During November 19-23, an intensive sampling expedition in the coastal region off western Taiwan (Cruise #: ORII-1248) was carried out. A total of 27 stations were occupied to collect large-volume seawater for dissolved and particulate 234Th measurements. In addition to the basic hygrographic parameters (T, S, fluorescence and light transmission), separate samples for the measurements of nutrients, particulate organic carbon, primary productivity and bacteria production were also collected. The investigation is aimed to provide information of particle dynamics in the nearshore waters of highly populated west coast of Taiwan. Latitudinal distributions of fluorescence and light transmission evidently indicate that particle compositions in the northern and southern regimes are very different. Divided by Cho-Shuei River system at about 23°40’N, particles in the northern regime are characterized by terrigeneous characteristics whereas those in the southern regime are dominated by biological origin. Resulted from high turbidity, the dissolved 234Th activities are extremely low, ranging between <0.1 dpm/L and 0.75 dpm/L, and show drastic latitudinal variability. Low dissolved 234Th activities are usually associated with the five river systems reported with high particulate loads. Particulate 234Th activities showed less drastic change than dissolved 234Th in the southern regime (average value of ~0.3 dpm/L), whereas those in the northern regime are mirror-imaged with dissolved 234Th activities. Large deficiency of 234Th relative to 238U indicates an active scavenging-removal phenomena prevailing in the nearshore waters. An advection-scavenging-removal model was be adopted to derive scavenging and removal rates of 234Th. Dissolved 234Th residence time and particulate 234Th residence time are <0-16 days and <0-10 days, respectively.目錄……………………………………………………………………….I 圖目錄…………………………………………………………………..III 中文摘要………………………………………………….......................V 英文摘要………………………………………………..…....................VI 第一章 緒論……………………………………………………………..1 第二章 研究方法………………………………………………………..3 2.1表水監測（Underway）與溫鹽深儀（CTD）資料…..…………3 2.1.1探針型號………………………………………………..3 2.1.2 Underway與CTD數據檢討………………….………..3 2.1.3數據率定………………………………………………..4 2.2水樣分析……………………………………………………...4 2.2.1總懸浮顆粒濃度（TSM）……………………………….4 2.2.2溶解態與顆粒態234Th活度（DTh, PTh）…..….……….5 2.2.3顆粒態有機碳濃度（POC）……………………………..5 第三章 結果與討論………………………………………………..……8 3.1台灣西部近岸海域環境特徵……………………..…………...8 3.2 234Th清除機制…..………...…...…………………………….17 3.3分佈係數……………………………………………………...22 3.4清除模式……………………………………………………...26 3.4.1二維不可逆清除模式…………………………………..26 3.4.2 234Th停留時間與清除速率……...…………………….30第四章 結論……………………………………………………………36 參考資料…………..…………………………………..………………..38 附錄1 測站位置、經緯度、深度，以及河流名稱………………………42 附錄2 ORII-1248航次分析參數與參與單位………………………….43 附錄3 探針型號與序號…..……………………………………………44 附錄4.1 溫鹽深儀（CTD）與表水溫鹽儀（SCTD）溫度參數相關圖…45 附錄4.2 CTD與SCTD鹽度參數相關圖……..………………….…….45 附錄4.3 CTD與SCTD消光係數相關圖……………………….……...46 附錄4.4 CTD與SCTD螢光值相關圖……………………….………...46 附錄5 總懸浮顆粒濃度（TSM）與消光係數（BAC）相關圖…………47 附錄6 測站參數資料…………………………………..………………48 圖目錄 圖 頁數 1 ORII-1248採樣測站…………………………………………………7 1.1 ORII-1248航跡圖……………………………………...…….............7 2 台灣西部近岸水體溫度與鹽度隨緯度的變化……………………10 3 台灣西部近岸水體螢光值與消光係數隨緯度的變化……………11 4.1 螢光值與消光係數相關圖…………………….…………….....….12 4.2 色素總濃度與總懸浮顆粒濃度相關圖………………..………….12 5 葉綠素a濃度與總懸浮顆粒濃度隨緯度的變化……………….…13 6 台灣西部近岸水體顆粒體色素含量和顆粒體有機碳含量隨緯度的 變化..………………………………….…………………………….14 7 曾文溪至高屏溪海域間，總懸浮顆粒濃度與葉綠素a濃度和磷酸 鹽濃度相關圖………...……………………………………..………15 8 台灣西部近岸水體溶解態234Th活度和矽酸鹽濃度隨緯度的變化… ………………………………………………………………………16 9 台灣西部近岸水體溶解態與顆粒態234Th活度隨緯度的變化.......20 10 曾文溪至高屏溪海域間，溶解態234Th活度與矽酸鹽濃度相關圖…. ……………………………………………………………................21 11 台灣西部近岸水體234Th分佈係數與碳分佈係數的對數值隨緯度的變化………..………………………………………………………...24 12本航次與其他近岸表水LogKdTh、LogTSM資料的比較…………..25 13水平傳送清除模式（advection-scavenging-removal model）……….32 14台灣西部近岸水體溶解態234Th與顆粒態234Th停留時間隨緯度的 變化…..……………………………………………………………..33 15溶解態234Th停留時間與總懸浮顆粒濃度相關圖…………………34 16台灣西部近岸水體清除速率常數與顆粒沉降速率常數隨緯度的變 化…..………………………………………......……………………3