紅柴海溝234Th, 210Pb, 及 210Po 生地化行為之比較

Comparative Geochemistry of 234Th, 210Pb, and 210Po in the Hung-Tsai Trough

周伶樺(Lin-Hwa Chou)

指導教授 ： 魏慶琳

國立臺灣大學/理學院/海洋研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00374

摘要

本論文利用海研一號784航次（2006年3月6日至8日）在台灣西南海域之紅柴海溝三個測站採集樣本，進行溶解相及顆粒相234Th、210Pb及210Po的分析，佐以營養鹽、POC、以及其他水文化學參數的垂直剖面，來了解這三種天然放射性核種的生地化作用有何異同，並與海研一號742航次（2004年12月24日至26日）及海研一號744航次（2005年3月3日至6日）的數據做比較。
OR1-784航次三個測站溶解相、顆粒相之234Th、210Pb、及210Po隨深度垂直變化趨勢一致，且測站之間差異不大。由OR1-784、OR1-742、OR1-744三個航次之234Th/238U與210Po/210Pb母子核種分布結果顯示，母子核種間活度不平衡現象的季節變化不明顯，唯210Pb/226Ra比值可看出春季大於1，而冬季則小於1。
整個紅柴海溝水體，234Th相對於母核種238U為缺乏的狀態，210Pb相對於母核種226Ra則顯現超量的現象。在紅柴海溝表層海水中，210Po相對於210Pb則呈現缺乏的現象，而中層海水210Po則為超量的情形。由234Th、210Pb、及210Po 的分佈係數比較，可看出在紅柴海溝內，此三核種對顆粒體的親和性順序為210Po＞234Th≒210Pb。
本論文利用盒子模式並納入水平傳輸的影響所估算之紅柴海溝水體中溶解相及顆粒相234Th、210Po滯留時間分別為8天及5天，15天及4天，總相210Pb滯留時間則為15天。
利用234Th通量作為顆粒態有機碳示蹤劑，估算得到紅柴海溝光透層（80 m）以上顆粒態有機碳輸出通量為40 mmolC/m2/d，若以210Po通量及顆粒體中210Po和有機碳比值估算得到顆粒態有機碳輸出通量則為64 mmolC/m2/d，兩結果相差不大。

關鍵字

紅柴海溝 ； 234Th ； 210Pb ； 210Po ； 滯留時間 ； 顆粒態有機碳

並列摘要

Large-volume seawater samples were collected from three locations during 6~8 March 2006 (OR1-784) in the Hung-Tsai Trough off Southwestern Taiwan for the determinations of dissolved and particulate 234Th,210Pb, and 210Po. Along with profiles of nutrients, particulate organic carbon, and other hydrographic parameters, the geochemical behaviors of the three radionulides were compared.
Detailed profiles of dissolved and particulate 234Th,210Pb, and 210Po activities showed no significant difference among the three sampling stations. By comparing the distributions of 234Th/238U and 210Po/210Pb ratios at the same station obtained from three cruises (OR1-784, OR1-742, and OR1-744), no seasonal variability for the disequilibria was found. However, the 210Pb/226Ra ratio showed an excess in the spring and deficient in the winter.
In the entire water column of the Hung-Tsai Trough, 234Th is deficient relative to 238U, and 210Pb is excessive relative to 226Ra. 210Po is deficient in the surface layer but is excessive in the intermediate layer relative to 210Pb. The distribution coefficients of 234Th,210Pb, and 210Po show the order of the affinity toward particulate matter is 210Po > 234Th ~ 210Pb in the Hung-Tsai Trough.
This study uses box model incorporating the horizontal advection to estimate the residence times of the three radionulides. The residence times of dissolved and particulate are 8 and 5 days, 15 and 4 days, and total 15 days, respectively, for 234Th, 210Po, and 210Pb in the water column of the Hung-Tsai Trough.
By using 234Th and 210Po as proxies of particulate organic carbon to estimate the export flux from the upper 80 m in the Hung-Tsia Trough, the export flux are 40 mmolC/m2/d and 64 mmolC/m2/d, respectively. The results show that the two approaches are similar.

並列關鍵字

Hung-Tsai Trough ； 234Th ； 210Pb ； 210Po ； residence time ； particulate organic carbon

參考文獻

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