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  • 學位論文

台灣西北近岸環境中釷-234、鉛-210和釙-210的地化特性比較

Comparative Geochemical of 234Th, 210Pb, and 210Po in the Nearshore Waters off Northwestern Taiwan

指導教授 : 魏慶琳

摘要


本論文利用海研二號1345航次於2006年4月17~20日採集台灣西北淡水河口近岸海域表水樣本,量測溶解態和顆粒態234Th、210Pb及210Po三核種於表水的活度,探討和比較此三核種於近岸的清除作用,並佐以葉綠素(Chlorophyll-a)、營養鹽 (NO2、NO3、PO4、SiO2、NH3) 、顆粒有機碳 (POC) 及其他化學參數,比較三核種的生地化循環和行為,並以這三核種作為顆粒體的示蹤劑,探討親顆粒微量元素和顆粒有機碳的通量。 於研究海域, 234Th活度受到顆粒清除作用的影響相對於母核種238U的活度,呈現不足的狀態;與其他研究不同,210Pb於研究海域的活度低於母核種226Ra活度,可能為226Ra於近岸的活度高於SiO2估算值使然; 210Po與210Pb活度於顆粒相及溶解相的比值於此研究區域皆大於1, 顯示此區域210Po再礦化作用相對於母核種210Pb有過剩的現象。 本論文以清除模式估算台灣西北近岸海域234Th、210Pb及210Po的移除通量及滯留時間。234Th於此研究區域的滯留時間範圍為3~15天,210Pb於此研究區域的滯留時間範圍為1~3天,210Po於此的滯留時間範圍則為13~40天。經過清除模式得到的234Th、210Pb及210Po三核種在台灣西北近岸的移除通量,分別為1093 ± 61 dpm/m2/d、755 ± 2 dpm/m2/d、74 ± 1 dpm/m2/d。以234Th、210Po作為海洋中顆粒有機碳的示蹤劑,運算出的顆粒有機碳輸出通量為6.9~33.4 mmol/m2/d。

並列摘要


Large-volume surface seawater samples were collected during 17~20 April 2006 (OR2-1345) in the nearshore waters off northwestern Taiwan for the determinations of dissolved and particulate 234Th, 210Pb, and 210Po. Along with the radionuclides, data of chlorophyll-a, nutrients, particulate organic carbon, and other hydrographic parameters were also determined. The aim of this study is to compare the geochemical behaviors of the three particle-reactive radionuclides and, using the three radionulides as particle tracers, to estimate the removal flux of particulate organic carbon in the nearshore water. In the study area, 234Th is deficient with respect to 238U due to enhanced particle scavenging. Different from most of the literatures, 210Pb is lower than 226Ra, which may be caused by inaccurate estimation of 226Ra activity by the SiO2-226Ra relationship. Activity ratio of 210Po to 210Pb ratios is > 1 in both dissolved and particulate phases, demonstrating regeneration of 210Po in the nearshore environment. Removal fluxes and residence times of 234Th, 210Pb, and 210Po in the nearshore waters off northwestern Taiwan were estimated by the scavenging model. The residence time ranges from 3 to 15 days, from 1 to 3 days, and from 13 to 40 days, for for 234Th, 210Pb, and 210Po, respectively. The removal fluxes of 234Th, 210Pb, and 210Po are 1093 ± 61 dpm/m2/d, 755 ± 2 dpm/m2/d, and 74 ± 1 dpm/m2/d, respectively. Using 234Th and 210Po as proxies of particulate organic carbon, the removal flux of POC ranges from 6.9 to 33.4 mmol/m2/d in the nearshore waters off northwestern Taiwan.

參考文獻


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被引用紀錄


田弘安(2015)。南海東沙島小潟湖內放射性核種(釷-234、鉛-210及釙-210)與顆粒體關係之探討〔碩士論文,國立臺灣大學〕。華藝線上圖書館。https://doi.org/10.6342%2fNTU.2015.01812

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