碩士 / 國立臺灣大學 / 海洋研究所 / 89 / Sedimentation Dynamics off Northeastern Taiwan
Elucidated from Fallout Nuclides
Abstract
Encompassing the southernmost continental shelf and slope of the East China Sea, the Ryukyu Arc, the Okinawa trough, and a series of submarine canyons and ridges, the sea off northeastern Taiwan is an extremely complex (and important) area for geological and oceanographic studies. Despite focussed attention and heavy studies in numerous aspects by local and international researchers, modern sedimentation in this area remains poorly understood. To fill this gap, thirteen sediment cores were collected from this area and analyzed for fallout nuclides of natural (210Pbex) and anthropogenic (137Cs and 239,240Pu) origin. The purpose of this thesis study is to elucidate the sources, pathways, flux and budget of sediments in this all-important area.
From down-core profiles of nuclides, the derived sedimentation rates vary from 0.06 to 1 g/cm2/yr except in the adjoining East China Sea and the Ilan Ridge where there is probably no net sedimentation. The highest sedimentation rate is found at the lower slope down the Ilan shelf; from that locale, sedimentation rate decreases offshore and also along the axis of the Kuroshio toward the northeast. The general distribution of sedimentation rate suggests that down-slope transport from the Ilan shelf may be an important source of sediments in the Southern Okinawa Trough.
Spatial variations of nuclide inventories in sediments are similar to the distribution pattern of sedimentation rate. The observed 137Cs inventory in sediments is on average ~40% of that expected from direct atmospheric input, reflecting the relatively lower affinity of 137Cs for particles and the blocking effect of the fairly deep water in the study area (1000m on average). As for 210Pb and 239,240Pu, their sedimentary inventories are higher than values expected from direct atmospheric input by one order of magnitude, indicating that the study area is a strong sink for particle reactive nuclides. The extra inventories must be accounted for by lateral transport of 210Pb and 239,240Pu from the open ocean by Kuroshio followed by enhanced scavenging in the study area.
From the distribution of sedimentation rate, sedimentation flux in the Southern Okinawa Trough covered in this study was calculated to be 13.6 Mt/yr. The three possible sediment sources are: the Lanyang River (8.0 Mt/yr), other rivers in eastern Taiwan (0-5.6 Mt/yr), and down slope transport from the East China Sea shelf via the submarine canyons (0-5.6 Mt/yr).
摘要 i
目錄 iv
圖目 vi
表目 viii
第一章 緒論
1-1. 台灣東北海域之地質及水文特性
1-1.1. 台灣東北海域之海洋地質概況 1
1-1.2. 水文流場概況 3
1-2. 研究背景 3
第二章 研究方法
2-1. 採樣區域 6
2-2. 沉積物採樣及分樣方法 6
2-3. 標本前處理
2-3.1. 前處理步驟 6
2-3.2. 沉積物物理性質計算 6
2-4. 分析方法及計算方式
2-4.1. 210Pb 9
2-4.2. 239,240Pu 11
2-4.3. 137Cs與214Pb 14
2-5. 分析儀器及其校正
2-5.1. 阿爾發能譜儀 14
2-5.2. 伽瑪能譜儀 16
2-6. 分析品質之監控
2-6.1. 阿爾發能譜儀 19
2-6.2. 伽瑪能譜儀 19
第三章 實驗結果與討論
3-1. 沉積物之累積作用：以210Pbex為指標
3-1.1. 210Pbex於沉積動力學的應用原理 23
3-1.2. 台灣東北海域由210Pbex估算出之表觀沉積速率 28
3-2. 沉積物之累積作用：以人工核種137Cs及239,240Pu為指標
3-2.1. 人工核種於沉積動力學的應用原理 29
3-2.2. 台灣東北海域以人工核種求得之沉積速率 31
3-3. 沉積物的混合作用 32
3-4. 沉積物中放射性核種之來源與分布
3-4.1. 210Pbex、137Cs及239,240Pu大氣輸入通量期望值 36
3-4.2. 210Pbex、137Cs及239,240Pu於沉積物中儲量分布 39
3-4.3. 210Pbex、137Cs及239,240Pu之來源 39
3-5. 南沖繩海槽沉積物來源 46
3-6. 南沖繩海槽之沉積物收支 49
第四章 結論 51
致謝 55
參考文獻 57
| Identifer | oai:union.ndltd.org:TW/089NTU00279025 |
| Date | January 2001 |
| Creators | Shih-Yu Lee, 李時雨 |
| Contributors | Chih-An Huh, Ju-Chin Chen, 扈治安, 陳汝勤 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 63 |
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