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博碩士論文 etd-0830110-203306 詳細資訊
Title page for etd-0830110-203306
論文名稱
Title
內波淺化對東沙環礁水文垂直混合影響之觀測研究
The observation of vertical mixing induced by shoaling of internal waves at Dongsha Atoll.
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
109
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2010-07-09
繳交日期
Date of Submission
2010-08-30
關鍵字
Keywords
淺化、東沙環礁、垂直混合、內波
internal waves, shoaling, Dongsha Atoll, Vertical mixing.
統計
Statistics
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The thesis/dissertation has been browsed 5684 times, has been downloaded 27 times.
中文摘要
摘要
南海內波由呂宋海峽產生,向西傳遞至南海北部,最後消散於西側大陸棚上,而東沙環礁為內波必經之處,當內波通過時其內部強勁的流場促使海水上下層造成強烈的混合及擴散,除此之外,內波能將深層冷水具高營養鹽的海水帶至淺層較暖的海水進行混合,本研究利用海研三號共7個航次CTD資料與4組採水資料並搭配錨錠溫度計串與衛星觀測進行分析,探討內波對東沙海域造成水文特性的差異。
由採水分析結果顯示溫度對營養鹽兩者關係顯示有良好的負相關,即低溫具有高營養鹽的特性,且測得環礁外圍氮磷比值其表層水為1:1,中下層水為12:1,低於Redfield-ratio值(16:1),具南海上層水之特性,氮鹽為限制浮游生物生長因子,為一貧營養鹽缺氮之海域,表層氮鹽因光合作用消耗殆盡。從OR3-1246航次與OR3-1291航次的CTD溫度、鹽度、螢光值濃度及密度之垂直結構與溫度計串資料顯示,當取樣在內波上時,下沉型內波能將表層暖水、低鹽度、高螢光值濃度及密度較低的水往下帶,於淺化過程中造成水體混合導致在垂直結構上螢光值濃度變高,且由OR3-1218航次(2007年4月28~29日)連續18小時CTD觀測發現,因下沉型內波的作用導致水團在垂直結構上混合的很均勻。
若取樣不在內波上時,由OR3-1291航次(2008年5月7日)CTD觀測得知當內波通過後比對無內波時,在水深50公尺,溫度差約6℃,鹽度差約0.23(psu),密度差約1.8( ),螢光值濃度差約0.07(μg/L),顯示當內波通過後,有18℃的冷水湧升至水深50公尺。在CTD密度方面,發現內波前水體主要為兩層水體,因內波影響經混合及擴散後使得水體呈多層分佈。
南海內波行經東沙環礁因地形變淺,及內波產生繞射作用而分裂成南北兩邊,最後會合至環礁西邊且繼續朝西北邊前進,為瞭解內波淺化對環礁外圍之影響,將環礁分區個別探討,由分析結果得知環礁南邊較另三區易產生營養鹽抬升的現象,而葉綠素濃度卻是環礁東邊和北邊高於南邊和西邊,顯示營養鹽及葉綠素濃度分佈可能受地形限制之影響,由於環礁東邊與北邊其水深較淺加上有大陸棚的支持,受內波影響將底層高營養鹽帶至陸棚區,並經由浮游生物反應使葉綠素濃度增高,而在環礁南邊和西邊,因水深較深且無陸棚區,高營養鹽的冷水抬升後無法滯留並隨水團移動,造成葉綠素濃度偏低,此結果印證了由衛星所拍攝的葉綠素影像常在環礁東邊與北邊發現有高葉綠素值產生的原因。
Abstract
Abstract
Internal waves have been identified as one of the most active mechanisms producing vertical mixing in continental slope and shelf waters. The major contribution of mixing are due to internal tides, however, shorter period internal waves are unlikely to be the main source of energy for mixing, especially on the inner part of the continental shelf. In this study, we observe the vertical mixing of huge internal waves in the Dongsha Atoll South China Sea. These solitary waves were originate near the Luzon Strait, propagated westward across the basin, evolving into internal solitary wave trains and dissipated at the western shallow continental shelf. The wave energy and phase speed reduced significantly during the shoaling process. Internal waves and their likely related induced mixing phenomena are analyzed based on multiple cruises of observations consisted of CTD hydrographic measurements, water samples and moored thermister strings. Data analyses show that the mixing processes are related to depths of water and the interfacial of wave. For depression wave in the deep water zone, upper layer water may push downward producing vertical mixing beyond the thermocline. The mixing usually dilutes the nutrients in the upper layer of water column. Statistics suggest that the N:P ratio is 12:1 which is lower than the standard value (16:1) indicating the region is nitrogen deficit, similar to most of the surface water in South China Sea.
The depression solitons in deep water may evolved to a packet of elevation waves in the shallow water area at “turning point” of approximately equal depth of upper and lower layers. The mixing of shallow water internal waves can entrain cold nutrient rich water from the lower layer into the frequently nutrient depleted subsurface layer to enhance the local coral reef ecosystem. For example, CTD profiles (2008.5.7) before and after the passage of internal wave show large differences. The vertical density distribution has dramatic change. The column was stratified in two layers in normal condition. The internal waves perturbed the water column into stepwise multi-layer density distribution. The water at 50 m showed temperature decrease by 6 ℃, salinity increase by 23 psu, density increase by 1.8 , fluorescence decrease by 0.065 μg/L etc. The MODIS chlorophyll images confirm the high concentration fertilized by the internal wave pumping near the NE region of the Dongsha Atoll.
目次 Table of Contents
目錄
中文摘要..................................................................................I
英文摘要................................................................................III
目錄.........................................................................................V
圖目錄...................................................................................VII
表目錄.................................................................................XVI
第一章、前言.........................................................................1
1-1.背景介紹..........................................................................1
1-2.文獻回顧..........................................................................4
1-3.研究目的.......................................................................11
第二章、現場觀測與資料蒐集..........................................13
2-1.CTD水文觀測...............................................................13
2-2.水質採樣資料...............................................................17
2-3.MODIS衛星資料..........................................................20
第三章、資料處理與分析方法..........................................21
3-1.資料品管.......................................................................21
3-1-1.CTD品管...................................................................21
3-1-2.採水資料品管...........................................................22
3-2.分析方法.........................................................................2
3-2-1.迴歸分析(Regression Analysis).....................22
3-2-2.浮力頻率(Buoyancy frequency).............................23
3-2-3.層化穩定參數(Richardson number)....................24
3-2-4.經驗正交函數分析(EOF).........................................25
第四章、結果與討論..........................................................26
4-1.溫度與營養鹽的關係...................................................26
4-2.內波前後溫度與中層營養鹽及葉綠素的差異...........32
4-3.內波之垂直混合作用...................................................37
4-4.環礁東、西、南、北邊營養鹽垂直分佈之比較.......59
4-4-1.環礁東邊與南邊.....................................................59
4-4-2.環礁北邊與西邊.....................................................64
4-5.溫度和螢光之EOF分析...............................................69
第五章、結論與建議..........................................................77
5-1.結論...............................................................................77
5-2.建議...............................................................................79
第六章、參考文獻..............................................................81
附錄A.CTD測站資料表......................................................84
附錄B.水質測站資料表......................................................88
參考文獻 References
第六章、參考文獻
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