台灣及香港海域珊瑚骨骼季節至百年尺度氣候與環境記錄

• Main Authors: 王博賢, Wang, Bo-Shian
• Other Authors: 地球科學系碩博士班, 游鎮烽, You, Chen-Feng
• Format: Thesis
• Language: English
• Published: 2011
• Subjects: Pacific; Ocean acidification
• Online Access: http://ir.lib.ncku.edu.tw/handle/987654321/114759; http://ir.lib.ncku.edu.tw/bitstream/987654321/114759/-1/index.html

造礁珊瑚骨骼的地球化學組成靈敏地反映礁區鄰近淺海環境變化，對於過去的氣候與海洋化學變化具有重要指標意義。為獲取更貼近自然的訊息，本研究首先發展一套符合實驗需求的標本清洗、化學前處理，乃至元素與硼、鉛同位素分析技術（第二章及附錄），並以此為基礎，應用於三支不同時間尺度的Porites屬珊瑚岩芯研究（先以一支綠島珊瑚岩芯、三年時間尺度作為測試，另外綠島及香港各有一支逾百年記錄的岩芯作為回推過去歷史的題材）。本文第三章著重於香港東岸淺海溶解態鋁、鋅及鉛濃度的時間序列變化。根據化學組成的變化，除了在二十世紀初期的海水溶解態鋁受造船工業影響而升高外，每逢戰爭時期，溶解態鋁濃度亦有明顯升高趨勢，然而鋅與鉛的變化則主要反映區域的工業活動；另外，近代的汙染源則主要來自中國南方的工業區。 延伸此章的概念於一支綠島北方的珊瑚岩芯（129年尺度），第五章使用鉛/鈣比值搭配鉛同位素示蹤技術。對應當地圍岩與氣溶膠鉛同位素組成，十九世紀末綠島北方的近岸海水的鉛主要由大氣輸入，而藉由當地圍岩化學風化而攜帶至海洋的鉛的比例則較低。然而，在使用含鉛汽油的時期（1920至1980年代），海水鉛濃度明顯提高（珊瑚鉛鈣比值升高），原本呈現區域特徵的鉛同位素訊號（亞洲-澳洲型分布）也明顯混入了源自北美的鉛（添入汽油的鉛錠）。為了解過去的海洋化學變化，第四章將所分析的珊瑚骨骼硼同位素轉換為pH指標。依據季節性珊瑚骨骼鍶鈣比值及氧、碳同位素為參考，間接驗證主控硼同位素組成變化的因子為海水pH值，因而忽略溫度及珊瑚共生藻對於硼同位素的影響；此假設與實驗室養殖的研究結果相符（H?nisch et al 2004）。本研究遂此重建立了綠島北方逾百年的表層海水歷史pH變化。結果顯示，海洋酸化在台灣東部海域並未呈現海洋酸化（石化工業排放二氧化碳所致）的趨勢；反之，藉頻譜分析結果，其長期的變化與週期約數十年的太平洋準週期氣候振盪（PDO，約45年為周期）有密切關聯。有趣的是，綠島珊瑚骨骼硼同位素和珊瑚海（Pelejero et al 2005）及澳洲大堡礁（Wei et la 2009）的珊瑚骨骼硼同位素記錄呈現反向趨勢的變化，反映了南北半球對稱性的氣候變化反應。 Scleractinian coral geochemistry reflects sensitively the change of shallow marine environment which implies further the past environmental conditions such as climate and seawater chemistry This work first developed experimental and analytical methodologies for coral sample pretreatments trace elements and boron and lead isotope ratio measurements (Chapter 2 and Appendices) These fundamental preparations were further applied on one short (3-year long record) and two centennial-long Porites coral cores Chapter 3 characterizes the secular variability of coral skeleton incorporated metallic ions aluminum (Al) zinc (Zn) and lead (Pb) in eastern Hong Kong Higher Al concentrations coincide tightly with the local war events associated with the dockyard industries held during the early 20th century while Zn and Pb were probably released mainly by industrial activities By contrast the major contaminants are recently contributed from the southern China industrial areas Furthermore a continuous study is carried out in a 129-year Lutao coral core (Chapter 5) based upon Pb/Ca ratio and lead isotope tracer According to the bedrock and aerosol Pb isotope compositions atmospheric deposition is preferred to contribute dissolved Pb in northern Lutao reef seawater rather than release from bedrock via chemical weathering during the late 19th century However the Pb/Ca results reveal considerable Pb input appear during the period of leaded gasoline (1920s to 1980s) This observation corresponds to the Pb isotope signature that the dominant local inputs (Asian-to-Australian type) in early stage was replaced by the exterior invasion (U S -Canadian type) Finally temporal variation of seawater pH is drawn in Chapter 4 based on boron isotope data The seasonal variation of δ11B with slight heavier in wet seasons is decoupled with Sr/Ca ratio and oxygen and carbon isotopes by which temperature and symbiotic effects on boron isotope are further ruled out This observation is consistent with the observation of coral culturing experiments that pH is the dominant factor on changing coralline δ11B (H?nisch et al 2004) Based upon this a centennial-long coral collected from northern Lutao was developed Unlike the expected ‘ocean acidification’ as a result of excessively industrial releasing of carbon dioxide (CO2) the reconstructed pH (by boron isotope) displays decadal fluctuation corresponding to the frequency of the Pacific decadal oscillation (PDO ~ 45 years) Interestingly the δ11B record fluctuates oppositely to those from the Coral Sea (Pelejero et al 2005) and the Great Barrier Reef (Wei et al 2009) as a result of hemispheric climatic dipole structure