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標題: | 重建末次冰期以來南海西部表層海水酸鹼值及水文特性 Deglacial changes in surface ocean pH and hydrologic condition in the western South China Sea |
作者: | Yun-Ju Sun 孫韻如 |
指導教授: | 任昊佳(Hao-Jia Ren),黃國芳(Kuo-Fang Huang) |
關鍵字: | 南海,硼同位素,pH值代用指標,微量元素比值代用指標, South China Sea,Boron isotopes pH-proxy,Trace element ratios multiproxies, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 解構古海洋碳循環及重建水文特徵有助於瞭解未來氣候在冰期/間冰期尺度下的變化。在末次冰消期間,深海儲存的二氧化碳隨著大洋湧升流上湧至表水,成為現今大氣中的二氧化碳的主要來源。現今的海洋學研究已知,由於大尺度海陸交互作用的影響,邊緣海對於驟變氣候的反應較大洋靈敏。然而,目前研究對於此時間段下邊緣海所扮演之角色仍瞭解甚少。因此,本研究試圖重建南海西部在末次冰消期間的表層海水酸鹼值及水文狀態(表層海水溫度、湧升強度)。本研究首先建立一套可量測少量有孔蟲殼體的硼同位素及微量元素比值的方法,利用微昇華技術純化硼同位素,並搭配多接收器感應耦合電漿質譜儀(MC-ICP-MS)及高解析感應耦合電漿質譜儀(HR-ICP-MS),對於硼同位素的分析精準度可優於 ±0.30 ‰ (2SD),而微量元素比值(Mg/Ca, B/Ca, Li/Ca, Ba/Ca and U/Ca)可優於 ±2.0 % (2SD)。
本研究分析取自岩心MD05-2901中的浮游有孔蟲 (Globigerinoides sacculifer) 並應用多個代用指標來研究末次冰期以來南海西部表層海洋的海水酸鹼值及水文特性。研究結果顯示,南海西部在末次冰消期間釋放出相較於現今更多的二氧化碳,成為大氣中二氧化碳的來源 (source)。在此時間段下,整個南海海水表溫主要受到緯度的影響,並且冰期時西部南海的海水表溫與晚全新世的海溫約相差3度。此外,結合有孔蟲殼體Ba/Ca所重建的湧升強度可得知,南海西部的水文特徵主要受東亞夏季季風所控制。 Deciphering ocean carbon system and hydrologic variability is a key to further our understanding of global carbon cycle and climate dynamics within the glacial-interglacial cycles. During the last deglaciation, oceanic carbon dioxide (CO2) outgassed from upwelling regions in the open ocean has been considered to be the main source of CO2 in the atmosphere. However, marginal seas receive less attention despite they are potential CO2 sources based on the modern observations and more sensitive to abrupt climate changes through ocean-atmosphere teleconnection. In this study, we focus on reconstructing surface ocean pH and hydrologic conditions (sea surface temperature and upwelling intensity) in the western South China Sea (W-SCS) during the last deglaciation. A new analytical protocol is established for measuring the isotopic composition of boron (δ11B) and trace element ratios (TEs) in small sample sizes (< 2 mg) of foraminifera using MC-ICP-MS and HR-ICP-MS, respectively. By applying micro-sublimation technique, the external precision for δ11B determination is better than ± 0.30 ‰ (2SD), while for TEs (e.g. Mg/Ca, B/Ca, Li/Ca, Ba/Ca and U/Ca) is better than ± 2.0 %, (2SD). Multi-proxies approach is applied for planktonic foraminifera (Globigerinoides sacculifer, mixed-layer dwelling species) collected from sediment core MD05-2901 (water depth 1454 m, located at the summer upwelling region off middle Vietnam) in the W-SCS The reconstructed surface water pH values derived from the δ11B values suggest that the W-SCS was a CO2 source throughout the last deglaciation, and the flux of CO2 was greater than that of the modern condition. This is most likely influenced by the degree of the basin-wide vertical mixing within the entire SCS basin during the last deglaciation. The Mg/Ca-SST record indicates a latitudinal control since the Last Glacial Maximum, and the late Holocene SST was ~3°C higher than the glacial period. Combining with the upwelling intensity derived from the foraminifera-based Ba/Ca record, the deglacial hydrologic variability in the W-SCS is mainly controlled by the East Asian Summer Monsoon. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/7716 |
DOI: | 10.6342/NTU201703149 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 地質科學系 |
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