臺灣博碩士論文加值系統

摘要
作為琉球隱沒系統弧後盆地的一部分，南沖繩海槽被認為是鄰近陸地的沉積物和有機物的重要貯庫。前人對石林隆堆 (GLM) 和棉花火山 (MHV) 熱液場址沉積物孔隙水的研究指出該區可能存在液態二氧化碳。本研究探討二氧化碳富集對沉積物碳地球化學──特別是陸源有機碳──的影響。與參考站點相比，兩個場址的富二氧化碳沉積物的溶解有機碳含量極高（達 11 mM），暗示有機物受到二氧化碳富集孔隙水溶解釋出。然而，總無機碳含量降低僅發生於MHV的富二氧化碳岩心，這暗示該站點暴露於二氧化碳富集狀態的時間比 GLM 富二氧化碳岩心更長。沒有明顯跡象表明，總有機碳和陸源有機碳 (以穩定碳同位素推算) 含量在富二氧化碳的沉積物中有減少。與之相對的是海源有機碳和木質素含量，兩者在MHV富含二氧化碳岩心的下部均有所降低。海源有機碳含量降低可能與是過去通量變化有關，但木質素含量降低與已發表的冰消期記錄不一致。此外，木質素的降解指標 ((Ad/Al)v) 在 MHV 富二氧化碳的沉積物中顯示出較低的比值。這些結果表明，在二氧化碳富集造成的長期弱酸性條件下，木質素發生了選擇性降解與釋出。整體而言，二氧化碳富集能對沉積物有機質造成降解或改變，但改變的程度取決於有機物的類型和沉積物暴露於二氧化碳富集狀態的時間。

Abstract
As part of the back-arc basin of the Ryukyu subduction system, the Southern Okinawa Trough is recognized as a significant repository for sediment and the associated organic matter from the nearby lands. Geochemical anomalies in the sedimentary porewaters of the Geolin Mound (GLM) and Mien-Hua Volcano (MHV) hydrothermal fields indicate the presence of CO2 impregnation. This study examines the effect of CO2 impregnation on sedimentary carbon geochemistry, with a specific focus on terrestrial organic matter. Compared to the reference sites, the CO2-rich sediment of both fields exhibited exceptionally high dissolved organic carbon (up to 11 mM), indicating the mobilization of organic matter by CO2. However, only the CO2-rich sediment of the MHV had lowered total inorganic carbon content, implying a longer exposure time to CO2 than the GLM CO2-rich sediment. There was no clear indication that the total organic carbon content and terrestrial organic carbon, derived from stable carbon isotopic values, decreased in the CO2-rich sediments. In contrast, isotopically derived marine organic carbon and lignin contents were both reduced in the lower part of the MHV CO2-rich core. While the lowered marine organic carbon contents may be explained by a changed carbon supply in the past, the lowered lignin contents do not align with the published deglaciation record. Moreover, the diagenetic alteration proxy of lignin ((Ad/Al)v) displayed a lowered ratios in the MHV CO2-rich sediment. These results suggest selective lignin depolymerization or mobilization under prolonged mild acidic conditions due to CO2 impregnation. Our results suggest that sedimentary organic matter undergoes alteration or degradation under the influence of CO2 impregnation, but the extent of change depends on the type of organic matter and the exposure time of the sediment to CO2.

Contents
論文審定書 ⅰ
摘要 ⅱ
Abstract ⅲ
Contents iv
List of figures vi
List of tables vii
Chapter 1. Introduction 1
1.1. Influence of hydrothermal systems on the chemistry of the marine environment 1
1.2. Water-rock interaction 1
1.3. Sedimentary hydrothermal system 3
1.4. CO2-rich sedimentary hydrothermal system of the Okinawa Trough 4
1.5. Impact of CO2 enrichment on sediment biogeochemistry 5
1.6. Purpose of this study 5
Chapter 2. Material and methods 8
2.1. Geological setting of the study area 8
2.2. Sample collection and pretreatment 9
2.3. Porewater analysis 11
2.4. Bulk analysis 11
2.5. Lignin analysis 12
2.6. Data processing 13
2.7. Data visualization 14
Chapter 3. Results 17
3.1. Porewater geochemistry 17
3.2. Solid-phase geochemistry 19
3.3. Solid-phase geochemistry of the surface sediment 21
Chapter 4. Discussion 26
4.1. Impact of CO2 enrichment on dissolved carbon 26
4.2. Impact of CO2 enrichment on solid-phase bulk carbon 27
4.3. Impact of CO2 enrichment on lignin 31
Chapter 5. Conclusion 35
References 36

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