| DI Pengfei,FENG Dong,CHEN Duofu. 2016. The distribution and variation in the gas composition of macro-seeps on the near-shore Lingtou Promontory in the South China Sea. Acta Oceanologica Sinica, 35(11):120－125 |
| The distribution and variation in the gas composition of macro-seeps on the near-shore Lingtou Promontory in the South China Sea |
| 南海北部莺歌海岭头岬近岸烃类渗漏喷口分布及气体地球化学 |
| Received:August 05, 2015 Revised:June 14, 2016 |
| DOI：10.1007/s13131-016-0955-1 |
| Key words:hydrocarbon seeps gas composition distribution nearshore Yinggehai northern South China Sea |
| 中文关键词: 烃类渗漏 气体组成 分布 莺歌海近岸 南海北部 |
| 基金项目: |
| Author Name | Affiliation | E-mail | | DI Pengfei | Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | | | FENG Dong | Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China | | | CHEN Duofu | Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China | dfchen@shou.edu.cn |
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| Abstract: |
| Natural hydrocarbon seeps in a marine environment are one of the important contributors to greenhouse gases in the atmosphere, including methane, which is significant to the global carbon cycling and climate change. Four hydrocarbon seep areas, the Lingtou Promontory, the Yinggehai Rivulet mouth, the Yazhou Bay and the Nanshan Promontory, occurring in the Yinggehai Basin delineate a near-shore gas bubble zone. The gas composition and geochemistry of venting bubbles and the spatial distribution of hydrocarbon seeps are surveyed on the near-shore Lingtou Promontory. The gas composition of the venting bubbles is mainly composed of CO2, CH4, N2 and O2, with minor amounts of non-methane hydrocarbons. The difference in the bubbles' composition is a possible consequence of gas exchange during bubble ascent. The seepage gases from the seafloor are characterized by a high CO2 content (67.35%) and relatively positive δ13CV-PDB values (-0.49×10-3-0.86×10-3), indicating that the CO2 is of inorganic origin. The relatively low CH4 content (23%) and their negative δ13CV-PDB values (-34.43×10-3--37.53×10-3) and high ratios of C1 content to C1-5 one (0.98-0.99) as well point to thermogenic gases. The hydrocarbon seeps on the 3.5 Hz sub-bottom profile display a linear arrangement and are sub-parallel to the No. 1 fault, suggesting that the hydrocarbon seeps may be associated with fracture activity or weak zones and that the seepage gases migrate laterally from the central depression of the Yinggehai Basin. |
| 中文摘要: |
| 烃类气体渗漏是海洋环境中甲烷等温室气体进入大气的一个重要来源。准确确定释放到大气中甲烷的量对全球碳循环与全球气候变化的影响有着重要的研究意义。莺歌海近岸海底分布着岭头岬、莺歌海河口、崖州湾和南山岬4个烃类渗漏活动区，并在海表面形成了一个近岸气泡带。本文通过对岭头岬渗漏区烃类渗漏喷口的空间分布与渗漏气泡的气体组成及其地球化学特征开展研究，发现岭头岬渗漏区渗漏的天然气气泡主要由CO2、CH4、N2和少量的重碳烃气体组成，与上升至海表面的气泡中气体组成明显不同，由此可见渗漏的天然气气泡在上升过程中可能发生了气体交换作用。海底渗漏气泡中二氧化碳含量高（67.35%）与，δ13CPDB比值为-0.49~0.86‰，表明二氧化碳是无机成因来源。而气泡中甲烷含量为23%，具有重δ13CPDB比值（-34.43~-37.53‰），高的干燥指数（0.98~0.99），表明甲烷为热成因来源，可能来自于中央坳陷区梅山组烃源岩。在3.5赫兹高分辨率的浅层剖面上，岭头岬渗漏区烃类渗漏喷口呈线性排列分布，且近平行于1号断层，表明烃类渗漏喷口的形成可能与薄弱带或小断裂有关，烃类气体沿着侧向运移通道运移至近岸海底。 |
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