Journal of Tropical Oceanography >
In situ quantification of oil-gas bubble seep flux from cold seeps at the seabed ― a case study of GC600 in the Gulf of Mexico
Received date: 2022-09-28
Revised date: 2022-11-22
Online published: 2023-03-14
Supported by
National Natural Science Foundation of China(41676046)
National Key R&D Program of China(2017YFC0307704)
Natural Science Foundation of Guangdong Province(2019A1515011809)
Key Research and Development Plan of Hainan Province(ZDYF2021SHFZ060)
Natural cold seeps in the marine environment are important sources of organic compounds, such as methane and other greenhouse gases, to the ocean and atmosphere. Accurate quantification of methane bubbles flux at hydrocarbon seeps is therefore necessary to evaluate their influence on the global methane budget and climate change. A deep-sea high-definition video time-lapse camera was used to observe the gaseous and oily bubbles released from Mega Plume 2 vent in the GC600 cold seep in the Gulf of Mexico and obtained the video clips of continuous oil bubble release. A semi-automatic bubble counting algorithm was used to estimate the oil bubble number and release rates of Mega Plume 2 from video data. Image processing techniques were used to determine the bubble type (oily, mixed, and gaseous), and size distribution. The Mega Plume 2 vent at GC600 released a mixture of oily and gaseous bubbles with an average diameter of 2.56 mm ±1.01 mm at a rate of 80.25 bubbles·s-1. The oil-gas bubbles flux released from Mega Plume 2 is 177.7 m3·yr-1 (19.55~106.62 T·yr-1). However, the bubbles release rate was not correlated with tidal effects and may be linked with other factors, such as hydrate, pressurization of oil and gas in reservoirs, and differential loading of sedimentary layers. Only through long-term in-situ observations of cold seeps over a significant spatial extent, we will be able to adequately obtain their activity characteristics and released flux in marine environments.
Key words: underwater camera system; oil bubble; release rates; bubbles flux; Gulf of Mexico
DI Pengfei , LI Niu , CHEN Duofu , Ian R MacDonald . In situ quantification of oil-gas bubble seep flux from cold seeps at the seabed ― a case study of GC600 in the Gulf of Mexico[J]. Journal of Tropical Oceanography, 2023 , 42(5) : 134 -143 . DOI: 10.11978/2022204
图1 墨西哥湾GC600渗漏区位置图(a)和海底地形图(b)图a中红色方框为研究位置; 图b中红色方块为Mega Plume 2喷口位置, 白色线表示海脊边缘, 黑色等值线表示海底数据空白区 Fig. 1 The location (a) and seafloor topographic map (b) of GC600 seep area in the Gulf of Mexico. The red box in Figure a is the study location. The red box in Figure b is the location of Mega Plume 2 seep vent. The white line indicates the edge of the ridge and the black contour line indicates blanking zone in subbottom data |
图3 图像处理方法示意图a. 将初始照片中已确定的裁剪窗口转换成灰度; b和c. 连续图像中已确定的裁剪窗口相减; d. 去掉恒定背景并识别出气泡; e. 采用高、中、低3个阈值分别用来代表气泡大小、气泡运动模糊和油含量 Fig. 3 Schematic diagram of the image processing method. (a) Original image from which a cropped window is determined and converted to a gray image; (b) and (c) The determined cropped window subtraction in the consecutive image; (d) Removing the constant background and identify bubbles; (e) Three thresholds (high, medium, and low) are determined to account for bubble size, motion blurring, and oil content |
图4 Mega Plume 2气泡尺寸分布和释放个数与其他冷泉渗漏喷口的结果对比Fig. 4 Bubble size distribution and releasing number of Mega Plume 2 compared to that of other cold seeps |
图5 Mega Plume 2气泡的平均直径与其他地区冷泉喷口结果比较Confetti和Sleep dragon站位数据来自Wang等(2016); Birthday Candle、Mega Plume 1和Rudyville站位数据来自Johansen等(2017); F站位喷口1、喷口2 和海马喷口1站位数据来自Di等(2020) Fig. 5 Bubble size average diameter from Mega Plume 2 compared with that of cold seeps at other regions. Data of Confetti and Sleep dragon stations were obtained from Wang et al (2016); data of Birthday Candle, Mega Plume 1 and Rudyville stations were obtained from Johansen et al (2017); data of site F 1, 2 and the Haima cold seep 1 were obtained from Di et al (2020) |
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