海底冷泉渗漏油气泡原位定量测定--以墨西哥湾GC600为例

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

海洋环境中冷泉渗漏是甲烷等有机化合物和其他温室气体进入海洋和大气的重要来源。准确定量确定冷泉渗漏的甲烷气泡通量对于评估它们对全球甲烷预算和气候变化有着重要的研究意义。采用高分辨率视频成像系统原位观察了墨西哥湾GC600冷泉渗漏区Mega Plume 2喷口,并获得了油气泡连续释放的视频片段。通过采用半自动气泡计数算法估算了Mega Plume 2喷口释放的油气泡个数及其释放速率。而通过图像处理技术确定了Mega Plume 2释放的油气泡的大小和尺寸分布。Mega Plume 2混合喷口释放的油气泡平均直径2.56mm±1.01mm,油气泡释放速率为80.25个·秒^(-1)。Mega Plume 2喷口年释放通量为177.7m^(3)·a^(-1)(19.55~106.62t·a^(-1))。然而,Mega Plume 2喷口的气泡释放速率与潮汐无关,可能与其他因素如水合物,油气藏增压及沉积层差异加载有关。只有对冷泉渗漏系统开展长期的原位在线观察,我们才能准确获取冷泉渗漏系统活动特征及其释放通量。

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 m^(3)·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.