基于单波束测深资料的海底冷泉动力学特征反演方法研究

为了准确理解冷泉水体中甲烷气体的分布规律,综合运用单波束测深数据和冷泉水体流场数据,建立了冷泉气泡上升、溶解速率的定量反演方法,利用现场海试资料对反演方法进行了验证,并对海试区域的冷泉气体溢出、溶解通量以及冷泉水体的甲烷浓度进行了估算。计算结果表明,考察船航向与冷泉水体流向的差异会对声学探测结果产生影响,当航向与流向的夹角大于±60°时,声学成像中冷泉倾角的误差将超过50%。同时,冷泉气泡上升速率的衰减与溢出口水深显著相关,相关系数可达0.9,并且冷泉上升流对上升速率的提升效果明显。水合物稳定带的分布对冷泉气泡的收缩速率影响显著,稳定带内、外收缩速率的差异可达3～4倍。冷泉气体通量的计算结果表明,调查区域内冷泉的溢出强度整体较大,同时溶解通量与水深之间呈现明显的分段效应。根据冷泉气体溶解通量估算的冷泉水体甲烷浓度与色谱分析结果具有较好的一致性。相关研究有助于实现对冷泉水体中甲烷气体分布的定量评估,为潜在海底冷泉区的圈划和海域天然气水合物的调查提供技术支撑。

Retrieval process of cold seep dynamic parameters based on single-beam echo sounder profiles

To accurately understand the distribution of methane gas in cold seep water on the basis of the single-beam echo sounder and seep water flow field datasets, a quantitative method for determining the rising and shrinking rates of the cold seep plume bubble is established and verified using trial data. Furthermore, the upward and diffusion fluxes of seepage and the methane concentration are computed. Results show that the difference between heading and flow directions of the cold seep water will affect the acoustic result. When the difference is greater than ±60°, the error of the cold seep inclination will exceed 50%. Meanwhile, the half-way decay rate of the cold seep bubble rising rate is significantly correlated with the water depth, with the correlation coefficient reaching 0.9. Moreover, the effect of bubble-induced upwelling on the rising rate is significant. The distribution of the gas-hydrate stability zone has a significant effect on the shrinking rate of the cold seep bubble, and the difference between internal and external diffusion rates of this zone can reach three to four times. The calculation results of the flux of cold seep gas show that the overflow intensity in the study area is large overall, and there is a significant segmentation effect between diffusion flux and water depth. In addition, based on the diffusion flux obtained, the distribution of methane concentration in the seawater of the trial area is estimated. The comparison of the chromatographic analysis of in situ water samples confirms the validity of the method. Relevant research would help in achieving a quantitative assessment of the distribution of methane gas in cold seep water and provide technical support for the exploration of cold seeps and seabed natural gas hydrates.