南海北部陆坡气泡羽状流的发现:多波束水体数据

Gas bubble plumes observed at north slope of South China Sea from multi-beam water column data

利用2016年在南海西北部陆坡琼东南海域采集的多波束水体数据,发现了海底气体渗漏至海水中形成的羽状流。在多波束数据上,羽状流成火焰状,直径大约为30~50m,从1 380多米的海底延伸至大约650m的深度,高度超过700m。在经过羽状流的浅剖剖面上,存在显示浅层气存在的声学空白区域,并识别出断裂和裂隙区域,但在水体中并无明显的异常。这可能是由于浅剖数据的分辨率不够未能捕捉到水体异常,或者气体渗漏具有间歇性。该海域存在明显的似海底反射显示,气体渗漏可能与水合物系统之间存在复杂的相互作用。由于缺乏经过羽状流的多道地震数据,难以对羽状流的形成机制进行进一步的推测。南海北部陆坡羽状流的发现对于理解被动大陆边缘的甲烷渗漏机制、水合物的形成与分解具有重要的意义。

Methane emission from seabed is a wide phenomenon around the world. Gas bubble plumes were observed in the Multi-Beam（MB） water column echo image with the newly （2016） acquired data in the north slope of South China Sea. Gas bubbles manifest themselves as flares on the MB image, and have the diameter of about 30 to 50 m. Plumes emanating from the - 1 380 m depth seabed to the - 650 m depth, resulting heights of 〉700 m. On the sub-bottom profile passing through the plume, we found the acoustic blanking zone which may indicate the gas mi- gration pathway, but no clear anomalies were observed in the water column. This may be explained by the low res- olution of the sub-bottom profiler image or the intermittence of the gas seepage. Lacking of multi-channel seismicand geochemistry data, we cannot further infer the formation mechanism of the gas plumes. The discovery of gas bubble plumes in the north slope of south china may improve our understanding of the methane seepage on the passive continental marginal, and the formation and dissociation of gas hydrates.