New discovery of submarine active cold seep and influencing factors of plume morphology in the South China Sea

The seafloor cold seep plume system serves as an important tracer for hydrate decomposition and has become a key research hotspot in deep-sea resource exploration. The reasons for gas release from cold seeps, as well as the morphology and influencing factors of plumes, are unclear in the South China Sea. This study focuses on the Baiyun Sag of the Shenhu area of the northern South China Sea, employing multibeam echosounder technology. We identified ten plumes, all exhibiting a consistent inclined flame-like morphology, mostly occurring in pairs. These plumes are linked to previously identified ancient cold seeps. We found that a dormant cold seep system has been reactivated. It is now the fourth active cold seep in the northern South China Sea. We named this cold seep Dongfanghong 3 based on the cruise number. The reactivation of the ancient cold seep system is influenced by global climate warming, ocean dynamics, and human activities. Human activities include the development of the nearby Liwan 3–1 gas field and exploratory drilling and are the primary driver among these factors. This process causes structural changes in seabed sediment layers and alters seawater environmental parameters. These changes lead to the reactivation of the ancient cold seep. The morphology and distribution of the plumes are influenced by sediment transport pathways, the inclination of the outlets, and ocean dynamics. Background currents can help sustain the drifting behavior of plumes. Changes in inclination at the top of plume are closely linked to flow field variations induced by internal solitary waves. The findings provide important theoretical support for assessing the influence of human activity and ecological risk warnings during the development of natural gas hydrates.