Yam Seep at Four-Way Closure Ridge: a prominent active gas seep system at the accretionary wedge SW offshore Taiwan

Abstract Hydroacoustic surveys at the accretionary wedge southwest of Taiwan reveal a confined active hydrocarbon seepage area ~ 49,000 m 2 in 1350 water depth on northern crest Four-Way Closure Ridge, which we call Yam Seep. In this study, multibeam and side-scan sonar data acquired during with an autonomous underwater vehicle expedition R/V Ocean Researcher I 2017 showed that is characterized by rough topography high seafloor backscatter. Seafloor observations video sled sediment sampling gravity corers MeBo drill rig SONNE 2018 revealed almost entirely covered intensely fractured methane-derived carbonates, indicate has been ongoing for thousands years. anomalies (‘flares’) column indicated presence several gas bubble emission sites mostly center eastern flank 2019. Drilling through massive carbonates northwestern part Seep induced free escape from 5.1 m. This suggests hydrates subsurface as seep located well within hydrate stability zone. The inter-disciplinary investigations demonstrate upward migration light hydrocarbons discharge considerable influence seabed properties.