Inferences on gas transport based on molecular and isotopic signatures of gases at acoustic chimneys and background sites in the Ulleung Basin

► We measured gas compositions from chimney and background sites in the Ulleung Basin. ► Methane and ethane originate from microbial activity via CO2 reduction. ► AOM and deep gas migration alter isotopic signatures of the source gas. ► Abnormally small εc reflects a twophase fluid transport at hydrate bearing sites.