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

摘要: Abstract We present results of a comparative study hydrocarbons collected at acoustic chimney sites and nearby non-chimney (background) in the Ulleung Basin (offshore Korea). At all sites, molecular (C 1 /C 2+ ratios ⩾ 600) isotopic (δ 13 C CH4 , δD δ C2H6 ) indicators point to microbial source methane ethane. Similarly, CO2 have minimum values sulfate–methane transition zone (SMTZ) throughout basin. These data document intense carbon cycling this horizon, whereby anaerobic oxidation (AOM) SMTZ generates dissolved inorganic pool depleted that is subsequently reduced generate observed minima . background isotope fractionation factor ( e c  = δ  − δ for gases ranges from 56–66, consistent with predicted methanogenesis driven predominantly by CO 2 reduction. However, measured two contain gas hydrate are significantly lower (30–46). conclude these abnormally small reflect phase fluid transport bearing sites. The composition sampled below (higher abundance enriched methane) indicates deep origin gas, which we postulate migrates upwardly sustains formation near seafloor. If so, can be used as potential geochemical indicator migration consequent development accumulations shallow marine systems.