SHALLOW SULFATE-METHANE INTERFACE IN NORTHEASTERN SOUTH CHINA SEA: AN INDICATOR OF STRONG METHANE SEEPAGE ON SEAFLOOR

The Northeastern part of the South China Sea (SCS) is rich in methane and there is methane seepage on the seafloor. Six sediment cores recovered from the northeastern SCS show that both sulfate and methane contents decrease with depth in the consuming zone of sulfate and methane. Headspace methane of these cores increases with depth and reaches an anomalous high at the bottom of cores. By extrapolation, the depth of sulfate-methane interface (SMI) in the cores of HD109, HD170, HD196A, HD200, HD319 and GC10 are located at 704cmbsf, 911cmbsf, 728cmbsf, 636cmbsf, 888cmbsf, 792cmbsf, respectively, indicating very shallow SMI depths. Strong methane seepage will intensify the co-consumption of sulfate and methane, leading to the shift of SMI depths towards the seafloor. The shallow SMIs, which often occur in gas hydrate localities worldwide, imply that the northeastern SCS is a good gas hydrate-prone setting.