As a new energy source, gas hydrate in marine has shown important economic significance. However, it is difficult to effectively and accurately identify the gas hydrate reservoirs, which has severely limited the geological survey for gas hydrate in the South China Sea. Previous studies indicated the iodine concentration in pore waters from marine sediments is a good tracer for gas hydrate. This study aims to identify relationship between the iodine concentration in pore water and the occurrence of gas hydrate reservoirs in the northern South China Sea.Methods:The pore water samples collected from sites HD86V and HD109 in the Southwest Taiwan Basin, which is one of the target areas for marine gas hydrate exploration in the northern South China Sea. The iodine concentration of samples was measured by ICPMS at Stake Key Laboratory for Mineral Deposits Research, Nanjing University.Results:The iodine concentrations in pore waters at sites HD86V and HD109 are 8.3~132 μmol/L and 7.4~118 μmol/L, respectively. Similar high iodine concentrations are also found in pore water at the Southeast Hainan Basin and Shenhu area, the northern South China Sea. Compared with the famous marine gas hydrate fields of the world, the iodine concentrations of pore water from the northern South China Sea are slightly low, which may result from the shallow sampling depth in this study. In addition, the positive correlation between iodine concentrations of pore water and CH4 contents of headspace gas is found in marine sediments at Site HD196A in the Southwest Taiwan Basin.Conclusions:As a strongly biophilic element, iodine commonly associated with marine organic matter and also has similar diffusion coefficients with CH4. So I- is commonly transported together with CH4 in aqueous fluids. The iodine concentrations in pore water are obviously higher than that of seawater at the northern South China Sea, which imply there have abundant organic matter or the gas hydrate. Moreover, the gas hydrate has been drilled in the area with high iodine concentrations. All these demonstrate that it is an effective way to trace the gas hydrate reservoirs in the South China Sea by identifying the abnormal high iodine concentration in pore water from marine sediments.