Stable carbon and nitrogen isotopic composition of gas hydrate-bearing sediment from Hydrate Ridge, Cascadia Margin

54 sediments were sampled at 5 sites, 1244, 1245, 1246, 1250 and 1251 from ODP Leg 204, Hydrate Ridge, Cascadia Margin. The stable carbon and nitrogen isotopic composition, δ13C of organic matter and δ15N, have been used to characterize the depositional variation of sediments with gas hydrate bearing. Values of δ13C of bulk organic matter range between −22.37‰ and −24.72‰ PDB, with a mean value of −23.54±1.17‰ PDB; δ15N of the same sedimentary samples range from 3.30‰ to 5.68‰, with a mean value of 4.49±1.19’; Values of C/N ratio range from 4.53 to 9.26, with a mean value of 6.90±2.37. The occurrence of gas hydrate changed the diagenetic evolution trend of the carbon and nitrogen in organic matter. The δ15N and C/N ratio depletion suggest that the nitrogen fixation related with the bacteria/archaea maybe occurred in the sediments near the hydrate. The stable carbon and nitrogen isotopic composition could be used to evaluate the depositional environment in the study area.