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

摘要

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, δ~(13)C of organic matter and δ~(15)N, have been used to characterize the depositional variation of sediments with gas hydrate bearing. Values of δ~(13)C of bulk organic matter range between -22.37 per thousand and -24.72 per thousand PDB, with a mean value of -23.54 ± 1.17 per thousand PDB; δ~(15)N of the same sedimentary samples range from 3.30 per thousand to 5.68 per thousand, with a mean value of 4.49 ± 1.19 per thousand; 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 δ~(15)N 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.