5:15 PM - 6:30 PM
[MIS09-P14] Characteristics of natural gas hydrate retrieved off Abashiri, the Sea of Okhotsk
Keywords:hydrate, the Sea of Okhotsk, stable isotope
Gas hydrate crystals were obtained and stored in liquid nitrogen for Raman spectroscopic analysis and calorimetry. Samples of hydrate-bound gas were obtained onboard and stored in 5-mL vials, and sediment gas were also obtained using a headspace gas method. We measured molecular and stable isotope compositions of these samples. We summarized the results as follows:
1) Gas hydrates belong to the cubic structure I, containing methane (more than 99%) and hydrogen sulfide (less than 1%). C1/C2+ ranges from 5,500 to 5,800.
2) Hydration number is estimated as 6.03±0.04, agrees well with 6.04±0.03 for synthetic methane hydrate (Sum et al., 1997).
3) Dissociation heat from hydrate to gas and water is estimated as 55.1±0.3 [kJ/mol], agrees well with 54.19±0.28 [kJ/mol] for synthetic methane hydrate (Handa, 1986).
4) Hydrate-bound gas is of microbial origin according to C1/C2+ and stable isotopes of hydrocarbons, however, delta 13C of ethane seems relatively large.
5) Gas hydrate in the NT13-20 PC06 core contains trace amount of ethane (several ppm), whereas that in the NT13-20 PC02 core contains about 100ppm of ethane.
6) SMI (sulfate-methane interface) depth of the sediment cores are less than 1m, indicating high methane flux off Abashiri.
We appreciate the support of the crew onboard R/V Natsushima during the NT13-20 cruise, and T/S Oshoro-Maru during the cruises of OS249, OS263, and C020. This study was supported by the Grant-in-Aid for Scientific Research (B) 25289142 and 26303021 of the Japan Society for the Promotion of Science (JSPS).
Handa (1986) Compositions, enthalpies of dissociation, and heat capacities in the range 85 to 270 K for clathrate hydrate of methane, ethane, and propane, and enthalpy of dissociation of isobutane hydrate, as determined by a heat-flow calorimeter. J Chem Thermodyn 18: 915-921.
Sum et al. (1997) Measurement of clathrate hydrates via Raman spectroscopy. J Phys Chem B 101: 7371-7377.