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doi:10.2204/iodp.proc.344.203.2016 Methods and materialsGas compositionThe HS samples were analyzed onboard by an Agilent 6890 Series II gas chromatograph (GC3) (see the “Methods” chapter [Harris et al., 2013b]). The VG samples were analyzed onshore by an Agilent 7890A gas chromatograph with a flame ionization detector and a thermal conductivity detector at Korea Institute of Geoscience and Mineral Resources (KIGAM). Isotope analysisA total of 43 HS samples from Sites U1380, U1412, and U1413 and 27 VG samples from Sites U1412 and U1413 were used for the gas isotopic analyses. The carbon (δ13CCH4 and δ13CCO2) and hydrogen (δDCH4) stable isotopic ratios of the gases were analyzed using an isotope ratio–monitoring gas chromatograph/mass spectrometer at Isotech, Champaign, IL. All isotopes are reported in the usual δ notation relative to Vienna Pee Dee Belemnite (V-PDB) for carbon and Vienna Standard Mean Ocean Water (V-SMOW) for hydrogen:
where R represents the 13C/12C ratio and D/H of the sample and standard for each isotope. The analytical reproducibility was ±0.1‰ for δ13C and ±2‰ for δD. Conversion ratioThe conversion ratio was calculated using the Rayleigh ratio (modified from Pohlman et al., 2009).
where
The model determines that the proportion of methane is produced by in situ methanogenesis. |
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