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doi:10.2204/iodp.proc.344.204.2016

Methods

Elemental analysis

A total of 214 squeeze cake samples from Sites U1380, U1412, U1413, and U1414 were used for geochemical analyses. A part of each squeeze cake was dried using a freeze dryer for 24 h at the Korea Institute of Geoscience and Mineral Resources (KIGAM). After the bulk sediment samples were dried, they were ground and homogenized in an agate mortar. TC and TN contents were measured by combustion method using a CHN-900 (LECO, USA) apparatus at KIGAM with detection limits of 0.001% for TC and 0.01% for TN. The reproducibility of TC and TN measurements, estimated from repeated analyses of the LECO soil standard (TC = 2.6 wt% and TN = 0.209 wt%) was <3% and <4%, respectively. TS contents were determined using an S-144DR (LECO, USA) at KIGAM with a detection limit of 0.001%. Four LECO standards (0.28, 0.95, 1.51, and 2.30 wt%) were used for the analysis of TS. The reproducibility of TS was monitored by repeated analysis of LECO standard (1.51 wt%) was <3%.

Rock-Eval pyrolysis

A Rock-Eval Turbo 6 (Vinci Technologies, France) instrument at KIGAM was utilized for the Rock-Eval pyrolysis. Free and adsorbed hydrocarbons released during programmed heating of a sample are recorded as the first peak in a pyrogram (S₁) under low temperature (<300°C). The second peak (S₂) in the pyrogram represents hydrocarbons released by kerogen cracking when the sample is heated from 300°C to 650°C. The maximum S₂ temperature is defined as T_max. CO₂, shown as the third peak (S₃) in the program, is also generated by kerogen degradation. When these components are normalized to the total organic carbon (TOC) content, the S₂ peak becomes the hydrogen index (HI = S₂ × 100/TOC) and S₃ becomes the oxygen index (OI = S₃ × 100/TOC) (Tissot and Welte, 1984; Peters, 1986). TOC was also measured by the Rock-Eval Turbo 6, summing up the pyrolyzed carbon (PC) and residual carbon (RC) (Arthur et al., 1998; Lafargue et al., 1998; Kim et al., 2007, 2014). IFP 160,000 (Vinci-Technologies, France) was used as standard for the Rock-Eval analysis. The reproductivity of TOC, S₂, S₃, and T_max is estimated from repeated analyses of the IFP 160,000 standard was better than 2%, 4%, 5%, and 1%, respectively.

Total inorganic carbon (TIC) was calculated as the difference between TC measured by the CHN-900 and TOC measured by the Rock-Eval Turbo 6:

Isotope analysis

The aliquots of powdered bulk samples from Sites U1380, U1412, and U1413 were pretreated with 3 M HCl to remove carbonate (CaCO₃) and inorganic nitrogen for the analysis of organic carbon (δ¹³C_org) and nitrogen (δ¹⁵N_org) isotope ratios (Kim et al., 2014). δ¹³C_org and δ¹⁵N_org were measured using a stable isotope ratio mass spectrometer system with elemental analyzer (Vision-EA, Isoprime, UK) at the National Instrumentation Center for Environmental Management (NICEM, Korea). Analytical reproducibility was ±0.1‰ for δ¹³C_org and ±0.2‰ for δ¹⁵N_org. All carbon and nitrogen isotopes are reported in the usual δ notation relative to Vienna Peedee belemnite (VPDB) for carbon and atmospheric N₂ for nitrogen:

where R represents the ¹³C/¹²C ratio and ¹⁵N/¹⁴N ratio of the sample and standard for each isotope.

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