Three holes were sampled from the Muroto Transect: Holes 1175A, 1176A, and Hole 1178A (Fig. F1) (Moore, Taira, Klaus, et al., 2001; Moore et al., 2001). Hole 1175A is located at 32°36´N, 134°39´E, in 2998 m water depth. Samples were taken from 2.47 to 8.31 meters below seafloor (mbsf). Because the sedimentation rate of the uppermost 23.42 m is 28 cm/k.y. (Shipboard Scientific Party, 2001a), the sampling interval ranges from 8.8 to 29.7 ka. The sediments consist predominantly of massive gray-brown to olive-gray hemipelagic clayey silt intercalated with volcanic ash layers at 1.10 and 6.40 mbsf (Shipboard Scientific Party, 2001a). Hole 1176A is located at 32°35´N, 134°40´E, in 3020 m water depth. Samples were taken from 0.05 to 10.21 mbsf. Because the sedimentation rate of the uppermost 11.94 m is 14 cm/k.y. (Shipboard Scientific Party, 2001b), the sampling interval ranges from 0.4 to 72.9 ka. The sediments consist predominantly of massive to faintly laminated gray to greenish gray hemipelagic silty clay intercalated with thin beds of sand (Shipboard Scientific Party, 2001b). Hole 1178A is located at 32°44´N, 134°29´E, in 1742 m water depth. Samples were taken from 0.03 to 10.00 mbsf. Because the sedimentation rate of the uppermost 7.60 m is 3 cm/k.y. (Shipboard Scientific Party, 2001c), the sampling interval ranges from 1 to 333 ka. The sediments consist of alternating hemipelagic beds of faintly laminated greenish brown silty clay and greenish brown sand-silt-clay intercalated with thin beds of sand and volcanic ash (Shipboard Scientific Party, 2001c).
Samples of ~20 cm3 in volume were taken on board and immediately frozen at -20°C.
Total of 123 freeze-dried sediment samples were analyzed for TOC using a LECO WR-112 carbon analyzer. The analyzer was attached to a halogen trap (antimony and potassium iodide). To remove carbonate carbon, the sample was acidified according to the following procedure. The sample (~0.1 g) was soaked in 1-M HCl solution in a ceramic crucible overnight and was heated at 110°C for 3 hr after adding new 1-M HCl. The sample was rinsed to remove chlorides by adding pure water twice and was heated again at 110°C for 3 hr. The precision of measurement was better than 0.01 wt%.
Total of 121 wet sediment samples (~2 g dry weight) were extracted five times by ultrasonication with 10 mL of dichloromethane/methanol (6/4 v/v). The lipid extract was separated into four fractions (F1: 3 mL of hexane; F2: 3 mL of hexane/toluene [3/1 v/v]; F3: 4 mL of toluene; F4: 3 mL of toluene/methanol [3/1 v/v]) by column chromatography (SiO2 with 5% distilled water, 5.5 mm x 45 mm). n-C36H74 was added as an internal standard into the F3 fraction.
Gas chromatography for the F3 fraction was conducted using a Hewlett-Packard 6890 gas chromatograph (GC) with on-column injection and electronic pressure control systems and a flame ionization detector. The column used was a capillary column coated with Chrompack CP-Sil5CB (60 m x 0.25 mm, 0.25-mm coating). The oven temperature was programmed from 70° to 290°C at 20°C/min, from 290° to 310°C at 0.5°C/min, and then was held at 310°C for 60 min. Helium was used as a carrier gas, and the flow velocity was maintained at 30 cm/s.
Gas chromatography-mass spectrometry was conducted using a Hewlett-Packard 5973 gas chromatograph-mass selective detector (MSD) with on-column injection and electronic pressure control systems and quadrupole MSD. The GC column and oven temperature and carrier pressure programs are the same as above. The MSD was run in the full scan ion monitoring mode (m/z 50-650). Electron impact spectra were obtained at 70 eV. Identification of compounds was achieved by comparison of their mass spectra and retention times with those in the literature and the lipid extracts from Emiliania huxleyi and Gephyrocapsa oceanica (Yamamoto et al., 2000).
The alkenone unsaturation index Uk'37 was calculated from the concentrations of di- and tri-unsaturated C37 alken-2-ones (C37MK) using the expression (Brassell et al., 1986):
The calculation of temperature was conducted according to the equation:
(T = temperature [°C]), based on an experimental result for cultured strain 55a of E. huxleyi (Prahl et al., 1988) with an estimated analytical accuracy of 0.5°C (Prahl and Wakeham, 1987).