was
calculated from the concentrations of di- and tri-unsaturated C37
alken-2-ones (C37MK) using the expression (Brassell et al., 1986)The sediments of Core 167-1016C-1H (0-9.2 mbsf) consist of gradationally interbedded dark gray to dark greenish gray diatom ooze with clay, grayish olive diatom clay, clayey diatom ooze, and light greenish yellow to light olive gray diatom nannofossil ooze with clay. Smear-slide observation indicates that diatom frustules compose 36%-60% of the sediments (Shipboard Scientific Party, 1997a). Our observation using soft X-ray radiographs reveals that burrows occur throughout the whole range of this core, indicating constantly oxic depositional environment (Fig. 2).
Core 167-1016C-1H was sealed in a N2-filled oxygen-impermeable plastic bag immediately after the recovery and stored in a refrigerator for three months until shore-based sampling. Samples of ~20 cm3 in volume were taken every 3 cm and immediately frozen in N2-filled Kapack bags.
Three hundred-four freeze-dried sediment samples at 3-cm intervals were analyzed for total organic carbon (TOC), total carbon (TC), and total nitrogen (TN) using a Yanaco MT-5 elemental analyzer. To remove carbonate carbon, the samples were acidified following the method of Yamamuro and Kayanne (1995). Inorganic carbon (IC) and calcium carbonate (CaCO3) contents were calculated according to the following equations:
One hundred and one freeze-dried sediment samples (1 g) taken at 9-cm intervals were extracted by ultrasonification with 10 mL of dichloromethane/methanol (6/4 v/v) for 5 min three times. The lipid extract was separated into five 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); and F5: 3 mL of methanol) by column chromatography (SiO2 with 5% distilled water, i.d. 5.5 mm, 45 mm long). n-C24D50 and n-C36H74 were added as internal standards into the F1 and F3 fractions, respectively.
Gas chromatography was conducted using a Hewlett Packard 5890 series II gas chromatograph (GC) with on-column injection and electronic pressure control systems and a flame ionization detector. The F1 (hydrocarbon) fraction was analyzed using a capillary column coated with Chrompack CP-Sil5CB (30 m long, i.d. 0.25 mm, 0.25 µm thick). The oven temperature was programmed from 70° to 130°C at 20°C/min, from 130° to 310°C at 4°C/min., and then held at 310°C for 15 min. The F3 (alkenone) fraction was analyzed using a capillary column coated with Chrompack CP-Sil5CB (60 m, i.d. 0.25 mm, 0.25 µm thick). The oven temperature was programmed from 70° to 310°C at 20°C/min and then 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 with on-column injection and electronic pressure control systems and quadrupole mass spectrometer. The GC column for F3 analysis and oven temperature and carrier pressure programs are the same as above. For F1 analysis, 60-m-long CP-Sil5CB (i.d. 0.25 mm, 0.25 µm thick) was used instead of 30-m-long column. The mass spectrometer 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.
The alkenone unsaturation
index was
calculated from the concentrations of di- and tri-unsaturated C37
alken-2-ones (C37MK) using the expression (Brassell et al., 1986)
= [C37:2MK]/([C37:2MK] + [C37:3MK]).
The calculation of
temperature was conducted according to the equation:
= 0.034T + 0.039 (T = temperature [°C]),
based on an experimental result for cultured strain 55a of Emiliania
huxleyi (Prahl et al., 1988) with an estimated analytical accuracy of
0.5°C (Prahl and
Wakeham, 1987). The additional unsaturation indices, 
and K37:4/K37, were calculated using the following
equations, respectively (Prahl et al., 1995):
= [C36:2ME]/([C36:2ME] + [C36:3ME]),
where [C36ME] is the concentration of C36 fatty acid-methyl ester, and
