The samples investigated were taken from Sites 1147 and 1148, mostly at an interval of 1.5 m for every core, and kept frozen until analysis. Site 1147 (18°50.11´N, 116°33.28´E; 3246 m water depth) was proposed to recover the continuous sequence of the uppermost hemipelagic sediments thought to be lost to slumping or channeling at Site 1148 (18°50.17´N, 116°33.94´E; 3294 m water depth). A total of 326 samples, covering a length of near 600 m, were analyzed.
About 3 g of each frozen sediment sample was placed into a 10-mL polytetrafluoroethylene centrifuge tube and thawed at room temperature. The samples were serially extracted with a rotary blender, using two 7-mL aliquots of methanol (MeOH), one 7-mL aliquot of trichloromethane (TCM):MeOH (1:1, v/v), and two 7-mL aliquots of TCM, each for 8 hr. The compounds C24D50 and C16D31O2H were added after the methanol extraction as standards for quantification. For each sample, the extracts were combined and back extracted by the addition of 15 mL of KCl solution. Then the separated water solution was extracted twice with 15 mL of TCM. The combined organic phase was concentrated to ~20 mL with a rotary evaporator at 35°C, dried with anhydrous Na2SO4, and concentrated again to ~0.5 mL.
Prior to instrumental analysis, the extracts were derivatized with bis-trimethylsilyl-trifluoroacetamide in pyridine at ~20°C for 2 days. Gas chromatography (GC)–mass spectrometry was performed on a Finnigan GC8000-Voyager equipped with an on-column injector and fitted with a Chrompack fused silica capillary column (32 m × 0.30 mm). Helium was used as the carrier gas, and the oven was programmed from 45°C to 120°C at 10°C/min, followed by 4°C/min to 300°C (30 min hold time). The mass spectrometer was operated with an electron energy of 70 eV and an ion source temperature of 250°C and scanned over mass range m/z 50–700 with a cycle time of 1.0 s. Compound identifications are based on comparison of relative GC retention times and mass spectra with those in literature. Quantification of lipids was performed by integration of their peak areas and comparing with the internal standards in total ion chromatograms. The recovery of internal standards of n-alkane, fatty acid, and cholesterol added to the blank is 95.8%, 92.3%, and 99.7%, respectively, and that to the matrix (marine sediment Soxhlet extracted with benzene:MeOH [7:3, v:v] for 72 hr) is 94.8%, 90.8%, and 98.8%, respectively.