-
CPI = [
(C25 – C33)odd/(C24 – C32)even + (C25 – C33)odd/(C26 – C34)even]/2.
Two sites were sampled on the Nazca and Carnegie Ridges: Sites 1237 and 1239, respectively (Fig. F1) (Mix, Tiedemann, Blum, et al., 2003). Site 1237 is located at 16°0.42´S, 76°22.69´W, at 3212 m water depth. Samples were taken from 0.01 to 180.04 meters composite depth (mcd). According to the age model of this site (Shipboard Scientific Party, 2003a), the ages of the samples range from 0 to 10.4 Ma. The sediments of the uppermost 41 mcd consist mostly of olive and olive-gray nannofossil-bearing silty clay. The sediments from 41 to 100 mcd consist mostly of light greenish gray clayey nannofossil ooze (Shipboard Scientific Party, 2003a). Site 1239 is located at 0°40.32´S, 82°4.86´W, in 1414 m water depth. Samples were taken from 0.01 to 489.40 mcd. According to the age model for this site (Shipboard Scientific Party, 2003b), the ages of the samples range from 0 to 6.56 Ma. Sediments are dominated by light to dark olive-gray foraminifer-nannofossil ooze with varying amounts of diatoms, clay, and micrite (Shipboard Scientific Party, 2003b).
A total of 135 freeze-dried sediment samples were analyzed for total carbon (TC) and total organic carbon (TOC) using a LECO WR-112 carbon analyzer, following the method of Yamamoto (2004). 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 (~0.1–0.5 g) was soaked in a 1-mol/L HCl solution in a ceramic crucible overnight and was heated at 150°C for 3 hr after adding more 1-mol/L HCl solution. The sample was rinsed twice to remove chlorides by adding pure water and then was heated again at 150°C for 3 hr. The precision of measurement for TC and TOC was better than 0.01 wt%. Inorganic carbon (IC) and calcium carbonate (CaCO3) contents were calculated according to the following equations:
and
A total of 43 freeze-dried sediment samples (1 g) were extracted by a Dionex ASE-200 accelerated solvent extractor (two times at 100°C and 1000 psi for 5 min) with a mixture of dichloromethane:methanol (6:4 v:v). The lipid extract was separated into four fractions (Fraction 1: 3 mL of hexane, Fraction 2: 3 mL of hexane/toluene [3:1 v:v], Fraction 3: 4 mL of toluene, and Fraction 4: 3 mL of toluene/methanol [3:1 v:v]) by column chromatography (SiO2 with 5% distilled water, 5.5-mm internal diameter [ID] x 45-mm long). n-C24H50 was added as an internal standard to Fraction 1 (n-alkanes). n-C36H74 was added as an internal standard to Fraction 3 (alkenones and alkenoates).
Gas chromatography for Fractions 1 and 3 was conducted using a Hewlett Packard 6890 gas chromatograph (GC) with on-column injection and electronic pressure control inlet systems and a flame ionization detector. The column used was a capillary column coated with Chrompack CP-Sil5CB (60 m long x 0.25 mm ID, 0.25 mm coating). The GC oven temperature for analysis of Fraction 1 was programmed from 70° to 130°C at 20°C/min, from 130° to 310°C at 20°C/min, and then was held at 310°C for 30 min. The GC oven temperature for analysis of Fraction 3 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 30 min. Helium was used as a carrier gas, and flow velocity was maintained at 30 cm/s.
The odd/even carbon number preference index (CPI) of long-chain n-alkanes (LNAs) was calculated using the following equation (Bray and Evans, 1961):
(C25 – C33)odd/(C24 – C32)even + (C25 – C33)odd/(C26 – C34)even]/2.
The average chain length (ACL) of LNAs was calculated using the following equation (Poynter and Eglinton, 1990):
The alkenone unsaturation index Uk´37 was calculated from the concentrations of di- and triunsaturated C37 alkenones (C37MK) using the following equation (Brassell et al., 1986; Prahl et al., 1998):
The calculation of temperature was conducted according to the following equation:
where T = temperature (°C), based on an experimental result for cultured Strain 55a of Emiliania huxleyi (Prahl et al., 1988) with an estimated accuracy of 0.5°C (Prahl and Wakeham, 1987).
