The shipboard organic geochemistry program for Leg 180 included (1) real time monitoring of volatile hydrocarbons as required by ODP safety regulations; (2) measurement of inorganic carbon and carbonate content of the sediments; and (3) elemental analyses of total nitrogen, sulfur, and carbon. All methods and instruments used during Leg 180 are described in detail by Emeis and Kvenvolden (1986), Kvenvolden and McDonald (1986), and in the "Explanatory Notes" chapter of the Leg 156 Initial Reports volume (Shipboard Scientific Party, 1995b).

For safety and pollution prevention, concentrations and distribution of light hydrocarbon gases, mainly methane (C₁), ethane (C₂), and propane (C₃), were monitored for each core following the standard headspace sampling method described by Kvenvolden and McDonald (1986). A 5-cm³ sediment sample was collected using a calibrated borer tool while the core was still on deck. The sample was placed in a 21.5-cm³ glass serum vial and sealed with a septum and metal crimp cap. When consolidated or lithified samples were encountered, chips of material were placed in the vial and sealed. Before gas analyses, the vial was heated to 60ºC for 30 min. A 5-cm³ subsample of the headspace gas was extracted from each vial using a standard glass syringe for gas chromatography (GC) analysis. When gas pockets were encountered, vacutainer samples were collected by penetrating the liner using a syringe connected to a penetration tool.

The constituents of the gas were analyzed using a HP5890 II gas chromatograph equipped with a 8 ft × in stainless steel column packed with HayeSep 5 and a flame ionization detector (FID). When heavier molecular-weight hydrocarbons (C₃) and above were detected, the sample was analyzed by a natural gas analyzer (NGA) used to quantify C₁ to C₆, nitrogen, oxygen, and carbon dioxide. Helium was used as the carrier gas. Data acquisition and processing were performed by a HP Chemstation. Chromatographic response was calibrated against authentic standards and the results reported as parts per million by volume (ppmv).

Inorganic carbon was determined using a Coulometrics 5011 carbon dioxide coulometer equipped with a System 140 carbonate carbon analyzer. Samples of 10-12 mg of freeze-dried ground sediment were weighed and then reacted with 2M HCl to liberate CO₂. The CO₂ was titrated and the change in light transmittance monitored by a photo detection cell. The weight percentage of calcium carbonate was calculated from the inorganic carbon content, assuming that all the CO₂ evolved was derived from dissolution of calcium carbonate by the following equation:

wt%CaCO₃ = wt%IC (inorganic carbon) × 8.33.

The amount of carbonate is expressed as weight percent (wt%), assuming all the carbonate was present as calcite. No correction was made for other carbonate minerals.

Total carbon, nitrogen, and sulfur were analyzed using a Carlo Erba 1500 CNS Analyzer. An aliquot of 12-15 mg freeze-dried ground sediment with a V₂O₅ catalyst was combusted at 1000ºC in a stream of oxygen. Nitrogen oxides were reduced to N₂. The mixture of N₂, CO₂, and SO₂ gases was separated by gas chromatography and detection was performed by a thermal conductivity detector (TCD). All measurements were calibrated by comparison to synthetic standards. The amount of total organic carbon (TOC) was calculated as the difference between total carbon (TC) and inorganic carbon (IC), i.e.,

wt%TOC = wt%TC - wt%IC.