The shipboard organic geochemistry program for Leg 190 included (1) real-time monitoring of volatile hydrocarbons as required by ODP safety regulations, (2) measurement of the 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 190 are described in detail by Kvenvolden (1985), Claypool and Kvenvolden (1983), and in the "Explanatory Notes" chapter of the Leg 156 Initial Reports volume (Shipboard Scientific Party, 1995).
For safety and pollution prevention, concentrations and distributions of light hydrocarbon gases, mainly methane, ethane, and propane, were monitored for each core following standard headspace sampling. Briefly, 5-cm3 sediment samples were collected using a calibrated borer tool while the core was still on deck. The samples were placed in 20-mL glass serum vials 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, vials were 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 chromatograph (GC) analysis. When gas pockets were encountered, vacutainer samples were collected by piercing the core liner using a syringe connected to a penetration tool.
The constituents of the gas were analyzed using an HP5890 Series II GC equipped with a 0.32 cm × 2.4 m stainless steel column filled with HayeSep R porous polymer packing (80/100 mesh). When heavier molecular-weight hydrocarbons (C3 and higher) were detected, the sample was analyzed by a natural gas analyzer, which quantifies C1 to C6, nitrogen, oxygen, and carbon dioxide concentrations. Helium was used as the carrier gas. Data acquisition and processing was performed using HP Chemstation software. Chromatographic response was calibrated against authentic standards, and the results are reported in parts per million by volume (ppmv).
Inorganic carbon (IC) 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 reacted with 2-M HCl to liberate CO2. The CO2 was titrated and the change in light transmittance monitored by a photodetection cell. The weight percentage of calcium carbonate was calculated from the IC content, assuming that all the evolved CO2 was derived from dissolution of calcium carbonate, using the following equation:
The amount of carbonate is expressed as weight percent, assuming all the carbonate was present as calcite. No correction was made for other carbonate minerals.
TC, nitrogen, and sulfur were analyzed using a Carlo Erba 1500 CNS Analyzer. An aliquot of 12-15 mg freeze-dried, ground sediment combined with V2O5 catalyst was combusted at 1000°C in a stream of oxygen. Nitrogen oxides were reduced to N2. The mixture of N2, CO2, and SO2 gases was separated by a GC equipped with a thermal conductivity detector. All measurements were calibrated by comparison to synthetic standards. The amount of TOC in weight percent was calculated as the difference between TC in weight percent and IC in weight percent by the following equation: