Routine monitoring of hydrocarbon gases was performed for Holes 1098A, 1099A, and 1099B (Table T27). The organic geochemistry analyses performed at Sites 1098 and 1099 included measurements of inorganic carbon and elemental analyses of carbon, sulfur, and nitrogen for Holes 1098C, 1099A, and 1099B (Table T28). Samples for inorganic carbon and elemental analyses were taken from each section, using care to avoid monospecific diatom oozes.

At Site 1098, headspace gas measurements give background levels of methane (<200 ppm) in the upper 25 mbsf and substantially higher values (>15,000 ppm) at greater depths (Table T27). At Site 1099, methane concentrations exceed background levels at all depths and reach a maximum (>100,000 ppm) at ~50 mbsf. No other hydrocarbon gases were detected at either site.

Sediment from Sites 1098 and 1099 contains uniformly low amounts (0.3 wt%) of inorganic carbon, except for slightly higher values at the base of Hole 1098C (Figs. F22, F23). The low values are comparable to those measured at other sites investigated during Leg 178. Total organic carbon concentrations are relatively high (1 wt%) in the uppermost 20-25 mbsf at Sites 1098 and 1099 and reflect the locally high primary productivity of diatoms. At both sites, total organic carbon decreases with depth as contents of terrigenous sediment increase (see "Lithostratigraphy"). Organic carbon decreases to zero in the carbonate-rich clay at the base of Hole 1098C. (This clay is not present in Holes 1098A and 1098B.) A negative covariance of total organic carbon and terrigenous sediment input suggests a dilution of organic carbon instead of a decrease in primary (diatom) productivity.

Sulfur is present throughout Holes 1098C and 1099A. The variations in concentration of sulfur generally follow the total organic carbon profiles. Nitrogen concentrations are near the lower detection limits of the CNS analyzer.