At Site 1128, in addition to routine monitoring of hydrocarbon gases for safety, analyses were conducted for inorganic carbon, total carbon, nitrogen, and sulfur. The analytical procedures are described in "Organic Geochemistry" in the "Explanatory Notes" chapter.
Concentrations of volatile hydrocarbons were routinely determined from every core in Holes 1128B and 1128D using standard ODP headspace sampling procedures. Only low concentrations of methane were detected; the maximum concentration was 6.2 ppm, and most samples have <3 ppm (Table T7). No heavier hydrocarbon gases (C2+) were detected.
Inorganic carbon concentrations were converted to calcium carbonate percentages (see "Organic Geochemistry" in the "Explanatory Notes" chapter). Calcium carbonate content has a bimodal pattern with increasing depth in Holes 1128B and 1128D (Table T8; Fig. F20). High carbonate values (75-90 wt%) are generally present in the upper 50 mbsf of Hole 1128B, decreasing from 50.3 to 138.4 mbsf to a low of 2.1 wt%. From 138.4 mbsf to the base of Hole 1128B, the carbonate content exhibits a second mode with a maximum concentration of 68 wt%. In Hole 1128D, with increasing depth from 241.4 mbsf, the carbonate content decreases from 52.6 wt% and generally has very low values (0-1 wt%) from 353 mbsf to total depth.
Organic carbon (Corg) is low throughout Hole 1128B. With the exception of two samples having values of 0.32 and 0.41 wt%, Corg concentrations are all <0.16 wt% from Hole 1128B (Table T8; Fig. F20). Because Corg values are 0 wt% from 200 to 276 mbsf and methane concentrations in the headspace samples in this depth range are barely above background level, organic carbon was not analyzed in samples from Hole 1128D.
Sulfur is present in only five samples in Hole 1128B, with values ranging from 0.05 to 0.21 wt%. Nitrogen was not detectable in any sample. Sulfur and nitrogen were not analyzed in samples from Hole 1128D.