As part of the shipboard safety and pollution-prevention monitoring program, hydrocarbon gases were analyzed in each core of Hole 1121B by the headspace technique. Methane and higher hydrocarbons could only be recognized in trace concentrations (<10 ppm). These low methane concentrations indicate low bacterial activity in the sediments, probably because of organic matter limitation. This result is corroborated by almost constant sulfate concentrations in pore waters throughout the hole (see "Inorganic Geochemistry").
The abundance of total, inorganic, and organic carbon and of calcium carbonate in sediments from Holes 1121A and 1121B is summarized in Table T7 (also in ASCII format). Random sampling of all lithologies was performed for carbonate analysis. Organic carbon was measured at a resolution of one sample per core.
Carbonate contents are highly variable throughout the section and lie in the range of 0.38 to 52.1 wt% (Fig. F21). The carbonate contents reflect varying biological productivity, and postdepositional carbonate dissolution in relation to the inferred paleowater depth and position of the lysocline.
Low organic-carbon contents (<0.36%) were found from eight measured samples. It suggests that the respiration of most of the organic matter occurred during sedimentation and early diagenesis caused by oxic water column conditions.
Ratios of organic carbon/nitrogen was calculated for Site 1121 samples using TOC and total nitrogen concentrations to help identify the origin of the organic matter. The ratios vary from 4.3 to 16.3 (Table T7). Because of (1) the small number of analyses, (2) low organic carbon and low total nitrogen contents, and (3) an obviously strong degradation of the organic matter, a clear indication of the organic matter source is not possible.