As part of the shipboard safety and pollution-prevention monitoring program, hydrocarbon gases were analyzed in each core of Hole 1124B and in each core below 10 mbsf of Hole 1124C. The headspace methane concentrations are very low (<10 ppm), and gas pockets were not encountered. This result corresponds to low amounts of metabolizable organic matter in the sediments and high interstitial sulfate concentrations above 15 mM, which imply no significant sulfate reduction in the sediments (see "Inorganic Geochemistry").
The abundances of total, inorganic, and organic carbon and of calcium carbonate in sediments from Holes 1124A, 1124B, and 1124C are summarized in Table T16 (also in ASCII format). Random sampling of all lithologies was performed for carbonate analysis, and for organic carbon measurements one sample per core was analyzed.
Carbonate contents vary between 0.1 and 88.3 wt% with an average of 36.3 wt% (Fig. F27). Variations are high in all sections. Between 100 and 200 mbsf, the average content is lower than in the rest of Hole 1124C. Below 300 mbsf, concentrations appear to be elevated, reflecting the transition from lithostratigraphic Unit II to Subunit IC (see "Lithostratigraphy"). The reddish brown to dark brown mudstone (lithostratigraphic Unit V) between 420 and 429 mbsf has a relatively low carbonate content, and the organic carbon content is not higher than in the rest of the sequence. Thus, this mudstone is not organic carbon rich, but rather has typical mudstone properties as indicated by natural gamma-ray intensity and magnetic susceptibility (see "Downhole Measurements" and "Paleomagnetism").
Sediments at Site 1124 average 0.31 wt% organic carbon (Fig. F28), which is in the normal range for deep-sea sediments as compiled by McIver (1975) from DSDP Legs 1 through 33. Variations are high without any apparent correlation with lithology. There is no indication of present-day bacterial degradation of organic matter as demonstrated by low methane concentrations. Thus, the organic matter may have been already degraded by bacteria, or large amounts are derived from terrigenous sources and are thus more refractory.
Organic carbon/nitrogen ratios were calculated for Site 1124 samples using organic carbon and total nitrogen concentrations to help identify the origin of their organic matter. The ratios vary from 0.2 to 12.6 with an average of 4.9 (Table T16). These low ratios are not accurate indicators of organic matter source. They may be an artifact of the low organic carbon content, combined with the tendency of clay minerals to adsorb ammonium ions generated during the degradation of organic matter (Müller, 1977). This interpretation is supported by unrealistically low atomic [C/N]a values below 5.0 for organic carbon-poor samples (<0.3 wt%).