As part of the shipboard safety and pollution-prevention monitoring program, hydrocarbon gases were analyzed for each core of Hole 1122A and each core below 60 mbsf of Hole 1122C by the headspace technique. Gas pockets were not encountered. The headspace methane concentrations increase rapidly below the seafloor (Fig. F31). In contrast to Site 1119 (see "Organic Geochemistry" in the "Site 1119" chapter), there is no well-defined concentration maximum in the section, but headspace methane concentrations of the sediments between 15 and 265 mbsf are much higher than in the uppermost sample and in the sediments below. The variation in this section (1,000-42,000 ppm) may reflect different sediment properties and/or different amounts of metabolizable organic matter in the methane-releasing sediments and, thus, changes in the sedimentary composition. The elevated methane concentrations are corroborated by low sulfate concentrations (see "Inorganic Geochemistry"). Below 265 mbsf, methane concentrations decrease suddenly by two orders of magnitude and are uniformly low down to the bottom of the hole. This distinct change matches the transition from lithostratigraphic Subunit IC to Subunit IB at 262 mbsf (see "Lithostratigraphy"), and may be a result of changes in the amount or type of organic matter. However, clear corresponding evidence of these changes cannot be found in the elemental composition (see "Carbonate and Organic Carbon").
The abundance of total, inorganic, and organic carbon and of calcium carbonate in sediments from Holes 1122A and 1122B is summarized in Table T14 (also in ASCII format). Random sampling of all lithologies was performed for carbonate analysis, and one sample per core was analyzed for organic carbon.
Carbonate contents are highly variable throughout the section and lie in the range from 0.1 to 76.5 wt% (Fig. F32). There is no clear correlation with depth, age, or lithology. Because of the obvious variation in the sedimentary composition, particularly the intercalated turbidites in the hemipelagic sediments, this may be an artifact of random sampling. Nevertheless, in the upper part of the section between 0 and 140 mbsf, with exception of the section from 60 to 80 mbsf (lithostratigraphic Subunits IA and IB) and between 300 and 420 mbsf, carbonate contents are lower on average than in the rest of the section.
Sediments at Site 1122 average 0.24 wt% organic carbon (Fig. F33), which is lower than the average for deep-sea sediments of 0.3% compiled by McIver (1975) from data of DSDP Legs 1 through 33. There is no clear correlation with depth, age, or lithology, though in the deeper part of the hole concentrations seem to decrease with increasing depth. Despite the high sedimentation rate, low organic carbon concentrations are probably a consequence of organic-matter degradation caused by the long exposure to an oxic water column.
Atomic organic carbon/nitrogen values were calculated for Site 1122 samples using TOC and total nitrogen concentrations to help identify the origin of the organic matter. The ratios vary from 0.2 to 25.9 with an average of 4.2 (Table T14). 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 degradation of organic matter (Müller, 1977). This interpretation is supported by unrealistically low atomic [C/N]a ratios below 4.0 for organic carbon-poor samples (<0.2 wt%).
Rock-Eval analyses were not made because of low organic carbon contents (see "Organic Geochemistry" in the "Explanatory Notes" chapter).