As part of the shipboard safety and pollution-prevention monitoring program, hydrocarbon gases were analyzed by the headspace technique in each core of Hole 1119B and in each core below 150 mbsf of Hole 1119C. When gas was encountered, analyses were made by vacutainer sampling. The headspace methane concentrations increase rapidly below the sediment surface to a maximum value of 36,400 ppm at 20.23 mbsf (Fig. F23). Below this depth, methane concentrations decrease to 3,155 ppm at 96.20 mbsf and fluctuate in the range between 1,500 and 8,000 ppm in the deeper parts of Holes 1119B and 1119C, respectively. However, between 110 and 160 mbsf, three distinct maxima occur with concentrations over 10,000 ppm. C1/C2 values are high in all samples, indicating a biogenic source of methane; ratios decrease with depth from values over 10,000 ppm to values of ~500 ppm. In summary, methane concentrations are moderate in headspace samples and hydrocarbons of lower volatility (C2+) could only be recognized in trace amounts. Vacutainer methane concentrations are much higher than in the headspace samples, showing the effect of different sampling techniques. The values are in the range 500,000 to 1,000,000 ppm. C1/C2 values are fairly constant (480-650 ppm) and decrease only slightly with depth.
The abundances of total, inorganic, and organic carbon and of calcium carbonate in sediments from Holes 1119B and 1119C are summarized in Table T13 (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 are highly variable throughout the sediment sequence and range from 0.9 to 72.7 wt% (Fig. F24). High carbonate concentrations occur at sediment depths between 300 and 420 mbsf, whereas contents are relatively low below 420 mbsf to the bottom of the hole. Above 300 mbsf, most of the samples have contents below 15 wt%. The range in carbonate content reflects a varying combination of fluctuating biological productivity, dilution by noncalcareous sedimentary components, and postdepositional carbonate dissolution forced by oxidation of organic matter.
Sediments at Site 1119 average 0.34 wt% TOC (Fig. F25), which is low for coastal sediments. This suggests varying environmental conditions in which (1) during deposition of carbonate ooze-rich sediments most of the organic matter is degraded and (2) during periods of low carbonate production the organic matter is diluted by siliciclastic sediments. Consequently, there is no correlation between carbonate and organic matter contents and between organic matter content and depth.
Organic carbon/nitrogen values were calculated for Site 1119 samples using TOC and total nitrogen concentrations to help identify the origin of the organic matter. The ratios vary from 0.2 to 9.0 with an average of 4.2 (Table T13). 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 (1) constant total nitrogen concentrations and (2) very low atomic [C/N]a ratios below 4.0 for organic carbon-poor samples (<0.3 wt%).
Rock-Eval analyses were not carried out because of low organic carbon contents (see "Organic Geochemistry" in the "Explanatory Notes" chapter).