RESULTS

Total N concentrations of sediments from Sites 1040, 1254, and 1255 vary from 832 to 2398 ppm (consistent with the data reported by Kimura, Silver, Blum, et al., 1997, and Morris, Villinger, Klaus, et al., 2003) with ¹⁵N values from +3.6 to +6.6 (Table T1; Fig. F2A, F2B). Both TN concentrations and ¹⁵N values increase with increasing depth within the uppermost 130 m of the section. Less distinct TN-¹⁵N covariance was observed for the deeper part of the section, in which down-hole TN and ¹⁵N decrease slightly with ¹⁵N values ranging from +3.4 to +4.6. Total N concentrations and ¹⁵N values are similar in sediments from Sites 1040 and 1254 obtained from similar depths. Three samples from Site 1255 gave values more scattered than those from Site 1040 (see Table T1; Fig. F2), possibly because of slightly different pretreatments (H₂O rinsing for two samples and 6-N HCl rinsing for one sample; see the "Appendix"), but more likely as a result of heterogeneity within the sediments in the wedge (Kimura, Silver, Blum, et al., 1997).

In contrast with the TN concentrations and isotopic data, TOC concentrations and C-isotope compositions show no systematic change with depth (Fig. F3). All samples from Sites 1040, 1254, and 1255 contain 0.85–3.06 wt% TOC, with most values between 1 and 2 wt%. These values are near but slightly higher than the concentrations reported by Kimura, Silver, Blum, et al., 1997, and Lutz et al., 2000, with ¹³C values from –26.6 to –21.1. The only two samples with TOC >2 wt% are from Sites 1254 and 1255. Most sediment samples from Sites 1254 and 1255 have TOC concentrations and ¹³C values similar to those of sediments obtained from Site 1040 from similar depths (Table T1; Fig. F3A, F3B).

Carbonate is not abundant in wedge sediments from Site 1040, and all samples examined in this study contain <4 wt% CaCO₃ (Table T1; Fig. F4A). Kimura, Silver, Blum, et al. (1997) reported higher CaCO₃ concentrations, as much as 9 wt%, for the same section. These data were obtained using a carbonate carbon analyzer. The reason for these different CaCO₃ concentrations is unknown but likely related to the very different analytical methods. In our laboratory, we measure CO₂ yields using a high-vacuum extraction line with a mercury manometer. ¹³C values of carbonates vary significantly from –26.1 to +4.1, with most values between –8 and +4.1), and ¹⁸O values range from +30.0 to +36.4. As in the case for TOC, CaCO₃ concentrations and C- and O-isotope compositions do not show significant coherent change as a function of depth (Fig. F4).