As a part of the shipboard safety and pollution program, volatile hydrocarbons (methane, ethane, and propane) were measured in the sediments of Site 1092 from every core in Hole 1092A using the standard ODP headspace sampling techniques (Table T11; Fig. F13). Headspace methane concentrations were quite low (2-5 parts per million by volume [ppmv]) throughout the sedimentary sequence. Ethane, propane, and other higher molecular weight hydrocarbons were not observed.
Shipboard chemical analyses of the interstitial water from Site 1092 followed the procedures for Sites 1088-1091. Twenty interstitial water samples from Hole 1092A were taken (one per core) to a depth of 183 mbsf (Table T12; Fig. F14).
The downhole gradients in most of the dissolved species are gradual and unremarkable. The maximum in Cl- of ~563 mM is reached at ~33 mbsf and is somewhat broader and less intense than those observed at neighboring Sites 1091 and 1093. This difference is probably the result of the absence of diatom mats at Site 1092, yielding lower sedimentation rates and higher diffusion rates in the upper 100 mbsf. The major cations (Ca, Mg, and Sr) behave in a manner similar to that seen in Sites 1088 and 1090, and, qualitatively, the behavior is similar to that of Site 1089 below its Ca+2 minimum. Silicate rises very gradually to values near 1000 µM, consistent with biogenic sedimentation and little influence from clays, zeolites, or cherts. Generally speaking, the agreement is excellent between these results and those obtained previously at nearby Site 704 (Froelich et al., 1991). One exception is a significant offset between the chloride profiles of the two sites, a difference for which we have no obvious explanation.
The redox characteristics of Site 1092 can be characterized as generally oxic or suboxic throughout the section. Sulfate reduction rates are very low as indicated by the absence of H2S (by scent) and the minor decreases in sulfate concentrations to ~26 mM at the bottom of the section. Ammonium increases moderately downhole to a relatively constant value of ~75 µM below 90 mbsf. Phosphate concentrations are low throughout the section, registering barely above detection limits below 50 mbsf. Mn+2 was below detection limits for all samples, and Fe+2 was not measured at this site.
The shipboard solid phase analysis at Site 1092 consisted of measurements of inorganic carbon throughout the sedimentary sequence of Hole 1092A, and preliminary measurements of total carbon (TC), total nitrogen (TN), and total sulfur in selected samples from Cores 177-1092A-1H through 10H (Table T13; Fig. F15; for methods see "Geochemistry" in the "Explanatory Notes" chapter). Calcium carbonate (CaCO3) contents in Hole 1092A range from 16.7 to 94.6 wt%, with an average value of 80.2 wt%. Above 50 mbsf, a minimum value (16.7 wt%) of CaCO3 concentrations was observed at 29 mbsf within the section of nannofossil- and foraminifer-bearing diatom ooze (see "Lithostratigraphy"). CaCO3 contents are consistently very high (average value of 88 wt%) from 50 mbsf to the bottom of the section.
Total organic carbon (TOC) contents vary between 0 and 0.7 wt%, with an average value of 0.16 wt%. Most TOC concentrations, taken as the difference between TC and carbonate carbon measurements, are below 0.1 wt%. Many samples have concentrations below the detection limits of the shipboard analytical technique, because these sediments are mainly composed of calcareous microfossils. TN contents are generally low (0 to 0.07 wt%). Sulfur was not detected. TOC/TN values vary between 0.5 and 11.0, indicating a predominance of marine organic material. However, these low TOC/TN values are probably underestimated because of the low TOC contents of the sediment. Pyrolysis analyses were not performed because of the low organic-carbon content of the sediments.