As a part of the shipboard safety and pollution program, volatile hydrocarbons (methane, ethane, and propane) were measured in the sediments of Holes 1094A and 1094D using the standard ODP headspace sampling techniques. Headspace methane concentrations were quite low (2 to 5 parts per million by volume [ppmv]) in the sedimentary sequence at Site 1094 (Table T14; Fig. F20). Ethane, propane, and other higher molecular weight hydrocarbons were not observed.
Shipboard chemical analyses of the interstitial water from Site 1094 followed the procedures for Sites 1088-1093. The results from the standard shipboard analyses of 5-cm whole rounds are presented in Table T15 and Figure F21, and were obtained from 16 interstitial water samples from Hole 1094A (to a depth of 155 mbsf) and two samples from Hole 1094D (from 158 to 166 mbsf). Interstitial water samples were taken from every core throughout the entire section except when recovery was insufficient.
After splitting the cores, two porcellanite (opal-CT) layers were discovered in Hole 1094A at ~68 and ~104 mbsf, and a porcellanite concretion was discovered at 142 mbsf. The same porcellanite intervals were also observed in Hole 1094D, along with an additional layer at ~164 mbsf (see "Lithostratigraphy"). Five intervals comprising the porcellanites (68 and 104 mbsf in Hole 1094A; 68, 142, and 164 mbsf in Hole 1094D) were sampled at closely spaced intervals near the porcellanites, using two adjacent 10-cm3 plugs for squeezing ~20 cm3 of sediment in small-volume titanium squeezers. A very limited number of shipboard analyses were performed on the samples from three of the porcellanite intervals, and these data are presented in Table T16.
The chlorinity profile from Site 1094 is clearly influenced by the diffusional barriers imposed by the porcellanite layer at 68 mbsf and, therefore, provides an interesting comparison with the profiles at Sites 1091 and 1093. If it were not for the porcellanite at 68 mbsf, the trend of the Cl- profile would probably be nearly identical to these other sites, showing a maximum of ~570 mM at 50-60 mbsf (considered by some as a by-product of the ice-age increase in salinity). However, there is a sharp discontinuity in the Cl- maximum at Site 1094, indicating that vertical exchange of interstitial water across the porcellanite layer became severely impeded at some time. The conformity to the Cl- trend established in Sites 1093 and 1091 below the porcellanite layer suggests that the Cl- maximum was in place before the formation of the diffusional barrier. Therefore, if the maximum is indeed associated with the last ice age, then the porcellanite must be significantly younger than 20 ka. However, it is possible that the porcellanite might be older if the Cl- maximum at Site 1094 is a remnant of an earlier ice age.
The diffusional barriers do not affect the major cation profiles (Ca, Mg, Sr, and K), which all show virtually no change from seawater values downhole. This lack of variability suggests little or no influence from diagenetic processes (such as carbonate recrystallization, or ash or clay alteration) downhole, at least above 200 mbsf. Dissolved silica increases gradually downhole, but there is some suggestion of reduced concentrations of silica in and around the porcellanite layers. This observation will be quantified more precisely with shore-based laboratory analyses, particularly on the high-resolution samples bracketing the porcellanites.
The sediments at Site 1094 can be classified as suboxic, because there is no evidence for sulfate reduction; sulfate concentrations at the bottom of Hole 1094A are indistinguishable from seawater values. There are some basic similarities between the redox characteristics of Site 1094 and those of the other diatom sites, namely Sites 1091 and 1093; however, there are also significant differences. Dissolved phosphate reaches a maximum in the upper 20 mbsf at Site 1094, just as in the other sites. On the other hand, ammonium and alkalinity also rise sharply to near maximum values in the upper 20 mbsf at Site 1094, unlike Sites 1091 and 1093, where ammonium and alkalinity increase more gradually to maximum values at around 150 mbsf (see "Geochemistry" in the "Site 1091" and "Site 1093" chapters). In addition, the peak in phosphate is significantly greater than can be accounted for by the increases in ammonium and alkalinity. The phosphate profile follows the Mn+2 profile almost exactly, suggesting that reactive metal (oxy)hydroxide phases may contribute partially to interstitial water phosphate. Because there are similarities in the phosphate and Mn+2 profiles at Sites 1091 and 1093, metal oxide-bound phosphate may partly explain the shallow phosphate peaks observed at those sites as well. This observation does not negate the possibility that there is a shallow reactive organic fraction and a deeper, more refractory organic fraction in diatomacous oozes, as discussed in the previous site chapters. It simply implies that some phosphate may be transiently associated with metal oxides before being released to interstitial waters.
Considering Sites 1091, 1093, and 1094 together, the behavior of the redox-sensitive species delineates a consistent pattern in diatom ooze sedimentation. There must be some, as yet unknown, aspect of diatom organic-matter remineralization that not only allows sulfate to remain high (even in the absence of diffusion of sulfate from seawater, as in the case of Site 1094), but also allows the downhole mobility and reduction of reactive metals.
The shipboard solid phase analysis at Site 1094 consisted of measurements of inorganic carbon, total carbon, total nitrogen (TN), and total sulfur (TS) throughout the sedimentary sequence of Site 1094 (Table T17; Fig. F22; see "Explanatory Notes" chapter for methods). CaCO3 contents at Site 1094 were generally low, ranging from 0.0 to 41.6 wt%, with an average value of 6.6 wt%. CaCO3 was not detected in the sediments above 30 mbsf in the upper Pleistocene section, but this is likely an artifact of the low-resolution sampling because some carbonate intervals were observed over this interval (see "Lithostratigraphy"). Below 30 mbsf, CaCO3 shows a generally increasing trend downhole. Relatively high CaCO3 corresponds to intervals of nannofossil- and foraminifer-bearing diatom ooze (see "Lithostratigraphy").
Total organic carbon (TOC) contents vary between 0.41 and 1.09 wt%, with an average value of 0.83 wt% in the Pleistocene section. TS concentrations vary between 0.07 and 0.36 wt%. TN contents are quite low (0.02-0.04 wt%) and are probably underestimated because the measurements of these samples were performed under poor analytical conditions (an air leak in the carbon-nitrogen-sulfur analyzer). Although TOC/TN values vary between 15.7 and 67.9, the higher TOC/TN values are likely also overestimated in the sediments of Site 1094 (Fig. F22). These lower TN and higher TOC/TN values will likely be modified by detailed shore-based analysis. Pyrolysis analyses were not performed because of the organic-carbon-poor nature of the sediments.