As part of the shipboard safety and pollution program, volatile hydrocarbons (methane, ethane, and propane) were measured in the sediments of Site 1088 from every core using the standard ODP headspace sampling technique. Results are presented in Table T10 and Figure F16. Headspace methane concentrations were generally low (4-11 parts per million by volume [ppmv]) throughout the sedimentary sequence at Site 1088, except for the uppermost sediments, which showed slightly higher values of 39 ppmv. Traces of ethane and propane were detected in the uppermost sediments (Sample 177-1088B-1H-4, 0-5 cm). Higher molecular weight hydrocarbon gases were not observed.
Shipboard chemical analyses of interstitial water in the sediments from Site 1088 included measurements of salinity, pH, alkalinity, chlorinity, calcium, magnesium, sulfate, silica, phosphate, ammonium, strontium, and lithium (see "Geochemistry" in the "Explanatory Notes" chapter for details on methods). The results from the shipboard analyses are presented in Table T11 and Figure F17. The results represent 35 interstitial water samples taken from Hole 1088B to a depth of 116 mbsf and seven samples taken from Hole 1088C from 129 to 230 mbsf; the total of 42 samples is considered to represent a single continuous profile.
Chlorinity increases downhole, with a slight local maximum at ~40 mbsf. This pattern may result from the downward diffusion of higher salinity water associated with the last glacial maximum (McDuff, 1985). The reason an increase is not also observed in Na+ is probably because Na+ concentrations are determined by charge balance calculations and thus Na+ concentrations include the errors associated with measurement of all major cations and anions.
The sediments from this low-sedimentation-rate site are rich in carbonate throughout the length of the profile, and carbonate recrystallization processes apparently dictate some of the interstitial chemistry. For example, the increases in Ca+2 and Sr+2 are consistent with biogenic carbonate dissolution.
The sediments are only mildly reducing as indicated by a decrease in sulfate from bottom-water values of 29 to ~20 mM at 230 mbsf. Sulfate depletion with depth is accompanied by corresponding increases in NH4+, with a high degree of inverse correlation between sulfate and NH4+ (Fig. F18). The mildly reducing character of these sediments and generally slow rates of organic matter diagenesis are also indicated by the near constant alkalinity with depth.
Dissolved silica increases to a nearly constant value of ~900 µM, close to saturation for opal. There is a local maximum at ~25-30 mbsf that may be associated with diatom-rich layers, supported by diatom abundances observed in smear slides from this site (see "Lithostratigraphy"). The small local minimum in dissolved silica just below the maximum is likely the result of some sediment constituent, perhaps aluminum, exerting control over silica solubility (see van Beusekom et al., 1997, and references therein). Without some local control over silica solubility, the local minimum in dissolved silica would probably have been smoothed out by diffusional processes.
Phosphate concentrations in the interstitial waters of Site 1088 are low throughout the profile, likely as a consequence of elevated Ca+2 and formation of an authigenic phosphorus-bearing phase like carbonate fluorapatite (Filippelli and Delaney, 1996).
A total of 140 sediment samples were analyzed for inorganic carbon by coulometric titration at Site 1088. Calcium carbonate (CaCO3) contents vary between 83.6 and 95.7 wt%, with an average value of 91.4 wt% (Table T12; Fig. F19). In the upper 30 m, which corresponds to the lithofacies of nannofossil foraminifer ooze with IRD (see "Lithostratigraphy"), CaCO3 contents are slightly lower than deeper in the section. CaCO3 contents are also slightly lower in the sediments from 90 to 127 mbsf.